[3.6] bpo-30714: ALPN changes for OpenSSL 1.1.0f (#3093)

OpenSSL 1.1.0 to 1.1.0e aborted the handshake when server and client
could not agree on a protocol using ALPN. OpenSSL 1.1.0f changed that.
The most recent version now behaves like OpenSSL 1.0.2 again. The ALPN
callback can pretend to not been set.

See openssl/openssl#3158 for more details

Signed-off-by: Christian Heimes <christian@python.org>
(cherry picked from commit a5c1bab)

Doc/library/ssl.rst

@@ -1442,8 +1442,9 @@ to speed up repeated connections from the same clients.
    This method will raise :exc:`NotImplementedError` if :data:`HAS_ALPN` is
    False.
 
-   OpenSSL 1.1.0+ will abort the handshake and raise :exc:`SSLError` when
-   both sides support ALPN but cannot agree on a protocol.
+   OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise :exc:`SSLError`
+   when both sides support ALPN but cannot agree on a protocol. 1.1.0f+
+   behaves like 1.0.2, :meth:`SSLSocket.selected_alpn_protocol` returns None.
 
    .. versionadded:: 3.5
 

Lib/test/test_ssl.py

@@ -3258,8 +3258,9 @@ def test_alpn_protocols(self):
                 except ssl.SSLError as e:
                     stats = e
 
-                if expected is None and IS_OPENSSL_1_1:
-                    # OpenSSL 1.1.0 raises handshake error
+                if (expected is None and IS_OPENSSL_1_1
+                        and ssl.OPENSSL_VERSION_INFO < (1, 1, 0, 6)):
+                    # OpenSSL 1.1.0 to 1.1.0e raises handshake error
                     self.assertIsInstance(stats, ssl.SSLError)
                 else:
                     msg = "failed trying %s (s) and %s (c).\n" \

Misc/NEWS.d/next/Tests/2017-07-25-15-27-44.bpo-30715.Sp7bTF.rst

@@ -0,0 +1,2 @@
+Address ALPN callback changes for OpenSSL 1.1.0f. The latest version behaves
+like OpenSSL 1.0.2 and no longer aborts handshake.