From 13b302c70282620d21f72fbc1cd43b0adf784096 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20Gabriel=20Pieroli=20da=20Silva?=
 <joaogabrielpieroli18@gmail.com>
Date: Tue, 13 Oct 2026 20:24:45 -0300
Subject: [PATCH] gh-159044: Restore string conversion for HTTP tunnel header
 values (GH-159216) (cherry picked from commit
 8138bf11a5d32e8db003a86606be8e4c61e14d4b)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: João Gabriel Pieroli da Silva <joaogabrielpieroli18@gmail.com>
Co-authored-by: LorenaMBorges <lborgescomp@gmail.com>
---
 Doc/library/http.client.rst                     |  3 ++-
 Lib/http/client.py                              |  2 +-
 Lib/test/test_httplib.py                        | 17 +++++++++++++++++
 ...26-10-12-00-00-00.gh-issue-159044.Tr8kXv.rst |  4 ++++
 4 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-10-12-00-00-00.gh-issue-159044.Tr8kXv.rst

diff --git a/Doc/library/http.client.rst b/Doc/library/http.client.rst
index 4002fc697ceaa5..ab557f1805e104 100644
--- a/Doc/library/http.client.rst
+++ b/Doc/library/http.client.rst
@@ -370,7 +370,8 @@ HTTPConnection Objects
    proxy server).
 
    The *headers* argument should be a mapping of extra HTTP headers to send with
-   the CONNECT request.
+   the CONNECT request. Non-string header values are converted to strings via
+   :func:`str`.
 
    As HTTP/1.1 is used for HTTP CONNECT tunnelling request, `as per the RFC
    <https://datatracker.ietf.org/doc/html/rfc7231#section-4.3.6>`_, a HTTP ``Host:``
diff --git a/Lib/http/client.py b/Lib/http/client.py
index 7ef99e7201c005..3fdf3a36f180ef 100644
--- a/Lib/http/client.py
+++ b/Lib/http/client.py
@@ -1013,7 +1013,7 @@ def _tunnel(self):
         headers = [connect]
         for header, value in self._tunnel_headers.items():
             header_bytes = header.encode("latin-1")
-            value_bytes = value.encode("latin-1")
+            value_bytes = str(value).encode("latin-1")
             if not _is_legal_header_name(header_bytes):
                 raise ValueError('Invalid header name %r' % (header_bytes,))
             if _is_illegal_header_value(value_bytes):
diff --git a/Lib/test/test_httplib.py b/Lib/test/test_httplib.py
index 5b1d6e0aa52079..bd8cdfe55c6b4d 100644
--- a/Lib/test/test_httplib.py
+++ b/Lib/test/test_httplib.py
@@ -2766,6 +2766,23 @@ def _create_connection(address, timeout=None, source_address=None):
         self.assertIsNotNone(exc)
         self.assertTrue(sock.file_closed)
 
+    def test_tunnel_nonstr_headers(self):
+        class CustomObject:
+            def __str__(self):
+                return 'custom-str'
+
+        self.conn.set_tunnel('destination.com', headers={
+            'None-Value': None,
+            'Integer-Value': 9,
+            'Custom-Value': CustomObject(),
+        })
+
+        self.conn.request('HEAD', '/', '')
+
+        self.assertIn(b'None-Value: None\r\n', self.conn.sock.data)
+        self.assertIn(b'Integer-Value: 9\r\n', self.conn.sock.data)
+        self.assertIn(b'Custom-Value: custom-str\r\n', self.conn.sock.data)
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)
diff --git a/Misc/NEWS.d/next/Library/2026-10-12-00-00-00.gh-issue-159044.Tr8kXv.rst b/Misc/NEWS.d/next/Library/2026-10-12-00-00-00.gh-issue-159044.Tr8kXv.rst
new file mode 100644
index 00000000000000..ef51dc8eca1066
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-12-00-00-00.gh-issue-159044.Tr8kXv.rst
@@ -0,0 +1,4 @@
+Restore the previous behaviour of :meth:`http.client.HTTPConnection.set_tunnel`
+where header values that are not strings (such as :const:`None`, :class:`int`
+or other objects) are converted with :class:`str` instead of raising
+:exc:`AttributeError` when the request is sent.