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17.2. Server Responses and Status Codes
The server's response to a
client request is grouped into three parts. The first line is the
server response line, which contains the HTTP version number, a
three-digit number indicating the status of the request (called a
server response code or status
code), and a short phrase describing the status. The
response line is followed by the header information and an entity
body if there is one.
Status codes are typically generated by web servers. However, they
can also be generated by CGI scripts that bypass the
server's precooked headers and supply their own.
Status codes are grouped as follows.
|
Code range
|
Response meaning
|
|
100-199
|
Informational
|
|
200-299
|
Client request successful
|
|
300-399
|
Client request redirected, further action necessary
|
|
400-499
|
Client request incomplete
|
|
500-599
|
Server errors
|
HTTP defines only a few specific codes in each range, although
servers may define their own as needed. If a client receives a code
it does not recognize, it should understand its basic meaning from
its numerical range. While most web browsers handle codes in the
100-, 200-, and 300-range silently, some error codes in the 400- and
500-range are commonly reported back to the user (e.g.,
"404 Not Found").
17.2.1. Informational
A response in the range of 100-199 is
informational, indicating that the client's request
was received and is being processed.
- 100 Continue
-
The initial part of the request has been
received and the client may continue with its request.
- 101 Switching Protocols
-
The server is complying with a client request to switch protocols to
the one specified in the Upgrade header field.
17.2.2. Client Request Successful
A response in the range of 200-299 means that the
client's request was successful.
- 200 OK
-
The client's request was successful, and the
server's response contains the requested data.
- 201 Created
-
This status code is used whenever a new URI is created. With this
result code, the Location header is given by the
server to specify where the new data was placed.
- 202 Accepted
-
The request was accepted but not immediately acted upon. More
information about the transaction may be given in the entity body of
the server's response. Note that there is no
guarantee that the server will actually honor the request, even
though it may seem like a legitimate request at the time of
acceptance.
- 203 Non-Authoritative Information
-
The information in the entity header is from a local or third-party
copy and not from the original server.
- 204 No Content
-
A status code and header are given in the response, but there is no
entity body in the reply. On receiving this response, browsers should
not update their document view. This is a useful code for an imagemap
handler to return when the user clicks on useless or blank areas of
an image.
- 205 Reset Content
-
The browser should clear the form used for this transaction for
additional input. Appropriate for data-entry CGI applications.
- 206 Partial Content
-
The server is returning partial data of the size requested. Used in
response to a request specifying a Range header.
The server must specify the range included in the response with the
Content-Range header.
17.2.3. Redirection
A response code in the 300-399 range indicates that the request was
not performed, and the client needs to take further action for a
successful request.
- 300 Multiple Choices
-
The requested URI refers to more than one resource. For example, the
URI could refer to a document that has been translated into many
languages. The entity body returned by the server could have a list
of more specific data about how to choose the correct resource.
- 301 Moved Permanently
-
The requested URI is no longer used by the server, and the operation
specified in the request was not performed. The new location for the
requested document is specified in the Location
header. All future requests for the document should use the new URI.
- 302 Found
-
The requested URI temporarily has a new URI. The
Location header points to the new location. If
this is in response to a GET or a HEAD, the client should use the new
URI to resolve the request immediately after receiving the response.
- 303 See Other
-
The requested URI can be found at a different URI (specified in the
Location header) and should be retrieved by a GET
on that resource.
- 304 Not Modified
-
This is the response code to an If-Modified-Since
header, where the URI has not been modified since the specified date.
The entity body is not sent, and the client should use its own local
copy.
- 305 Use Proxy
-
The requested URI must be accessed through the proxy in the
Location header.
- 307 Temporary Redirect
-
The requested URI has moved temporarily. The
Location header points to the new location.
Immediately after receiving this status code, the client should use
the new URI to resolve the request, but the old URI should be used
for all future requests.
17.2.4. Client Request Incomplete
A response code in the range of 400-499 means that the
client's request was incomplete and may indicate
further information is required from the client.
- 400 Bad Request
-
This response code indicates that the server detected a syntax error
in the client's request.
- 401 Unauthorized
-
The result code is given along
with the WWW-Authenticate header to indicate that
the request lacked proper authorization, and the client should supply
proper authorization when requesting this URI again.
- 402 Payment Required
-
This code is not yet implemented in HTTP. However, it may, one day,
indicate that a payment is required to receive the document on the
server.
- 403 Forbidden
-
The request was denied for a
reason the server does not want to (or has no means to) indicate to
the client.
- 404 Not Found
-
The
document at the specified URI does not exist.
- 405 Method Not Allowed
-
This code is given with the Allow header and
indicates that the method used by the client is not supported for
this URI.
- 406 Not Acceptable
-
The URI specified by the client exists, but not in a format preferred
by the client. Along with this code, the server provides the
Content-Language,
Content-Encoding, and
Content-Type headers.
- 407 Proxy Authentication Required
-
The proxy server needs to authorize the request before forwarding it.
Used with the Proxy-Authenticate header.
- 408 Request Time-out
-
This response code means the client did not produce a full request
within some predetermined time (usually specified in the
server's configuration), and the server is
disconnecting the network connection.
- 409 Conflict
-
This code indicates that the request conflicts with another request
or with the server's configuration. Information
about the conflict should be returned in the data portion of the
reply.
- 410 Gone
-
This code indicates that the requested URI no longer exists and has
been permanently removed from the server.
- 411 Length Required
-
The server will not accept the request without a
Content-Length header supplied in the request.
- 412 Precondition Failed
-
The condition specified by one or more If...
headers in the request evaluated to false.
- 413 Request Entity Too Large
-
The server will not process the request because its entity body is
too large.
- 414 Request-URI Too Long
-
The server will not process the request because its requested URI is
too large.
- 415 Unsupported Media Type
-
The server will not process the request because its entity body is in
an unsupported format.
- 416 Requested Range Not Satisfiable
-
The server detected a Range header that contained
no valid values for the target. In addition, an
If-Range header was omitted.
- 417 Expectation Failed
-
The condition specified in an Expect header could
not be satisfied.
17.2.5. Server Errors
Response codes in the range of 500-599 indicate that the server
encountered an error and may be unable to perform the
client's request.
- 500 Internal Server Error
-
This code indicates
that a part of the server (for example, a CGI program) has crashed or
encountered a configuration error.
- 501 Not Implemented
-
This code indicates that the client requested an action that cannot
be performed by the server.
- 502 Bad Gateway
-
This code indicates that the server (or proxy) encountered invalid
responses from another server (or proxy).
- 503 Service Unavailable
-
This code means that the service is temporarily unavailable but
should be restored in the future. If the server knows when it will be
available again, a Retry-After header may also be
supplied.
- 504 Gateway Time-out
-
This response is like 408 (Request
Time-out) except that a gateway or proxy has timed out.
- 505 HTTP Version not supported
-
The server will not support the HTTP protocol version used in the
request.
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| 17. HTTP |  | 17.3. HTTP Headers |
Copyright © 2003 O'Reilly & Associates. All rights reserved.