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)
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.
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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.
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.
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.
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]).
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 220.127.116.11). This can be used as another fallback. For example:
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.
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.