RFC 8969: HTTP 397 Tolerating

Internet Engineering Task Force (IETF)                          B. Dover
Request for Comments: 8969
Category: Standards Track                                     April 2020
ISSN: 2071-1769


    An HTTP Status Code to Indicate Request Noncomformity While Still
                     Making Best-Effort Response

Abstract

   This document specifies a Hypertext Transfer Protocol (HTTP) status
   code for use when resource was accessed in a nonconforming manner
   but the request will be handled anyway.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8969.

Copyright Notice

   Copyright (c) 2020 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
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   (http://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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.









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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  397 Tolerating  . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   This document specifies a Hypertext Transfer Protocol (HTTP) status
   code for use when a server operator has received a request that
   violates standards for making such a request, but which the server
   will respond to under best-faith interpretation of client intent.

   This status code can be used to alert clients of their standards
   breakage and the potential that future requests of this type might
   not be handled as desired by this or other internet servers in the
   future.

   [RFC761] Section 2.10 discusses the Robustness Principle under which
   one should be liberal in what one accepts; in keeping with that
   principle, servers should make a best effort to handle non-conforming
   requests; this status code additionally provides a way to communicate
   to the client that it is doing so, and how to avoid potential breakage
   in the future.

2.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  397 Tolerating

   This status code indicates that the server has found a standards
   violation in the client request, but will respond in good faith
   anyway to the most likely intended conforming request.

   Responses using this status code SHOULD include an explanation, in
   the header, of the details of the standards breakage; what the
   client sent, versus what the client should have sent. For example:







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   HTTP/1.1 397 Tolerating
   Link: <https://www.example.org/news>;
   Content-Type: text/html
   Request-Nonconformity: This request used the HTTP header "Referrer",
     which is most likely intended to be the standard HTTP header
     "Referer"; request will be handled on this assumption, and the
     client is advised to update code to "Referer" for future requests.
   Request-Nonconformant-Part: Referrer: http://search.example.com
   Request-Interpreted-As: Referer: http://search.example.com
   Tolerated-Until: Fri, 30 Apr 2020 06:05:18 GMT


   The use of the 397 status code does not imply an obligation to
   tolerate the nonconformity in the future. Servers MAY specify the
   tolerance's ending time with the Tolerated-Until response header.

   Clients SHOULD monitor their server logs for computer-initiated API
   requests in order to detect 397 responses and appropriately update
   their software in order to conform with relevant RFCs.

   A 397 response MUST be followed by another HTTP response, similar
   to other 300-series HTTP status codes, where such response makes
   the best guess at what the client intended; in the example above, that
   would be the response the client would have received from "Referer".

4.  IANA Considerations

   The HTTP Status Codes Registry has been updated with the following
   entry:

   o  Code: 397

   o  Description: Tolerating

   o  Specification: RFC 8969

   The Standard Header Registry has been updated with the following
   entries:

4.1.  Request-Nonconformity

   o  Header Name: Request-Nonconformity

   o  Description: Human-readable explanation about what is wrong
      with the request.

   o  Reference: RFC 8969




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4.2.  Request-Nonconformant-Part

   o  Header Name: Request-Nonconformant-Part

   o  Description: Repeats back the part of the request that is non-
      conforming.

   o  Reference: RFC 8969

4.3.  Request-Interpreted-As

   o  Header Name: Request-Interpreted-As

   o  Description: The corrected version of the non-conformant part
      that the server will interpret the request as.

   o  Reference: RFC 8969

4.4.  Tolerated-Until

   o  Header Name: Tolerated-Until

   o  Description: The date and time, formatted per [RFC7231], after
      which the server will stop thusly correcting this request error.

   o  Reference: RFC 8969

6.  References

6.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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>.

6.2.  Informative References

   [RFC761]   Postel, J., "DoD standard Transmission Control Protocol",
              RFC 761, DOI 10.17487/RFC0761, January 1980,
              <https://www.rfc-editor.org/info/rfc761>.





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   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, DOI 10.17487/
              RFC1122, October 1989,
              <https://www.rfc-editor.org/info/rfc1122>.

Acknowledgements

   Thanks to the field of numerology for providing 97 as the number
   for tolerance.

Author's Address

   Ben Dover

   Email: benjamin.jeremiah.dover@gmail.com





















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