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Internet Engineering Task Force (IETF)                        J. ReschkeRequest for Comments: 7238                                    greenbytesCategory: Experimental                                         June 2014ISSN: 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 document is not an Internet Standards Track specification; it is   published for examination, experimental implementation, and   evaluation.   This document defines an Experimental Protocol for the Internet   community.  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).  Not   all documents approved by the IESG are a candidate for any level of   Internet Standard; seeSection 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/rfc7238.Copyright Notice   Copyright (c) 2014 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                       Experimental                      [Page 1]

RFC 7238                  HTTP Status Code 308                 June 2014Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Notational Conventions  . . . . . . . . . . . . . . . . . . . .23.  308 Permanent Redirect  . . . . . . . . . . . . . . . . . . . .24.  Deployment Considerations . . . . . . . . . . . . . . . . . . .35.  Security Considerations . . . . . . . . . . . . . . . . . . . .46.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .47.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .58.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .58.1.  Normative References  . . . . . . . . . . . . . . . . . . .58.2.  Informative References  . . . . . . . . . . . . . . . . . .51.  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 HTTP does not define a   permanent variant of status code 307; this specification adds the   status code 308, defining this missing variant (Section 3).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].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.Reschke                       Experimental                      [Page 2]

RFC 7238                  HTTP Status Code 308                 June 2014   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, initial use of status code 308 will be 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]).   Note that many existing HTML-based user agents will emulate a refresh   when encountering an HTML <meta> refresh directive ([HTML]).  This   can be used as another fallback.  For example:   Client request:     GET / HTTP/1.1     Host: example.comReschke                       Experimental                      [Page 3]

RFC 7238                  HTTP Status Code 308                 June 2014   Server response:     HTTP/1.1 308 Permanent Redirect     Content-Type: text/html; charset=UTF-8     Location: http://example.com/new     Content-Length: 454     <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"                           "http://www.w3.org/TR/html4/strict.dtd">     <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]).6.  IANA Considerations   The registration below has been added to 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>):   +-------+--------------------+---------------------------------+   | Value | Description        | Reference                       |   +-------+--------------------+---------------------------------+   | 308   | Permanent Redirect |Section 3 of this specification |   +-------+--------------------+---------------------------------+Reschke                       Experimental                      [Page 4]

RFC 7238                  HTTP Status Code 308                 June 20147.  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, Eran Hammer-Lahav,   Bjoern Hoehrmann, Subramanian Moonesamy, Peter Saint-Andre, and   Robert Sparks for feedback on this document.8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC 3986, January 2005.   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer              Protocol (HTTP/1.1): Message Syntax and Routing",RFC 7230, June 2014.   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer              Protocol (HTTP/1.1): Semantics and Content",RFC 7231,              June 2014.   [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",RFC 7234, June 2014.8.2.  Informative References   [HTML]     Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01              Specification", W3C Recommendation REC-html401-19991224,              December 1999,              <http://www.w3.org/TR/1999/REC-html401-19991224>.              Latest version available at              <http://www.w3.org/TR/html401>.Reschke                       Experimental                      [Page 5]

RFC 7238                  HTTP Status Code 308                 June 2014Author'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                       Experimental                      [Page 6]