bpo-43332: Buffer proxy connection setup packets before sending. (GH-24780)

We now buffer the CONNECT request + tunnel HTTP headers into a single
send call.  This prevents the OS from generating multiple network
packets for connection setup when not necessary, improving efficiency.
(cherry picked from commit c25910a135c2245accadb324b40dd6453015e056)

Co-authored-by: Gregory P. Smith <greg@krypto.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/Lib/test/test_httplib.py b/Lib/test/test_httplib.py
index 28943f0..0fe8ead 100644
--- a/Lib/test/test_httplib.py
+++ b/Lib/test/test_httplib.py
@@ -10,6 +10,7 @@ import threading
 import warnings
 
 import unittest
+from unittest import mock
 TestCase = unittest.TestCase
 
 from test import support
@@ -2021,6 +2022,23 @@ class TunnelTests(TestCase):
         # This test should be removed when CONNECT gets the HTTP/1.1 blessing
         self.assertNotIn(b'Host: proxy.com', self.conn.sock.data)
 
+    def test_tunnel_connect_single_send_connection_setup(self):
+        """Regresstion test for https://bugs.python.org/issue43332."""
+        with mock.patch.object(self.conn, 'send') as mock_send:
+            self.conn.set_tunnel('destination.com')
+            self.conn.connect()
+            self.conn.request('GET', '/')
+        mock_send.assert_called()
+        # Likely 2, but this test only cares about the first.
+        self.assertGreater(
+                len(mock_send.mock_calls), 1,
+                msg=f'unexpected number of send calls: {mock_send.mock_calls}')
+        proxy_setup_data_sent = mock_send.mock_calls[0][1][0]
+        self.assertIn(b'CONNECT destination.com', proxy_setup_data_sent)
+        self.assertTrue(
+                proxy_setup_data_sent.endswith(b'\r\n\r\n'),
+                msg=f'unexpected proxy data sent {proxy_setup_data_sent!r}')
+
     def test_connect_put_request(self):
         self.conn.set_tunnel('destination.com')
         self.conn.request('PUT', '/', '')