HTTPSConnection: prefer the context's check_hostname attribute over the constructor parameter (#22959)

Doc/library/http.client.rst

@@ -69,17 +69,12 @@ The module provides the following classes:
    *key_file* and *cert_file* are deprecated, please use
    :meth:`ssl.SSLContext.load_cert_chain` instead, or let
    :func:`ssl.create_default_context` select the system's trusted CA
-   certificates for you.
+   certificates for you.  The *check_hostname* parameter is also deprecated; the
+   :attr:`SSLContext.check_hostname` attribute of *context* should be used
+   instead.
 
    Please read :ref:`ssl-security` for more information on best practices.
 
-   .. note::
-      If *context* is specified and has a :attr:`~ssl.SSLContext.verify_mode`
-      of either :data:`~ssl.CERT_OPTIONAL` or :data:`~ssl.CERT_REQUIRED`, then
-      by default *host* is matched against the host name(s) allowed by the
-      server's certificate.  If you want to change that behaviour, you can
-      explicitly set *check_hostname* to False.
-
    .. versionchanged:: 3.2
       *source_address*, *context* and *check_hostname* were added.
 

Lib/http/client.py

@@ -1210,8 +1210,8 @@ else:
                 context = ssl._create_default_https_context()
             will_verify = context.verify_mode != ssl.CERT_NONE
             if check_hostname is None:
-                check_hostname = will_verify
+                check_hostname = context.check_hostname
-            elif check_hostname and not will_verify:
+            if check_hostname and not will_verify:
                 raise ValueError("check_hostname needs a SSL context with "
                                  "either CERT_OPTIONAL or CERT_REQUIRED")
             if key_file or cert_file:

Lib/test/test_httplib.py

@@ -882,6 +882,7 @@ class HTTPSTest(TestCase):
         server = self.make_server(CERT_fakehostname)
         context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
         context.verify_mode = ssl.CERT_REQUIRED
+        context.check_hostname = True
         context.load_verify_locations(CERT_fakehostname)
         h = client.HTTPSConnection('localhost', server.port, context=context)
         with self.assertRaises(ssl.CertificateError):
@@ -892,11 +893,24 @@ class HTTPSTest(TestCase):
         with self.assertRaises(ssl.CertificateError):
             h.request('GET', '/')
         # With check_hostname=False, the mismatching is ignored
+        context.check_hostname = False
         h = client.HTTPSConnection('localhost', server.port, context=context,
                                    check_hostname=False)
         h.request('GET', '/nonexistent')
         resp = h.getresponse()
         self.assertEqual(resp.status, 404)
+        # The context's check_hostname setting is used if one isn't passed to
+        # HTTPSConnection.
+        context.check_hostname = False
+        h = client.HTTPSConnection('localhost', server.port, context=context)
+        h.request('GET', '/nonexistent')
+        self.assertEqual(h.getresponse().status, 404)
+        # Passing check_hostname to HTTPSConnection should override the
+        # context's setting.
+        h = client.HTTPSConnection('localhost', server.port, context=context,
+                                   check_hostname=True)
+        with self.assertRaises(ssl.CertificateError):
+            h.request('GET', '/')
 
     @unittest.skipIf(not hasattr(client, 'HTTPSConnection'),
                      'http.client.HTTPSConnection not available')

Misc/NEWS

@@ -39,6 +39,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #22959: In the constructor of http.client.HTTPSConnection, prefer the
+  context's check_hostname attribute over the *check_hostname* parameter.
+
 - Issue #16043: Add a default limit for the amount of data xmlrpclib.gzip_decode
   will return. This resolves CVE-2013-1753.