5.1.2 Request-URI

The Request-URI is a Uniform Resource Identifier (section 3.2) and identifies the resource upon which to apply the request.

          Request-URI    = "*" | absoluteURI | abs_path

The three options for Request-URI are dependent on the nature of the request. The asterisk "*" means that the request does not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily apply to a resource. One example would be

          OPTIONS * HTTP/1.1

The absoluteURI form is required when the request is being made to a proxy. The proxy is requested to forward the request or service it from a valid cache, and return the response. Note that the proxy MAY forward the request on to another proxy or directly to the server specified by the absoluteURI. In order to avoid request loops, a proxy MUST be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example Request-Line would be:

          GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1

To allow for transition to absoluteURIs in all requests in future versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI form in requests, even though HTTP/1.1 clients will only generate them in requests to proxies.

The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute path of the URI MUST be transmitted (see section 3.2.1, abs_path) as the Request-URI, and the network location of the URI (net_loc) MUST be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin server would create a TCP connection to port 80 of the host "www.w3.org" and send the lines:

          GET /pub/WWW/TheProject.html HTTP/1.1
          Host: www.w3.org

followed by the remainder of the Request. Note that the absolute path cannot be empty; if none is present in the original URI, it MUST be given as "/" (the server root).

If a proxy receives a request without any path in the Request-URI and the method specified is capable of supporting the asterisk form of request, then the last proxy on the request chain MUST forward the request with "*" as the final Request-URI. For example, the request

          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. 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.