The Hypertext Transfer Protocol Status Code 308 (Permanent Redirect)

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

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This Internet-Draft will expire on August 9, 2015.¶

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.¶

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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.¶

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.¶

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].¶

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).¶

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]).¶

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>

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 TLS is one way to mitigate those attacks. See Section 9 of [RFC7230] for related attacks on authority and message integrity.¶

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.¶