OPTIONS http://www.ics.uci.edu:8001 HTTP/1.1

   would be forwarded by the proxy as

          OPTIONS * HTTP/1.1
          Host: www.ics.uci.edu:8001

   after connecting to port 8001 of host "www.ics.uci.edu".

   The Request-URI is transmitted in the format specified in section
   3.2.1.  The origin server MUST decode the Request-URI in order to
   properly interpret the request. Servers SHOULD respond to invalid
   Request-URIs with an appropriate status code.




 
RFC 2068                        HTTP/1.1                    January 1997


   In requests that they forward, proxies MUST NOT rewrite the
   "abs_path" part of a Request-URI in any way except as noted above to
   replace a null abs_path with "*", no matter what the proxy does in
   its internal implementation.

     Note: The "no rewrite" rule prevents the proxy from changing the
     meaning of the request when the origin server is improperly using a
     non-reserved URL character for a reserved purpose. Implementers
     should be aware that some pre-HTTP/1.1 proxies have been known to
     rewrite the Request-URI.

5.2 The Resource Identified by a Request

   HTTP/1.1 origin servers SHOULD be aware that the exact resource
   identified by an Internet request is determined by examining both the
   Request-URI and the Host header field.

   An origin server that does not allow resources to differ by the
   requested host MAY ignore the Host header field value. (But see
   section 19.5.1 for other requirements on Host support in HTTP/1.1.)

   An origin server that does differentiate resources based on the host
   requested (sometimes referred to as virtual hosts or vanity
   hostnames) MUST use the following rules for determining the requested
   resource on an HTTP/1.1 request:

     1. If Request-URI is an absoluteURI, the host is part of the
        Request-URI. Any Host header field value in the request MUST be
        ignored.

     2. If the Request-URI is not an absoluteURI, and the request
        includes a Host header field, the host is determined by the Host
        header field value.

     3. If the host as determined by rule 1 or 2 is not a valid host on
        the server, the response MUST be a 400 (Bad Request) error
        message.

   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
   attempt to use heuristics (e.g., examination of the URI path for
   something unique to a particular host) in order to determine what
   exact resource is being requested.

5.3 Request Header Fields

   The request-header fields allow the client to pass additional
   information about the request, and about the client itself, to the
   server. These fields act as request modifiers, with semantics




 
RFC 2068                        HTTP/1.1                    January 1997


   equivalent to the parameters on a programming language method
   invocation.

          request-header = Accept                   ; Section 14.1
                         | Accept-Charset           ; Section 14.2
                         | Accept-Encoding          ; Section 14.3
                         | Accept-Language          ; Section 14.4
                         | Authorization            ; Section 14.8
                         | From                     ; Section 14.22
                         | Host                     ; Section 14.23
                         | If-Modified-Since        ; Section 14.24
                         | If-Match                 ; Section 14.25
                         | If-None-Match            ; Section 14.26
                         | If-Range                 ; Section 14.27
                         | If-Unmodified-Since      ; Section 14.28
                         | Max-Forwards             ; Section 14.31
                         | Proxy-Authorization      ; Section 14.34
                         | Range                    ; Section 14.36
                         | Referer                  ; Section 14.37
                         | User-Agent               ; Section 14.42

   Request-header field names can be extended reliably only in