gh-70765: avoid waiting for HTTP headers when parsing HTTP/0.9 requests (#139514)

Lib/test/test_httpservers.py

@@ -362,6 +362,43 @@ def test_head_via_send_error(self):
             self.assertEqual(b'', data)
 
 
+class HTTP09ServerTestCase(BaseTestCase):
+
+    class request_handler(NoLogRequestHandler, BaseHTTPRequestHandler):
+        """Request handler for HTTP/0.9 server."""
+
+        def do_GET(self):
+            self.wfile.write(f'OK: here is {self.path}\r\n'.encode())
+
+    def setUp(self):
+        super().setUp()
+        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.sock = self.enterContext(self.sock)
+        self.sock.connect((self.HOST, self.PORT))
+
+    def test_simple_get(self):
+        self.sock.send(b'GET /index.html\r\n')
+        res = self.sock.recv(1024)
+        self.assertEqual(res, b"OK: here is /index.html\r\n")
+
+    def test_invalid_request(self):
+        self.sock.send(b'POST /index.html\r\n')
+        res = self.sock.recv(1024)
+        self.assertIn(b"Bad HTTP/0.9 request type ('POST')", res)
+
+    def test_single_request(self):
+        self.sock.send(b'GET /foo.html\r\n')
+        res = self.sock.recv(1024)
+        self.assertEqual(res, b"OK: here is /foo.html\r\n")
+
+        self.sock.send(b'GET /bar.html\r\n')
+        res = self.sock.recv(1024)
+        # The server will not parse more input as it closed the connection.
+        # Note that the socket connection itself is still opened since the
+        # client is responsible for also closing it on their side.
+        self.assertEqual(res, b'')
+
+
 def certdata_file(*path):
     return os.path.join(os.path.dirname(__file__), "certdata", *path)