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Internet Engineering Task Force (IETF)                        J. ReschkeRequest for Comments: 7538                                    greenbytesObsoletes:7238                                               April 2015Category: Standards TrackISSN: 2070-1721The 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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.Reschke                      Standards Track                    [Page 1]

RFC 7538                  HTTP Status Code 308                April 2015Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Notational Conventions  . . . . . . . . . . . . . . . . . . .23.  308 Permanent Redirect  . . . . . . . . . . . . . . . . . . .34.  Deployment Considerations . . . . . . . . . . . . . . . . . .35.  Security Considerations . . . . . . . . . . . . . . . . . . .46.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .57.  References  . . . . . . . . . . . . . . . . . . . . . . . . .57.1.  Normative References  . . . . . . . . . . . . . . . . . .57.2.  Informative References  . . . . . . . . . . . . . . . . .5   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .6   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .61.  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 inSection 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   ExperimentalRFC 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].Reschke                      Standards Track                    [Page 2]

RFC 7538                  HTTP Status Code 308                April 20153.  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 ConsiderationsSection 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 inSection 7.1.4 of   [RFC7231]).Reschke                      Standards Track                    [Page 3]

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 (seeSection 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.  SeeSection 9 of [RFC7230] for related   attacks on authority and message integrity.Reschke                      Standards Track                    [Page 4]

RFC 7538                  HTTP Status Code 308                April 20156.  IANA Considerations   The "Hypertext Transfer Protocol (HTTP) Status Code Registry"   (defined inSection 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.  References7.1.  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,RFC3986, 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",RFC7230, 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/>.Reschke                      Standards Track                    [Page 5]

RFC 7538                  HTTP Status Code 308                April 2015Acknowledgements   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/Reschke                      Standards Track                    [Page 6]