https: support tls sni (server name indication) for https urls (issue3090)

SNI is a common way of sharing servers across multiple domains using separate
SSL certificates. As of Python 2.7.9 SSLContext has been backported from
Python 3. This patch changes sslutil's ssl_wrap_socket to use SSLContext and
take a server hostname as and argument. It also changes the url module to make
use of this argument.

The new code for 2.7.9 achieves it's task by attempting to get the SSLContext
object from the ssl module. If this fails the try/except goes back to what was
there before with the exception that the ssl_wrap_socket functions take a
server_hostname argument that doesn't get used. Assuming the SSLContext
exists, the arguments to wrap_socket at the module level are emulated on the
SSLContext. The SSLContext is initialized with the specified ssl_version. If
certfile is not None load_cert_chain is called with certfile and keyfile.
keyfile being None is not a problem, load_cert_chain will simply expect the
private key to be in the certificate file. verify_mode is set to cert_reqs. If
ca_certs is not None load_verify_locations is called with ca_certs as the
cafile. Finally the wrap_socket method of the SSLContext is called with the
socket and server hostname.

Finally, this fails test-check-commit-hg.t because the "new" function
ssl_wrap_socket has underscores in its names and underscores in its arguments.
All the underscore identifiers are taken from the other functions and as such
can't be changed to match naming conventions.

mercurial/sslutil.py

@@ -15,16 +15,40 b' try:'
     import ssl
     CERT_REQUIRED = ssl.CERT_REQUIRED
     PROTOCOL_TLSv1 = ssl.PROTOCOL_TLSv1
-    def ssl_wrap_socket(sock, keyfile, certfile, ssl_version=PROTOCOL_TLSv1,
-                cert_reqs=ssl.CERT_NONE, ca_certs=None):
-        sslsocket = ssl.wrap_socket(sock, keyfile, certfile,
-                                    cert_reqs=cert_reqs, ca_certs=ca_certs,
-                                    ssl_version=ssl_version)
-        # check if wrap_socket failed silently because socket had been closed
-        # - see http://bugs.python.org/issue13721
-        if not sslsocket.cipher():
-            raise util.Abort(_('ssl connection failed'))
-        return sslsocket
+    try:
+        ssl_context = ssl.SSLContext
+
+        def ssl_wrap_socket(sock, keyfile, certfile, ssl_version=PROTOCOL_TLSv1,
+                            cert_reqs=ssl.CERT_NONE, ca_certs=None,
+                            serverhostname=None):
+            sslcontext = ssl.SSLContext(ssl_version)
+            if certfile is not None:
+                sslcontext.load_cert_chain(certfile, keyfile)
+            sslcontext.verify_mode = cert_reqs
+            if ca_certs is not None:
+                sslcontext.load_verify_locations(cafile=ca_certs)
+
+            sslsocket = sslcontext.wrap_socket(sock,
+                                               server_hostname=serverhostname)
+            # check if wrap_socket failed silently because socket had been
+            # closed
+            # - see http://bugs.python.org/issue13721
+            if not sslsocket.cipher():
+                raise util.Abort(_('ssl connection failed'))
+            return sslsocket
+    except AttributeError:
+        def ssl_wrap_socket(sock, keyfile, certfile, ssl_version=PROTOCOL_TLSv1,
+                            cert_reqs=ssl.CERT_NONE, ca_certs=None,
+                            serverhostname=None):
+            sslsocket = ssl.wrap_socket(sock, keyfile, certfile,
+                                        cert_reqs=cert_reqs, ca_certs=ca_certs,
+                                        ssl_version=ssl_version)
+            # check if wrap_socket failed silently because socket had been
+            # closed
+            # - see http://bugs.python.org/issue13721
+            if not sslsocket.cipher():
+                raise util.Abort(_('ssl connection failed'))
+            return sslsocket
 except ImportError:
     CERT_REQUIRED = 2
 
@@ -33,7 +57,8 b' except ImportError:'
     import socket, httplib
 
     def ssl_wrap_socket(sock, keyfile, certfile, ssl_version=PROTOCOL_TLSv1,
-                        cert_reqs=CERT_REQUIRED, ca_certs=None):
+                        cert_reqs=CERT_REQUIRED, ca_certs=None,
+                        serverhostname=None):
         if not util.safehasattr(socket, 'ssl'):
             raise util.Abort(_('Python SSL support not found'))
         if ca_certs:

mercurial/url.py

@@ -185,7 +185,8 b' class httpconnection(keepalive.HTTPConne'
             self.sock.connect((self.host, self.port))
             if _generic_proxytunnel(self):
                 # we do not support client X.509 certificates
-                self.sock = sslutil.ssl_wrap_socket(self.sock, None, None)
+                self.sock = sslutil.ssl_wrap_socket(self.sock, None, None,
+                                                    serverhostname=self.host)
         else:
             keepalive.HTTPConnection.connect(self)
 
@@ -341,7 +342,7 b' if has_https:'
                 _generic_proxytunnel(self)
                 host = self.realhostport.rsplit(':', 1)[0]
             self.sock = sslutil.ssl_wrap_socket(
-                self.sock, self.key_file, self.cert_file,
+                self.sock, self.key_file, self.cert_file, serverhostname=host,
                 **sslutil.sslkwargs(self.ui, host))
             sslutil.validator(self.ui, host)(self.sock)