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Versions: 00

Network Working Group                                           S. Dalal
Internet-Draft
Intended status: Standards Track                                E. Wilde
Expires: August 30, 2019                               February 26, 2019


                      The Deprecation HTTP Header
                   draft-dalal-deprecation-header-00

Abstract

   The HTTP Deprecation response header can be used to signal to
   consumers of a URI-identified resource that the use of the resource
   has been deprecated.  Additionally, the deprecation link relation can
   be used to link to a resource that provides additional context for
   the deprecation, and possibly ways in which clients can find a
   replacement for the deprecated resource.

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 August 30, 2019.

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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The Deprecation HTTP Response Header Field  . . . . . . . . .   3
     2.1.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   3
       2.1.1.  Version . . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.2.  Date  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The Deprecation Link Relation Type  . . . . . . . . . . . . .   5
     3.1.  Documentation . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Policy  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Recommend Replacement . . . . . . . . . . . . . . . . . . . .   6
   5.  Sunset  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  The Deprecation Response Header Field . . . . . . . . . .   7
     6.2.  The Deprecation Link Relation Type  . . . . . . . . . . .   7
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Deprecation of a URI-identified resource is a technique to
   communicate information about the lifecycle of a resource.  It
   encourages applications to migrate away from the resource and
   discourage applications from forming new dependencies on the
   resource, and informs applications of the risk of continuing
   dependence upon the resource.

   The act of deprecation does not change any behavior of the resource.
   It just informs client of the fact that a resource is deprecated.
   The Deprecation HTTP response header field MAY be used to convey this
   fact at runtime to clients.  The header field can carry additional
   information such as since when the deprecation is in effect.

   In addition to the Deprecation header field the resource provider can
   use other header fields to convey additional information related to
   deprecation.  For example, information such as where to find
   documentation related to the deprecation or what should be used as an
   alternate and when the deprecated resource would be unreachable, etc.



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   Alternates of a resource can be similar resource(s) or a newer
   version of the same resource.

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 specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234] and includes, by reference, the "token" rule,
   DQUOTE (double quote) rule, the SP (space) rule and the "rule"
   extension that allows for compact definition of comma-separated lists
   using a '#' operator (similar to how the '*' operator indicates
   repetition), HTTP-date rule as defined within Sections 3.2.6 and 7 of
   [RFC7230] and Section 7.1.1 of [RFC7231].

2.  The Deprecation HTTP Response Header Field

   The "Deprecation" HTTP response header field allows a server to
   communicate to a client that the URI-identified resource in context
   of the message is deprecated.  It can also provide information that
   the resource is deprecated since which version.

2.1.  Syntax

   The "Deprecation" response header contains the header name
   "Deprecation" followed by a ":" and a property(s).  Each property
   consists of a name-value-pair.  Servers SHOULD NOT send Deprecation
   headers that fail to conform to the following grammar:

   deprecation-header = "Deprecation:" SP "version"=vval, "date"=dval,
                        *( extension )
   extension = property-name "=" property-value
   property-name = DQUOTE token DQUOTE
   token = <token, defined as in [RFC7230], Section 3.2.6>
   vval = property-value
   property-value = DQUOTE *( pchar ) DQUOTE
   pchar = %x23 / %x2B-3A / %x41-5A / %x61-7A / %x7C
         ; US-ASCII characters
   dval = DQUOTE HTTP-date DQUOTE

   Note that some of the grammatical terms above reference documents
   that use different grammatical notations than this document (which
   uses ABNF from [RFC5234]).




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   Servers SHOULD NOT include more than one "Deprecation" header field
   in the same response.  If a server sends multiple responses
   containing "Deprecation" headers concurrently to the user agent
   (e.g., when communicating with the user agent over multiple sockets),
   these responses create a "race condition" that can lead to
   unpredictable behavior.

   The value of "Deprecation" response header field could consist of at
   least 1 standard property: "date" or "version" as shown below.
   Either of "version" or "date" is REQUIRED and both are also allowed.

   Deprecation: version="version", date="date"

2.1.1.  Version

   The value of the "version" property, if present, could be the version
   of the resource that is deprecated.  The value of "version" would be
   an opaque version identifier.  For resources that use date-based
   versioning scheme, the value would be accordingly.

   Following example indicates that the version v1 of the resource in
   context is deprecated.

   Deprecation: version="v1"

   Following example shows that the version 2018-11-08 (November 8,
   2018) of the resource in context is deprecated.  Here the versioning
   scheme used is date-based.

   Deprecation: version="2018-11-08"

2.1.2.  Date

   The value of "date" property, if present, would be the date when
   resource was deprecated.  It would be in the form of a quoted HTTP-
   date timestamp, as defined in Section 7.1.1.1 of [RFC7231].

   Following example shows that the resource in context is deprecated on
   Friday, November 11, 2018 at 23:59:59 GMT.

   Deprecation: date="Fri, 11 Nov 2018 23:59:59 GMT"

   Date could be in future too.  If the value of "date" is in future, it
   means that the resource would be deprecated on the given date in
   future.






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3.  The Deprecation Link Relation Type

   In addition to the Deprecation HTTP header, the server could use a
   "Link" header(s) to communicate to the client where to find more
   information about deprecation of the resource in context.  This
   information could be in the form of documentation of the resource
   including details about the deprecation related aspects of the
   resource or the deprecation policy of the resource provider or both
   for example.

3.1.  Documentation

   For a URI-identified resource, deprecation could involve one or more
   parts of request, response or both.  These parts could be one or more
   of the following.

   o  URI - deprecation of one ore more query parameter(s) or path
      element(s)

   o  method - HTTP method for the resource is deprecated

   o  request header - one or more HTTP request header(s) is deprecated

   o  response header - HTTP response header(s) is deprecated

   o  request body - request body contains one or more deprecated
      element(s)

   o  response body - response body contains one or more deprecated
      element(s)

   The purpose of the "Deprecation" header is to provide just enough
   "hints" about the deprecation to the client application developer.
   It is safe to assume that on reception of the "Deprecation" header,
   the client developer would look up the resource's documentation in
   order to find deprecation related semantics.  The resource developer
   could provide a link to the resource documentation using a "Link"
   header with relation type "deprecation" as shown below.

   Deprecation: version="v1"
   Link: <https://developer.example.com/v1/customers>; rel="deprecation"
          type="text/html"

   where content at "https://developer.example.com/v1/customers" would
   be annotated to show deprecation of the relevant parts of the
   "customers" resource.





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3.2.  Policy

   Resource provider would typically document versioning and deprecation
   policy with the resource documentation.  To inform the client
   application developer of the deprecation policy, the resource
   provider could use the "deprecation" relation type as shown below.

   Deprecation: version="v1"
   Link: <https://developer.example.com/deprecation>; rel="deprecation"
          type="text/html"

   where deprecation policy of the resource provider "example.com" is
   described at "https://developer.example.com/deprecation".

4.  Recommend Replacement

   "Link" [RFC8288] header could be used in addition to the
   "Deprecation" header to recommend the client application about
   available alternates to the deprecated resource.  Following relation
   types as defined in [RFC8288] are RECOMMENDED to use for the purpose.

   o  "successor-version": Points to a resource containing the successor
      version.  [RFC5829]

   o  "latest-version": Points to a resource containing the latest
      (e.g., current) version.  [RFC5829]

   o  "alternate": Designates a substitute.  [W3C.REC-html401-19991224]

   Following example provides link to the successor version of the v1
   version of "customer" resource that is deprecated.

   Deprecation: version="v1"
   Link: <https://api.example.com/v2/customers>; rel="successor-version"

   This example provides link to an alternate resource to the "customer"
   resource that is deprecated.

   Deprecation: version="2018-11-11"
   Link: <https://api.example.com/v1/clients>; rel="alternate"

5.  Sunset

   In addition to the deprecation related information, if the resource
   provider wants to convey to the client application that the
   deprecated resource is expected to become unresponsive at a specific
   point in time, the [Sunset] header could be used in addition to the
   "Deprecation" header.



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   Following example indicates that the resource in context has been
   deprecated since version v2 and its sunset date is Friday, November
   11, 2020 at 23:59:59 GMT.

   Deprecation: version="v2"
   Sunset: Fri, 11 Nov 2020 23:59:59 GMT

   Following example shows that the resource in context has been
   deprecated since Friday, November 11, 2018 at 23:59:59 GMT and its
   sunset date is Friday, November 11, 2020 at 23:59:59 GMT.

   Deprecation: date="Fri, 11 Nov 2018 23:59:59 GMT"
   Sunset: Fri, 11 Nov 2020 23:59:59 GMT

6.  IANA Considerations

6.1.  The Deprecation Response Header Field

   The "Deprecation" response header should be added to the permanent
   registry of message header fields (see [RFC3864]), taking into
   account the guidelines given by HTTP/1.1 [RFC7231].

   Header Field Name: Deprecation

   Applicable Protocol: Hypertext Transfer Protocol (HTTP)

   Status: Standard

   Author: Sanjay Dalal <sanjay.dalal@cal.berkeley.edu>,
           Erik Wilde <erik.wilde@dret.net>

   Change controller: IETF

   Specification document: this specification,
               Section 2 "The Deprecation HTTP Response Header Field"

6.2.  The Deprecation Link Relation Type

   The "deprecation" link relation type should be added to the permanent
   registry of link relation types according to Section 4.2 of
   [RFC8288]:










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   Relation Type: deprecation

   Applicable Protocol: Hypertext Transfer Protocol (HTTP)

   Status: Standard

   Author: Sanjay Dalal <sanjay.dalal@cal.berkeley.edu>,
           Erik Wilde <erik.wilde@dret.net>

   Change controller: IETF

   Specification document: this specification,
           Section 3 "The Deprecation Link Relation Type"

7.  Implementation Status

   Note to RFC Editor: Please remove this section before publication.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   Organization: Zapier

   Description: Zapier uses two custom HTTP headers named "X-API-
   Deprecation-Date" and "X-API-Deprecation-Info"

   Reference: https://zapier.com/engineering/api-geriatrics/

   Organization: IBM

   IBM uses a custom HTTP header named "Deprecated"



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   Reference:
   https://www.ibm.com/support/knowledgecenter/en/SS42VS_7.3.1/
   com.ibm.qradar.doc/c_rest_api_getting_started.html

   Organization: Ultipro

   Description: Ultipro uses the HTTP "Warning" header as described in
   Section 5.5 of [RFC7234] with code "299"

   Reference: https://connect.ultipro.com/api-deprecation

   Organization: Clearbit

   Description: Clearbit uses a custom HTTP header named "X-API-Warn"

   Reference: https://blog.clearbit.com/dealing-with-deprecation/

   Organization: PayPal

   Description: PayPal uses a custom HTTP header named "PayPal-
   Deprecated"

   Reference: https://github.com/paypal/api-standards/blob/master/api-
   style-guide.md#runtime

8.  Security Considerations

   The content of a "Link" header field is not secure, private or
   integrity-guaranteed, and due caution should be exercised when using
   it.  Use of Transport Layer Security (TLS) with HTTP ([RFC7230] is
   currently the only end-to-end way to provide such protection.

   The suggested "Link" header fields make extensive use of IRIs and
   URIs.  See [RFC3987] for security considerations relating to IRIs.
   See [RFC3986] for security considerations relating to URIs.  See
   [RFC7230] for security considerations relating to HTTP headers.

   Applications that take advantage of typed links should consider the
   attack vectors opened by automatically following, trusting, or
   otherwise using links gathered from the HTTP headers.  In particular,
   Link headers that use the "successor-version", "latest-version" or
   "alternate" relation types should be treated with due caution.  See
   [RFC5829] for security considerations relating to these link relation
   types.







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9.  Example

   Just deprecation header without any Link headers.

   Deprecation: version="v1"

   Deprecation header with link to the successor version.

   Deprecation: version="v1"
   Link: <https://api.example.com/v2/customers>; rel="successor-version"

   Deprecation header with links for the successor version and for the
   API developer's deprecation policy.  Also, it shows sunset date for
   the deprecated version (v1).

   Deprecation: version="v1"
   Sunset: Fri, 11 Nov 2020 23:59:59 GMT
   Link: <https://api.example.com/v2/customers>; rel="successor-version"
   Link: <https://developer.example.com/deprecation>; rel="deprecation"

10.  References

10.1.  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>.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              DOI 10.17487/RFC3864, September 2004,
              <https://www.rfc-editor.org/info/rfc3864>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
              January 2005, <https://www.rfc-editor.org/info/rfc3987>.

   [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>.

   [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              RFC 7234, DOI 10.17487/RFC7234, June 2014,
              <https://www.rfc-editor.org/info/rfc7234>.

   [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>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/info/rfc8288>.

10.2.  Informative References

   [Deprecation]
              Marks, S., "JEP 277 - Enhanced Deprecation", 2017,
              <http://openjdk.java.net/jeps/277>.

   [RFC5829]  Brown, A., Clemm, G., and J. Reschke, Ed., "Link Relation
              Types for Simple Version Navigation between Web
              Resources", RFC 5829, DOI 10.17487/RFC5829, April 2010,
              <https://www.rfc-editor.org/info/rfc5829>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [Sunset]   Wilde, E., "The Sunset HTTP Header Field", 2019,
              <https://tools.ietf.org/html/
              draft-wilde-sunset-header-11>.

Appendix A.  Acknowledgments

   The authors would like to thank Mark Nottingham and Nikhil Kolekar
   for reviewing this specification.




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   The authors take all responsibility for errors and omissions.

Authors' Addresses

   Sanjay Dalal

   Email: sanjay.dalal@cal.berkeley.edu
   URI:   https://github.com/sdatspun2


   Erik Wilde

   Email: erik.wilde@dret.net
   URI:   http://dret.net/netdret





































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