10.3.6 305 Use Proxy

   The requested resource MUST be accessed through the proxy given by
   the Location field. The Location field gives the URL of the proxy.
   The recipient is expected to repeat the request via the proxy.

10.4 Client Error 4xx

   The 4xx class of status code is intended for cases in which the
   client seems to have erred. Except when responding to a HEAD request,
   the server SHOULD include an entity containing an explanation of the
   error situation, and whether it is a temporary or permanent
   condition. These status codes are applicable to any request method.
   User agents SHOULD display any included entity to the user.

     Note: If the client is sending data, a server implementation using
     TCP should be careful to ensure that the client acknowledges
     receipt of the packet(s) containing the response, before the server
     closes the input connection. If the client continues sending data
     to the server after the close, the server's TCP stack will send a
     reset packet to the client, which may erase the client's



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     unacknowledged input buffers before they can be read and
     interpreted by the HTTP application.

10.4.1 400 Bad Request

   The request could not be understood by the server due to malformed
   syntax. The client SHOULD NOT repeat the request without
   modifications.

10.4.2 401 Unauthorized

   The request requires user authentication. The response MUST include a
   WWW-Authenticate header field (section 14.46) containing a challenge
   applicable to the requested resource. The client MAY repeat the
   request with a suitable Authorization header field (section 14.8). If
   the request already included Authorization credentials, then the 401
   response indicates that authorization has been refused for those
   credentials. If the 401 response contains the same challenge as the
   prior response, and the user agent has already attempted
   authentication at least once, then the user SHOULD be presented the
   entity that was given in the response, since that entity MAY include
   relevant diagnostic information. HTTP access authentication is
   explained in section 11.

10.4.3 402 Payment Required

   This code is reserved for future use.

10.4.4 403 Forbidden

   The server understood the request, but is refusing to fulfill it.
   Authorization will not help and the request SHOULD NOT be repeated.
   If the request method was not HEAD and the server wishes to make
   public why the request has not been fulfilled, it SHOULD describe the
   reason for the refusal in the entity. This status code is commonly
   used when the server does not wish to reveal exactly why the request
   has been refused, or when no other response is applicable.

10.4.5 404 Not Found

   The server has not found anything matching the Request-URI. No
   indication is given of whether the condition is temporary or
   permanent.








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   If the server does not wish to make this information available to the
   client, the status code 403 (Forbidden) can be used instead. The 410
   (Gone) status code SHOULD be used if the server knows, through some
   internally configurable mechanism, that an old resource is
   permanently unavailable and has no forwarding address.

10.4.6 405 Method Not Allowed

   The method specified in the Request-Line is not allowed for the
   resource identified by the Request-URI. The response MUST include an
   Allow header containing a list of valid methods for the requested
   resource.