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IETF RFC 7538
Last modified on Monday, April 6th, 2015
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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)
 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 in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7538.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 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 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 2
3. 308 Permanent Redirect . . . . . . . . . . . . . . . . . . . 3
4. Deployment Considerations . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
HTTP defines a set of status codes for the purpose of redirecting a
request to a different URI ([RFC 3986]). The history of these status
codes is summarized in Section 6.4 of [RFC 7231], 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 [RFC 7231] 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.
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 [RFC 2119].
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RFC 7538 HTTP Status Code 308 April 2015
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 [RFC 7230]) to
one or more of the new references sent by the server, where possible.
The server SHOULD generate a Location header field ([RFC 7231],
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
[RFC 7234], Section 4.2.2).
Note: This status code is similar to 301 (Moved Permanently)
([RFC 7231], Section 6.4.2), except that it does not allow changing
the request method from POST to GET.
4. Deployment Considerations
Section 6 of [RFC 7231] requires recipients to treat unknown 3xx
status codes the same way as status code 300 (Multiple Choices)
([RFC 7231], 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
[RFC 7231]).
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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 (see Section 9 of [RFC 7231]).
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 [RFC 7230] for related
attacks on authority and message integrity.
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RFC 7538 HTTP Status Code 308 April 2015
6. IANA Considerations
The "Hypertext Transfer Protocol (HTTP) Status Code Registry"
(defined in Section 8.2 of [RFC 7231] 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. References
7.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005,
<http://www.rfc-editor.org/info/RFC 3986>.
[RFC 7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", RFC
7230, June 2014, <http://www.rfc-editor.org/info/RFC 7230>.
[RFC 7231] 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/RFC 7231>.
[RFC 7234] 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/RFC 7234>.
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 2015
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, 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
RFC TOTAL SIZE: 11189 bytes
PUBLICATION DATE: Monday, April 6th, 2015
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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