# 18.21 `CGIHTTPServer` -- CGI-capable HTTP request handler

The `CGIHTTPServer` module defines a request-handler class, interface compatible with `BaseHTTPServer.BaseHTTPRequestHandler` and inherits behavior from `SimpleHTTPServer.SimpleHTTPRequestHandler` but can also run CGI scripts.

Note: This module can run CGI scripts on Unix and Windows systems; on Mac OS it will only be able to run Python scripts within the same process as itself.

Note: CGI scripts run by the `CGIHTTPRequestHandler` class cannot execute redirects (HTTP code 302), because code 200 (script output follows) is sent prior to execution of the CGI script. This pre-empts the status code.

The `CGIHTTPServer` module defines the following class:

class `CGIHTTPRequestHandler`( | request, client_address, server)

  This class is used to serve either files or output of CGI scripts from the current directory and below. Note that mapping HTTP hierarchic structure to local directory structure is exactly as in `SimpleHTTPServer.SimpleHTTPRequestHandler`.

  The class will however, run the CGI script, instead of serving it as a file, if it guesses it to be a CGI script. Only directory-based CGI are used -- the other common server configuration is to treat special extensions as denoting CGI scripts.

  The `do_GET()` and `do_HEAD()` functions are modified to run CGI scripts and serve the output, instead of serving files, if the request leads to somewhere below the `cgi_directories` path.

The `CGIHTTPRequestHandler` defines the following data member:

`cgi_directories`
  This defaults to `['/cgi-bin', '/htbin']` and describes directories to treat as containing CGI scripts.

The `CGIHTTPRequestHandler` defines the following methods:

`do_POST`( | )

  This method serves the `'POST'` request type, only allowed for CGI scripts. Error 501, "Can only POST to CGI scripts", is output when trying to POST to a non-CGI url.

Note that CGI scripts will be run with UID of user nobody, for security reasons. Problems with the CGI script will be translated to error 403.

For example usage, see the implementation of the `test()` function.

See Also:

Module `BaseHTTPServer`:
  Base class implementation for Web server and request handler.