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Versions: 00 01

Network Working Group                                           S. Dalal
Internet-Draft
Intended status: Standards Track                                E. Wilde
Expires: December 19, 2019                                 June 17, 2019


                   The Deprecation HTTP Header Field
                   draft-dalal-deprecation-header-01

Abstract

   The HTTP Deprecation response header field can be used to signal to
   consumers of a URI-identified resource that 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 December 19, 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
   3.  The Deprecation Link Relation Type  . . . . . . . . . . . . .   4
     3.1.  Documentation . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Recommend Replacement . . . . . . . . . . . . . . . . . . . .   5
   5.  Sunset  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Resource Behavior . . . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  The Deprecation Response Header Field . . . . . . . . . .   6
     7.2.  The Deprecation Link Relation Type  . . . . . . . . . . .   7
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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,
   discourages applications from forming new dependencies on the
   resource, and informs applications about 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 information
   indicating 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.
   Alternates of a resource can be similar resource(s) or a newer
   version of the same resource.



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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 specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234] and includes, by reference, the 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 or will be deprecated.

2.1.  Syntax

   The "Deprecation" response header field describes the deprecation.
   It either shows the deprecation date, which may be in the future (the
   resource context will be deprecated at that date) or in the past (the
   resource context has been deprecated at that date), or it simply
   flags the resource context as being deprecated:

   Deprecation = HTTP-date / "true"

   Servers MUST NOT include more than one "Deprecation" header field in
   the same response.

   The date, if present, is the date when the resource context was or
   will be deprecated.  It is in the form of an HTTP-date timestamp, as
   defined in Section 7.1.1.1 of [RFC7231].

   The following example shows that the resource context has been
   deprecated on Friday, November 11, 2018 at 23:59:59 GMT:

   Deprecation: Sun, 11 Nov 2018 23:59:59 GMT

   The deprecation date can be in the future.  If the value of "date" is
   in the future, it means that the resource will be deprecated at the
   given date in future.

   If the deprecation date is not known, the header field can carry the
   simple string "true", indicating that the resource context is
   deprecated, without indicating when that happened:



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       Deprecation: true

3.  The Deprecation Link Relation Type

   In addition to the Deprecation HTTP header field, the server can use
   links with the "deprecation" link relation type to communicate to the
   client where to find more information about deprecation of the
   context.  This can happen before the actual deprecation, to make a
   deprecation policy discoverable, or after deprecation, when there may
   be documentation about the deprecation, and possibly documentation of
   how to manage it.

   This specification places no restrictions on the representation of
   the interlinked deprecation policy.  In particular, the deprecation
   policy may be available as human-readable documentation or as
   machine-readable description.

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.

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




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   In this example, the interlinked content provides additional
   information about the deprecation of the resource context.  In this
   example, there is no Deprecation header field in the response, and
   thus the resource is not deprecated.  However, the resource already
   exposes a link where information is available how deprecation is
   managed for the context.  This may be documentation explaining the
   use of the Deprecation header field, and also explaining under which
   circumstances and with which policies (announcement before
   deprecation; continued operation after deprecation) deprecation might
   be happening.

   The following example uses the same link header, but also announces a
   deprecation date using a Deprecation header field.

Deprecation: Sun, 11 Nov 2018 23:59:59 GMT
Link: <https://developer.example.com/deprecation>; rel="deprecation"; type="text/html"

   Given that the deprecation date is in the past, the linked resource
   may have been updated to include information about the deprecation,
   allowing clients to discover information about the deprecation that
   happened.

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]

   The following example provides link to the successor version of the
   requested resource that is deprecated.

   Deprecation: Sun, 11 Nov 2018 23:59:59 GMT
   Link: <https://api.example.com/v2/customers>; rel="successor-version"

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

   Deprecation: Sun, 11 Nov 2018 23:59:59 GMT
   Link: <https://api.example.com/v1/clients>; rel="alternate"



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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 [RFC8594] header could be used in addition to the
   "Deprecation" header.

   The 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: Sun, 11 Nov 2018 23:59:59 GMT
   Sunset: Wed, 11 Nov 2020 23:59:59 GMT

6.  Resource Behavior

   The act of deprecation does not change any behavior of the resource.
   Deprecated resources SHOULD keep functioning as before, allowing
   consumers to still use the resources in the same way as they did
   before the resources were declared deprecated.

7.  IANA Considerations

7.1.  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"








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7.2.  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]:

   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"

8.  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"



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

   Organization: IBM

   IBM uses a custom HTTP header named "Deprecated"

   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

9.  Security Considerations

   The Deprecation header field SHOULD be treated as a hint, meaning
   that the resource is indicating (and not guaranteeing with certainty)
   that it is deprecated.  Applications consuming the resource SHOULD
   check the resource documentation to verify authenticity and accuracy.
   Resource documentation SHOULD provide additional information about
   the deprecation including recommendation(s) for replacement.

   In cases, where the Deprecation header field value is a date in
   future, it can lead to information that otherwise might not be
   available.  Therefore, applications consuming the resource SHOULD
   verify the resource documentation and if possible, consult the
   resource developer to discuss potential impact due to deprecation and
   plan for possible transition to recommended resource.





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   In cases where "Link" header is used to provide more documentation
   and/or recommendation for replacement, one should assume that the
   content of the "Link" header field may not be secure, private or
   integrity-guaranteed, and due caution should be exercised when using
   it.  Applications consuming the resource SHOULD check the referred
   resource documentation to verify authenticity and accuracy.

   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.

10.  Examples

   The first example shows a deprecation header field without date
   information:

   Deprecation: true

   The second example shows a deprecation header with date information
   and a link to the successor version:

   Deprecation: Sun, 11 Nov 2018 23:59:59 GMT
   Link: <https://api.example.com/v2/customers>; rel="successor-version"

   The third example shows a deprecation header field with links for the
   successor version and for the API's deprecation policy.  In addition,
   it shows the sunset date for the deprecated resource:

Deprecation: Sun, 11 Nov 2018 23:59:59 GMT
Sunset: Wed, 11 Nov 2020 23:59:59 GMT
Link: <https://api.example.com/v2/customers>; rel="successor-version", <https://developer.example.com/deprecation>; rel="deprecation"

11.  References

11.1.  Normative References







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   [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>.

   [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>.





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11.2.  Informative References

   [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>.

   [RFC8594]  Wilde, E., "The Sunset HTTP Header Field", RFC 8594,
              DOI 10.17487/RFC8594, May 2019,
              <https://www.rfc-editor.org/info/rfc8594>.

Appendix A.  Acknowledgments

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

   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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