- From: Melvin Carvalho <melvincarvalho@gmail.com>
- Date: Sun, 6 May 2012 11:30:12 +0200
- To: public-rww <public-rww@w3.org>
- Message-ID: <CAKaEYhJybq6wvbN8ntcC0c6NbaqM_8wCFfdcNZuki1kniuUdBA@mail.gmail.com>
Just in case this one slipped thru the net. (I'll add it to the wiki too)
428 (Precondition Required) looks interesting especially in relation to 409
(Conflict)
[snippet from design issues read-write linked data]
"Note: 409 Conflict
A SPARQL update message often contains both a DELETE and then an INSERT.
This may be used to update a field from one value to another. When more
than one application or user is using the same data, there may arise times
when the DELETE fails because another user has already deleted the same
data. In this case it very important that the delete does not fail
silently. The HTTP server MUST return error status 409. ("409 Conflict"
indicates that the request could not be processed because of conflict in
the request, such as an edit conflict). The client can then for example
inform the user by backing out the change the user was trying to make, or
it can retry a reservation later. The atomicity of the DELETE,INSERT
function can be used to provide various mutual exclusion systems, such as
reserving a resource or generating unique sequential numbers, and so on."
http://tools.ietf.org/html/rfc6585
Table of Contents
1. Introduction ....................................................2
2. Requirements ....................................................2
3. 428 Precondition Required .......................................2
4. 429 Too Many Requests ...........................................3
5. 431 Request Header Fields Too Large .............................4
6. 511 Network Authentication Required .............................4
7. Security Considerations .........................................6
8. IANA Considerations .............................................7
9. References ......................................................7
Appendix A. Acknowledgements .......................................9
Appendix B. Issues Raised by Captive Portals .......................9
1. Introduction
This document specifies additional HTTP [RFC2616] status codes for a
variety of common situations, to improve interoperability and avoid
confusion when other, less precise status codes are used.
Note that these status codes are optional; servers cannot be required
to support them. However, because clients will treat unknown status
codes as a generic error of the same class (e.g., 499 is treated as
400 if it is not recognized), they can be safely deployed by existing
servers (see [RFC2616] Section 6.1.1 for more information).
2. Requirements
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. 428 Precondition Required
The 428 status code indicates that the origin server requires the
request to be conditional.
Its typical use is to avoid the "lost update" problem, where a client
GETs a resource's state, modifies it, and PUTs it back to the server,
when meanwhile a third party has modified the state on the server,
leading to a conflict. By requiring requests to be conditional, the
server can assure that clients are working with the correct copies.
Responses using this status code SHOULD explain how to resubmit the
request successfully. For example:
HTTP/1.1 428 Precondition Required
Content-Type: text/html
Nottingham & Fielding Standards Track [Page 2]
RFC 6585 Additional HTTP Status Codes April 2012
<html>
<head>
<title>Precondition Required</title>
</head>
<body>
<h1>Precondition Required</h1>
<p>This request is required to be conditional;
try using "If-Match".</p>
</body>
</html>
Responses with the 428 status code MUST NOT be stored by a cache.
4. 429 Too Many Requests
The 429 status code indicates that the user has sent too many
requests in a given amount of time ("rate limiting").
The response representations SHOULD include details explaining the
condition, and MAY include a Retry-After header indicating how long
to wait before making a new request.
For example:
HTTP/1.1 429 Too Many Requests
Content-Type: text/html
Retry-After: 3600
<html>
<head>
<title>Too Many Requests</title>
</head>
<body>
<h1>Too Many Requests</h1>
<p>I only allow 50 requests per hour to this Web site per
logged in user. Try again soon.</p>
</body>
</html>
Note that this specification does not define how the origin server
identifies the user, nor how it counts requests. For example, an
origin server that is limiting request rates can do so based upon
counts of requests on a per-resource basis, across the entire server,
or even among a set of servers. Likewise, it might identify the user
by its authentication credentials, or a stateful cookie.
Responses with the 429 status code MUST NOT be stored by a cache.
Nottingham & Fielding Standards Track [Page 3]
RFC 6585 Additional HTTP Status Codes April 2012
5. 431 Request Header Fields Too Large
The 431 status code indicates that the server is unwilling to process
the request because its header fields are too large. The request MAY
be resubmitted after reducing the size of the request header fields.
It can be used both when the set of request header fields in total is
too large, and when a single header field is at fault. In the latter
case, the response representation SHOULD specify which header field
was too large.
For example:
HTTP/1.1 431 Request Header Fields Too Large
Content-Type: text/html
<html>
<head>
<title>Request Header Fields Too Large</title>
</head>
<body>
<h1>Request Header Fields Too Large</h1>
<p>The "Example" header was too large.</p>
</body>
</html>
Responses with the 431 status code MUST NOT be stored by a cache.
6. 511 Network Authentication Required
The 511 status code indicates that the client needs to authenticate
to gain network access.
The response representation SHOULD contain a link to a resource that
allows the user to submit credentials (e.g., with an HTML form).
Note that the 511 response SHOULD NOT contain a challenge or the
login interface itself, because browsers would show the login
interface as being associated with the originally requested URL,
which may cause confusion.
The 511 status SHOULD NOT be generated by origin servers; it is
intended for use by intercepting proxies that are interposed as a
means of controlling access to the network.
Responses with the 511 status code MUST NOT be stored by a cache.
Nottingham & Fielding Standards Track [Page 4]
RFC 6585 Additional HTTP Status Codes April 2012
6.1. The 511 Status Code and Captive Portals
The 511 status code is designed to mitigate problems caused by
"captive portals" to software (especially non-browser agents) that is
expecting a response from the server that a request was made to, not
the intervening network infrastructure. It is not intended to
encourage deployment of captive portals -- only to limit the damage
caused by them.
A network operator wishing to require some authentication, acceptance
of terms, or other user interaction before granting access usually
does so by identifying clients who have not done so ("unknown
clients") using their Media Access Control (MAC) addresses.
Unknown clients then have all traffic blocked, except for that on TCP
port 80, which is sent to an HTTP server (the "login server")
dedicated to "logging in" unknown clients, and of course traffic to
the login server itself.
For example, a user agent might connect to a network and make the
following HTTP request on TCP port 80:
GET /index.htm HTTP/1.1
Host: www.example.com
Upon receiving such a request, the login server would generate a 511
response:
HTTP/1.1 511 Network Authentication Required
Content-Type: text/html
<html>
<head>
<title>Network Authentication Required</title>
<meta http-equiv="refresh"
content="0; url=https://login.example.net/">
</head>
<body>
<p>You need to <a href="https://login.example.net/">
authenticate with the local network</a> in order to gain
access.</p>
</body>
</html>
Here, the 511 status code assures that non-browser clients will not
interpret the response as being from the origin server, and the META
HTML element redirects the user agent to the login server.
Received on Sunday, 6 May 2012 09:30:42 UTC