Explain HTTP error codes 300 series.
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| 300 |
Multiple Choices |
The requested resource corresponds to any one of a set of representations,
each with its own specific location, and agent- driven negotiation information
is being provided so that the user (or user agent) can select a
preferred representation and redirect its request to that location.
Unless it was a HEAD request, the response SHOULD include an entity
containing a list of resource characteristics and location(s)
from which the user or user agent can choose the one most appropriate.
The entity format is specified by the media type given in the Content- Type
header field. Depending upon the format and the capabilities of
the user agent, selection of the most appropriate choice MAY be performed
automatically. However, this specification does not define any standard
for such automatic selection.
If the server has a preferred choice of representation, it SHOULD
include the specific URI for that representation in the Location field;
user agents MAY use the Location field value for automatic redirection.
This response is cacheable unless indicated otherwise.
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| 301 |
Moved Permanently |
The requested resource has been assigned a new permanent URI and
any future references to this resource SHOULD use one of the returned URIs.
Clients with link editing capabilities ought to automatically
re-link references to the Request-URI to one or more of the new references
returned by the server, where possible. This response is cacheable unless
indicated otherwise.
The new permanent URI SHOULD be given by the Location field in the response.
Unless the request method was HEAD, the entity of the response SHOULD contain
a short hypertext note with a hyperlink to the new URI(s).
If the 301 status code is received in response to a request other than
GET or HEAD, the user agent MUST NOT automatically redirect the request
unless it can be confirmed by the user, since this might change the
conditions under which the request was issued.
Note: When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request.
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| 302 |
Found |
The requested resource resides temporarily under a different URI.
Since the redirection might be altered on occasion, the client SHOULD
continue to use the Request-URI for future requests. This response
is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response.
Unless the request method was HEAD, the entity of the response SHOULD
contain a short hypertext note with a hyperlink to the new URI(s).
If the 302 status code is received in response to a request other
than GET or HEAD, the user agent MUST NOT automatically redirect
the request unless it can be confirmed by the user, since this
might change the conditions under which the request was issued.
Note: RFC 1945 and RFC 2068 specify that the client is not allowed
to change the method on the redirected request. However, most
existing user agent implementations treat 302 as if it were a 303
response, performing a GET on the Location field-value regardless
of the original request method. The status codes 303 and 307 have
been added for servers that wish to make unambiguously clear which
kind of reaction is expected of the client.
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| 303 |
See Other |
The response to the request can be found under a different URI and
SHOULD be retrieved using a GET method on that resource. This method
exists primarily to allow the output of a POST-activated script to
redirect the user agent to a selected resource. The new URI is not
a substitute reference for the originally requested resource. The 303
response MUST NOT be cached, but the response to the second (redirected)
request might be cacheable.
The different URI SHOULD be given by the Location field in the response.
Unless the request method was HEAD, the entity of the response SHOULD
contain a short hypertext note with a hyperlink to the new URI(s).
Note: Many pre HTTP/1.1 user agents do not understand the 303 status.
When interoperability with such clients is a concern, the 302
status code may be used instead, since most user agents react to
a 302 response as described here for 303.
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| 304 |
Not Modified |
If the client has performed a conditional GET request and access is allowed,
but the document has not been modified, the server SHOULD respond with this
status code. The 304 response MUST NOT contain a message-body, and thus
is always terminated by the first empty line after the header fields.
The response MUST include the following header fields:
-
Date, unless its omission is required
If a clockless origin server obeys these rules, and proxies and clients
add their own Date to any response received without one, caches will
operate correctly.
- ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request
-
Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant.
If the conditional GET used a strong cache validator, the response SHOULD NOT
include other entity-headers. Otherwise (i.e., the conditional GET used a
weak validator), the response MUST NOT include other entity-headers; this
prevents inconsistencies between cached entity-bodies and updated headers.
If a 304 response indicates an entity not currently cached, then the cache
MUST disregard the response and repeat the request without the conditional.
If a cache uses a received 304 response to update a cache entry,
the cache MUST update the entry to reflect any new field values given
in the response.
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| 305 |
Use Proxy |
The requested resource MUST be accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 responses MUST only be generated by origin servers.
Note: RFC 2068 was not clear that 305 was intended to redirect a
single request, and to be generated by origin servers only. Not
observing these limitations has significant security consequences.
|
| 306 |
(Unused) |
The 306 status code was used in a previous version of the specification,
is no longer used, and the code is reserved.
|
| 307 |
Temporary Redirect |
The requested resource resides temporarily under a different URI. Since the
redirection MAY be altered on occasion, the client SHOULD continue to use the
Request-URI for future requests. This response is only cacheable if indicated
by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response.
Unless the request method was HEAD, the entity of the response SHOULD contain
a short hypertext note with a hyperlink to the new URI(s), since many pre-HTTP/1.1
user agents do not understand the 307 status. Therefore, the note SHOULD contain
the information necessary for a user to repeat the original request on the new URI.
If the 307 status code is received in response to a request other than GET or HEAD,
the user agent MUST NOT automatically redirect the request unless it can be
confirmed by the user, since this might change the conditions under which
the request was issued.
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