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HTTP                                                           A. Wright
Internet-Draft                                         November 21, 2019
Intended status: Experimental
Expires: May 24, 2020


         Reporting Progress of Long-Running Operations in HTTP
                     draft-wright-http-progress-02

Abstract

   This document defines a mechanism for following the real-time
   progress of long-running operations over HTTP.

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 https://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 May 24, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
     1.2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Status Document Workflow  . . . . . . . . . . . . . . . . . .   3
     2.1.  Initial Request . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Status Document Request . . . . . . . . . . . . . . . . .   4
     2.3.  Closing the Operation . . . . . . . . . . . . . . . . . .   4
     2.4.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  The "102 Processing" status code  . . . . . . . . . . . .   6
       3.1.1.  Use of the "Location" header in 102 Processing  . . .   7
     3.2.  The "Progress" header . . . . . . . . . . . . . . . . . .   7
     3.3.  The "Status-URI" header . . . . . . . . . . . . . . . . .   8
     3.4.  The "processing" preference . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     4.1.  Status URIs . . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Denial of Service . . . . . . . . . . . . . . . . . . . .   9
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   HTTP is often used for making and observing the progress of long-
   running operations, including:

   o  Copying, patching, or deleting large sets of files

   o  Waiting on a task to be started at a specific time

   o  Adding an operation to a lengthy queue

   o  Working through a multi-step operation, e.g. provisioning a server

   o  Receiving updates to a long running task, e.g. construction of a
      building

   This document specifies a way to receive updates from the server on
   progress of such an operation, by defining a "progress" HTTP
   preference indicating the client would prefer to receive regular
   progress updates, a header for describing the current progress, and a
   1xx interim response to convey this progress information.






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1.1.  Notational Conventions

   The key words "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] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document uses ABNF as defined in [RFC5234] and imports grammar
   rules from [RFC7230] and [RFC8187].

   Examples in this document may add whitespace for clarity, or omit
   some HTTP headers for brevity; requests and responses may require
   additional Host, Connection, and/or Content-Length headers to be
   properly received.

1.2.  Scope

   This document is only intended to provide a mechanism for relaying
   the progress of a long-running operation, it does not intend to be a
   mechanism for subscribing to updates on a resource in general.

2.  Status Document Workflow

   The Status Document Workflow uses a status document that is related
   to a single request.  This status document is updated with the status
   of the operation, until the operation completes, finalizing the
   status document with the result of the operation.  No format is
   defined for the status document, any suitable information may be
   included, and the contents MAY be content-negotiated.

   The server SHOULD keep the status document available for a period of
   time after the operation finishes.

2.1.  Initial Request

   To begin, the client makes the initial request with an unsafe method.
   For example, "POST http://example.com/resource".

   o  If the operation finishes quickly, the server can issue the final
      response with a non-1xx, non-202 status code.  The server may
      respond with any response allowed by HTTP, including a document
      describing the result of the operation, a representation of the
      new state of the resource, or a minimal representation.

   o  If the client sent a "Prefer: processing" preference, the server
      SHOULD issue a "102 Processing" interim response upon receipt of
      the request, and every time there is an update to the operation



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      progress.  The first interim response SHOULD include a "Location"
      header identifying the status document created for this request.
      When the request finishes, respond normally with the final non-
      1xx, non-202 status code.

   o  If the request includes "Prefer: respond-async, wait=n", and has
      been running longer than the preferred wait time, then background
      the operation and emit "202 Accepted", with a "Location" header.
      If the server emitted a 102 Processing interim response, this will
      be the same header as before.

   If the server responds with the result of the operation, or a
   representation of the new state of the resource, the "Content-
   Location" header identifies where this document can be requested in
   the future.

   Note that clients may make requests with all of the above
   preferences; they can all be honored at the same time, see below for
   an example.

2.2.  Status Document Request

   If the client received an operation status document from the initial
   unsafe request, it may make a GET request to this document to re-
   download the result of the request.

   The client may do this for any reason, including:

   o  The operation resulted in a 202 Accepted response and the client
      wants to know if the operation finished.

   o  The user wants to review the outcome of the request after having
      discarded the initial 2xx (non-202) response.

   o  The connection was reset before the initial request could respond
      with a non-1xx status code.

   If the client makes this request with the "Prefer: processing"
   preference, the server SHOULD send an initial "102 Processing"
   header, and "102 Processing" responses for every progress update
   until the operation completes.

2.3.  Closing the Operation

   The client MAY acknowledge it has reacted to the completed operation
   by issuing a "DELETE" request on the status document.  Servers SHOULD
   limit requests on the status document to the user that issued the
   initial request.



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   Servers MAY delete the status document any time after the operation
   finishes, but SHOULD wait a period of time long enough for clients to
   check back on the operation on another business day.

2.4.  Example

   Clients may send any combination of preferences in a request.  In
   this example, the client issues a POST request to capture a
   photograph of a scenic landscape by issuing a POST request to
   "http://example.com/capture", and the server generates a status
   document for this request at "http://example.com/capture?request=42".

   POST http://example.com/capture HTTP/1.1
   Prefer: processing, respond-async, wait=20


   To which the server might reply:

   HTTP/1.1 102 Processing
   Location: <?request=42>
   Progress: 0/3 "Herding cats"

   HTTP/1.1 102 Processing
   Progress: 1/3 "Knitting sweaters"

   HTTP/1.1 102 Processing
   Progress: 2/3 "Slaying dragons"

   HTTP/1.1 201 Created
   Progress: 3/3 "Available"
   Location: </photos/42>
   Content-Location: <?request=42>
   Content-Type: text/plain

   The photographer uploaded your image to:
     <http://example.com/photos/42>

   If this same request took significantly longer (more than 20
   seconds), then due to the respond-async preference, the response
   might look like this instead:











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   HTTP/1.1 102 Processing
   Progress: 0/3 "Herding cats"
   Location: </status>

   HTTP/1.1 102 Processing
   Progress: 1/3 "Knitting sweaters"

   HTTP/1.1 202 Accepted
   Location: </status>
   Content-Location: </status>
   Content-Type: text/plain

   The photographer is on step 2: Knitting sweaters

   The client can re-subscribe to updates by making a GET request to the
   status document with "Prefer: processing":

   GET http://example.com/capture?request=42 HTTP/1.1
   Prefer: processing, respond-async, wait=20

   HTTP/1.1 102 Processing
   Progress: 1/3 "Knitting sweaters"

   HTTP/1.1 102 Processing
   Progress: 2/3 "Slaying dragons"

   HTTP/1.1 200 OK
   Progress: 3/3 "Available"
   Status-URI: 201 </capture>
   Content-Type: text/plain

   The photographer uploaded your image to:
     <http://example.com/photos/42>

3.  Definitions

3.1.  The "102 Processing" status code

   The 102 (Processing) status code is an interim response used to
   inform the client that the server has accepted the request, but has
   not yet completed it.  This status code SHOULD send this status when
   the request could potentially take long enough to time out
   connections due to inactivity, or when there is new progress to
   report via a "Progress" or "Status-URI" header.

   The "102 Processing" status was first described by WebDAV in
   [RFC2518], but was not included in subsequent revisions of WebDAV for




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   lack of implementations.  This document updates the semantics of the
   "102 Processing" status code first defined there.

3.1.1.  Use of the "Location" header in 102 Processing

   The meaning of a Location header [RFC7231] is the same as in a "202
   Accepted" response: It identifies a document that will be updated
   with the progress, current status, and result of the operation.

   A Location header SHOULD be sent in the first "102 Processing"
   response, as well as the "202 Accepted" response to the same request.

3.2.  The "Progress" header

   The "Progress" header is used to indicate the current progress on an
   operation being run by the origin server.  Use of this header implies
   the server supports "102 Processing" responses and the "processing"
   preference.

   Progress        = fraction *( WS progress-remark )
   progress-remark = fraction / comment / quoted-string / ext-value
   fraction        = 1*DIGIT "/" [ 1*DIGIT ]
   comment         = <comment, see [RFC7230], Section 3.2.6>
   quoted-string   = <quoted-string, see [RFC7230], Section 3.2.6>
   ext-value       = <ext-value, see [RFC8187]>

   The Progress header lists data about the current operation and
   summarizes operations that have finished.  It contains a fraction,
   and any number of remarks.

   The fraction numerator specifies the number of operations that have
   completed.  It may also represent the zero-indexed identifier of the
   current operation.  The numerator MUST NOT decrease in value.

   The fraction denominator specifies the total expected operations to
   be completed before a final status code can be delivered.  If
   specified, the denominator MUST NOT be smaller than the numerator.
   The denominator MAY be omitted when the length of the operation is
   unknown.  If additional tasks need to be performed, the denominator
   MAY increase.  The numerator MUST NOT decrease in value and MUST NOT
   disappear once introduced.

   The remark is some sort of indication of the current task being
   carried out.  For example, if multiple files are being operated on,
   it might refer to the most recent file to be opened.  Four forms are
   provided:





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   o  Use of additional "fraction" productions are permitted to indicate
      progress on a subordinate operation.  For example, a data transfer
      in progress as part of a multi-step operation.

   o  Use of the "comment" production implies the text is not intended
      for end users.

   o  The "ext-value" provides a label for users.  If the HTTP server
      supports localization, the server SHOULD negotiate a language
      using "Accept-Language", if it exists in the request.  This
      language does not necessarily have to be the same as the "Content-
      Language".

   o  The "quoted-string" is also supported if the text is entirely
      7-bit ASCII.  This is suitable for reporting filenames or similar
      data not in any particular language.

   Multiple remarks MAY be used.  Remarks MUST be listed in descending
   significance; if multiple fractions are presented, remarks describe
   the operation identified by the previous fraction.

   Example usage:

   Progress: 0/1
   Progress: 66/ (tries) utf-8'en'Generating%20prime%20number
   Progress: 5/16 UTF-8'ja-JP'%e9%a3%9f%e3%81%b9%e3%81%a6
   Progress: 3/20 "POST http://example.com/item/3" 8020/8591489 (bytes)

3.3.  The "Status-URI" header

   The Status-URI header reports the status of an operation performed on
   a resource by another request.

   The Status-URI header MAY be used any number of times in a "101
   Processing" response to report the result of a subordinate operation
   for the request.

   Status-URI    = #status-pair
   status-pair   = status-code OWS "<" URI-Reference ">"
   status-code   = <status-code, see [RFC7230], Section 3.1.2>
   URI-Reference = <URI-reference, see [RFC7230], Section 2.7>

   Example usage:

   Status-URI: 507 <http://example.com/photo/41>
   Status-URI: 200 <http://example.com/capture>





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3.4.  The "processing" preference

   The "processing" HTTP preference [RFC7240] specifies if the server
   should emit "102 Processing" status responses.

   When performing a unsafe action, the server should emit interim "102
   Processing" responses until the action finishes.

   In a GET or HEAD request to a status document, it means the client is
   only interested in the result of the operation that the status
   document is about, and the server should send "102 Processing"
   updates until then.  The "respond-async" and "wait" preferences are
   ignored here as the request is not performing an action.

4.  Security Considerations

4.1.  Status URIs

   The fact that this operation produces a URI for each operation means
   that third parties can look at the requests being made by a user.
   Servers SHOULD ensure that only the user who made the request has
   access to the status document.  Servers SHOULD generate URIs with
   sufficient entropy, although URIs supposed to be considered public
   knowledge (see HTTP).

4.2.  Denial of Service

   This may expose information about load, which may allow attackers to
   better exploit weak points already under stress.  Servers with this
   functionality may make it cheap for server operators to accept work-
   intensive tasks.  Usual precautions about mitigating denial-of-
   service attacks should be exercised.

5.  References

5.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.





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   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7240]  Snell, J., "Prefer Header for HTTP", RFC 7240,
              DOI 10.17487/RFC7240, June 2014,
              <https://www.rfc-editor.org/info/rfc7240>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8187]  Reschke, J., "Indicating Character Encoding and Language
              for HTTP Header Field Parameters", RFC 8187,
              DOI 10.17487/RFC8187, September 2017,
              <https://www.rfc-editor.org/info/rfc8187>.

5.2.  Informative References

   [RFC2518]  Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
              Jensen, "HTTP Extensions for Distributed Authoring --
              WEBDAV", RFC 2518, DOI 10.17487/RFC2518, February 1999,
              <https://www.rfc-editor.org/info/rfc2518>.

Author's Address

   Austin Wright

   Email: aaa@bzfx.net
















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