HTTPAPI                                                         S. Dalal
Internet-Draft
Intended status: Standards Track                                E. Wilde
Expires: 13 June 2024                                   11 December 2023


                   The Deprecation HTTP Header Field
                draft-ietf-httpapi-deprecation-header-03

Abstract

   The Deprecation HTTP response header field is used to signal to
   consumers of a URI-identified resource that the resource will be or
   has been deprecated.  Additionally, the deprecation link relation can
   be used to link to a resource that provides additional information
   about planned or existing deprecation, and possibly ways in which
   clients can best manage deprecation.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-httpapi-deprecation-
   header/.

   Discussion of this document takes place on the HTTPAPI Working Group
   mailing list (mailto:httpapi@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/httpapi/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/httpapi/.  Working Group
   information can be found at https://ietf-wg-httpapi.github.io/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-httpapi/deprecation-header.

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
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   This Internet-Draft will expire on 13 June 2024.

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Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
   2.  The Deprecation HTTP Response Header Field
     2.1.  Syntax
     2.2.  Scope
   3.  The Deprecation Link Relation Type
     3.1.  Documentation
       3.1.1.  Security Considerations
   4.  Sunset
   5.  Resource Behavior
   6.  IANA Considerations
     6.1.  The Deprecation HTTP Response Header Field
     6.2.  The Deprecation Link Relation Type
   7.  Examples
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Appendix A.  Implementation Status
     A.1.  Implementing the Deprecation Header Field
     A.2.  Implementing the Concept
   Appendix B.  Changes from Draft-02
   Appendix C.  Acknowledgments
   Authors' Addresses

1.  Introduction

   Deprecation of an HTTP resource (Section 3.1 of [HTTP]) communicates
   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 continued dependence upon the
   resource.

   The act of deprecation does not change any behavior of the resource.
   It informs clients of the fact that a resource will be or is
   deprecated.  The Deprecation HTTP response header field can be used
   to convey this at runtime to clients and carries information
   indicating when the deprecation will be in effect.

   In addition to the Deprecation header field, the resource provider
   can use other header fields to convey additional information related
   to deprecation.  This can be information such as where to find
   documentation related to the deprecation, what can be used as a
   replacement, and when a deprecated resource becomes non-operational.

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 sf-date format
   as defined in [SFBIS].

   The term "resource" is to be interpreted as defined in Section 3.1 of
   [HTTP].

2.  The Deprecation HTTP Response Header Field

   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 of
   the resource identified with the response it occurred within (see
   Section 6.4.2 of [HTTP]).  It conveys 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).  Deprecation is an Item Structured Header [RFC8941].
   Refer to Section 3.3.7 of [SFBIS] for ABNF of sf-date:

   Deprecation = sf-date

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

   The date is the date when the resource was or will be deprecated.  It
   is in the form of an Structured Field Date as defined in
   Section 3.3.7 of [SFBIS].

   The following example shows that the resource context has been
   deprecated on Friday, June 30, 2023 at 23:59:59 GMT:

   Deprecation: @1688169599

   The deprecation date can be in the future.  This means that the
   resource will be deprecated at the indicated date in the future.

2.2.  Scope

   The Deprecation header field applies to the resource identified with
   the response it occurred within (see Section 6.4.2 of [HTTP]),
   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.  When doing so, 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.  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 related resources and, thus, might allow them to implement
   behavior that allows them to make educated guesses about resources
   becoming deprecated.

   For example, an API might not use Deprecation header fields on all of
   its resources, but only on designated resources such as the API's
   home document.  This means that deprecation information is available,
   but in order to get it, clients have to periodically inspect the home
   document.  In this example, the extended context of the Deprecation
   header field would be all resources provided by the API, while the
   visibility of the information would only be on the home document.

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 linked deprecation policy.  In particular, the deprecation policy
   may be available as human-readable documentation or as machine-
   readable description.

3.1.  Documentation

   The purpose of the Deprecation header field is to provide a hint
   about deprecation to the resource consumer.  Upon reception of the
   Deprecation header field, the client developer can look up the
   resource's documentation in order to find deprecation related
   information.  The resource provider can provide a link to the
   resource documentation using a Link header field with relation type
   deprecation as shown below:

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

   In this example the linked content provides additional information
   about deprecation of the resource context.  There is no Deprecation
   header field in the response, and thus the resource is not (yet)
   deprecated.  However, the resource already exposes a link where
   information is available how deprecation is managed for the resource
   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 field, but also
   announces a deprecation date using a Deprecation header field:

   Deprecation: @1688169599
   Link: <https://developer.example.com/deprecation>;
         rel="deprecation"; type="text/html"

   Given that the deprecation date is in the past, the linked
   information resource may have been updated to include information
   about the deprecation, allowing consumers to discover information
   about the deprecation and how to best manage it.

3.1.1.  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 will be or 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, potentially including
   recommendation(s) for replacement.

   In cases where the Deprecation header field value is a date in the
   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 a Link header field is used to provide documentation,
   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.

4.  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 field.

   The timestamp given in the Sunset header field MUST NOT be earlier
   than the one given in the Deprecation header field.

   The following example shows that the resource in context has been
   deprecated since Friday, June 30, 2023 at 23:59:59 GMT and its sunset
   date is Sunday, June 30, 2024 at 23:59:59 GMT.  Please note that for
   historical reasons the Sunset HTTP header field uses a different data
   type for date.

   Deprecation: @1688169599
   Sunset: Sun, 30 Jun 2024 23:59:59 GMT

5.  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.

6.  IANA Considerations

6.1.  The Deprecation HTTP Response Header Field

   The Deprecation response header field should be added to the
   "Hypertext Transfer Protocol (HTTP) Field Name Registry" registry
   (Section 16.3.1 of [HTTP])

   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 (Section 4.2 of [LINK]).

   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.  Examples

   The following example does not show complete HTTP interaction.  It
   only shows those HTTP header fields in a response that are relevant
   for resource deprecation.

   Deprecation: @1688169599
   Link: <https://developer.example.com/deprecation>; rel="deprecation"

8.  References

8.1.  Normative References

   [HTTP]     Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

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

   [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/rfc/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/rfc/rfc5234>.

   [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/rfc/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/rfc/rfc8174>.

   [RFC8941]  Nottingham, M. and P. Kamp, "Structured Field Values for
              HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
              <https://www.rfc-editor.org/rfc/rfc8941>.

   [SFBIS]    Nottingham, M. and P.-H. Kamp, "Structured Field Values
              for HTTP", 6 November 2023,
              <https://datatracker.ietf.org/doc/draft-ietf-httpbis-
              sfbis/>.

8.2.  Informative References

   [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/rfc/rfc7942>.

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

Appendix A.  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".

A.1.  Implementing the Deprecation Header Field

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

   Organization: Apollo

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

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

   Organization: Zalando

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

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

   Organization: Palantir Technologies

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

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

   Organization: IETF Internet Draft, Registration Protocols Extensions

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

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

   Organization: E-Voyageurs Technologies

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

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

   Organization: Open-Xchange

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

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

   Organization: MediaWiki

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

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

A.2.  Implementing the Concept

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

   Organization: Zapier

   *  Description: Zapier uses two custom HTTP header fields named X-
      API-Deprecation-Date and X-API-Deprecation-Info

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

   Organization: IBM

   *  Description: IBM uses a custom HTTP header field 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 field 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 field named X-API-
      Warn

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

   Organization: PayPal

   *  Description: PayPal uses a custom HTTP header field named PayPal-
      Deprecated

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

Appendix B.  Changes from Draft-02

   This revision has made the following changes:

   *  Date format is changed from IMF-fixdate rule as defined in
      Section 5.6.7 of [HTTP] to Structured Field for Date as defined in
      Section 3.3.7 of [SFBIS].

Appendix C.  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


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