This specification provides no mechanism for an NPH script to be
   identified on the basis of its output data alone.  By convention,
   therefore, any particular script can only ever provide output of one
   type (NPH or CGI) and hence the script itself is described as an 'NPH
   script'.  A server with NPH support MUST provide an implementation-
   defined mechanism for identifying NPH scripts, perhaps based on the
   name or location of the script.

5.2.  NPH Response

   There MUST be a system-defined method for the script to send data
   back to the server or client; a script MUST always return some data.
   Unless defined otherwise, this will be the same as for conventional
   CGI scripts.

   Currently, NPH scripts are only defined for HTTP client requests.  An
   (HTTP) NPH script MUST return a complete HTTP response message,
   currently described in section 6 of the HTTP specifications [1], [4].
   The script MUST use the SERVER_PROTOCOL variable to determine the
   appropriate format for a response.  It MUST also take account of any
   generic or protocol-specific meta-variables in the request as might
   be mandated by the particular protocol specification.

   The server MUST ensure that the script output is sent to the client
   unmodified.  Note that this requires the script to use the correct
   character set (US-ASCII [9] and ISO 8859-1 [10] for HTTP) in the
   header fields.  The server SHOULD attempt to ensure that the script
   output is sent directly to the client, with minimal internal and no
   transport-visible buffering.





 
RFC 3875                    CGI Version 1.1                 October 2004


   Unless the implementation defines otherwise, the script MUST NOT
   indicate in its response that the client can send further requests
   over the same connection.

6.  CGI Response

6.1.  Response Handling

   A script MUST always provide a non-empty response, and so there is a
   system-defined method for it to send this data back to the server.
   Unless defined otherwise, this will be via the 'standard output' file
   descriptor.

   The script MUST check the REQUEST_METHOD variable when processing the
   request and preparing its response.

   The server MAY implement a timeout period within which data must be
   received from the script.  If a server implementation defines such a
   timeout and receives no data from a script within the timeout period,
   the server MAY terminate the script process.

6.2.  Response Types

   The response comprises a message-header and a message-body, separated
   by a blank line.  The message-header contains one or more header
   fields.  The body may be NULL.

      generic-response = 1*header-field NL [ response-body ]

   The script MUST return one of either a document response, a local
   redirect response or a client redirect (with optional document)
   response.  In the response definitions below, the order of header
   fields in a response is not significant (despite appearing so in the
   BNF).  The header fields are defined in section 6.3.

      CGI-Response = document-response | local-redir-response |
                     client-redir-response | client-redirdoc-response

6.2.1.  Document Response

   The CGI script can return a document to the user in a document
   response, with an optional error code indicating the success status
   of the response.

      document-response = Content-Type [ Status ] *other-field NL
                          response-body






 
RFC 3875                    CGI Version 1.1                 October 2004


   The script MUST return a Content-Type header field.  A Status header
   field is optional, and status 200 'OK' is assumed if it is omitted.
   The server MUST make any appropriate modifications to the script's
   output to ensure that the response to the client complies with the
   response protocol version.