The Hypertext Transfer Protocol Status Code 308 (Permanent Redirect)
draft-ietf-httpbis-rfc7238bis-01

Abstract

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

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on March 20, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Notational Conventions
• 3. 308 Permanent Redirect
• 4. Deployment Considerations
• 5. Security Considerations
• 6. IANA Considerations
• 7. Acknowledgements
• 8. References
• 8.1. Normative References
• 8.2. Informative References

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:

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).

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].

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, 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 in Section 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.com
  
  

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 (see Section 9 of [RFC7231]).

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) needs to be updated with the registration below: