gh-109096: Deprecate `http.server.CGIHTTPRequestHandler` (#109387)

Deprecate `http.server.CGIHTTPRequestHandler`.

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Doc/library/http.server.rst

@@ -502,11 +502,24 @@ following command runs an HTTP/1.1 conformant server::
    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.
 
+   .. deprecated-removed:: 3.13 3.15
+
+      :class:`CGIHTTPRequestHandler` is being removed in 3.15.  CGI has not
+      been considered a good way to do things for well over a decade. This code
+      has been unmaintained for a while now and sees very little practical use.
+      Retaining it could lead to further :ref:`security considerations
+      <http.server-security>`.
+
 :class:`CGIHTTPRequestHandler` can be enabled in the command line by passing
 the ``--cgi`` option::
 
         python -m http.server --cgi
 
+.. deprecated-removed:: 3.13 3.15
+
+   :mod:`http.server` command line ``--cgi`` support is being removed
+   because :class:`CGIHTTPRequestHandler` is being removed.
+
 .. _http.server-security:
 
 Security Considerations

Doc/whatsnew/3.13.rst

@@ -248,6 +248,13 @@ Deprecated
   practice.
   (Contributed by Victor Stinner in :gh:`106535`.)
 
+* :mod:`http.server`: :class:`http.server.CGIHTTPRequestHandler` now emits a
+  :exc:`DeprecationWarning` as it will be removed in 3.15.  Process based CGI
+  http servers have been out of favor for a very long time.  This code was
+  outdated, unmaintained, and rarely used.  It has a high potential for both
+  security and functionality bugs.  This includes removal of the ``--cgi``
+  flag to the ``python -m http.server`` command line in 3.15.
+
 * :mod:`typing`: Creating a :class:`typing.NamedTuple` class using keyword arguments to denote
   the fields (``NT = NamedTuple("NT", x=int, y=int)``) is deprecated, and will
   be disallowed in Python 3.15. Use the class-based syntax or the functional
@@ -414,6 +421,11 @@ Pending Removal in Python 3.14
 Pending Removal in Python 3.15
 ------------------------------
 
+* :class:`http.server.CGIHTTPRequestHandler` will be removed along with its
+  related ``--cgi`` flag to ``python -m http.server``.  It was obsolete and
+  rarely used.  No direct replacement exists.  *Anything* is better than CGI
+  to interface a web server with a request handler.
+
 * :class:`typing.NamedTuple`:
 
   * The undocumented keyword argument syntax for creating NamedTuple classes

Lib/http/server.py

@@ -2,18 +2,18 @@
 
 Note: BaseHTTPRequestHandler doesn't implement any HTTP request; see
 SimpleHTTPRequestHandler for simple implementations of GET, HEAD and POST,
-and CGIHTTPRequestHandler for CGI scripts.
+and (deprecated) CGIHTTPRequestHandler for CGI scripts.
 
-It does, however, optionally implement HTTP/1.1 persistent connections,
-as of version 0.3.
+It does, however, optionally implement HTTP/1.1 persistent connections.
 
 Notes on CGIHTTPRequestHandler
 ------------------------------
 
-This class implements GET and POST requests to cgi-bin scripts.
+This class is deprecated. It implements GET and POST requests to cgi-bin scripts.
 
-If the os.fork() function is not present (e.g. on Windows),
-subprocess.Popen() is used as a fallback, with slightly altered semantics.
+If the os.fork() function is not present (Windows), subprocess.Popen() is used,
+with slightly altered but never documented semantics.  Use from a threaded
+process is likely to trigger a warning at os.fork() time.
 
 In all cases, the implementation is intentionally naive -- all
 requests are executed synchronously.
@@ -986,6 +986,12 @@ class CGIHTTPRequestHandler(SimpleHTTPRequestHandler):
 
     """
 
+    def __init__(self, *args, **kwargs):
+        import warnings
+        warnings._deprecated("http.server.CGIHTTPRequestHandler",
+                             remove=(3, 15))
+        super().__init__(*args, **kwargs)
+
     # Determine platform specifics
     have_fork = hasattr(os, 'fork')
 

Lib/test/test_httpservers.py

@@ -699,11 +699,20 @@ print("</pre>")
         "This test can't be run reliably as root (issue #13308).")
 class CGIHTTPServerTestCase(BaseTestCase):
     class request_handler(NoLogRequestHandler, CGIHTTPRequestHandler):
-        pass
+        _test_case_self = None  # populated by each setUp() method call.
+
+        def __init__(self, *args, **kwargs):
+            with self._test_case_self.assertWarnsRegex(
+                    DeprecationWarning,
+                    r'http\.server\.CGIHTTPRequestHandler'):
+                # This context also happens to catch and silence the
+                # threading DeprecationWarning from os.fork().
+                super().__init__(*args, **kwargs)
 
     linesep = os.linesep.encode('ascii')
 
     def setUp(self):
+        self.request_handler._test_case_self = self  # practical, but yuck.
         BaseTestCase.setUp(self)
         self.cwd = os.getcwd()
         self.parent_dir = tempfile.mkdtemp()
@@ -780,6 +789,7 @@ class CGIHTTPServerTestCase(BaseTestCase):
         os.chdir(self.parent_dir)
 
     def tearDown(self):
+        self.request_handler._test_case_self = None
         try:
             os.chdir(self.cwd)
             if self._pythonexe_symlink:

Misc/NEWS.d/next/Library/2023-09-15-12-20-23.gh-issue-109096.VksX1D.rst

@@ -0,0 +1,3 @@
+:class:`http.server.CGIHTTPRequestHandler` has been deprecated for removal
+in 3.15.  Its design is old and the web world has long since moved beyond
+CGI.