gh-135056: Add a --header argument to http.server cli.

Author: aisipos

Lib/http/server.py

@@ -1048,6 +1048,11 @@ def _main(args=None):
                              '(default: %(default)s)')
     parser.add_argument('--cors', action='store_true',
                         help='Enable Access-Control-Allow-Origin: * header')
+    parser.add_argument('-H', '--header', nargs=2, action='append',
+                        # metavar='HEADER VALUE',
+                        metavar=('HEADER', 'VALUE'),
+                        help='Add a custom response header '
+                             '(can be used multiple times)')
     args = parser.parse_args(args)
 
     if not args.tls_cert and args.tls_key:
@@ -1085,7 +1090,12 @@ class HTTPSDualStackServer(DualStackServerMixin, ThreadingHTTPSServer):
         pass
 
     ServerClass = HTTPSDualStackServer if args.tls_cert else HTTPDualStackServer
-    response_headers = {'Access-Control-Allow-Origin': '*'} if args.cors else None
+    response_headers = {}
+    if args.cors:
+        response_headers['Access-Control-Allow-Origin'] = '*'
+    for header, value in args.header or []:
+        response_headers[header] = value
+
 
     test(
         HandlerClass=SimpleHTTPRequestHandler,
@@ -1096,7 +1106,7 @@ class HTTPSDualStackServer(DualStackServerMixin, ThreadingHTTPSServer):
         tls_cert=args.tls_cert,
         tls_key=args.tls_key,
         tls_password=tls_key_password,
-        response_headers=response_headers
+        response_headers=response_headers or None
     )
 
 

Lib/test/test_httpservers.py

@@ -1399,6 +1399,18 @@ def test_cors_flag(self, mock_func):
         mock_func.assert_called_once_with(**call_args)
         mock_func.reset_mock()
 
+    @mock.patch('http.server.test')
+    def test_header_flag(self, mock_func):
+        self.invoke_httpd('--header', 'h1', 'v1', '-H', 'h2', 'v2')
+        call_args = self.args | dict(
+            response_headers={
+                'h1': 'v1',
+                'h2': 'v2'
+            }
+        )
+        mock_func.assert_called_once_with(**call_args)
+        mock_func.reset_mock()
+
     @unittest.skipIf(ssl is None, "requires ssl")
     @mock.patch('http.server.test')
     def test_tls_cert_and_key_flags(self, mock_func):