The Hypertext Transfer Protocol Status Code 308 (Permanent Redirect)
RFC 7538

Internet Engineering Task Force (IETF)                        J. Reschke
Request for Comments: 7538                                    greenbytes
Obsoletes: 7238                                               April 2015
Category: Standards Track
ISSN: 2070-1721

  The Hypertext Transfer Protocol Status Code 308 (Permanent Redirect)

Abstract

   This document specifies the additional Hypertext Transfer Protocol
   (HTTP) status code 308 (Permanent Redirect).

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/rfc7538.

Copyright Notice

   Copyright (c) 2015 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
   (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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RFC 7538                  HTTP Status Code 308                April 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   2
   3.  308 Permanent Redirect  . . . . . . . . . . . . . . . . . . .   3
   4.  Deployment Considerations . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   HTTP defines a set of status codes for the purpose of redirecting a
   request to a different URI ([RFC3986]).  The history of these status
   codes is summarized in Section 6.4 of [RFC7231], which also
   classifies the existing status codes into four categories.

   The first of these categories contains the status codes 301 (Moved
   Permanently), 302 (Found), and 307 (Temporary Redirect), which can be
   classified as below:

   +-------------------------------------------+-----------+-----------+
   |                                           | Permanent | Temporary |
   +-------------------------------------------+-----------+-----------+
   | Allows changing the request method from   | 301       | 302       |
   | POST to GET                               |           |           |
   | Does not allow changing the request       | -         | 307       |
   | method from POST to GET                   |           |           |
   +-------------------------------------------+-----------+-----------+

   Section 6.4.7 of [RFC7231] states that it does not define a permanent
   variant of status code 307; this specification adds the status code
   308, defining this missing variant (Section 3).

   This specification contains no technical changes from the
   Experimental RFC 7238, which it obsoletes.

2.  Notational Conventions

   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].

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RFC 7538                  HTTP Status Code 308                April 2015

3.  308 Permanent Redirect

   The 308 (Permanent Redirect) status code indicates that the target
   resource has been assigned a new permanent URI and any future
   references to this resource ought to use one of the enclosed URIs.
   Clients with link editing capabilities ought to automatically re-link
   references to the effective request URI (Section 5.5 of [RFC7230]) to
   one or more of the new references sent by the server, where possible.

   The server SHOULD generate a Location header field ([RFC7231],
   Section 7.1.2) in the response containing a preferred URI reference
   for the new permanent URI.  The user agent MAY use the Location field
   value for automatic redirection.  The server's response payload
   usually contains a short hypertext note with a hyperlink to the new
   URI(s).

   A 308 response is cacheable by default; i.e., unless otherwise
   indicated by the method definition or explicit cache controls (see
   [RFC7234], Section 4.2.2).

      Note: This status code is similar to 301 (Moved Permanently)
      ([RFC7231], Section 6.4.2), except that it does not allow changing
      the request method from POST to GET.

4.  Deployment Considerations

   Section 6 of [RFC7231] requires recipients to treat unknown 3xx
   status codes the same way as status code 300 (Multiple Choices)
   ([RFC7231], Section 6.4.1).  Thus, servers will not be able to rely
   on automatic redirection happening similar to status codes 301, 302,
   or 307.

   Therefore, the use of status code 308 is restricted to cases where
   the server has sufficient confidence in the client's understanding
   the new code or when a fallback to the semantics of status code 300
   is not problematic.  Server implementers are advised not to vary the
   status code based on characteristics of the request, such as the
   User-Agent header field ("User-Agent Sniffing") -- doing so usually
   results in code that is both hard to maintain and hard to debug and
   would also require special attention to caching (i.e., setting a
   "Vary" response header field, as defined in Section 7.1.4 of
   [RFC7231]).

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RFC 7538                  HTTP Status Code 308                April 2015

   Note that many existing HTML-based user agents will emulate a refresh
   when encountering an HTML <meta> refresh directive ([HTML],
   Section 4.2.5.3).  This can be used as another fallback.  For
   example:

   Client request:

     GET / HTTP/1.1
     Host: example.com

   Server response:

     HTTP/1.1 308 Permanent Redirect
     Content-Type: text/html; charset=UTF-8
     Location: http://example.com/new
     Content-Length: 356

     <!DOCTYPE HTML>
     <html>
        <head>
           <title>Permanent Redirect</title>
           <meta http-equiv="refresh"
                 content="0; url=http://example.com/new">
        </head>
        <body>
           <p>
              The document has been moved to
              <a href="http://example.com/new"
              >http://example.com/new</a>.
           </p>
        </body>
     </html>

5.  Security Considerations

   All security considerations that apply to HTTP redirects apply to the
   308 status code as well (see Section 9 of [RFC7231]).

   Unsecured communication over the Internet is subject to man-in-the-
   middle modification of messages, including changing status codes or
   redirect targets.  Use of Transport Layer Security (TLS) is one way
   to mitigate those attacks.  See Section 9 of [RFC7230] for related
   attacks on authority and message integrity.

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RFC 7538                  HTTP Status Code 308                April 2015

6.  IANA Considerations

   The "Hypertext Transfer Protocol (HTTP) Status Code Registry"
   (defined in Section 8.2 of [RFC7231] and located at
   <http://www.iana.org/assignments/http-status-codes>) has been updated
   to reference this specification.

   +-------+--------------------+----------------------------------+
   | Value | Description        | Reference                        |
   +-------+--------------------+----------------------------------+
   | 308   | Permanent Redirect | Section 3 of this specification  |
   +-------+--------------------+----------------------------------+

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing", RFC
              7230, June 2014, <http://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,
              June 2014, <http://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, June 2014,
              <http://www.rfc-editor.org/info/rfc7234>.

7.2.  Informative References

   [HTML]     Hickson, I., Berjon, R., Faulkner, S., Leithead, T., Doyle
              Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", W3C
              Recommendation REC-html5-20141028, October 2014,
              <http://www.w3.org/TR/2014/REC-html5-20141028/>.

              Latest version available at <http://www.w3.org/TR/html5/>.

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RFC 7538                  HTTP Status Code 308                April 2015

Acknowledgements

   The definition for the new status code 308 reuses text from the
   HTTP/1.1 definitions of status codes 301 and 307.

   Furthermore, thanks to Ben Campbell, Cyrus Daboo, Adrian Farrell,
   Eran Hammer-Lahav, Bjoern Hoehrmann, Barry Leiba, Subramanian
   Moonesamy, Kathleen Moriarty, Peter Saint-Andre, Robert Sparks, and
   Roy Fielding for feedback on this document.

Author's Address

   Julian F. Reschke
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   EMail: julian.reschke@greenbytes.de
   URI:   http://greenbytes.de/tech/webdav/

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