HTTPAPI                                                         S. Dalal
Internet-Draft
Intended status: Standards Track                                E. Wilde
Expires: January 11, 2022                                  July 10, 2021


                   The Deprecation HTTP Header Field
                draft-ietf-httpapi-deprecation-header-02

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
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   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 11, 2022.

Copyright Notice

   Copyright (c) 2021 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
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   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  . . . . . . . . . . . .   3
     2.1.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The Deprecation Link Relation Type  . . . . . . . . . . . . .   4
     3.1.  Documentation . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Recommend Replacement . . . . . . . . . . . . . . . . . . . .   6
   5.  Sunset  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Resource Behavior . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  The Deprecation HTTP Response Header  . . . . . . . . . .   7
     7.2.  The Deprecation Link Relation Type  . . . . . . . . . . .   7
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Implementing the Deprecation Header . . . . . . . . . . .   8
     8.2.  Implementing the Concept  . . . . . . . . . . . . . . . .  10
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Deprecation of an HTTP resource as defined in Section 2 of [RFC7231]
   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



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   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.

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 IMF-fixdate
   rule as defined in Section 7.1.1.1 of [RFC7231].

   The term "resource" is to be interpreted as defined in Section 2 of
   [RFC7231], that is identified by an URI.

2.  The Deprecation HTTP Response Header

   The "Deprecation" HTTP response header field allows a server to
   communicate to a client that the 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 = IMF-fixdate / "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 IMF-fixdate timestamp.

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

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






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   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:

   Deprecation: true

2.2.  Scope

   The Deprecation header field applies to the resource that returns it,
   meaning that it announces the upcoming deprecation of that specific
   resource.  However, there may be scenarios where the scope of the
   announced deprecation is larger than just the single resource where
   it appears.

   Resources are free to define such an increased scope, and usually
   this scope will be documented by the resource so that consumers of
   the resource know about the increased scope and can behave
   accordingly.  However, it is important to take into account that such
   increased scoping is invisible for consumers who are unaware of the
   increased scoping rules.  This means that these consumers will not be
   aware of the increased scope, and they will not interpret Deprecation
   information different from its standard meaning (i.e., it applies to
   the resource only).

   Using such an increased scope still may make sense, as Deprecation
   information is only a hint anyway; thus, it is optional information
   that cannot be depended on, and clients should always be implemented
   in ways that allow them to function without Deprecation information.
   Increased scope information may help clients to glean additional
   hints from resources and, thus, might allow them to implement
   behavior that allows them to make educated guesses about resources
   becoming deprecated.

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.





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   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 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"

   In this example the interlinked content provides additional
   information about the deprecation of the resource context.  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.





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   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

   The "Link" [RFC8288] header field can be used in addition to the
   "Deprecation" header field to inform the client about available
   alternatives to the deprecated resource.  The following relation
   types as defined in [RFC8288] are RECOMMENDED to use for this
   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"

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 HTTP header field [RFC8594] can be used in
   addition to the "Deprecation" header.




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   The timestamp given in the "Sunset" header field MUST be the later or
   the same as the one given in the "Deprecation" header field.

   The following example shows that the resource in context has been
   deprecated since Sunday, November 11, 2018 at 23:59:59 GMT and its
   sunset date is Wednesday, 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 HTTP Response Header

   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"

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]:







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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"

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".

8.1.  Implementing the Deprecation Header

   This is a list of implementations that implement the deprecation
   header field:

   Organization: Apollo

   o  Description: Deprecation header is returned when deprecated
      functionality (as declared in the GraphQL schema) is accessed




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   o  Reference: https://www.npmjs.com/package/apollo-server-tools

   Organization: Zalando

   o  Description: Deprecation header is recommended as the preferred
      way to communicate API deprecation in Zalando API designs.

   o  Reference: https://opensource.zalando.com/restful-api-
      guidelines/#deprecation

   Organization: Palantir Technologies

   o  Description: Deprecation header is incorporated in code generated
      by conjure-java, a CLI to generate Java POJOs and interfaces from
      Conjure API definitions

   o  Reference: https://github.com/palantir/conjure-java

   Organization: IETF Internet Draft, Registration Protocols Extensions

   o  Description: Deprecation link relation is returned in Registration
      Data Access Protocol (RDAP) notices to indicate deprecation of
      jCard in favor of JSContact.

   o  Reference: https://tools.ietf.org/html/draft-loffredo-regext-rdap-
      jcard-deprecation

   Organization: E-Voyageurs Technologies

   o  Description: Deprecation header is incorporated in Hesperides, a
      configuration management tool providing universal text file
      templating and properties editing through a REST API or a webapp.

   o  Reference: https://github.com/voyages-sncf-
      technologies/hesperides/blob/master/documentation/lightweight-
      architecture-decision-records/deprecated_endpoints.md

   Organization: Open-Xchange

   o  Description: Deprecation header is used in Open-Xchange appsuite-
      middleware

   o  Reference: https://github.com/open-xchange/appsuite-middleware

   Organization: MediaWiki






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   o  Description: Core REST API of MediaWiki would use Deprecation
      header for endpoints that have been deprecated because a new
      endpoint provides the same or better functionality.

   o  Reference: https://phabricator.wikimedia.org/T232485

8.2.  Implementing the Concept

   This is a list of implementations that implement the general concept,
   but do so using different mechanisms:

   Organization: Zapier

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

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

   Organization: IBM

   o  Description: IBM uses a custom HTTP header named "Deprecated"

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

   Organization: Ultipro

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

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

   Organization: Clearbit

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

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

   Organization: PayPal

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

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





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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.

   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"



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   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

   [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>.





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   [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>.

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>.

   [W3C.REC-html401-19991224]
              Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
              Specification", World Wide Web Consortium Recommendation
              REC-html401-19991224, December 1999,
              <https://www.w3.org/TR/1999/REC-html401-19991224>.

Appendix A.  Acknowledgments

   The authors would like to thank Nikhil Kolekar, Darrel Miller, Mark
   Nottingham, and Roberto Polli for their contributions.

   The authors take all responsibility for errors and omissions.

Authors' Addresses

   Sanjay Dalal

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



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   Erik Wilde

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















































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