o respond appropriately with a message in the same protocol
        version used by the client.

   HTTP/1.0 clients must:

      o recognize the format of the Status-Line for HTTP/1.0 responses;

      o understand any valid response in the format of HTTP/0.9 or
        HTTP/1.0.

   Proxy and gateway applications must be careful in forwarding requests
   that are received in a format different than that of the
   application's native HTTP version. Since the protocol version
   indicates the protocol capability of the sender, a proxy/gateway must
   never send a message with a version indicator which is greater than
   its native version; if a higher version request is received, the
   proxy/gateway must either downgrade the request version or respond
   with an error. Requests with a version lower than that of the
   application's native format may be upgraded before being forwarded;
   the proxy/gateway's response to that request must follow the server
   requirements listed above.








 
RFC 1945                        HTTP/1.0                        May 1996


3.2  Uniform Resource Identifiers

   URIs have been known by many names: WWW addresses, Universal Document
   Identifiers, Universal Resource Identifiers [2], and finally the
   combination of Uniform Resource Locators (URL) [4] and Names (URN)
   [16]. As far as HTTP is concerned, Uniform Resource Identifiers are
   simply formatted strings which identify--via name, location, or any
   other characteristic--a network resource.

3.2.1 General Syntax

   URIs in HTTP can be represented in absolute form or relative to some
   known base URI [9], depending upon the context of their use. The two
   forms are differentiated by the fact that absolute URIs always begin
   with a scheme name followed by a colon.

       URI            = ( absoluteURI | relativeURI ) [ "#" fragment ]

       absoluteURI    = scheme ":" *( uchar | reserved )

       relativeURI    = net_path | abs_path | rel_path

       net_path       = "//" net_loc [ abs_path ]
       abs_path       = "/" rel_path
       rel_path       = [ path ] [ ";" params ] [ "?" query ]

       path           = fsegment *( "/" segment )
       fsegment       = 1*pchar
       segment        = *pchar

       params         = param *( ";" param )
       param          = *( pchar | "/" )

       scheme         = 1*( ALPHA | DIGIT | "+" | "-" | "." )
       net_loc        = *( pchar | ";" | "?" )
       query          = *( uchar | reserved )
       fragment       = *( uchar | reserved )

       pchar          = uchar | ":" | "@" | "&" | "=" | "+"
       uchar          = unreserved | escape
       unreserved     = ALPHA | DIGIT | safe | extra | national

       escape         = "%" HEX HEX
       reserved       = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+"
       extra          = "!" | "*" | "'" | "(" | ")" | ","
       safe           = "$" | "-" | "_" | "."
       unsafe         = CTL | SP | <"> | "#" | "%" | "<" | ">"
       national       = <any OCTET excluding ALPHA, DIGIT,




 
RFC 1945                        HTTP/1.0                        May 1996


                        reserved, extra, safe, and unsafe>

   For definitive information on URL syntax and semantics, see RFC 1738
   [4] and RFC 1808 [9]. The BNF above includes national characters not
   allowed in valid URLs as specified by RFC 1738, since HTTP servers
   are not restricted in the set of unreserved characters allowed to
   represent the rel_path part of addresses, and HTTP proxies may
   receive requests for URIs not defined by RFC 1738.

3.2.2 http URL