Reject invalid server names (#3480)

Make sure that server_names used in auth headers are sane, and reject them with
a sensible error code, before they disappear off into the depths of the system.

tests/http/test_endpoint.py

@@ -0,0 +1,46 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from synapse.http.endpoint import parse_server_name
+from tests import unittest
+
+
+class ServerNameTestCase(unittest.TestCase):
+    def test_parse_server_name(self):
+        test_data = {
+            'localhost': ('localhost', None),
+            'my-example.com:1234': ('my-example.com', 1234),
+            '1.2.3.4': ('1.2.3.4', None),
+            '[0abc:1def::1234]': ('[0abc:1def::1234]', None),
+            '1.2.3.4:1': ('1.2.3.4', 1),
+            '[0abc:1def::1234]:8080': ('[0abc:1def::1234]', 8080),
+        }
+
+        for i, o in test_data.items():
+            self.assertEqual(parse_server_name(i), o)
+
+    def test_parse_bad_server_names(self):
+        test_data = [
+            "",  # empty
+            "localhost:http",  # non-numeric port
+            "1234]",  # smells like ipv6 literal but isn't
+        ]
+        for i in test_data:
+            try:
+                parse_server_name(i)
+                self.fail(
+                    "Expected parse_server_name(\"%s\") to throw" % i,
+                )
+            except ValueError:
+                pass