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Versions: (draft-bierman-netconf-restconf) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 RFC 8040

Network Working Group                                         A. Bierman
Internet-Draft                                                 YumaWorks
Intended status: Standards Track                            M. Bjorklund
Expires: January 7, 2016                                  Tail-f Systems
                                                               K. Watsen
                                                        Juniper Networks
                                                            July 6, 2015


                           RESTCONF Protocol
                     draft-ietf-netconf-restconf-07

Abstract

   This document describes an HTTP-based protocol that provides a
   programmatic interface for accessing data defined in YANG, using the
   datastores defined in NETCONF.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 7, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Simple Subset of NETCONF Functionality  . . . . . . . . .   5
     1.2.  Data Model Driven API . . . . . . . . . . . . . . . . . .   6
     1.3.  Coexistence with NETCONF  . . . . . . . . . . . . . . . .   7
     1.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   8
       1.4.1.  NETCONF . . . . . . . . . . . . . . . . . . . . . . .   8
       1.4.2.  HTTP  . . . . . . . . . . . . . . . . . . . . . . . .   8
       1.4.3.  YANG  . . . . . . . . . . . . . . . . . . . . . . . .   9
       1.4.4.  Terms . . . . . . . . . . . . . . . . . . . . . . . .  10
       1.4.5.  URI Template  . . . . . . . . . . . . . . . . . . . .  11
       1.4.6.  Tree Diagrams . . . . . . . . . . . . . . . . . . . .  11
   2.  Transport Protocol Requirements . . . . . . . . . . . . . . .  12
     2.1.  Integrity and Confidentiality . . . . . . . . . . . . . .  12
     2.2.  HTTPS with X.509v3 Certificates . . . . . . . . . . . . .  12
     2.3.  Certificate Validation  . . . . . . . . . . . . . . . . .  12
     2.4.  Authenticated Server Identity . . . . . . . . . . . . . .  12
     2.5.  Authenticated Client Identity . . . . . . . . . . . . . .  12
   3.  Resources . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     3.1.  Root Resource Discovery . . . . . . . . . . . . . . . . .  14
     3.2.  RESTCONF Resource Types . . . . . . . . . . . . . . . . .  15
     3.3.  API Resource  . . . . . . . . . . . . . . . . . . . . . .  15
       3.3.1.  {+restconf}/data  . . . . . . . . . . . . . . . . . .  16
       3.3.2.  {+restconf}/operations  . . . . . . . . . . . . . . .  17
     3.4.  Datastore Resource  . . . . . . . . . . . . . . . . . . .  17
       3.4.1.  Edit Collision Detection  . . . . . . . . . . . . . .  18
     3.5.  Data Resource . . . . . . . . . . . . . . . . . . . . . .  18
       3.5.1.  Encoding Data Resource Identifiers in the Request URI  19
       3.5.2.  Defaults Handling . . . . . . . . . . . . . . . . . .  22
     3.6.  Operation Resource  . . . . . . . . . . . . . . . . . . .  22
       3.6.1.  Encoding Operation Input Parameters . . . . . . . . .  23
       3.6.2.  Encoding Operation Output Parameters  . . . . . . . .  24
       3.6.3.  Encoding Operation Errors . . . . . . . . . . . . . .  25
     3.7.  Schema Resource . . . . . . . . . . . . . . . . . . . . .  25
     3.8.  Event Stream Resource . . . . . . . . . . . . . . . . . .  26
     3.9.  Errors Media Type . . . . . . . . . . . . . . . . . . . .  27
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     4.1.  OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . .  28
     4.2.  HEAD  . . . . . . . . . . . . . . . . . . . . . . . . . .  28
     4.3.  GET . . . . . . . . . . . . . . . . . . . . . . . . . . .  28
     4.4.  POST  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
       4.4.1.  Create Resource Mode  . . . . . . . . . . . . . . . .  30
       4.4.2.  Invoke Operation Mode . . . . . . . . . . . . . . . .  31
     4.5.  PUT . . . . . . . . . . . . . . . . . . . . . . . . . . .  31



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     4.6.  PATCH . . . . . . . . . . . . . . . . . . . . . . . . . .  32
       4.6.1.  Plain Patch . . . . . . . . . . . . . . . . . . . . .  33
     4.7.  DELETE  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     4.8.  Query Parameters  . . . . . . . . . . . . . . . . . . . .  34
       4.8.1.  The "content" Query Parameter . . . . . . . . . . . .  35
       4.8.2.  The "depth" Query Parameter . . . . . . . . . . . . .  36
       4.8.3.  The "fields" Query Parameter  . . . . . . . . . . . .  36
       4.8.4.  The "insert" Query Parameter  . . . . . . . . . . . .  37
       4.8.5.  The "point" Query Parameter . . . . . . . . . . . . .  38
       4.8.6.  The "filter" Query Parameter  . . . . . . . . . . . .  38
       4.8.7.  The "start-time" Query Parameter  . . . . . . . . . .  39
       4.8.8.  The "stop-time" Query Parameter . . . . . . . . . . .  40
       4.8.9.  The "with-defaults" Query Parameter . . . . . . . . .  40
   5.  Messages  . . . . . . . . . . . . . . . . . . . . . . . . . .  41
     5.1.  Request URI Structure . . . . . . . . . . . . . . . . . .  41
     5.2.  Message Headers . . . . . . . . . . . . . . . . . . . . .  43
     5.3.  Message Encoding  . . . . . . . . . . . . . . . . . . . .  44
     5.4.  RESTCONF Meta-Data  . . . . . . . . . . . . . . . . . . .  44
     5.5.  Return Status . . . . . . . . . . . . . . . . . . . . . .  44
     5.6.  Message Caching . . . . . . . . . . . . . . . . . . . . .  45
   6.  Notifications . . . . . . . . . . . . . . . . . . . . . . . .  45
     6.1.  Server Support  . . . . . . . . . . . . . . . . . . . . .  45
     6.2.  Event Streams . . . . . . . . . . . . . . . . . . . . . .  45
     6.3.  Subscribing to Receive Notifications  . . . . . . . . . .  48
       6.3.1.  NETCONF Event Stream  . . . . . . . . . . . . . . . .  49
     6.4.  Receiving Event Notifications . . . . . . . . . . . . . .  49
   7.  Error Reporting . . . . . . . . . . . . . . . . . . . . . . .  51
     7.1.  Error Response Message  . . . . . . . . . . . . . . . . .  53
   8.  RESTCONF module . . . . . . . . . . . . . . . . . . . . . . .  55
   9.  RESTCONF Monitoring . . . . . . . . . . . . . . . . . . . . .  61
     9.1.  restconf-state/capabilities . . . . . . . . . . . . . . .  61
       9.1.1.  Query Parameter URIs  . . . . . . . . . . . . . . . .  62
       9.1.2.  The "defaults" Protocol Capability URI  . . . . . . .  62
     9.2.  restconf-state/streams  . . . . . . . . . . . . . . . . .  63
     9.3.  RESTCONF Monitoring Module  . . . . . . . . . . . . . . .  63
   10. YANG Module Library . . . . . . . . . . . . . . . . . . . . .  67
     10.1.  modules  . . . . . . . . . . . . . . . . . . . . . . . .  67
       10.1.1.  modules/module . . . . . . . . . . . . . . . . . . .  68
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  68
     11.1.  The "restconf" Relation Type . . . . . . . . . . . . . .  68
     11.2.  YANG Module Registry . . . . . . . . . . . . . . . . . .  68
     11.3.  application/yang Media Sub Types . . . . . . . . . . . .  69
     11.4.  RESTCONF Capability URNs . . . . . . . . . . . . . . . .  70
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  71
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  72
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  72
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  72
     14.2.  Informative References . . . . . . . . . . . . . . . . .  75



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   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  75
     A.1.  06 - 07 . . . . . . . . . . . . . . . . . . . . . . . . .  75
     A.2.  05 - 06 . . . . . . . . . . . . . . . . . . . . . . . . .  76
     A.3.  04 - 05 . . . . . . . . . . . . . . . . . . . . . . . . .  76
     A.4.  03 - 04 . . . . . . . . . . . . . . . . . . . . . . . . .  76
     A.5.  02 - 03 . . . . . . . . . . . . . . . . . . . . . . . . .  77
     A.6.  01 - 02 . . . . . . . . . . . . . . . . . . . . . . . . .  78
     A.7.  00 - 01 . . . . . . . . . . . . . . . . . . . . . . . . .  78
     A.8.  bierman:restconf-04 to ietf:restconf-00 . . . . . . . . .  79
   Appendix B.  Open Issues  . . . . . . . . . . . . . . . . . . . .  79
   Appendix C.  Example YANG Module  . . . . . . . . . . . . . . . .  80
     C.1.  example-jukebox YANG Module . . . . . . . . . . . . . . .  80
   Appendix D.  RESTCONF Message Examples  . . . . . . . . . . . . .  86
     D.1.  Resource Retrieval Examples . . . . . . . . . . . . . . .  86
       D.1.1.  Retrieve the Top-level API Resource . . . . . . . . .  86
       D.1.2.  Retrieve The Server Module Information  . . . . . . .  87
       D.1.3.  Retrieve The Server Capability Information  . . . . .  88
     D.2.  Edit Resource Examples  . . . . . . . . . . . . . . . . .  89
       D.2.1.  Create New Data Resources . . . . . . . . . . . . . .  89
       D.2.2.  Detect Resource Entity Tag Change . . . . . . . . . .  90
       D.2.3.  Edit a Datastore Resource . . . . . . . . . . . . . .  91
     D.3.  Query Parameter Examples  . . . . . . . . . . . . . . . .  92
       D.3.1.  "content" Parameter . . . . . . . . . . . . . . . . .  92
       D.3.2.  "depth" Parameter . . . . . . . . . . . . . . . . . .  95
       D.3.3.  "fields" Parameter  . . . . . . . . . . . . . . . . .  98
       D.3.4.  "insert" Parameter  . . . . . . . . . . . . . . . . .  99
       D.3.5.  "point" Parameter . . . . . . . . . . . . . . . . . . 100
       D.3.6.  "filter" Parameter  . . . . . . . . . . . . . . . . . 101
       D.3.7.  "start-time" Parameter  . . . . . . . . . . . . . . . 101
       D.3.8.  "stop-time" Parameter . . . . . . . . . . . . . . . . 101
       D.3.9.  "with-defaults" Parameter . . . . . . . . . . . . . . 102
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 103

1.  Introduction

   There is a need for standard mechanisms to allow Web applications to
   access the configuration data, operational data, data-model specific
   protocol operations, and event notifications within a networking
   device, in a modular and extensible manner.

   This document describes an HTTP [RFC7230] based protocol called
   RESTCONF, for accessing data defined in YANG [RFC6020], using
   datastores defined in NETCONF [RFC6241].

   The NETCONF protocol defines configuration datastores and a set of
   Create, Retrieve, Update, Delete (CRUD) operations that can be used
   to access these datastores.  The YANG language defines the syntax and
   semantics of datastore content, operational data, protocol



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   operations, and event notifications.  RESTCONF uses HTTP operations
   to provide CRUD operations on a NETCONF datastore containing YANG-
   defined data.  Since NETCONF protocol operations are not relevant,
   the user should not need any prior knowledge of NETCONF in order to
   use RESTCONF.

   Configuration data and state data are exposed as resources that can
   be retrieved with the GET method.  Resources representing
   configuration data can be modified with the DELETE, PATCH, POST, and
   PUT methods.  Data is encoded with either XML [W3C.REC-xml-20081126]
   or JSON [RFC7158].

   Data-model specific protocol operations defined with the YANG "rpc"
   statement can be invoked with the POST method.  Data-model specific
   event notifications defined with the YANG "notification" statement
   can be accessed.

1.1.  Simple Subset of NETCONF Functionality

   An HTTP-based management protocol does not need to mirror the
   functionality of the NETCONF protocol, but it needs to be compatible
   with NETCONF.  A simplified transaction model is needed that allows
   basic CRUD operations on a hierarchy of conceptual resources.  This
   represents a limited subset of the transaction capabilities of the
   NETCONF protocol.

   The HTTP POST, PUT, PATCH, and DELETE methods are used to edit data
   resources represented by YANG data models.  These basic edit
   operations allow the running configuration to be altered in an all-
   or-none fashion.  This is similar to the "rollback-on-error"
   capability in NETCONF.  Edits are usually applied to one data
   resource instance at a time.

   The base RESTCONF protocol is intentionally simple to allow
   deployment for as many use cases as possible.  Additional
   functionality can be defined in external documents, outside the scope
   of this document.

   RESTCONF is not intended to replace NETCONF, but rather provide an
   additional simplified interface that follows REST principles and is
   compatible with a resource-oriented device abstraction.

   The following figure shows the system components:








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         +-----------+           +-----------------+
         |  Web app  | <-------> |                 |
         +-----------+   HTTP    | network device  |
                                 |                 |
         +-----------+           |   +-----------+ |
         |  NMS app  | <-------> |   | datastore | |
         +-----------+  NETCONF  |   +-----------+ |
                                 +-----------------+

1.2.  Data Model Driven API

   RESTCONF combines the simplicity of the HTTP protocol with the
   predictability and automation potential of a schema-driven API.
   Using YANG, a client can predict all resource endpoints, much like
   using URI Templates [RFC6570], but in a more holistic manner.  This
   strategy obviates the need for responses provided by the server to
   contain HATEOAS links, originally described in Roy Fielding's
   doctoral dissertation [rest-dissertation].

   In contrast, a REST client using HATEOAS principles would not use any
   data modeling language to define the application-specific content of
   the API.  The client would need to discover each new child resource
   as it traverses the URIs to discover the server capabilities.  This
   approach has the following significant weaknesses with regards to
   control of complex networking devices:

   o  inefficient performance: configuration APIs will be quite complex
      and may require thousands of protocol messages to discover all the
      schema information.  Typically the data type information has to be
      passed in the protocol messages, which is also wasteful overhead.

   o  no data model richness: without a data model, the schema-level
      semantics and validation constraints are not available to the
      application.

   o  no tool automation: API automation tools need some sort of content
      schema to function.  Such tools can automate various programming
      and documentation tasks related to specific data models.

   Data models such as YANG modules serve as an "API contract" that will
   be honored by the server.  An application designer can code to the
   data model, knowing in advance important details about the exact
   protocol operations and datastore content a conforming server
   implementation will support.

   RESTCONF provides the YANG module capability information supported by
   the server, in case the client wants to use it.  The URIs for custom




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   protocol operations and datastore content are predictable, based on
   the YANG module definitions.

   Operational experience with CLI and SNMP indicates that operators
   learn the 'location' of specific service or device related data and
   do not expect such information to be arbitrary and discovered each
   time the client opens a management session to a server.

   The RESTCONF protocol operates on a conceptual datastore defined with
   the YANG data modeling language.  The server lists each YANG module
   it supports using the "ietf-yang-library" YANG module, defined in
   [I-D.ietf-netconf-yang-library].  The server MUST implement the
   "ietf-yang-library" module, which SHOULD identify all the YANG
   modules used by the server.

   The conceptual datastore contents, data-model-specific operations and
   event notifications are identified by this set of YANG modules.  All
   RESTCONF content identified as either a data resource, operation
   resource, or event stream resource is defined with the YANG language.

   The classification of data as configuration or non-configuration is
   derived from the YANG "config" statement.  Data ordering behavior is
   derived from the YANG "ordered-by" statement.

   The RESTCONF datastore editing model is simple and direct, similar to
   the behavior of the :writable-running capability in NETCONF.  Each
   RESTCONF edit of a datastore resource is activated upon successful
   completion of the transaction.

1.3.  Coexistence with NETCONF

   RESTCONF can be implemented on a device that supports NETCONF.

   If the device supports :writable-running, all edits to configuration
   nodes in {+restconf}/data are performed in the running configuration
   datastore.

   Otherwise, if the device supports :candidate, all edits to
   configuration nodes in {+restconf}/data are performed in the
   candidate configuration datastore.  The candidate is automatically
   committed to running after a successful edit.

   If the device supports :startup, the device automatically copies the
   content of running to startup after running has been updated as a
   consequence of a RESTCONF edit operation.






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   If a datastore that would be modified by a RESTCONF operation has an
   active lock, the RESTCONF edit operation MUST fail with a 409
   (Conflict) error code.

1.4.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14, [RFC2119].

1.4.1.  NETCONF

   The following terms are defined in [RFC6241]:

   o  candidate configuration datastore

   o  client

   o  configuration data

   o  datastore

   o  configuration datastore

   o  protocol operation

   o  running configuration datastore

   o  server

   o  startup configuration datastore

   o  state data

   o  user

1.4.2.  HTTP

   The following terms are defined in [RFC3986]:

   o  fragment

   o  path

   o  query

   The following terms are defined in [RFC7230]:



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   o  header

   o  message-body

   o  request-line

   o  request URI

   o  status-line

   The following terms are defined in [RFC7231]:

   o  method

   o  request

   o  resource

   The following terms are defined in [RFC7232]:

   o  entity tag

1.4.3.  YANG

   The following terms are defined in [RFC6020]:

   o  container

   o  data node

   o  key leaf

   o  leaf

   o  leaf-list

   o  list

   o  presence container (or P-container)

   o  RPC operation (now called protocol operation)

   o  non-presence container (or NP-container)

   o  ordered-by system

   o  ordered-by user




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1.4.4.  Terms

   The following terms are used within this document:

   o  API resource: a resource with the media type "application/
      yang.api+xml" or "application/yang.api+json".

   o  data resource: a resource with the media type "application/
      yang.data+xml" or "application/yang.data+json".  Containers,
      leafs, list entries and anyxml nodes can be data resources.

   o  datastore resource: a resource with the media type "application/
      yang.datastore+xml" or "application/yang.datastore+json".
      Represents a datastore.

   o  edit operation: a RESTCONF operation on a data resource using
      either a POST, PUT, PATCH, or DELETE method.

   o  event stream resource: This resource represents an SSE (Server-
      Sent Events) event stream.  The content consists of text using the
      media type "text/event-stream", as defined by the HTML5
      specification.  Each event represents one <notification> message
      generated by the server.  It contains a conceptual system or data-
      model specific event that is delivered within an event
      notification stream.  Also called a "stream resource".

   o  media-type: HTTP uses Internet media types [RFC2046] in the
      Content-Type and Accept header fields in order to provide open and
      extensible data typing and type negotiation.

   o  operation: the conceptual RESTCONF operation for a message,
      derived from the HTTP method, request URI, headers, and message-
      body.

   o  operation resource: a resource with the media type "application/
      yang.operation+xml" or "application/yang.operation+json".

   o  patch: a generic PATCH request on the target datastore or data
      resource.  The media type of the message-body content will
      identify the patch type in use.

   o  plain patch: a specific PATCH request type that can be used for
      simple merge operations.

   o  query parameter: a parameter (and its value if any), encoded
      within the query component of the request URI.





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   o  RESTCONF capability: An optional RESTCONF protocol feature
      supported by the server, which is identified by an IANA registered
      NETCONF Capability URI, and advertised with an entry in the
      "capability" leaf-list in Section 9.3.

   o  retrieval request: a request using the GET or HEAD methods.

   o  target resource: the resource that is associated with a particular
      message, identified by the "path" component of the request URI.

   o  schema resource: a resource with the media type "application/
      yang".  The YANG representation of the schema can be retrieved by
      the client with the GET method.

   o  stream list: the set of data resource instances that describe the
      event stream resources available from the server.  This
      information is defined in the "ietf-restconf-monitoring" module as
      the "stream" list.  It can be retrieved using the target resource
      "{+restconf}/data/ietf-restconf-monitoring:restconf-state/streams/
      stream".  The stream list contains information about each stream,
      such as the URL to retrieve the event stream data.

1.4.5.  URI Template

   Throughout this document, the URI template [RFC6570] syntax
   "{+restconf}" is used to refer to the RESTCONF API entry point
   outside of an example.  See Section 3.1 for details.

   For simplicity, all of the examples in this document assume
   "/restconf" as the discovered RESTCONF API root path.

1.4.6.  Tree Diagrams

   A simplified graphical representation of the data model is used in
   this document.  The meaning of the symbols in these diagrams is as
   follows:

   o  Brackets "[" and "]" enclose list keys.

   o  Abbreviations before data node names: "rw" means configuration
      data (read-write) and "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node, "!"
      means a presence container, and "*" denotes a list and leaf-list.

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").




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   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  Transport Protocol Requirements

2.1.  Integrity and Confidentiality

   HTTP [RFC7230] is an application layer protocol that may be layered
   on any reliable transport-layer protocol.  RESTCONF is defined on top
   of HTTP, but due to the sensitive nature of the information conveyed,
   RESTCONF requires that the transport-layer protocol provides both
   data integrity and confidentiality, such as are provided by the TLS
   protocol [RFC5246].

2.2.  HTTPS with X.509v3 Certificates

   Given the nearly ubiquitous support for HTTP over TLS [RFC7230],
   RESTCONF implementations MUST support the "https" URI scheme, which
   has the IANA assigned default port 443.  Consistent with the
   exclusive use of X.509v3 certificates for NETCONF over TLS
   [draft-ietf-netconf-rfc5539bis-10], use of certificates in RESTCONF
   is also limited to X.509v3 certificates.

2.3.  Certificate Validation

   When presented an X.509 certificate, the RESTCONF peer MUST use X.509
   certificate path validation [RFC5280] to verify the integrity of the
   certificate.  The presented X.509 certificate MAY also be considered
   valid if it matches a locally configured certificate fingerprint.  If
   X.509 certificate path validation fails and the presented X.509
   certificate does not match a locally configured certificate
   fingerprint, the connection MUST be terminated as defined in
   [RFC5246].

2.4.  Authenticated Server Identity

   The RESTCONF client MUST carefully examine the certificate presented
   by the RESTCONF server to determine if it meets the client's
   expectations.  The RESTCONF client MUST check the identity of the
   server according to Section 6 of [RFC6125], including processing the
   outcome as described in Section 6.6 of [RFC6125].

2.5.  Authenticated Client Identity

   The RESTCONF server MUST authenticate client access to any protected
   resource using HTTP Authentication [RFC7235].  If the RESTCONF client
   is not authenticated to access a resource, the server MUST send a
   response with status code 401 (Unauthorized) and a WWW-Authenticate



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   header field containing at least one challenge applicable to the
   target resource.  The RESTCONF server MAY advertise support for any
   number of authentication schemes but, in order to ensure
   interoperability, the RESTCONF server MUST advertise at least one of
   the following authentication schemes:

   o  Basic [draft-ietf-httpauth-basicauth-update-03]

   o  Digest [draft-ietf-httpauth-digest-09]

   o  ClientCertificate [draft-thomson-httpbis-cant-01]

   These authentication schemes are selected for to their similarity to
   the authentication schemes supported by NETCONF.  In particular, the
   Basic and Digest authentication schemes both directly provide an
   identity and verification of a shared secret, much like NETCONF over
   SSH, when using the SSH "password" authentication method [RFC4252].
   Similarly, the ClientCertificate authentication scheme is much like
   NETCONF over TLS's use of X.509 client-certificates.  When using the
   ClientCertificate authentication scheme, the RESTCONF server MUST
   derive the identity of the RESTCONF client using the algorithm
   defined in Section 7 of [draft-ietf-netconf-rfc5539bis-10].

   The RESTCONF client identity determined from any HTTP authentication
   scheme is hereafter known as the "RESTCONF username" and subject to
   the NETCONF Access Control Module (NACM) [RFC6536].

3.  Resources

   The RESTCONF protocol operates on a hierarchy of resources, starting
   with the top-level API resource itself (Section 3.1).  Each resource
   represents a manageable component within the device.

   A resource can be considered a collection of conceptual data and the
   set of allowed methods on that data.  It can contain nested child
   resources.  The child resource types and methods allowed on them are
   data-model specific.

   A resource has its own media type identifier, represented by the
   "Content-Type" header in the HTTP response message.  A resource can
   contain zero or more nested resources.  A resource can be created and
   deleted independently of its parent resource, as long as the parent
   resource exists.

   All RESTCONF resources are defined in this document except specific
   datastore contents, protocol operations, and event notifications.
   The syntax and semantics for these resource types are defined in YANG
   modules.



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   The RESTCONF resources are accessed via a set of URIs defined in this
   document.  The set of YANG modules supported by the server will
   determine the data model specific operations, top-level data node
   resources, and event notification messages supported by the server.

   The RESTCONF protocol does not include a resource discovery
   mechanism.  Instead, the definitions within the YANG modules
   advertised by the server are used to construct a predictable
   operation or data resource identifier.

3.1.  Root Resource Discovery

   In line with the best practices defined by [RFC7320], RESTCONF
   enables deployments to specify where the RESTCONF API is located.
   When first connecting to a RESTCONF server, a RESTCONF client MUST
   determine the root of the RESTCONF API.  The client discovers this by
   getting the "/.well-known/host-meta" resource ([RFC6415]) and using
   the <Link> element containing the "restconf" attribute :

      Request
      -------
      GET /.well-known/host-meta users HTTP/1.1
      Host: example.com
      Accept: application/xrd+xml

      Response
      --------
      HTTP/1.1 200 OK
      Content-Type: application/xrd+xml
      Content-Length: nnn

      <XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
          <Link rel='restconf' href='/restconf'/>
      </XRD>

   Once discovering the RESTCONF API root, the client MUST prepend it to
   any subsequent request to a RESTCONF resource.  For instance, using
   the "/restconf" path discovered above, the client can now determine
   the operations supported by the the server.  In this example a custom
   "play" operation is supported:











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      Request
      -------
      GET /restconf/operations  HTTP/1.1
      Host: example.com
      Accept: application/yang.api+json

      Response
      --------
      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Last-Modified: Sun, 22 Apr 2012 01:00:14 GMT
      Content-Type: application/yang.api+json

      { "operations" : { "play" : [ null ] } }

3.2.  RESTCONF Resource Types

   The RESTCONF protocol defines a set of application specific media
   types to identify each of the available resource types.  The
   following resource types are defined in RESTCONF:

              +-----------+---------------------------------+
              | Resource  | Media Type                      |
              +-----------+---------------------------------+
              | API       | application/yang.api+xml        |
              |           | application/yang.api+json       |
              | Datastore | application/yang.datastore+xml  |
              |           | application/yang.datastore+json |
              | Data      | application/yang.data+xml       |
              |           | application/yang.data+json      |
              | Errors    | application/yang.errors+xml     |
              |           | application/yang.errors+json    |
              | Operation | application/yang.operation+xml  |
              |           | application/yang.operation+json |
              | Schema    | application/yang                |
              +-----------+---------------------------------+

                           RESTCONF Media Types

3.3.  API Resource

   The API resource contains the entry points for the RESTCONF datastore
   and operation resources.  It is the top-level resource located at
   {+restconf} and has the media type "application/yang.api+xml" or
   "application/yang.api+json".



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   YANG Tree Diagram for an API Resource:

      +--rw restconf
         +--rw data
         +--rw operations

   The "application/yang.api" restconf-media-type extension in the
   "ietf-restconf" module defined in Section 8 is used to specify the
   structure and syntax of the conceptual child resources within the API
   resource.

   The API resource can be retrieved with the GET method.

   This resource has the following child resources:

            +----------------+--------------------------------+
            | Child Resource | Description                    |
            +----------------+--------------------------------+
            | data           | Contains all data resources    |
            | operations     | Data-model specific operations |
            +----------------+--------------------------------+

                           RESTCONF API Resource

3.3.1.  {+restconf}/data

   This mandatory resource represents the combined configuration and
   operational data resources that can be accessed by a client.  It
   cannot be created or deleted by the client.  The datastore resource
   type is defined in Section 3.4.

   Example:

   This example request by the client would retrieve only the non-
   configuration data nodes that exist within the "library" resource,
   using the "content" query parameter (see Section 4.8.1).

      GET /restconf/data/example-jukebox:jukebox/library
         ?content=nonconfig  HTTP/1.1
      Host: example.com
      Accept: application/yang.data+xml

   The server might respond:








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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:30 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+xml

      <library xmlns="https://example.com/ns/example-jukebox">
        <artist-count>42</artist-count>
        <album-count>59</album-count>
        <song-count>374</song-count>
      </library>

3.3.2.  {+restconf}/operations

   This optional resource is a container that provides access to the
   data-model specific protocol operations supported by the server.  The
   server MAY omit this resource if no data-model specific operations
   are advertised.

   Any data-model specific operations defined in the YANG modules
   advertised by the server MAY be available as child nodes of this
   resource.

   Operation resources are defined in Section 3.6.

3.4.  Datastore Resource

   The "{+restconf}/data" subtree represents the datastore resource
   type, which is a collection of configuration and operational data
   nodes.

   This resource type is an abstraction of the system's underlying
   datastore implementation.  It is used to simplify resource editing
   for the client.  The RESTCONF datastore resource is a conceptual
   collection of all configuration and operational data that is present
   on the device.

   Configuration edit transaction management and configuration
   persistence are handled by the server and not controlled by the
   client.  A datastore resource can only be written directly with the
   PATCH method.  Each RESTCONF edit of a datastore resource is saved to
   non-volatile storage in an implementation-specific matter by the
   server.







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3.4.1.  Edit Collision Detection

   Two "edit collision detection" mechanisms are provided in RESTCONF,
   for datastore and data resources.

3.4.1.1.  Timestamp

   The last change time is maintained and the "Last-Modified"
   ([RFC7232], Section 2.2) header is returned in the response for a
   retrieval request.  The "If-Unmodified-Since" header can be used in
   edit operation requests to cause the server to reject the request if
   the resource has been modified since the specified timestamp.

   The server MUST maintain a last-modified timestamp for the top-level
   {+restconf}/data resource and SHOULD maintain last-modified
   timestamps for descendant resources.  For all resources, the server
   MUST return the "Last-Modified" header when the resource is retrieved
   with the GET or HEAD methods.  If the server does not maintain a
   timestamp for a resource, it MUST return the timestamp of the
   resource's ancestor, a process that may recurse up to the top-level
   {+restconf}/data resource.  Only changes to configuration data
   resources within the datastore affect the timestamp.

3.4.1.2.  Entity tag

   A unique opaque string is maintained and the "ETag" ([RFC7232],
   Section 2.3) header is returned in the response for a retrieval
   request.  The "If-Match" header can be used in edit operation
   requests to cause the server to reject the request if the resource
   entity tag does not match the specified value.

   The server MUST maintain an entity tag for the top-level
   {+restconf}/data resource and SHOULD maintain entity tags for
   descendant resources.  For all resources, the server MUST return the
   "ETag" header when the resource is retrieved with the GET or HEAD
   methods.  If the server does not maintain an entity tag for a
   resource, it MUST return the entity tag of the resource's ancestor, a
   process that may recurse up to the top-level {+restconf}/data
   resource.  Only changes to configuration data resources within the
   datastore affect the entity tag.

3.5.  Data Resource

   A data resource represents a YANG data node that is a descendant node
   of a datastore resource.  Each YANG-defined data node can be uniquely
   targeted by the request-line of an HTTP operation.  Containers,
   leafs, list entries and anyxml nodes are data resources.




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   The representation maintained for each data resource is the YANG
   defined subtree for that node.  HTTP operations on a data resource
   affect both the targeted data node and all its descendants, if any.

   For configuration data resources, the server MAY maintain a last-
   modified timestamp for the resource, and return the "Last-Modified"
   header when it is retrieved with the GET or HEAD methods.  If
   maintained, the resource timestamp MUST be set to the current time
   whenever the resource or any configuration resource within the
   resource is altered.

   For configuration data resources, the server MAY maintain a resource
   entity tag for the resource, and return the "ETag" header when it is
   retrieved as the target resource with the GET or HEAD methods.  If
   maintained, the resource entity tag MUST be updated whenever the
   resource or any configuration resource within the resource is
   altered.

   A data resource can be retrieved with the GET method.  Data resources
   are accessed via the "{+restconf}/data" entry point.  This sub-tree
   is used to retrieve and edit data resources.

   A configuration data resource can be altered by the client with some
   or all of the edit operations, depending on the target resource and
   the specific operation.  Refer to Section 4 for more details on edit
   operations.

   The resource definition version for a data resource is identified by
   the revision date of the YANG module containing the YANG definition
   for the data resource.

3.5.1.  Encoding Data Resource Identifiers in the Request URI

   In YANG, data nodes are named with an absolute XPath expression,
   defined in [XPath], starting from the document root to the target
   resource.  In RESTCONF, URL encoded path expressions are used
   instead.

   A predictable location for a data resource is important, since
   applications will code to the YANG data model module, which uses
   static naming and defines an absolute path location for all data
   nodes.

   A RESTCONF data resource identifier is not an XPath expression.  It
   is encoded from left to right, starting with the top-level data node,
   according to the "api-path" rule in Section 3.5.1.1.  The node name
   of each ancestor of the target resource node is encoded in order,
   ending with the node name for the target resource.



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   If a data node in the path expression is a YANG list node, then the
   key values for the list (if any) MUST be encoded according to the
   following rules:

   o  The key leaf values for a data resource representing a YANG list
      MUST be encoded using one path segment [RFC3986].

   o  If there is only one key leaf value, the path segment is
      constructed by having the list name followed by an "=" followed by
      the single key leaf value.

   o  If there are multiple key leaf values, the value of each leaf
      identified in the "key" statement is encoded in the order
      specified in the YANG "key" statement, with a comma separating
      them.

   o  The key value is specified as a string, using the canonical
      representation for the YANG data type.  Any reserved characters
      MUST be encoded with escape sequences, according to [RFC2396],
      Section 2.4.

   o  All the components in the "key" statement MUST be encoded.
      Partial instance identifiers are not supported.

   o  Quoted strings are supported in the key leaf values.  Quoted
      strings MUST be used to express empty strings.  (example:
      list=foo,'',baz).

   o  The "list-instance" ABNF rule defined in Section 3.5.1.1
      represents the syntax of a list instance identifier.

   o  Resource URI values returned in Location headers for data
      resources MUST identify the module name, even if there are no
      conflicting local names when the resource is created.  This
      ensures the correct resource will be identified even if the server
      loads a new module that the old client does not know about.

   Examples:













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      container top {
          list list1 {
              key "key1 key2 key3";
               ...
               list list2 {
                   key "key4 key5";
                   ...
                   leaf X { type string; }
               }
           }
       }

   For the above YANG definition, URI with key leaf values will be
   encoded as follows (line wrapped for display purposes only):

       /restconf/data/example-top:top/list1=key1val,key2val,key3val3/
          list2=key4val,key5val/X

3.5.1.1.  ABNF For Data Resource Identifiers

   The "api-path" ABNF syntax is used to construct RESTCONF path
   identifiers:

       api-path = "/"  |
                  ("/" api-identifier
                    0*("/" (api-identifier | list-instance )))

       api-identifier = [module-name ":"] identifier   ;; note 1

       module-name = identifier

       list-instance = api-identifier "=" key-value ["," key-value]*

       key-value = string      ;; note 1

       string = <a quoted or unquoted string>

       ;; An identifier MUST NOT start with
       ;; (('X'|'x') ('M'|'m') ('L'|'l'))
       identifier  = (ALPHA / "_")
                     *(ALPHA / DIGIT / "_" / "-" / ".")

   Note 1: The syntax for "api-identifier" and "key-value" MUST conform
   to the JSON identifier encoding rules in Section 4 of
   [I-D.ietf-netmod-yang-json].






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3.5.2.  Defaults Handling

   RESTCONF requires that a server report its default handling mode (see
   Section 9.1.2 for details).  If the optional "with-defaults" query
   parameter is supported by the server, a client may use it to control
   retrieval of default values (see Section 4.8.9 for details).

   If the target of a GET method is a data node that represents a leaf
   that has a default value, and the leaf has not been given a value
   yet, the server MUST return the default value that is in use by the
   server.

   If the target of a GET method is a data node that represents a
   container or list that has any child resources with default values,
   for the child resources that have not been given value yet, the
   server MAY return the default values that are in use by the server,
   in accordance with its reported default handing mode and query
   parameters passed by the client.

3.6.  Operation Resource

   An operation resource represents a protocol operation defined with
   the YANG "rpc" statement.  It is invoked using a POST method on the
   operation resource.

      POST {+restconf}/operations/<operation>

   The <operation> field identifies the module name and rpc identifier
   string for the desired operation.

   For example, if "module-A" defined a "reset" operation, then invoking
   the operation from "module-A" would be requested as follows:

      POST /restconf/operations/module-A:reset HTTP/1.1
      Server example.com

   If the "rpc" statement has an "input" section, then a message-body
   MAY be sent by the client in the request, otherwise the request
   message MUST NOT include a message-body.

   If the operation is successfully invoked, and if the "rpc" statement
   has an "output" section, then a message-body MAY be sent by the
   server in the response, otherwise the response message MUST NOT
   include a message-body in the response message, and MUST send a "204
   No Content" status-line instead.






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   If the operation is not successfully invoked, then a message-body
   SHOULD be sent by the server, containing an "errors" resource, as
   defined in Section 3.9.

3.6.1.  Encoding Operation Input Parameters

   If the "rpc" statement has an "input" section, then the "input" node
   is provided in the message-body, corresponding to the YANG data
   definition statements within the "input" section.

   Example:

   The following YANG definition is used for the examples in this
   section.

     module example-ops {
      namespace "https://example.com/ns/example-ops";
      prefix "ops";

       rpc reboot {
         input {
           leaf delay {
             units seconds;
             type uint32;
             default 0;
           }
           leaf message { type string; }
           leaf language { type string; }
         }
       }

       rpc get-reboot-info {
         output {
           leaf reboot-time {
             units seconds;
             type uint32;
           }
           leaf message { type string; }
           leaf language { type string; }
         }
       }
     }

   The client might send the following POST request message:

      POST /restconf/operations/example-ops:reboot HTTP/1.1
      Host: example.com
      Content-Type: application/yang.operation+xml



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      <input xmlns="https://example.com/ns/example-ops">
       <delay>600</delay>
       <message>Going down for system maintenance</message>
       <language>en-US</language>
      </input>

   The server might respond:

      HTTP/1.1 204 No Content
      Date: Mon, 25 Apr 2012 11:01:00 GMT
      Server: example-server

3.6.2.  Encoding Operation Output Parameters

   If the "rpc" statement has an "output" section, then the "output"
   node is provided in the message-body, corresponding to the YANG data
   definition statements within the "output" section.

   Example:

   The "example-ops" YANG module defined in Section 3.6.1 is used for
   the examples in this section.

   The client might send the following POST request message:

      POST /restconf/operations/example-ops:get-reboot-info HTTP/1.1
      Host: example.com
      Accept: application/yang.operation+json

   The server might respond:

      HTTP/1.1 200 OK
      Date: Mon, 25 Apr 2012 11:10:30 GMT
      Server: example-server
      Content-Type: application/yang.operation+json

      {
        "example-ops:output" : {
          "reboot-time" : 30,
          "message" : "Going down for system maintenance",
          "language" : "en-US"
        }
      }








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3.6.3.  Encoding Operation Errors

   If any errors occur while attempting to invoke the operation, then an
   "errors" data structure is returned with the appropriate error
   status.

   Using the "reset" operation example above, the client might send the
   following POST request message:

      POST /restconf/operations/example-ops:reboot HTTP/1.1
      Host: example.com
      Content-Type: application/yang.operation+xml

      <input xmlns="https://example.com/ns/example-ops">
       <delay>-33</delay>
       <message>Going down for system maintenance</message>
       <language>en-US</language>
      </input>

   The server might respond with an "invalid-value" error:

      HTTP/1.1 400 Bad Request
      Date: Mon, 25 Apr 2012 11:10:30 GMT
      Server: example-server
      Content-Type: application/yang.errors+xml

      <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
       <error>
        <error-type>protocol</error-type>
        <error-tag>invalid-value</error-tag>
        <error-path xmlns:err="https://example.com/ns/example-ops">
          err:input/err:delay
        </error-path>
        <error-message>Invalid input parameter</error-message>
       </error>
      </errors>

3.7.  Schema Resource

   The server can optionally support retrieval of the YANG modules it
   supports, using the "ietf-yang-library" module, defined in
   [I-D.ietf-netconf-yang-library].

   To retrieve a YANG module, a client first needs to get the URL for
   retrieving the schema.

   The client might send the following GET request message:




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      GET /restconf/data/ietf-yang-library:modules/module=
         example-jukebox,2014-07-03/schema HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond:

      HTTP/1.1 200 OK
      Date: Mon, 25 Apr 2012 11:10:30 GMT
      Server: example-server
      Content-Type: application/yang.data+json

      {
        "ietf-yang-library:schema":
         "https://example.com/mymodules/example-jukebox/2015-06-04"
      }

   Next the client needs to retrieve the actual YANG schema.

   The client might send the following GET request message:

      GET https://example.com/mymodules/example-jukebox/2015-06-04
         HTTP/1.1
      Host: example.com
      Accept: application/yang

   The server might respond:

      module example-jukebox {

         // contents of YANG module deleted for this example...

      }

3.8.  Event Stream Resource

   An "event stream" resource represents a source for system generated
   event notifications.  Each stream is created and modified by the
   server only.  A client can retrieve a stream resource or initiate a
   long-poll server sent event stream, using the procedure specified in
   Section 6.3.

   A notification stream functions according to the NETCONF
   Notifications specification [RFC5277].  The available streams can be
   retrieved from the stream list, which specifies the syntax and
   semantics of a stream resource.





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3.9.  Errors Media Type

   An "errors" media type is a collection of error information that is
   sent as the message-body in a server response message, if an error
   occurs while processing a request message.  It is not considered a
   resource type because no instances can be retrieved with a GET
   request.

   The "ietf-restconf" YANG module contains the "application/
   yang.errors" restconf-media-type extension which specifies the syntax
   and semantics of an "errors" media type.  RESTCONF error handling
   behavior is defined in Section 7.

4.  Operations

   The RESTCONF protocol uses HTTP methods to identify the CRUD
   operation requested for a particular resource.

   The following table shows how the RESTCONF operations relate to
   NETCONF protocol operations:

         +----------+--------------------------------------------+
         | RESTCONF | NETCONF                                    |
         +----------+--------------------------------------------+
         | OPTIONS  | none                                       |
         | HEAD     | none                                       |
         | GET      | <get-config>, <get>                        |
         | POST     | <edit-config> (operation="create")         |
         | PUT      | <edit-config> (operation="create/replace") |
         | PATCH    | <edit-config> (operation="merge")          |
         | DELETE   | <edit-config> (operation="delete")         |
         +----------+--------------------------------------------+

                     Table 1: CRUD Methods in RESTCONF

   The NETCONF "remove" operation attribute is not supported by the HTTP
   DELETE method.  The resource must exist or the DELETE method will
   fail.  The PATCH method is equivalent to a "merge" operation when
   using a plain patch (see Section 4.6.1), other media-types may
   provide more granular control.

   Access control mechanisms may be used to limit what operations can be
   used.  In particular, RESTCONF is compatible with the NETCONF Access
   Control Model (NACM) [RFC6536], as there is a specific mapping
   between RESTCONF and NETCONF operations, defined in Table 1.  The
   resource path needs to be converted internally by the server to the
   corresponding YANG instance-identifier.  Using this information, the
   server can apply the NACM access control rules to RESTCONF messages.



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   The server MUST NOT allow any operation to any resources that the
   client is not authorized to access.

   Implementation of all methods (except PATCH) are defined in
   [RFC7231].  This section defines the RESTCONF protocol usage for each
   HTTP method.

4.1.  OPTIONS

   The OPTIONS method is sent by the client to discover which methods
   are supported by the server for a specific resource (e.g., GET, POST,
   DELETE, etc.).

   The server SHOULD implement this method, however the same information
   could be extracted from the YANG modules and the RESTCONF protocol
   specification.

   If the PATCH method is supported, then the "Accept-Patch" header MUST
   be supported and returned in the response to the OPTIONS request, as
   defined in [RFC5789].

4.2.  HEAD

   The HEAD method is sent by the client to retrieve just the headers
   that would be returned for the comparable GET method, without the
   response message-body.  It is supported for all resource types,
   except operation resources.

   The request MUST contain a request URI that contains at least the
   entry point.  The same query parameters supported by the GET method
   are supported by the HEAD method.

   The access control behavior is enforced as if the method was GET
   instead of HEAD.  The server MUST respond the same as if the method
   was GET instead of HEAD, except that no response message-body is
   included.

4.3.  GET

   The GET method is sent by the client to retrieve data and meta-data
   for a resource.  It is supported for all resource types, except
   operation resources.  The request MUST contain a request URI that
   contains at least the entry point.

   The server MUST NOT return any data resources for which the user does
   not have read privileges.  If the user is not authorized to read the
   target resource, an error response containing a "403 Forbidden" or
   "404 Not Found" status-line is returned to the client.



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   If the user is authorized to read some but not all of the target
   resource, the unauthorized content is omitted from the response
   message-body, and the authorized content is returned to the client.

   Example:

   The client might request the response headers for an XML
   representation of the "library" resource:

      GET /restconf/data/example-jukebox:jukebox/
        library/artist=Foo%20Fighters/album  HTTP/1.1
      Host: example.com
      Accept: application/yang.data+xml

   The server might respond:

      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:02:40 GMT
      Server: example-server
      Content-Type: application/yang.data+xml
      Cache-Control: no-cache
      Pragma: no-cache
      ETag: a74eefc993a2b
      Last-Modified: Mon, 23 Apr 2012 11:02:14 GMT

      <album xmlns="http://example.com/ns/example-jukebox">
       <name>Wasting Light</name>
       <genre xmlns:g="http://example.com/ns/example-jukebox">
         g:alternative
       </genre>
       <year>2011</2011>
      </album>

4.4.  POST

   The POST method is sent by the client to create a data resource or
   invoke an operation resource.  The server uses the target resource
   media type to determine how to process the request.

      +-----------+------------------------------------------------+
      | Type      | Description                                    |
      +-----------+------------------------------------------------+
      | Datastore | Create a top-level configuration data resource |
      | Data      | Create a configuration data child resource     |
      | Operation | Invoke a protocol operation                    |
      +-----------+------------------------------------------------+

                     Resource Types that Support POST



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4.4.1.  Create Resource Mode

   If the target resource type is a datastore or data resource, then the
   POST is treated as a request to create a top-level resource or child
   resource, respectively.  The message-body is expected to contain the
   content of a child resource to create within the parent (target
   resource).  The data-model for the child tree is the subtree is
   defined by YANG for the child resource.

   The "insert" and "point" query parameters are supported by the POST
   method for datastore and data resource types, as specified in the
   YANG definition in Section 8.

   If the POST method succeeds, a "201 Created" status-line is returned
   and there is no response message-body.  A "Location" header
   identifying the child resource that was created MUST be present in
   the response in this case.

   If the user is not authorized to create the target resource, an error
   response containing a "403 Forbidden" or "404 Not Found" status-line
   is returned to the client.  All other error responses are handled
   according to the procedures defined in Section 7.

   Example:

   To create a new "jukebox" resource, the client might send:

      POST /restconf/data HTTP/1.1
      Host: example.com
      Content-Type: application/yang.data+json

      { "example-jukebox:jukebox" : [null] }

   If the resource is created, the server might respond as follows.
   Note that the "Location" header line is wrapped for display purposes
   only:

      HTTP/1.1 201 Created
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Location: https://example.com/restconf/data/
          example-jukebox:jukebox
      Last-Modified: Mon, 23 Apr 2012 17:01:00 GMT
      ETag: b3a3e673be2

   Refer to Appendix D.2.1 for more resource creation examples.





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4.4.2.  Invoke Operation Mode

   If the target resource type is an operation resource, then the POST
   method is treated as a request to invoke that operation.  The
   message-body (if any) is processed as the operation input parameters.
   Refer to Section 3.6 for details on operation resources.

   If the POST request succeeds, a "200 OK" status-line is returned if
   there is a response message-body, and a "204 No Content" status-line
   is returned if there is no response message-body.

   If the user is not authorized to invoke the target operation, an
   error response containing a "403 Forbidden" or "404 Not Found"
   status-line is returned to the client.  All other error responses are
   handled according to the procedures defined in Section 7.

   Example:

   In this example, the client is invoking the "play" operation defined
   in the "example-jukebox" YANG module.

   A client might send a "play" request as follows:

      POST /restconf/operations/example-jukebox:play   HTTP/1.1
      Host: example.com
      Content-Type: application/yang.operation+json

      {
        "example-jukebox:input" : {
          "playlist" : "Foo-One",
          "song-number" : 2
        }
      }

   The server might respond:

      HTTP/1.1 204 No Content
      Date: Mon, 23 Apr 2012 17:50:00 GMT
      Server: example-server

4.5.  PUT

   The PUT method is sent by the client to create or replace the target
   resource.

   The only target resource media type that supports PUT is the data
   resource.  The message-body is expected to contain the content used
   to create or replace the target resource.



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   The "insert" (Section 4.8.4) and "point" (Section 4.8.5) query
   parameters are supported by the PUT method for data resources.

   Consistent with [RFC7231], if the PUT request creates a new resource,
   a "201 Created" status-line is returned.  If an existing resource is
   modified, either "200 OK" or "204 No Content" are returned.

   If the user is not authorized to create or replace the target
   resource an error response containing a "403 Forbidden" or "404 Not
   Found" status-line is returned to the client.  All other error
   responses are handled according to the procedures defined in
   Section 7.

   Example:

   An "album" child resource defined in the "example-jukebox" YANG
   module is replaced or created if it does not already exist.

   To replace the "album" resource contents, the client might send as
   follows.  Note that the request-line is wrapped for display purposes
   only:

      PUT /restconf/data/example-jukebox:jukebox/
         library/artist=Foo%20Fighters/album=Wasting%20Light   HTTP/1.1
      Host: example.com
      Content-Type: application/yang.data+json

      {
        "example-jukebox:album" : {
          "name" : "Wasting Light",
          "genre" : "example-jukebox:alternative",
          "year" : 2011
        }
      }

   If the resource is updated, the server might respond:

      HTTP/1.1 204 No Content
      Date: Mon, 23 Apr 2012 17:04:00 GMT
      Server: example-server
      Last-Modified: Mon, 23 Apr 2012 17:04:00 GMT
      ETag: b27480aeda4c

4.6.  PATCH

   RESTCONF uses the HTTP PATCH method defined in [RFC5789] to provide
   an extensible framework for resource patching mechanisms.  It is
   optional to implement by the server.  Each patch type needs a unique



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   media type.  Zero or more PATCH media types MAY be supported by the
   server.  The media types supported by a server can be discovered by
   the client by sending an OPTIONS request (see Section 4.1).

   If the target resource instance does not exist, the server MUST NOT
   create it.

   If the PATCH request succeeds, a "200 OK" status-line is returned if
   there is a message-body, and "204 No Content" is returned if no
   response message-body is sent.

   If the user is not authorized to alter the target resource an error
   response containing a "403 Forbidden" or "404 Not Found" status-line
   is returned to the client.  All other error responses are handled
   according to the procedures defined in Section 7.

4.6.1.  Plain Patch

   The plain patch mechanism merges the contents of the message body
   with the target resource.  If the target resource is a datastore
   resource (see Section 3.4), the message body MUST be either
   application/yang.datastore+xml or application/yang.datastore+json.
   If then the target resource is a data resource (see Section 3.5),
   then the message body MUST be either application/yang.data+xml or
   application/yang.data+json.

   Plain patch can used to create or update, but not delete, a child
   resource within the target resource.  Please see
   [I-D.ietf-netconf-yang-patch] for an alternate media-type supporting
   more granular control.  The YANG Patch Media Type allows multiple
   sub-operations (e.g., merge, delete) within a single PATCH operation.

   Example:

   To replace just the "year" field in the "album" resource (instead of
   replacing the entire resource with the PUT method), the client might
   send a plain patch as follows.  Note that the request-line is wrapped
   for display purposes only:

      PATCH /restconf/data/example-jukebox:jukebox/
         library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
      Host: example.com
      If-Match: b8389233a4c
      Content-Type: application/yang.data+xml

      <album xmlns="http://example.com/ns/example-jukebox">
       <year>2011</year>
      </album>



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   If the field is updated, the server might respond:

      HTTP/1.1 204 No Content
      Date: Mon, 23 Apr 2012 17:49:30 GMT
      Server: example-server
      Last-Modified: Mon, 23 Apr 2012 17:49:30 GMT
      ETag: b2788923da4c

4.7.  DELETE

   The DELETE method is used to delete the target resource.  If the
   DELETE request succeeds, a "204 No Content" status-line is returned,
   and there is no response message-body.

   If the user is not authorized to delete the target resource then an
   error response containing a "403 Forbidden" or "404 Not Found"
   status-line is returned to the client.  All other error responses are
   handled according to the procedures defined in Section 7.

   Example:

   To delete a resource such as the "album" resource, the client might
   send:

      DELETE /restconf/data/example-jukebox:jukebox/
         library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
      Host: example.com

   If the resource is deleted, the server might respond:

      HTTP/1.1 204 No Content
      Date: Mon, 23 Apr 2012 17:49:40 GMT
      Server: example-server

4.8.  Query Parameters

   Each RESTCONF operation allows zero or more query parameters to be
   present in the request URI.  The specific parameters that are allowed
   depends on the resource type, and sometimes the specific target
   resource used, in the request.











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   +---------------+---------+-----------------------------------------+
   | Name          | Methods | Description                             |
   +---------------+---------+-----------------------------------------+
   | content       | GET     | Select config and/or non-config data    |
   |               |         | resources                               |
   | depth         | GET     | Request limited sub-tree depth in the   |
   |               |         | reply content                           |
   | fields        | GET     | Request a subset of the target resource |
   |               |         | contents                                |
   | filter        | GET     | Boolean notification filter for event   |
   |               |         | stream resources                        |
   | insert        | POST,   | Insertion mode for user-ordered data    |
   |               | PUT     | resources                               |
   | point         | POST,   | Insertion point for user-ordered data   |
   |               | PUT     | resources                               |
   | start-time    | GET     | Replay buffer start time for event      |
   |               |         | stream resources                        |
   | stop-time     | GET     | Replay buffer stop time for event       |
   |               |         | stream resources                        |
   | with-defaults | GET     | Control retrieval of default values     |
   +---------------+---------+-----------------------------------------+

                         RESTCONF Query Parameters

   Query parameters can be given in any order.  Each parameter can
   appear at most once in a request URI.  A default value may apply if
   the parameter is missing.

   Refer to Appendix D.3 for examples of query parameter usage.

   If vendors define additional query parameters, they SHOULD use a
   prefix (such as the enterprise or organization name) for query
   parameter names in order to avoid collisions with other parameters.

4.8.1.  The "content" Query Parameter

   The "content" parameter controls how descendant nodes of the
   requested data nodes will be processed in the reply.

   The allowed values are:

    +-----------+-----------------------------------------------------+
    | Value     | Description                                         |
    +-----------+-----------------------------------------------------+
    | config    | Return only configuration descendant data nodes     |
    | nonconfig | Return only non-configuration descendant data nodes |
    | all       | Return all descendant data nodes                    |
    +-----------+-----------------------------------------------------+



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   This parameter is only allowed for GET methods on datastore and data
   resources.  A 400 Bad Request error is returned if used for other
   methods or resource types.

   The default value is determined by the "config" statement value of
   the requested data nodes.  If the "config" value is "false", then the
   default for the "content" parameter is "nonconfig".  If "config" is
   "true" then the default for the "content" parameter is "config".

   This query parameter MUST be supported by the server.

4.8.2.  The "depth" Query Parameter

   The "depth" parameter is used to specify the number of nest levels
   returned in a response for a GET method.  The first nest-level
   consists of the requested data node itself.  Any child nodes which
   are contained within a parent node have a depth value that is 1
   greater than its parent.

   The value of the "depth" parameter is either an integer between 1 and
   65535, or the string "unbounded".  "unbounded" is the default.

   This parameter is only allowed for GET methods on API, datastore, and
   data resources.  A 400 Bad Request error is returned if it used for
   other methods or resource types.

   By default, the server will include all sub-resources within a
   retrieved resource, which have the same resource type as the
   requested resource.  Only one level of sub-resources with a different
   media type than the target resource will be returned.

   If the "depth" query parameter URI is listed in the "capability"
   leaf-list in Section 9.3, then the server supports the "depth" query
   parameter.

4.8.3.  The "fields" Query Parameter

   The "fields" query parameter is used to optionally identify data
   nodes within the target resource to be retrieved in a GET method.
   The client can use this parameter to retrieve a subset of all nodes
   in a resource.

   A value of the "fields" query parameter matches the following rule:

     fields-expr = path '(' fields-expr / '*' ')' /
                   path ';' fields-expr /
                   path
     path = api-identifier [ '/' path ]



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   "api-identifier" is defined in Section 3.5.1.1.

   ";" is used to select multiple nodes.  For example, to retrieve only
   the "genre" and "year" of an album, use: "fields=genre;year".

   Parentheses are used to specify sub-selectors of a node.  For
   example, to retrieve only the "label" and "catalogue-number" of an
   album, use: "fields=admin(label;catalogue-number)".

   "/" is used in a path to retrieve a child node of a node.  For
   example, to retrieve only the "label" of an album, use:
   "fields=admin/label".

   This parameter is only allowed for GET methods on api, datastore, and
   data resources.  A 400 Bad Request error is returned if used for
   other methods or resource types.

   If the "fields" query parameter URI is listed in the "capability"
   leaf-list in Section 9.3, then the server supports the "fields"
   parameter.

4.8.4.  The "insert" Query Parameter

   The "insert" parameter is used to specify how a resource should be
   inserted within a user-ordered list.

   The allowed values are:

   +--------+----------------------------------------------------------+
   | Value  | Description                                              |
   +--------+----------------------------------------------------------+
   | first  | Insert the new data as the new first entry.              |
   | last   | Insert the new data as the new last entry.               |
   | before | Insert the new data before the insertion point, as       |
   |        | specified by the value of the "point" parameter.         |
   | after  | Insert the new data after the insertion point, as        |
   |        | specified by the value of the "point" parameter.         |
   +--------+----------------------------------------------------------+

   The default value is "last".

   This parameter is only supported for the POST and PUT methods.  It is
   also only supported if the target resource is a data resource, and
   that data represents a YANG list or leaf-list that is ordered by the
   user.






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   If the values "before" or "after" are used, then a "point" query
   parameter for the insertion parameter MUST also be present, or a 400
   Bad Request error is returned.

   The "insert" query parameter MUST be supported by the server.

4.8.5.  The "point" Query Parameter

   The "point" parameter is used to specify the insertion point for a
   data resource that is being created or moved within a user ordered
   list or leaf-list.

   The value of the "point" parameter is a string that identifies the
   path to the insertion point object.  The format is the same as a
   target resource URI string.

   This parameter is only supported for the POST and PUT methods.  It is
   also only supported if the target resource is a data resource, and
   that data represents a YANG list or leaf-list that is ordered by the
   user.

   If the "insert" query parameter is not present, or has a value other
   than "before" or "after", then a 400 Bad Request error is returned.

   This parameter contains the instance identifier of the resource to be
   used as the insertion point for a POST or PUT method.

   The "point" query parameter MUST be supported by the server.

4.8.6.  The "filter" Query Parameter

   The "filter" parameter is used to indicate which subset of all
   possible events are of interest.  If not present, all events not
   precluded by other parameters will be sent.

   This parameter is only allowed for GET methods on a text/event-stream
   data resource.  A 400 Bad Request error is returned if used for other
   methods or resource types.

   The format of this parameter is an XPath 1.0 expression, and is
   evaluated in the following context:

   o  The set of namespace declarations is the set of prefix and
      namespace pairs for all supported YANG modules, where the prefix
      is the YANG module name, and the namespace is as defined by the
      "namespace" statement in the YANG module.





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   o  The function library is the core function library defined in XPath
      1.0.

   o  The set of variable bindings is empty.

   o  The context node is the root node.

   The filter is used as defined in [RFC5277], Section 3.6.  If the
   boolean result of the expression is true when applied to the
   conceptual "notification" document root, then the event notification
   is delivered to the client.

   If the "filter" query parameter URI is listed in the "capability"
   leaf-list in Section 9.3, then the server supports the "filter" query
   parameter.

4.8.7.  The "start-time" Query Parameter

   The "start-time" parameter is used to trigger the notification replay
   feature and indicate that the replay should start at the time
   specified.  If the stream does not support replay, per the
   "replay-support" attribute returned by stream list entry for the
   stream resource, then the server MUST return the HTTP error code 400
   Bad Request.

   The value of the "start-time" parameter is of type "date-and-time",
   defined in the "ietf-yang" YANG module [RFC6991].

   This parameter is only allowed for GET methods on a text/event-stream
   data resource.  A 400 Bad Request error is returned if used for other
   methods or resource types.

   If this parameter is not present, then a replay subscription is not
   being requested.  It is not valid to specify start times that are
   later than the current time.  If the value specified is earlier than
   the log can support, the replay will begin with the earliest
   available notification.

   If this query parameter is supported by the server, then the "replay"
   query parameter URI MUST be listed in the "capability" leaf-list in
   Section 9.3.  The "stop-time" query parameter MUST also be supported
   by the server.

   If the "replay-support" leaf is present in the "stream" entry
   (defined in Section 9.3) then the server MUST support the
   "start-time" and "stop-time" query parameters for that stream.





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4.8.8.  The "stop-time" Query Parameter

   The "stop-time" parameter is used with the replay feature to indicate
   the newest notifications of interest.  This parameter MUST be used
   with and have a value later than the "start-time" parameter.

   The value of the "stop-time" parameter is of type "date-and-time",
   defined in the "ietf-yang" YANG module [RFC6991].

   This parameter is only allowed for GET methods on a text/event-stream
   data resource.  A 400 Bad Request error is returned if used for other
   methods or resource types.

   If this parameter is not present, the notifications will continue
   until the subscription is terminated.  Values in the future are
   valid.

   If this query parameter is supported by the server, then the "replay"
   query parameter URI MUST be listed in the "capability" leaf-list in
   Section 9.3.  The "start-time" query parameter MUST also be supported
   by the server.

   If the "replay-support" leaf is present in the "stream" entry
   (defined in Section 9.3) then the server MUST support the
   "start-time" and "stop-time" query parameters for that stream.

4.8.9.  The "with-defaults" Query Parameter

   The "with-defaults" parameter is used to specify how information
   about default data nodes should be returned in response to GET
   requests on data resources.

   If the server supports this capability, then it MUST implement the
   behavior in Section 4.5.1 of [RFC6243], except applied to the
   RESTCONF GET operation, instead of the NETCONF operations.

   +-------------------+-----------------------------------------------+
   | Value             | Description                                   |
   +-------------------+-----------------------------------------------+
   | report-all        | All data nodes are reported                   |
   | trim              | Data nodes set to the YANG default are not    |
   |                   | reported                                      |
   | explicit          | Data nodes set by the client are not reported |
   | report-all-tagged | All data nodes are reported and defaults are  |
   |                   | tagged                                        |
   +-------------------+-----------------------------------------------+





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   If the "with-defaults" parameter is set to "report-all" then the
   server MUST adhere to the defaults reporting behavior defined in
   Section 3.1 of [RFC6243].

   If the "with-defaults" parameter is set to "trim" then the server
   MUST adhere to the defaults reporting behavior defined in Section 3.2
   of [RFC6243].

   If the "with-defaults" parameter is set to "explicit" then the server
   MUST adhere to the defaults reporting behavior defined in Section 3.3
   of [RFC6243].

   If the "with-defaults" parameter is set to "report-all-tagged" then
   the server MUST adhere to the defaults reporting behavior defined in
   Section 3.4 of [RFC6243].

   If the "with-defaults" parameter is not present then the server MUST
   adhere to the defaults reporting behavior defined in its "basic-mode"
   parameter for the "defaults" protocol capability URI, defined in
   Section 9.1.2.

   If the server includes the "with-defaults" query parameter URI in the
   "capability" leaf-list in Section 9.3, then the "with-defaults" query
   parameter MUST be supported.

5.  Messages

   The RESTCONF protocol uses HTTP entities for messages.  A single HTTP
   message corresponds to a single protocol method.  Most messages can
   perform a single task on a single resource, such as retrieving a
   resource or editing a resource.  The exception is the PATCH method,
   which allows multiple datastore edits within a single message.

5.1.  Request URI Structure

   Resources are represented with URIs following the structure for
   generic URIs in [RFC3986].

   A RESTCONF operation is derived from the HTTP method and the request
   URI, using the following conceptual fields:

        <OP> /<restconf>/<path>?<query>#<fragment>









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         ^       ^        ^       ^         ^
         |       |        |       |         |
       method  entry  resource  query    fragment

         M       M        O        O         I

       M=mandatory, O=optional, I=ignored

       <text> replaced by client with real values

   o  method: the HTTP method identifying the RESTCONF operation
      requested by the client, to act upon the target resource specified
      in the request URI.  RESTCONF operation details are described in
      Section 4.

   o  entry: the root of the RESTCONF API configured on this HTTP
      server, discovered by getting the ".well-known/host-meta"
      resource, as described in Section 3.1.

   o  resource: the path expression identifying the resource that is
      being accessed by the operation.  If this field is not present,
      then the target resource is the API itself, represented by the
      media type "application/yang.api".

   o  query: the set of parameters associated with the RESTCONF message.
      These have the familiar form of "name=value" pairs.  Most query
      parameters are optional to implement by the server and optional to
      use by the client.  Each optional query parameter is identified by
      a URI.  The server MUST list the optional query parameter URIs it
      supports in the "capabilities" list defined in Section 9.3.

   There is a specific set of parameters defined, although the server
   MAY choose to support query parameters not defined in this document.
   The contents of the any query parameter value MUST be encoded
   according to [RFC2396], Section 3.4.  Any reserved characters MUST be
   encoded with escape sequences, according to [RFC2396], Section 2.4.

   o  fragment: This field is not used by the RESTCONF protocol.

   When new resources are created by the client, a "Location" header is
   returned, which identifies the path of the newly created resource.
   The client MUST use this exact path identifier to access the resource
   once it has been created.

   The "target" of an operation is a resource.  The "path" field in the
   request URI represents the target resource for the operation.





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5.2.  Message Headers

   There are several HTTP header lines utilized in RESTCONF messages.
   Messages are not limited to the HTTP headers listed in this section.

   HTTP defines which header lines are required for particular
   circumstances.  Refer to each operation definition section in
   Section 4 for examples on how particular headers are used.

   There are some request headers that are used within RESTCONF, usually
   applied to data resources.  The following tables summarize the
   headers most relevant in RESTCONF message requests:

   +---------------------+---------------------------------------------+
   | Name                | Description                                 |
   +---------------------+---------------------------------------------+
   | Accept              | Response Content-Types that are acceptable  |
   | Content-Type        | The media type of the request body          |
   | Host                | The host address of the server              |
   | If-Match            | Only perform the action if the entity       |
   |                     | matches ETag                                |
   | If-Modified-Since   | Only perform the action if modified since   |
   |                     | time                                        |
   | If-Unmodified-Since | Only perform the action if un-modified      |
   |                     | since time                                  |
   +---------------------+---------------------------------------------+

                         RESTCONF Request Headers

   The following tables summarize the headers most relevant in RESTCONF
   message responses:

   +---------------+---------------------------------------------------+
   | Name          | Description                                       |
   +---------------+---------------------------------------------------+
   | Allow         | Valid actions when 405 error returned             |
   | Cache-Control | The cache control parameters for the response     |
   | Content-Type  | The media type of the response message-body       |
   | Date          | The date and time the message was sent            |
   | ETag          | An identifier for a specific version of a         |
   |               | resource                                          |
   | Last-Modified | The last modified date and time of a resource     |
   | Location      | The resource identifier for a newly created       |
   |               | resource                                          |
   +---------------+---------------------------------------------------+

                         RESTCONF Response Headers




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5.3.  Message Encoding

   RESTCONF messages are encoded in HTTP according to [RFC7230].  The
   "utf-8" character set is used for all messages.  RESTCONF message
   content is sent in the HTTP message-body.

   Content is encoded in either JSON or XML format.  A server MUST
   support XML encoding and MAY support JSON encoding.  XML encoding
   rules for data nodes are defined in [RFC6020].  The same encoding
   rules are used for all XML content.  JSON encoding rules are defined
   in [I-D.ietf-netmod-yang-json].  This encoding is valid JSON, but
   also has special encoding rules to identify module namespaces and
   provide consistent type processing of YANG data.

   Request input content encoding format is identified with the Content-
   Type header.  This field MUST be present if a message-body is sent by
   the client.

   Response output content encoding format is identified with the Accept
   header in the request, or if is not specified, the request input
   encoding format is used.  If there was no request input, then the
   default output encoding is XML.  File extensions encoded in the
   request are not used to identify format encoding.

5.4.  RESTCONF Meta-Data

   The RESTCONF protocol needs to retrieve the same meta-data that is
   used in the NETCONF protocol.  Information about default leafs, last-
   modified timestamps, etc. are commonly used to annotate
   representations of the datastore contents.  This meta-data is not
   defined in the YANG schema because it applies to the datastore, and
   is common across all data nodes.

   This information is encoded as attributes in XML.  JSON encoding of
   meta-data is defined in [I-D.ietf-netmod-yang-metadata].

5.5.  Return Status

   Each message represents some sort of resource access.  An HTTP
   "status-line" header line is returned for each request.  If a 4xx or
   5xx range status code is returned in the status-line, then the error
   information will be returned in the response, according to the format
   defined in Section 7.1.








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5.6.  Message Caching

   Since the datastore contents change at unpredictable times, responses
   from a RESTCONF server generally SHOULD NOT be cached.

   The server SHOULD include a "Cache-Control" header in every response
   that specifies whether the response should be cached.  A "Pragma"
   header specifying "no-cache" MAY also be sent in case the
   "Cache-Control" header is not supported.

   Instead of using HTTP caching, the client SHOULD track the "ETag"
   and/or "Last-Modified" headers returned by the server for the
   datastore resource (or data resource if the server supports it).  A
   retrieval request for a resource can include the "If-None-Match" and/
   or "If-Modified-Since" headers, which will cause the server to return
   a "304 Not Modified" status-line if the resource has not changed.
   The client MAY use the HEAD method to retrieve just the message
   headers, which SHOULD include the "ETag" and "Last-Modified" headers,
   if this meta-data is maintained for the target resource.

6.  Notifications

   The RESTCONF protocol supports YANG-defined event notifications.  The
   solution preserves aspects of NETCONF Event Notifications [RFC5277]
   while utilizing the Server-Sent Events [W3C.CR-eventsource-20121211]
   transport strategy.

6.1.  Server Support

   A RESTCONF server is not required to support RESTCONF notifications.
   Clients may determine if a server supports RESTCONF notifications by
   using the HTTP operation OPTIONS, HEAD, or GET on the stream list.
   The server does not support RESTCONF notifications if an HTTP error
   code is returned (e.g., 404 Not Found).

6.2.  Event Streams

   A RESTCONF server that supports notifications will populate a stream
   resource for each notification delivery service access point.  A
   RESTCONF client can retrieve the list of supported event streams from
   a RESTCONF server using the GET operation on the stream list.

   The "restconf-state/streams" container definition in the
   "ietf-restconf-monitoring" module (defined in Section 9.3) is used to
   specify the structure and syntax of the conceptual child resources
   within the "streams" resource.

   For example:



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   The client might send the following request:

      GET /restconf/data/ietf-restconf-monitoring:restconf-state/
         streams HTTP/1.1
      Host: example.com
      Accept: application/yang.data+xml

   The server might send the following response:

      HTTP/1.1 200 OK
      Content-Type: application/yang.api+xml








































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      <streams
        xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
         <stream>
            <name>NETCONF</name>
            <description>default NETCONF event stream
            </description>
            <replay-support>true</replay-support>
            <replay-log-creation-time>
               2007-07-08T00:00:00Z
            </replay-log-creation-time>
            <access>
               <encoding>xml</encoding>
               <location>https://example.com/streams/NETCONF
               </location>
            </access>
            <access>
               <encoding>json</encoding>
               <location>https://example.com/streams/NETCONF-JSON
               </location>
            </access>
         </stream>
         <stream>
            <name>SNMP</name>
            <description>SNMP notifications</description>
            <replay-support>false</replay-support>
            <access>
               <encoding>xml</encoding>
               <location>https://example.com/streams/SNMP</location>
            </access>
         </stream>
         <stream>
            <name>syslog-critical</name>
            <description>Critical and higher severity
            </description>
            <replay-support>true</replay-support>
            <replay-log-creation-time>
               2007-07-01T00:00:00Z
            </replay-log-creation-time>
            <access>
               <encoding>xml</encoding>
               <location>
                 https://example.com/streams/syslog-critical
               </location>
            </access>
         </stream>
      </streams>





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6.3.  Subscribing to Receive Notifications

   RESTCONF clients can determine the URL for the subscription resource
   (to receive notifications) by sending an HTTP GET request for the
   "location" leaf with the stream list entry.  The value returned by
   the server can be used for the actual notification subscription.

   The client will send an HTTP GET request for the URL returned by the
   server with the "Accept" type "text/event-stream".

   The server will treat the connection as an event stream, using the
   Server Sent Events [W3C.CR-eventsource-20121211] transport strategy.

   The server MAY support query parameters for a GET method on this
   resource.  These parameters are specific to each notification stream.

   For example:

   The client might send the following request:

      GET /restconf/data/ietf-restconf-monitoring:restconf-state/
         streams/stream=NETCONF/access=xml/location HTTP/1.1
      Host: example.com
      Accept: application/yang.data+xml

   The server might send the following response:

      HTTP/1.1 200 OK
      Content-Type: application/yang.api+xml

      <location
        xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
        https://example.com/streams/NETCONF
      </location>

   The RESTCONF client can then use this URL value to start monitoring
   the event stream:

      GET /streams/NETCONF HTTP/1.1
      Host: example.com
      Accept: text/event-stream
      Cache-Control: no-cache
      Connection: keep-alive

   A RESTCONF client MAY request the server compress the events using
   the HTTP header field "Accept-Encoding".  For instance:





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      GET /streams/NETCONF HTTP/1.1
      Host: example.com
      Accept: text/event-stream
      Cache-Control: no-cache
      Connection: keep-alive
      Accept-Encoding: gzip, deflate

6.3.1.  NETCONF Event Stream

   The server SHOULD support the "NETCONF" notification stream defined
   in [RFC5277].  For this stream, RESTCONF notification subscription
   requests MAY specify parameters indicating the events it wishes to
   receive.  These query parameters are optional to implement, and only
   available if the server supports them.

            +------------+---------+-------------------------+
            | Name       | Section | Description             |
            +------------+---------+-------------------------+
            | start-time | 4.8.7   | replay event start time |
            | stop-time  | 4.8.8   | replay event stop time  |
            | filter     | 4.8.6   | boolean content filter  |
            +------------+---------+-------------------------+

                      NETCONF Stream Query Parameters

   The semantics and syntax for these query parameters are defined in
   the sections listed above.  The YANG encoding MUST be converted to
   URL-encoded string for use in the request URI.

   Refer to Appendix D.3.6 for filter parameter examples.

6.4.  Receiving Event Notifications

   RESTCONF notifications are encoded according to the definition of the
   event stream.  The NETCONF stream defined in [RFC5277] is encoded in
   XML format.

   The structure of the event data is based on the "notification"
   element definition in Section 4 of [RFC5277].  It MUST conform to the
   schema for the "notification" element in Section 4 of [RFC5277],
   except the XML namespace for this element is defined as:

     urn:ietf:params:xml:ns:yang:ietf-restconf

   For JSON encoding purposes, the module name for the "notification"
   element is "ietf-restconf".





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   Two child nodes within the "notification" container are expected,
   representing the event time and the event payload.  The "event-time"
   node is defined within the "ietf-restconf" module namespace.  The
   name and namespace of the payload element are determined by the YANG
   module containing the notification-stmt.

   In the following example, the YANG module "example-mod" is used:

     module example-mod {
       namespace "http://example.com/event/1.0";

       notification event {
        leaf event-class { type string; }
        container reporting-entity {
          leaf card { type string; }
        }
        leaf severity { type string; }
       }
     }

   An example SSE event notification encoded using XML:

      data: <notification
      data:    xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
      data:    <event-time>2013-12-21T00:01:00Z</event-time>
      data:    <event xmlns="http://example.com/event/1.0">
      data:       <event-class>fault</event-class>
      data:       <reporting-entity>
      data:           <card>Ethernet0</card>
      data:       </reporting-entity>
      data:       <severity>major</severity>
      data:     </event>
      data: </notification>

   An example SSE event notification encoded using JSON:

      data: {
      data:   "ietf-restconf:notification": {
      data:     "event-time": "2013-12-21T00:01:00Z",
      data:     "example-mod:event": {
      data:       "event-class": "fault",
      data:       "reporting-entity": { "card": "Ethernet0" },
      data:       "severity": "major"
      data:     }
      data:   }
      data: }





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   Alternatively, since neither XML nor JSON are whitespace sensitive,
   the above messages can be encoded onto a single line.  For example:

   For example: ('\' line wrapping added for formatting only)

      XML:

      data: <notification xmlns="urn:ietf:params:xml:ns:yang:ietf-rest\
      conf"><event-time>2013-12-21T00:01:00Z</event-time><event xmlns="\
      http://example.com/event/1.0"><event-class>fault</event-class><re\
      portingEntity><card>Ethernet0</card></reporting-entity><severity>\
      major</severity></event></notification>

      JSON:

      data: {"ietf-restconf:notification":{"event-time":"2013-12-21\
      T00:01:00Z","example-mod:event":{"event-class": "fault","repor\
      tingEntity":{"card":"Ethernet0"},"severity":"major"}}}

   The SSE specifications supports the following additional fields:
   event, id and retry.  A RESTCONF server MAY send the "retry" field
   and, if it does, RESTCONF clients SHOULD use it.  A RESTCONF server
   SHOULD NOT send the "event" or "id" fields, as there are no
   meaningful values that could be used for them that would not be
   redundant to the contents of the notification itself.  RESTCONF
   servers that do not send the "id" field also do not need to support
   the HTTP header "Last-Event-Id".  RESTCONF servers that do send the
   "id" field MUST still support the "startTime" query parameter as the
   preferred means for a client to specify where to restart the event
   stream.

7.  Error Reporting

   HTTP status-lines are used to report success or failure for RESTCONF
   operations.  The <rpc-error> element returned in NETCONF error
   responses contains some useful information.  This error information
   is adapted for use in RESTCONF, and error information is returned for
   "4xx" class of status codes.

   The following table summarizes the return status codes used
   specifically by RESTCONF operations:










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   +---------------------------+---------------------------------------+
   | Status-Line               | Description                           |
   +---------------------------+---------------------------------------+
   | 100 Continue              | POST accepted, 201 should follow      |
   | 200 OK                    | Success with response message-body    |
   | 201 Created               | POST to create a resource success     |
   | 202 Accepted              | POST to create a resource accepted    |
   | 204 No Content            | Success without response message-body |
   | 304 Not Modified          | Conditional operation not done        |
   | 400 Bad Request           | Invalid request message               |
   | 403 Forbidden             | Access to resource denied             |
   | 404 Not Found             | Resource target or resource node not  |
   |                           | found                                 |
   | 405 Method Not Allowed    | Method not allowed for target         |
   |                           | resource                              |
   | 409 Conflict              | Resource or lock in use               |
   | 412 Precondition Failed   | Conditional method is false           |
   | 413 Request Entity Too    | too-big error                         |
   | Large                     |                                       |
   | 414 Request-URI Too Large | too-big error                         |
   | 415 Unsupported Media     | non RESTCONF media type               |
   | Type                      |                                       |
   | 500 Internal Server Error | operation-failed                      |
   | 501 Not Implemented       | unknown-operation                     |
   | 503 Service Unavailable   | Recoverable server error              |
   +---------------------------+---------------------------------------+

                    HTTP Status Codes used in RESTCONF

   Since an operation resource is defined with a YANG "rpc" statement, a
   mapping between the NETCONF <error-tag> value and the HTTP status
   code is needed.  The specific error condition and response code to
   use are data-model specific and might be contained in the YANG
   "description" statement for the "rpc" statement.

















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                 +-------------------------+-------------+
                 | <error-tag>             | status code |
                 +-------------------------+-------------+
                 | in-use                  | 409         |
                 | invalid-value           | 400         |
                 | too-big                 | 413         |
                 | missing-attribute       | 400         |
                 | bad-attribute           | 400         |
                 | unknown-attribute       | 400         |
                 | bad-element             | 400         |
                 | unknown-element         | 400         |
                 | unknown-namespace       | 400         |
                 | access-denied           | 403         |
                 | lock-denied             | 409         |
                 | resource-denied         | 409         |
                 | rollback-failed         | 500         |
                 | data-exists             | 409         |
                 | data-missing            | 409         |
                 | operation-not-supported | 501         |
                 | operation-failed        | 500         |
                 | partial-operation       | 500         |
                 | malformed-message       | 400         |
                 +-------------------------+-------------+

                   Mapping from error-tag to status code

7.1.  Error Response Message

   When an error occurs for a request message on a data resource or an
   operation resource, and a "4xx" class of status codes (except for
   status code "403 Forbidden"), then the server SHOULD send a response
   message-body containing the information described by the "errors"
   container definition within the YANG module Section 8.  The Content-
   Type of this response message MUST be application/yang.errors (see
   example below).

   The client MAY specify the desired encoding for error messages by
   specifying the appropriate media-type in the Accept header.  If no
   error media is specified, the server MUST assume that "application/
   yang.errors+xml" was specified.  All of the examples in this
   document, except for the one below, assume the default XML encoding
   will be returned if there is an error.

   YANG Tree Diagram for <errors> Data:







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      +--ro errors
         +--ro error
            +--ro error-type       enumeration
            +--ro error-tag        string
            +--ro error-app-tag?   string
            +--ro error-path?      instance-identifier
            +--ro error-message?   string
            +--ro error-info

   The semantics and syntax for RESTCONF error messages are defined in
   the "application/yang.errors" restconf-media-type extension in
   Section 8.

   Examples:

   The following example shows an error returned for an "lock-denied"
   error that can occur if a NETCONF client has locked a datastore.  The
   RESTCONF client is attempting to delete a data resource.  Note that
   an Accept header is used to specify the desired encoding for the
   error message.  This example's use of the Accept header is especially
   notable since the DELETE method typically doesn't return a message-
   body and hence Accept headers are typically not passed.

      DELETE /restconf/data/example-jukebox:jukebox/
         library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
      Host: example.com
      Accept: application/yang.errors+json

   The server might respond:

      HTTP/1.1 409 Conflict
      Date: Mon, 23 Apr 2012 17:11:00 GMT
      Server: example-server
      Content-Type: application/yang.errors+json

      {
        "ietf-restconf:errors": {
          "error": {
            "error-type": "protocol",
            "error-tag": "lock-denied",
            "error-message": "Lock failed, lock already held"
          }
        }
      }

   The following example shows an error returned for a "data-exists"
   error on a data resource.  The "jukebox" resource already exists so
   it cannot be created.



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   The client might send:

      POST /restconf/data/example-jukebox:jukebox HTTP/1.1
      Host: example.com

   The server might respond (some lines wrapped for display purposes):

      HTTP/1.1 409 Conflict
      Date: Mon, 23 Apr 2012 17:11:00 GMT
      Server: example-server
      Content-Type: application/yang.errors+xml

      <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
        <error>
          <error-type>protocol</error-type>
          <error-tag>data-exists</error-tag>
          <error-path
            xmlns:rc="urn:ietf:params:xml:ns:yang:ietf-restconf"
            xmlns:jb="https://example.com/ns/example-jukebox">
            /rc:restconf/rc:data/jb:jukebox
          </error-path>
          <error-message>
            Data already exists, cannot create new resource
          </error-message>
        </error>
      </errors>

8.  RESTCONF module

   The "ietf-restconf" module defines conceptual definitions within an
   extension and two groupings, which are not meant to be implemented as
   datastore contents by a server.  E.g., the "restconf" container is
   not intended to be implemented as a top-level data node (under the
   "/restconf/data" entry point).

   RFC Ed.: update the date below with the date of RFC publication and
   remove this note.

   <CODE BEGINS> file "ietf-restconf@2015-06-04.yang"

   module ietf-restconf {
     namespace "urn:ietf:params:xml:ns:yang:ietf-restconf";
     prefix "rc";

     organization
       "IETF NETCONF (Network Configuration) Working Group";

     contact



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       "WG Web:   <http://tools.ietf.org/wg/netconf/>
        WG List:  <mailto:netconf@ietf.org>

        WG Chair: Mehmet Ersue
                  <mailto:mehmet.ersue@nsn.com>

        WG Chair: Mahesh Jethanandani
                  <mailto:mjethanandani@gmail.com>

        Editor:   Andy Bierman
                  <mailto:andy@yumaworks.com>

        Editor:   Martin Bjorklund
                  <mailto:mbj@tail-f.com>

        Editor:   Kent Watsen
                  <mailto:kwatsen@juniper.net>";

     description
       "This module contains conceptual YANG specifications
        for basic RESTCONF media type definitions used in
        RESTCONF protocol messages.

        Note that the YANG definitions within this module do not
        represent configuration data of any kind.
        The 'restconf-media-type' YANG extension statement
        provides a normative syntax for XML and JSON message
        encoding purposes.

        Copyright (c) 2015 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note.

     // RFC Ed.: remove this note
     // Note: extracted from draft-ietf-netconf-restconf-06.txt




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     // RFC Ed.: update the date below with the date of RFC publication
     // and remove this note.
     revision 2015-06-04 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: RESTCONF Protocol.";
     }

     extension restconf-media-type {
      argument media-type-id {
        yin-element true;
      }
      // RFC Ed.: replace draft-ietf-netmod-yang-json with RFC number
      // in the description below, and remove this note.
      description
        "This extension is used to specify a YANG data structure which
         represents a conceptual RESTCONF media type.
         Data definition statements within this extension specify
         the generic syntax for the specific media type.

         YANG is mapped to specific encoding formats outside the
         scope of this extension statement. RFC 6020 defines XML
         encoding rules for all RESTCONF media types that use
         the '+xml' suffix. draft-ietf-netmod-yang-json defines
         JSON encoding rules for all RESTCONF media types that
         use the '+json' suffix.

         The 'media-type-id' parameter value identifies the media type
         that is being defined. It contains the string associated
         with the generic media type, i.e., no suffix is specified.

         This extension is ignored unless it appears as a top-level
         statement. It SHOULD contain data definition statements
         that result in exactly one container data node definition.
         This allows compliant translation to an XML instance
         document for each media type.

         The module name and namespace value for the YANG module using
         the extension statement is assigned to instance document data
         conforming to the data definition statements within
         this extension.

         The sub-statements of this extension MUST follow the
         'data-def-stmt' rule in the YANG ABNF.

         The XPath document root is the extension statement itself,
         such that the child nodes of the document root are



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         represented by the data-def-stmt sub-statements within
         this extension. This conceptual document is the context
         for the following YANG statements:

            - must-stmt
            - when-stmt
            - path-stmt
            - min-elements-stmt
            - max-elements-stmt
            - mandatory-stmt
            - unique-stmt
            - ordered-by
            - instance-identifier data type

         The following data-def-stmt sub-statements have special
         meaning when used within a restconf-resource extension
         statement.

         - The list-stmt is not required to have a key-stmt defined.
         - The if-feature-stmt is ignored if present.
         - The config-stmt is ignored if present.
         - The available identity values for any 'identityref'
           leaf or leaf-list nodes is limited to the module
           containing this extension statement, and the modules
           imported into that module.
         ";
     }

     rc:restconf-media-type "application/yang.errors" {
       uses errors;
     }

     rc:restconf-media-type "application/yang.api" {
       uses restconf;
     }

     grouping errors {
       description
         "A grouping that contains a YANG container
          representing the syntax and semantics of a
          YANG Patch errors report within a response message.";

       container errors {
         description
           "Represents an error report returned by the server if
            a request results in an error.";

         list error {



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           description
             "An entry containing information about one
              specific error that occurred while processing
              a RESTCONF request.";
           reference "RFC 6241, Section 4.3";

           leaf error-type {
             type enumeration {
               enum transport {
                 description "The transport layer";
               }
               enum rpc {
                 description "The rpc or notification layer";
               }
               enum protocol {
                 description "The protocol operation layer";
               }
               enum application {
                 description "The server application layer";
               }
             }
             mandatory true;
             description
               "The protocol layer where the error occurred.";
           }

           leaf error-tag {
             type string;
             mandatory true;
             description
               "The enumerated error tag.";
           }

           leaf error-app-tag {
             type string;
             description
               "The application-specific error tag.";
           }

           leaf error-path {
             type instance-identifier;
             description
               "The YANG instance identifier associated
                with the error node.";
           }

           leaf error-message {
             type string;



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             description
               "A message describing the error.";
           }

           anyxml error-info {
              description
                "Arbitrary XML that represents a container
                 of additional information for the error report.";
           }
         }
       }
     }

     grouping restconf {
       description
         "Conceptual container representing the
          application/yang.api resource type.";

       container restconf {
         description
           "Conceptual container representing the
            application/yang.api resource type.";

         container data {
           description
             "Container representing the application/yang.datastore
              resource type. Represents the conceptual root of all
              operational data and configuration data supported by
              the server.  The child nodes of this container can be
              any data resource (application/yang.data), which are
              defined as top-level data nodes from the YANG modules
              advertised by the server in the ietf-restconf-monitoring
              module.";
         }

         container operations {
           description
             "Container for all operation resources
              (application/yang.operation),

              Each resource is represented as an empty leaf with the
              name of the RPC operation from the YANG rpc statement.

              E.g.;

                 POST /restconf/operations/show-log-errors

                 leaf show-log-errors {



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                   type empty;
                 }
             ";
         }
       }
     }

   }

   <CODE ENDS>

9.  RESTCONF Monitoring

   The "ietf-restconf-monitoring" module provides information about the
   RESTCONF protocol capabilities and event notification streams
   available from the server.  A RESTCONF server MUST implement the
   "/restconf-state/capabilities" container in this module.

   YANG Tree Diagram for "ietf-restconf-monitoring" module:

      +--ro restconf-state
         +--ro capabilities
         |  +--ro capability*   inet:uri
         +--ro streams
            +--ro stream* [name]
               +--ro name                        string
               +--ro description?                string
               +--ro replay-support?             boolean
               +--ro replay-log-creation-time?   yang:date-and-time
               +--ro access* [type]
                  +--ro encoding  string
                  +--ro location  inet:uri

9.1.  restconf-state/capabilities

   This mandatory container holds the RESTCONF protocol capability URIs
   supported by the server.

   The server MUST maintain a last-modified timestamp for this
   container, and return the "Last-Modified" header when this data node
   is retrieved with the GET or HEAD methods.

   The server SHOULD maintain an entity-tag for this container, and
   return the "ETag" header when this data node is retrieved with the
   GET or HEAD methods.

   The server MUST include a "capability" URI leaf-list entry for the
   "defaults" mode used by the server, defined in Section 9.1.2.



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   The server MUST include a "capability" URI leaf-list entry
   identifying each supported optional protocol feature.  This includes
   optional query parameters and MAY include other capability URIs
   defined outside this document.

9.1.1.  Query Parameter URIs

   A new set of RESTCONF Capability URIs are defined to identify the
   specific query parameters (defined in Section 4.8) supported by the
   server.

   The server MUST include a "capability" leaf-list entry for each
   optional query parameter that it supports.

   +------------+--------+---------------------------------------------+
   | Name       | Sectio | URI                                         |
   |            | n      |                                             |
   +------------+--------+---------------------------------------------+
   | depth      | 4.8.2  | urn:ietf:params:restconf:capability:depth:1 |
   |            |        | .0                                          |
   | fields     | 4.8.3  | urn:ietf:params:restconf:capability:fields: |
   |            |        | 1.0                                         |
   | filter     | 4.8.6  | urn:ietf:params:restconf:capability:filter: |
   |            |        | 1.0                                         |
   | replay     | 4.8.7  | urn:ietf:params:restconf:capability:replay: |
   |            | 4.8.8  | 1.0                                         |
   | with-      | 4.8.9  | urn:ietf:params:restconf:capability:with-   |
   | defaults   |        | defaults:1.0                                |
   +------------+--------+---------------------------------------------+

                       RESTCONF Query Parameter URIs

9.1.2.  The "defaults" Protocol Capability URI

   This URI identifies the defaults handling mode that is used by the
   server for processing default leafs in requests for data resources.
   A parameter named "basic-mode" is required for this capability URI.
   The "basic-mode" definitions are specified in the "With-Defaults
   Capability for NETCONF" [RFC6243].

      +----------+--------------------------------------------------+
      | Name     | URI                                              |
      +----------+--------------------------------------------------+
      | defaults | urn:ietf:params:restconf:capability:defaults:1.0 |
      +----------+--------------------------------------------------+

                     RESTCONF defaults capability URI




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   This protocol capability URI MUST be supported by the server, and
   MUST be listed in the "capability" leaf-list in Section 9.3.

   +------------+------------------------------------------------------+
   | Value      | Description                                          |
   +------------+------------------------------------------------------+
   | report-all | No data nodes are considered default                 |
   | trim       | Values set to the YANG default-stmt value are        |
   |            | default                                              |
   | explicit   | Values set by the client are never considered        |
   |            | default                                              |
   +------------+------------------------------------------------------+

   If the "basic-mode" is set to "report-all" then the server MUST
   adhere to the defaults handling behavior defined in Section 2.1 of
   [RFC6243].

   If the "basic-mode" is set to "trim" then the server MUST adhere to
   the defaults handling behavior defined in Section 2.2 of [RFC6243].

   If the "basic-mode" is set to "explicit" then the server MUST adhere
   to the defaults handling behavior defined in Section 2.3 of
   [RFC6243].

   Example: (split for display purposes only)

      urn:ietf:params:restconf:capability:defaults:1.0?
           basic-mode=explicit

9.2.  restconf-state/streams

   This optional container provides access to the event notification
   streams supported by the server.  The server MAY omit this container
   if no event notification streams are supported.

   The server will populate this container with a stream list entry for
   each stream type it supports.  Each stream contains a leaf called
   "events" which contains a URI that represents an event stream
   resource.

   Stream resources are defined in Section 3.8.  Notifications are
   defined in Section 6.

9.3.  RESTCONF Monitoring Module

   The "ietf-restconf-monitoring" module defines monitoring information
   for the RESTCONF protocol.




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   The "ietf-yang-types" and "ietf-inet-types" modules from [RFC6991]
   are used by this module for some type definitions.

   RFC Ed.: update the date below with the date of RFC publication and
   remove this note.

   <CODE BEGINS> file "ietf-restconf-monitoring@2015-06-19.yang"

   module ietf-restconf-monitoring {
     namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring";
     prefix "rcmon";

     import ietf-yang-types { prefix yang; }
     import ietf-inet-types { prefix inet; }

     organization
       "IETF NETCONF (Network Configuration) Working Group";

     contact
       "WG Web:   <http://tools.ietf.org/wg/netconf/>
        WG List:  <mailto:netconf@ietf.org>

        WG Chair: Mehmet Ersue
                  <mailto:mehmet.ersue@nsn.com>

        WG Chair: Mahesh Jethanandani
                  <mailto:mjethanandani@gmail.com>

        Editor:   Andy Bierman
                  <mailto:andy@yumaworks.com>

        Editor:   Martin Bjorklund
                  <mailto:mbj@tail-f.com>

        Editor:   Kent Watsen
                  <mailto:kwatsen@juniper.net>";

     description
       "This module contains monitoring information for the
        RESTCONF protocol.

        Copyright (c) 2015 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions



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        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note.

     // RFC Ed.: remove this note
     // Note: extracted from draft-ietf-netconf-restconf-06.txt

     // RFC Ed.: update the date below with the date of RFC publication
     // and remove this note.
     revision 2015-06-19 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: RESTCONF Protocol.";
     }

     container restconf-state {
       config false;
       description
         "Contains RESTCONF protocol monitoring information.";

       container capabilities {
         description
           "Contains a list of protocol capability URIs";

         leaf-list capability {
           type inet:uri;
           description "A RESTCONF protocol capability URI.";
         }
       }

       container streams {
         description
           "Container representing the notification event streams
            supported by the server.";
          reference
            "RFC 5277, Section 3.4, <streams> element.";

         list stream {
           key name;
           description
             "Each entry describes an event stream supported by
              the server.";



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           leaf name {
             type string;
             description "The stream name";
             reference "RFC 5277, Section 3.4, <name> element.";
           }

           leaf description {
             type string;
             description "Description of stream content";
             reference
               "RFC 5277, Section 3.4, <description> element.";
           }

           leaf replay-support {
             type boolean;
             description
               "Indicates if replay buffer supported for this stream.
                If 'true', then the server MUST support the 'start-time'
                and 'stop-time' query parameters for this stream.";
             reference
               "RFC 5277, Section 3.4, <replaySupport> element.";
           }

           leaf replay-log-creation-time {
             when "../replay-support" {
               description
                 "Only present if notification replay is supported";
             }
             type yang:date-and-time;
             description
               "Indicates the time the replay log for this stream
                was created.";
             reference
               "RFC 5277, Section 3.4, <replayLogCreationTime>
                element.";
           }

           list access {
             key encoding;
             min-elements 1;
             description
               "The server will create an entry in this list for each
                encoding format that is supported for this stream.
                The media type 'application/yang.stream' is expected
                for all event streams. This list identifies the
                sub-types supported for this stream.";

             leaf encoding {



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               type string;
               description
                 "This is the secondary encoding format within the
                  'text/event-stream' encoding used by all streams.
                  The type 'xml' is supported for the media type
                  'application/yang.stream+xml'. The type 'json'
                  is supported for the media type
                  'application/yang.stream+json'.";

             }

             leaf location {
               type inet:uri;
               mandatory true;
               description
                 "Contains a URL that represents the entry point
                  for establishing notification delivery via server
                  sent events.";
             }
           }
         }
       }
     }

   }

   <CODE ENDS>

10.  YANG Module Library

   The "ietf-yang-library" module defined in
   [I-D.ietf-netconf-yang-library] provides information about the YANG
   modules and submodules used by the RESTCONF server.  Implementation
   is mandatory for RESTCONF servers.  All YANG modules and submodules
   used by the server MUST be identified in the YANG module library.

10.1.  modules

   This mandatory container holds the identifiers for the YANG data
   model modules supported by the server.

   The server MUST maintain a last-modified timestamp for this
   container, and return the "Last-Modified" header when this data node
   is retrieved with the GET or HEAD methods.

   The server SHOULD maintain an entity-tag for this container, and
   return the "ETag" header when this data node is retrieved with the
   GET or HEAD methods.



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10.1.1.  modules/module

   This mandatory list contains one entry for each YANG data model
   module supported by the server.  There MUST be an instance of this
   list for every YANG module that is used by the server.

   The contents of this list are defined in the "module" YANG list
   statement in [I-D.ietf-netconf-yang-library].

   The server MAY maintain a last-modified timestamp for each instance
   of this list entry, and return the "Last-Modified" header when this
   data node is retrieved with the GET or HEAD methods.  If not
   supported then the timestamp for the parent "modules" container MAY
   be used instead.

   The server MAY maintain an entity-tag for each instance of this list
   entry, and return the "ETag" header when this data node is retrieved
   with the GET or HEAD methods.  If not supported then the timestamp
   for the parent "modules" container MAY be used instead.

11.  IANA Considerations

11.1.  The "restconf" Relation Type

   This specification registers the "restconf" relation type in the Link
   Relation Type Registry defined by [RFC5988]:

      Relation Name:  restconf

      Description:  Identifies the root of RESTCONF API as configured
                    on this HTTP server.  The "restconf" relation
                    defines the root of the API defined in RFCXXXX.
                    Subsequent revisions of RESTCONF will use alternate
                    relation values to support protocol versioning.

      Reference:  RFC XXXX

   `

11.2.  YANG Module Registry

   This document registers two URIs in the IETF XML registry [RFC3688].
   Following the format in RFC 3688, the following registration is
   requested to be made.







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        URI: urn:ietf:params:xml:ns:yang:ietf-restconf
        Registrant Contact: The NETMOD WG of the IETF.
        XML: N/A, the requested URI is an XML namespace.

        URI: urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring
        Registrant Contact: The NETMOD WG of the IETF.
        XML: N/A, the requested URI is an XML namespace.

   This document registers two YANG modules in the YANG Module Names
   registry [RFC6020].

     name:         ietf-restconf
     namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf
     prefix:       rc
     // RFC Ed.: replace XXXX with RFC number and remove this note
     reference:    RFC XXXX

     name:         ietf-restconf-monitoring
     namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring
     prefix:       rcmon
     // RFC Ed.: replace XXXX with RFC number and remove this note
     reference:    RFC XXXX

11.3.  application/yang Media Sub Types

   The parent MIME media type for RESTCONF resources is application/
   yang, which is defined in [RFC6020].  This document defines the
   following sub-types for this media type.























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      - api
      - data
      - datastore
      - errors
      - operation
      - stream

      Type name: application

      Subtype name: yang.xxx

      Required parameters: none

      Optional parameters: See section 4.8 in RFC XXXX

      Encoding considerations: 8-bit

      Security considerations: See Section 12 in RFC XXXX

      Interoperability considerations: none

      // RFC Ed.: replace XXXX with RFC number and remove this note
      Published specification: RFC XXXX

11.4.  RESTCONF Capability URNs

      [Note to RFC Editor:
       The RESTCONF Protocol Capability Registry does not yet exist;
       Need to ask IANA to create it; remove this note for publication
      ]

   This document defines a registry for RESTCONF capability identifiers.
   The name of the registry is "RESTCONF Capability URNs".  The registry
   shall record for each entry:

   o  the name of the RESTCONF capability.  By convention, this name is
      prefixed with the colon ':' character.

   o  the URN for the RESTCONF capability.

   This document registers several capability identifiers in "RESTCONF
   Capability URNs" registry:









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     Index
        Capability Identifier
     ------------------------

     :defaults
         urn:ietf:params:restconf:capability:defaults:1.0

     :depth
         urn:ietf:params:restconf:capability:depth:1.0

     :fields
         urn:ietf:params:restconf:capability:fields:1.0

     :filter
         urn:ietf:params:restconf:capability:filter:1.0

     :replay
         urn:ietf:params:restconf:capability:replay:1.0

     :with-defaults
         urn:ietf:params:restconf:capability:with-defaults:1.0

12.  Security Considerations

   This section provides security considerations for the resources
   defined by the RESTCONF protocol.  Security considerations for HTTPS
   are defined in [RFC2818].  Security considerations for the content
   manipulated by RESTCONF can be found in the documents defining data
   models.

   This document does not specify an authentication scheme, but it does
   require that an authenticated NETCONF username be associated with
   each HTTP request.  The authentication scheme MAY be implemented in
   the underlying transport layer (e.g., client certificates) or within
   the HTTP layer (e.g., Basic Auth, OAuth, etc.).  RESTCONF does not
   itself define an authentication mechanism.  Authentication MUST occur
   in a lower layer.  Implementors SHOULD provide a comprehensive
   authorization scheme with RESTCONF and ensure that the resulting
   NETCONF username is made available to the RESTCONF server.

   Authorization of individual user access to operations and data MAY be
   configured via NETCONF Access Control Model (NACM) [RFC6536], as
   specified in Section 4.

   Configuration information is by its very nature sensitive.  Its
   transmission in the clear and without integrity checking leaves
   devices open to classic eavesdropping and false data injection
   attacks.  Configuration information often contains passwords, user



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   names, service descriptions, and topological information, all of
   which are sensitive.  Because of this, this protocol SHOULD be
   implemented carefully with adequate attention to all manner of attack
   one might expect to experience with other management interfaces.

   Different environments may well allow different rights prior to and
   then after authentication.  When an operation is not properly
   authorized, the RESTCONF server MUST return HTTP error status code
   401 Unauthorized.  Note that authorization information can be
   exchanged in the form of configuration information, which is all the
   more reason to ensure the security of the connection.

13.  Acknowledgements

   The authors would like to thank the following people for their
   contributions to this document: Ladislav Lhotka, Juergen
   Schoenwaelder, Rex Fernando, Robert Wilton, and Jonathan Hansford.

14.  References

14.1.  Normative References

   [I-D.ietf-netconf-yang-library]
              Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
              Library", draft-ietf-netconf-yang-library-01 (work in
              progress), July 2015.

   [I-D.ietf-netmod-yang-json]
              Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              draft-ietf-netmod-yang-json-04 (work in progress), June
              2015.

   [I-D.ietf-netmod-yang-metadata]
              Lhotka, L., "Defining and Using Metadata with YANG",
              draft-ietf-netmod-yang-metadata-01 (work in progress),
              June 2015.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2396]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 2396,
              August 1998.




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   [RFC2818]  Rescorla, E., "The IETF XML Registry", RFC 2818, May 2000.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC4252]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, January 2006.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, July 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and T. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5789]  Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC
              5789, March 2010.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988, October 2010.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, June 2011.

   [RFC6243]  Bierman, A. and B. Lengyel, "With-defaults Capability for
              NETCONF", RFC 6243, June 2011.

   [RFC6415]  Hammer-Lahav, E. and B. Cook, "Web Host Metadata", RFC
              6415, October 2011.




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   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536, March
              2012.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570, March 2012.

   [RFC6991]  Schoenwaelder, J., "Common YANG Data Types", RFC 6991,
              July 2013.

   [RFC7158]  Bray, T., Ed., "The JSON Data Interchange Format", RFC
              7158, March 2013.

   [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", RFC 7230, June
              2014.

   [RFC7231]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content", RFC 7231, June 2014.

   [RFC7232]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Conditional Requests", RFC 7232, June 2014.

   [RFC7235]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Authentication", RFC 7235, June 2014.

   [RFC7320]  Nottingham, M., "URI Design and Ownership", BCP 190, RFC
              7320, July 2014.

   [W3C.CR-eventsource-20121211]
              Hickson, I., "Server-Sent Events", World Wide Web
              Consortium CR CR-eventsource-20121211, December 2012,
              <http://www.w3.org/TR/2012/CR-eventsource-20121211>.

   [W3C.REC-xml-20081126]
              Yergeau, F., Maler, E., Paoli, J., Sperberg-McQueen, C.,
              and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

   [XPath]    Clark, J. and S. DeRose, "XML Path Language (XPath)
              Version 1.0", World Wide Web Consortium Recommendation
              REC-xpath-19991116, November 1999,
              <http://www.w3.org/TR/1999/REC-xpath-19991116>.






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   [draft-ietf-httpauth-basicauth-update-03]
              Reschke, J., "The 'Basic' HTTP Authentication Scheme",
              draft-ietf-httpauth-basicauth-update-03 (work in
              progress), Dec 2014.

   [draft-ietf-httpauth-digest-09]
              Shekh-Yusef, R., Reschke, D., and S. Bremer, "HTTP Digest
              Access Authentication", draft-ietf-httpauth-digest-09
              (work in progress), Dec 2014.

   [draft-ietf-netconf-rfc5539bis-10]
              Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
              NETCONF Protocol over Transport Layer Security (TLS) with
              Mutual X.509 Authentication", draft-ietf-netconf-
              rfc5539bis-10 (work in progress), Dec 2014.

   [draft-thomson-httpbis-cant-01]
              Thomson, M., "Client Authentication over New TLS
              Connection", draft-thomson-httpbis-cant-01 (work in
              progress), Jul 2014.

14.2.  Informative References

   [I-D.ietf-netconf-yang-patch]
              Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
              Media Type", draft-ietf-netconf-yang-patch-05 (work in
              progress), July 2015.

   [rest-dissertation]
              Fielding, R., "Architectural Styles and the Design of
              Network-based Software Architectures", 2000.

Appendix A.  Change Log

       -- RFC Ed.: remove this section before publication.

   The RESTCONF issue tracker can be found here: https://github.com/
   netconf-wg/restconf/issues

A.1.  06 - 07

   o  fixed all issues identified in email from Jernej Tuljak in netconf
      email 2015-06-22

   o  fixed error example bug where error-urlpath was still used.
      Changed to error-path.

   o  added mention of YANG Patch and informative reference



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A.2.  05 - 06

   o  fixed RESTCONF issue #23 (ietf-restconf-monitoring bug)

A.3.  04 - 05

   o  changed term 'notification event' to 'event notification'

   o  removed intro text about framework and meta-model

   o  removed early mention of API resources

   o  removed term unified datastore and cleaned up text about NETCONF
      datastores

   o  removed text about not immediate persistence of edits

   o  removed RESTCONF-specific data-resource-identifier typedef and its
      usage

   o  clarified encoding of key leafs

   o  changed several examples from JSON to XML encoding

   o  made 'insert' and 'point' query parameters mandatory to implement

   o  removed ":insert" capability URI

   o  renamed stream/encoding to stream/access

   o  renamed stream/encoding/type to stream/access/encoding

   o  renamed stream/encoding/events to stream/access/location

   o  changed XPath from informative to normative reference

   o  changed rest-dissertation from normative to informative reference

   o  changed example-jukebox playlist 'id' from a data-resource-
      identifier to a leafref pointing at the song name

A.4.  03 - 04

   o  renamed 'select' to 'fields' (#1)

   o  moved collection resource and page capability to draft-ietf-
      netconf-restconf-collection-00 (#3)




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   o  added mandatory "defaults" protocol capability URI (#4)

   o  added optional "with-defaults" query parameter URI (#4)

   o  clarified authentication procedure (#9)

   o  moved ietf-yang-library module to draft-ietf-netconf-yang-
      library-00 (#13)

   o  clarified that JSON encoding of module name in a URI MUST follow
      the netmod-yang-json encoding rules (#14)

   o  added restconf-media-type extension (#15)

   o  remove "content" query parameter URI and made this parameter
      mandatory (#16)

   o  clarified datastore usage

   o  changed lock-denied error example

   o  added with-defaults query parameter example

   o  added term "RESTCONF Capability"

   o  changed NETCONF Capability URI registry usage to new RESTCONF
      Capability URI Registry usage

A.5.  02 - 03

   o  added collection resource

   o  added "page" query parameter capability

   o  added "limit" and "offset" query parameters, which are available
      if the "page" capability is supported

   o  added "stream list" term

   o  fixed bugs in some examples

   o  added "encoding" list within the "stream" list to allow different
      <events> URLs for XML and JSON encoding.

   o  made XML MUST implement and JSON MAY implement for servers

   o  re-add JSON notification examples (previously removed)




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   o  updated JSON references

A.6.  01 - 02

   o  moved query parameter definitions from the YANG module back to the
      plain text sections

   o  made all query parameters optional to implement

   o  defined query parameter capability URI

   o  moved 'streams' to new YANG module (ietf-restconf-monitoring)

   o  added 'capabilities' container to new YANG module (ietf-restconf-
      monitoring)

   o  moved 'modules' container to new YANG module (ietf-yang-library)

   o  added new leaf 'module-set-id' (ietf-yang-library)

   o  added new leaf 'conformance' (ietf-yang-library)

   o  changed 'schema' leaf to type inet:uri that returns the location
      of the YANG schema (instead of returning the schema directly)

   o  changed 'events' leaf to type inet:uri that returns the location
      of the event stream resource (instead of returning events
      directly)

   o  changed examples for yang.api resource since the monitoring
      information is no longer in this resource

   o  closed issue #1 'select parameter' since no objections to the
      proposed syntax

   o  closed "encoding of list keys" issue since no objection to new
      encoding of list keys in a target resource URI.

   o  moved open issues list to the issue tracker on github

A.7.  00 - 01

   o  fixed content=nonconfig example (non-config was incorrect)

   o  closed open issue 'message-id'.  There is no need for a message-id
      field, and RFC 2392 does not apply.





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   o  closed open issue 'server support verification'.  The headers used
      by RESTCONF are widely supported.

   o  removed encoding rules from section on RESTCONF Meta-Data.  This
      is now defined in "I-D.lhotka-netmod-yang-json".

   o  added media type application/yang.errors to map to errors YANG
      grouping.  Updated error examples to use new media type.

   o  closed open issue 'additional datastores'.  Support may be added
      in the future to identify new datastores.

   o  closed open issue 'PATCH media type discovery'.  The section on
      PATCH has an added sentence on the Accept-Patch header.

   o  closed open issue 'YANG to resource mapping'.  Current mapping of
      all data nodes to resources will be used in order to allow
      mandatory DELETE support.  The PATCH operation is optional, as
      well as the YANG Patch media type.

   o  closed open issue '_self links for HATEOAS support'.  It was
      decided that they are redundant because they can be derived from
      the YANG module for the specific data.

   o  added explanatory text for the 'select' parameter.

   o  added RESTCONF Path Resolution section for discovering the root of
      the RESTCONF API using the /.well-known/host-meta.

   o  added an "error" media type to for structured error messages

   o  added Secure Transport section requiring TLS

   o  added Security Considerations section

   o  removed all references to "REST-like"

A.8.  bierman:restconf-04 to ietf:restconf-00

   o  updated open issues section

Appendix B.  Open Issues

       -- RFC Ed.: remove this section before publication.

   The RESTCONF issues are tracked on github.com:

      https://github.com/netconf-wg/restconf/issues



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Appendix C.  Example YANG Module

   The example YANG module used in this document represents a simple
   media jukebox interface.

   YANG Tree Diagram for "example-jukebox" Module

      +--rw jukebox!
         +--rw library
         |  +--rw artist* [name]
         |  |  +--rw name     string
         |  |  +--rw album* [name]
         |  |     +--rw name     string
         |  |     +--rw genre?   identityref
         |  |     +--rw year?    uint16
         |  |     +--rw admin
         |  |     |  +--rw label?              string
         |  |     |  +--rw catalogue-number?   string
         |  |     +--rw song* [name]
         |  |        +--rw name        string
         |  |        +--rw location    string
         |  |        +--rw format?     string
         |  |        +--rw length?     uint32
         |  +--ro artist-count?   uint32
         |  +--ro album-count?    uint32
         |  +--ro song-count?     uint32
         +--rw playlist* [name]
         |  +--rw name           string
         |  +--rw description?   string
         |  +--rw song* [index]
         |     +--rw index    uint32
         |     +--rw id       leafref
         +--rw player
            +--rw gap?   decimal64

     rpcs:

      +---x play
         +--ro input
            +--ro playlist       string
            +--ro song-number    uint32

C.1.  example-jukebox YANG Module

   module example-jukebox {

      namespace "http://example.com/ns/example-jukebox";
      prefix "jbox";



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      organization "Example, Inc.";
      contact "support at example.com";
      description "Example Jukebox Data Model Module";
      revision "2015-04-04" {
        description "Initial version.";
        reference "example.com document 1-4673";
      }

      identity genre {
        description "Base for all genre types";
      }

      // abbreviated list of genre classifications
      identity alternative {
        base genre;
        description "Alternative music";
      }
      identity blues {
        base genre;
        description "Blues music";
      }
      identity country {
        base genre;
        description "Country music";
      }
      identity jazz {
        base genre;
        description "Jazz music";
      }
      identity pop {
        base genre;
        description "Pop music";
      }
      identity rock {
        base genre;
        description "Rock music";
      }

      container jukebox {
        presence
          "An empty container indicates that the jukebox
           service is available";

        description
          "Represents a jukebox resource, with a library, playlists,
           and a play operation.";

        container library {



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          description "Represents the jukebox library resource.";

          list artist {
            key name;

            description
              "Represents one artist resource within the
               jukebox library resource.";

            leaf name {
              type string {
                length "1 .. max";
              }
              description "The name of the artist.";
            }

            list album {
              key name;

              description
                "Represents one album resource within one
                 artist resource, within the jukebox library.";

              leaf name {
                type string {
                  length "1 .. max";
                }
                description "The name of the album.";
              }

              leaf genre {
                type identityref { base genre; }
                description
                  "The genre identifying the type of music on
                   the album.";
              }

              leaf year {
                type uint16 {
                  range "1900 .. max";
                }
                description "The year the album was released";
              }

              container admin {
                description
                  "Administrative information for the album.";




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                leaf label {
                  type string;
                  description "The label that released the album.";
                }
                leaf catalogue-number {
                  type string;
                  description "The album's catalogue number.";
                }
              }

              list song {
                key name;

                description
                  "Represents one song resource within one
                   album resource, within the jukebox library.";

                leaf name {
                  type string {
                     length "1 .. max";
                  }
                  description "The name of the song";
                }
                leaf location {
                  type string;
                  mandatory true;
                  description
                   "The file location string of the
                    media file for the song";
                }
                leaf format {
                  type string;
                  description
                    "An identifier string for the media type
                     for the file associated with the
                     'location' leaf for this entry.";
                }
                leaf length {
                  type uint32;
                  units "seconds";
                  description
                    "The duration of this song in seconds.";
                }
              }   // end list 'song'
            }   // end list 'album'
          }  // end list 'artist'

          leaf artist-count {



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             type uint32;
             units "songs";
             config false;
             description "Number of artists in the library";
          }
          leaf album-count {
             type uint32;
             units "albums";
             config false;
             description "Number of albums in the library";
          }
          leaf song-count {
             type uint32;
             units "songs";
             config false;
             description "Number of songs in the library";
          }
        }  // end library

        list playlist {
          key name;

          description
            "Example configuration data resource";

          leaf name {
            type string;
            description
              "The name of the playlist.";
          }
          leaf description {
            type string;
            description
              "A comment describing the playlist.";
          }
          list song {
            key index;
            ordered-by user;

            description
              "Example nested configuration data resource";

            leaf index {    // not really needed
              type uint32;
              description
                "An arbitrary integer index for this playlist song.";
            }
            leaf id {



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              type leafref {
                path "/jbox:jukebox/jbox:library/jbox:artist/" +
                     "jbox:album/jbox:song/jbox:name";
              }
              mandatory true;
              description
                "Song identifier. Must identify an instance of
                 /jukebox/library/artist/album/song/name.";
            }
          }
        }

        container player {
          description
            "Represents the jukebox player resource.";

          leaf gap {
            type decimal64 {
              fraction-digits 1;
              range "0.0 .. 2.0";
            }
            units "tenths of seconds";
            description "Time gap between each song";
          }
        }
      }

      rpc play {
        description "Control function for the jukebox player";
        input {
          leaf playlist {
            type string;
            mandatory true;
            description "playlist name";
          }
          leaf song-number {
            type uint32;
            mandatory true;
            description "Song number in playlist to play";
          }
        }
      }
   }








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Appendix D.  RESTCONF Message Examples

   The examples within this document use the normative YANG module
   defined in Section 8 and the non-normative example YANG module
   defined in Appendix C.1.

   This section shows some typical RESTCONF message exchanges.

D.1.  Resource Retrieval Examples

D.1.1.  Retrieve the Top-level API Resource

   The client may start by retrieving the top-level API resource, using
   the entry point URI "{+restconf}".

      GET /restconf   HTTP/1.1
      Host: example.com
      Accept: application/yang.api+json

   The server might respond as follows:

      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Content-Type: application/yang.api+json

      {
        "ietf-restconf:restconf": {
          "data" : [ null ],
          "operations" : {
             "play" : [ null ]
          }
        }
      }

   To request that the response content to be encoded in XML, the
   "Accept" header can be used, as in this example request:

      GET /restconf HTTP/1.1
      Host: example.com
      Accept: application/yang.api+xml

   The server will return the same response either way, which might be
   as follows :







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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.api+xml

      <restconf xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
        <data/>
        <operations>
          <play xmlns="https://example.com/ns/example-jukebox"/>
        </operations>
      </restconf>

D.1.2.  Retrieve The Server Module Information

   In this example the client is retrieving the modules information from
   the server in JSON format:

      GET /restconf/data/ietf-yang-library:modules HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond as follows.

     HTTP/1.1 200 OK
     Date: Mon, 23 Apr 2012 17:01:00 GMT
     Server: example-server
     Cache-Control: no-cache
     Pragma: no-cache
     Last-Modified: Sun, 22 Apr 2012 01:00:14 GMT
     Content-Type: application/yang.data+json

     {
       "ietf-yang-library:modules": {
         "module": [
           {
             "name" : "foo",
             "revision" : "2012-01-02",
             "schema" : "https://example.com/mymodules/foo/2012-01-02",
             "namespace" : "http://example.com/ns/foo",
             "feature" : [ "feature1", "feature2" ],
             "conformance" : "implement"
           },
           {
             "name" : "foo-types",
             "revision" : "2012-01-05",
             "schema" :



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               "https://example.com/mymodules/foo-types/2012-01-05",
             "schema" : [null],
             "namespace" : "http://example.com/ns/foo-types",
             "conformance" : "import"
           },
           {
             "name" : "bar",
             "revision" : "2012-11-05",
             "schema" : "https://example.com/mymodules/bar/2012-11-05",
             "namespace" : "http://example.com/ns/bar",
             "feature" : [ "bar-ext" ],
             "conformance" : "implement",
             "submodule" : [
               {
                 "name" : "bar-submod1",
                 "revision" : "2012-11-05",
                 "schema" :
                  "https://example.com/mymodules/bar-submod1/2012-11-05"
               },
               {
                 "name" : "bar-submod2",
                 "revision" : "2012-11-05",
                 "schema" :
                  "https://example.com/mymodules/bar-submod2/2012-11-05"
               }
             ]
           }
         ]
       }
     }

D.1.3.  Retrieve The Server Capability Information

   In this example the client is retrieving the capability information
   from the server in JSON format, and the server supports all the
   RESTCONF query parameters, plus one vendor parameter:

      GET /restconf/data/ietf-restconf-monitoring:restconf-state/
          capabilities  HTTP/1.1
      Host: example.com
      Accept: application/yang.data+xml

   The server might respond as follows.  The extra whitespace in
   'capability' elements for display purposes only.







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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:02:00 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Last-Modified: Sun, 22 Apr 2012 01:00:14 GMT
      Content-Type: application/yang.data+xml

      <capabilities xmlns="">
       <capability>
        urn:ietf:params:restconf:capability:depth:1.0
       </capability>
       <capability>
        urn:ietf:params:restconf:capability:fields:1.0
       </capability>
       <capability>
        urn:ietf:params:restconf:capability:filter:1.0
       </capability>
       <capability>
        urn:ietf:params:restconf:capability:start-time:1.0
       </capability>
       <capability>
        urn:ietf:params:restconf:capability:stop-time:1.0
       </capability>
       <capability>
        http://example.com/capabilities/myparam
       </capability>
      </capabilities>

D.2.  Edit Resource Examples

D.2.1.  Create New Data Resources

   To create a new "artist" resource within the "library" resource, the
   client might send the following request.

      POST /restconf/data/example-jukebox:jukebox/library HTTP/1.1
      Host: example.com
      Content-Type: application/yang.data+json

      {
        "example-jukebox:artist" : {
          "name" : "Foo Fighters"
        }
      }






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   If the resource is created, the server might respond as follows.
   Note that the "Location" header line is wrapped for display purposes
   only:

      HTTP/1.1 201 Created
      Date: Mon, 23 Apr 2012 17:02:00 GMT
      Server: example-server
      Location: https://example.com/restconf/data/
          example-jukebox:jukebox/library/artist=Foo%20Fighters
      Last-Modified: Mon, 23 Apr 2012 17:02:00 GMT
      ETag: b3830f23a4c

   To create a new "album" resource for this artist within the "jukebox"
   resource, the client might send the following request.  Note that the
   request URI header line is wrapped for display purposes only:

      POST /restconf/data/example-jukebox:jukebox/
         library/artist=Foo%20Fighters  HTTP/1.1
      Host: example.com
      Content-Type: application/yang.data+json

      {
        "example-jukebox:album" : {
          "name" : "Wasting Light",
          "genre" : "example-jukebox:alternative",
          "year" : 2012    # note this is the wrong date
        }
      }

   If the resource is created, the server might respond as follows.
   Note that the "Location" header line is wrapped for display purposes
   only:

      HTTP/1.1 201 Created
      Date: Mon, 23 Apr 2012 17:03:00 GMT
      Server: example-server
      Location: https://example.com/restconf/data/
          example-jukebox:jukebox/library/artist=Foo%20Fighters/
          album=Wasting%20Light
      Last-Modified: Mon, 23 Apr 2012 17:03:00 GMT
      ETag: b8389233a4c

D.2.2.  Detect Resource Entity Tag Change

   In this example, the server just supports the mandatory datastore
   last-changed timestamp.  The client has previously retrieved the
   "Last-Modified" header and has some value cached to provide in the




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   following request to patch an "album" list entry with key value
   "Wasting Light".  Only the "year" field is being updated.

      PATCH /restconf/data/example-jukebox:jukebox/
        library/artist=Foo%20Fighters/album=Wasting%20Light/year
        HTTP/1.1
      Host: example.com
      If-Unmodified-Since: Mon, 23 Apr 2012 17:01:00 GMT
      Content-Type: application/yang.data+json

      { "example-jukebox:year" : "2011" }

   In this example the datastore resource has changed since the time
   specified in the "If-Unmodified-Since" header.  The server might
   respond:

      HTTP/1.1 412 Precondition Failed
      Date: Mon, 23 Apr 2012 19:01:00 GMT
      Server: example-server
      Last-Modified: Mon, 23 Apr 2012 17:45:00 GMT
      ETag: b34aed893a4c

D.2.3.  Edit a Datastore Resource

   In this example, the client modifies two different data nodes by
   sending a PATCH to the datastore resource:

      PATCH /restconf/data HTTP/1.1
      Host: example.com
      Content-Type: application/yang.datastore+xml





















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      <data xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
        <jukebox xmlns=""http://example.com/ns/example-jukebox">
          <library>
            <artist>
              <name>Foo Fighters</name>
              <album>
                <name>Wasting Light</name>
                <year>2011</year>
              </album>
            </artist>
            <artist>
              <name>Nick Cave</name>
              <album>
                <name>Tender Prey</name>
                <year>1988</year>
              </album>
            </artist>
          </library>
        </jukebox>
      </data>

D.3.  Query Parameter Examples

D.3.1.  "content" Parameter

   The "content" parameter is used to select the type of data child
   resources (configuration and/or not configuration) that are returned
   by the server for a GET method request.

   In this example, a simple YANG list that has configuration and non-
   configuration child resources.

     container events
       list event {
         key name;
         leaf name { type string; }
         leaf description { type string; }
         leaf event-count {
           type uint32;
           config false;
         }
       }
     }

   Example 1: content=all

   To retrieve all the child resources, the "content" parameter is set
   to "all".  The client might send:



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      GET /restconf/data/example-events:events?content=all
          HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond:

      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:11:30 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+json

      {
        "example-events:events" : {
          "event" : [
            {
              "name" : "interface-up",
              "description" : "Interface up notification count",
              "event-count" : 42
            },
            {
              "name" : "interface-down",
              "description" : "Interface down notification count",
              "event-count" : 4
            }
          ]
        }
      }

   Example 2: content=config

   To retrieve only the configuration child resources, the "content"
   parameter is set to "config" or omitted since this is the default
   value.  Note that the "ETag" and "Last-Modified" headers are only
   returned if the content parameter value is "config".

      GET /restconf/data/example-events:events?content=config
         HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond:







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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:11:30 GMT
      Server: example-server
      Last-Modified: Mon, 23 Apr 2012 13:01:20 GMT
      ETag: eeeada438af
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+json

      {
        "example-events:events" : {
          "event" : [
            {
              "name" : "interface-up",
              "description" : "Interface up notification count"
            },
            {
              "name" : "interface-down",
              "description" : "Interface down notification count"
            }
          ]
        }
      }

   Example 3: content=nonconfig

   To retrieve only the non-configuration child resources, the "content"
   parameter is set to "nonconfig".  Note that configuration ancestors
   (if any) and list key leafs (if any) are also returned.  The client
   might send:

      GET /restconf/data/example-events:events?content=nonconfig
         HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond:














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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:11:30 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+json

      {
        "example-events:events" : {
          "event" : [
            {
              "name" : "interface-up",
              "event-count" : 42
            },
            {
              "name" : "interface-down",
              "event-count" : 4
            }
          ]
        }
      }

D.3.2.  "depth" Parameter

   The "depth" parameter is used to limit the number of levels of child
   resources that are returned by the server for a GET method request.

   The depth parameter starts counting levels at the level of the target
   resource that is specified, so that a depth level of "1" includes
   just the target resource level itself.  A depth level of "2" includes
   the target resource level and its child nodes.

   This example shows how different values of the "depth" parameter
   would affect the reply content for retrieval of the top-level
   "jukebox" data resource.

   Example 1: depth=unbounded

   To retrieve all the child resources, the "depth" parameter is not
   present or set to the default value "unbounded".  Note that some
   strings are wrapped for display purposes only.

      GET /restconf/data/example-jukebox:jukebox?depth=unbounded
         HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond:



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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:11:30 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+json

      {
        "example-jukebox:jukebox" : {
          "library" : {
            "artist" : [
              {
                "name" : "Foo Fighters",
                "album" : [
                  {
                    "name" : "Wasting Light",
                    "genre" : "example-jukebox:alternative",
                    "year" : 2011,
                    "song" : [
                      {
                        "name" : "Wasting Light",
                        "location" :
                          "/media/foo/a7/wasting-light.mp3",
                        "format" : "MP3",
                        "length" " 286
                      },
                      {
                        "name" : "Rope",
                        "location" : "/media/foo/a7/rope.mp3",
                        "format" : "MP3",
                        "length" " 259
                      }
                    ]
                  }
                ]
              }
            ]
          },
          "playlist" : [
            {
              "name" : "Foo-One",
              "description" : "example playlist 1",
              "song" : [
                {
                  "index" : 1,
                  "id" : "https://example.com/restconf/data/
                        example-jukebox:jukebox/library/artist=
                        Foo%20Fighters/album=Wasting%20Light/



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                        song=Rope"
                },
                {
                  "index" : 2,
                  "id" : "https://example.com/restconf/data/
                        example-jukebox:jukebox/library/artist=
                        Foo%20Fighters/album=Wasting%20Light/song=
                        Bridge%20Burning"
                }
              ]
            }
          ],
          "player" : {
            "gap" : 0.5
          }
        }
      }

   Example 2: depth=1

   To determine if 1 or more resource instances exist for a given target
   resource, the value "1" is used.

      GET /restconf/data/example-jukebox:jukebox?depth=1 HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond:

      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:11:30 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+json

      {
        "example-jukebox:jukebox" : [null]
      }

   Example 3: depth=3

   To limit the depth level to the target resource plus 2 child resource
   layers the value "3" is used.

      GET /restconf/data/example-jukebox:jukebox?depth=3 HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json



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   The server might respond:

      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:11:30 GMT
      Server: example-server
      Cache-Control: no-cache
      Pragma: no-cache
      Content-Type: application/yang.data+json

      {
        "example-jukebox:jukebox" : {
          "library" : {
            "artist" : [ null ]
          },
          "playlist" : [
            {
              "name" : "Foo-One",
              "description" : "example playlist 1",
              "song" : [ null ]
            }
          ],
          "player" : {
            "gap" : 0.5
          }
        }
      }

D.3.3.  "fields" Parameter

   In this example the client is retrieving the API resource, but
   retrieving only the "name" and "revision" nodes from each module, in
   JSON format:

      GET /restconf/data?fields=modules/module(name;revision) HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond as follows.













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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Content-Type: application/yang.data+json

      {
        "ietf-yang-library:modules": {
          "module": [
            {
              "name" : "example-jukebox",
              "revision" : "2015-06-04"
            },
            {
              "name" : "ietf-inet-types",
              "revision" : "2013-07-15"
            },
            {
              "name" : "ietf-restconf-monitoring",
              "revision" : "2015-06-19"
            },
            {
              "name" : "ietf-yang-library",
              "revision" : "2015-07-03"
            },
            {
              "name" : "ietf-yang-types",
              "revision" : "2013-07-15"
            }

          ]
        }
      }

D.3.4.  "insert" Parameter

   In this example, a new first entry in the "Foo-One" playlist is being
   created.

   Request from client:












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      POST /restconf/data/example-jukebox:jukebox/
        playlist=Foo-One?insert=first HTTP/1.1
      Host: example.com
      Content-Type: application/yang.data+json

      {
        "example-jukebox:song" : {
           "index" : 1,
           "id" : "/example-jukebox:jukebox/library/
               artist=Foo%20Fighters/album=Wasting%20Light/song=Rope"
         }
      }

   Response from server:

      HTTP/1.1 201 Created
      Date: Mon, 23 Apr 2012 13:01:20 GMT
      Server: example-server
      Last-Modified: Mon, 23 Apr 2012 13:01:20 GMT
      Location: https://example.com/restconf/data/
         example-jukebox:jukebox/playlist=Foo-One/song=1
      ETag: eeeada438af

D.3.5.  "point" Parameter

   In this example, the client is inserting a new "song" resource within
   an "album" resource after another song.  The request URI is split for
   display purposes only.

   Request from client:

      POST /restconf/data/example-jukebox:jukebox/
         library/artist=Foo%20Fighters/album=Wasting%20Light?
         insert=after&point=%2Fexample-jukebox%3Ajukebox%2F
         library%2Fartist%2FFoo%20Fighters%2Falbum%2F
         Wasting%20Light%2Fsong%2FBridge%20Burning   HTTP/1.1
      Host: example.com
      Content-Type: application/yang.data+json

      {
        "example-jukebox:song" : {
          "name" : "Rope",
          "location" : "/media/foo/a7/rope.mp3",
          "format" : "MP3",
          "length" : 259
        }
      }




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   Response from server:

      HTTP/1.1 204 No Content

   1.  Date: Mon, 23 Apr 2012 13:01:20 GMT Server: example-server Last-
       Modified: Mon, 23 Apr 2012 13:01:20 GMT ETag: abcada438af

D.3.6.  "filter" Parameter

   The following URIs show some examples of notification filter
   specifications (lines wrapped for display purposes only):

      // filter = /event/event-class='fault'
      GET /mystreams/NETCONF?filter=%2Fevent%2Fevent-class%3D'fault'

      // filter = /event/severity<=4
      GET /mystreams/NETCONF?filter=%2Fevent%2Fseverity%3C%3D4

      // filter = /linkUp|/linkDown
      GET /mystreams/SNMP?filter=%2FlinkUp%7C%2FlinkDown

      // filter = /*/reporting-entity/card!='Ethernet0'
      GET /mystreams/NETCONF?
         filter=%2F*%2Freporting-entity%2Fcard%21%3D'Ethernet0'

      // filter = /*/email-addr[contains(.,'company.com')]
      GET /mystreams/critical-syslog?
         filter=%2F*%2Femail-addr[contains(.%2C'company.com')]

      // Note: the module name is used as prefix.
      // filter = (/example-mod:event1/name='joe' and
      //           /example-mod:event1/status='online')
      GET /mystreams/NETCONF?
        filter=(%2Fexample-mod%3Aevent1%2Fname%3D'joe'%20and
                %20%2Fexample-mod%3Aevent1%2Fstatus%3D'online')

D.3.7.  "start-time" Parameter

      // start-time = 2014-10-25T10:02:00Z
      GET /mystreams/NETCONF?start-time=2014-10-25T10%3A02%3A00Z

D.3.8.  "stop-time" Parameter

      // stop-time = 2014-10-25T12:31:00Z
      GET /mystreams/NETCONF?stop-time=2014-10-25T12%3A31%3A00Z






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D.3.9.  "with-defaults" Parameter

   Assume the same data model as defined in Appendix A.1 of [RFC6243].
   Assume the same data set as defined in Appendix A.2 of [RFC6243].  If
   the server defaults-uri basic-mode is "trim", the the following
   request for interface "eth1" might be as follows:

   Without query parameter:

      GET /restconf/data/interfaces/interface=eth1 HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond as follows.

      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Content-Type: application/yang.data+json

      {
        "example:interface": [
          {
            "name" : "eth1",
            "status" : "up"
          }
        ]
      }

   Note that the "mtu" leaf is missing because it is set to the default
   "1500", and the server defaults handling basic-mode is "trim".

   With query parameter:

      GET /restconf/data/interfaces/interface=eth1
         ?with-defaults=report-all HTTP/1.1
      Host: example.com
      Accept: application/yang.data+json

   The server might respond as follows.











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      HTTP/1.1 200 OK
      Date: Mon, 23 Apr 2012 17:01:00 GMT
      Server: example-server
      Content-Type: application/yang.data+json

      {
        "example:interface": [
          {
            "name" : "eth1",
            "mtu" : 1500,
            "status" : "up"
          }
        ]
      }

   Note that the server returns the "mtu" leaf because the "report-all"
   mode was requested with the "with-defaults" query parameter.

Authors' Addresses

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com


   Martin Bjorklund
   Tail-f Systems

   Email: mbj@tail-f.com


   Kent Watsen
   Juniper Networks

   Email: kwatsen@juniper.net















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