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
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provisions of BCP 78 and BCP 79.
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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.
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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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