Add a /versions endpoint. (#542)

And support Matrix v1.1.

changelog.d/542.feature

@@ -0,0 +1 @@
+Support Matrix v1.1.

sydent/http/httpserver.py

@@ -56,6 +56,7 @@
 from sydent.http.servlets.termsservlet import TermsServlet
 from sydent.http.servlets.threepidbindservlet import ThreePidBindServlet
 from sydent.http.servlets.threepidunbindservlet import ThreePidUnbindServlet
+from sydent.http.servlets.versions import VersionsServlet
 
 if TYPE_CHECKING:
     from sydent.sydent import Sydent
@@ -97,6 +98,7 @@ def __init__(self, sydent: "Sydent", lookup_pepper: str) -> None:
         matrix.putChild(b"identity", identity)
         identity.putChild(b"api", api)
         identity.putChild(b"v2", v2)
+        identity.putChild(b"versions", VersionsServlet())
         api.putChild(b"v1", v1)
 
         validate.putChild(b"email", email)

sydent/http/servlets/versions.py

@@ -0,0 +1,47 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# 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 twisted.web.server import Request
+
+from sydent.http.servlets import SydentResource, jsonwrap, send_cors
+from sydent.types import JsonDict
+
+
+class VersionsServlet(SydentResource):
+    isLeaf = True
+
+    @jsonwrap
+    def render_GET(self, request: Request) -> JsonDict:
+        """
+        Return the supported Matrix versions.
+        """
+        send_cors(request)
+
+        return {
+            "versions": [
+                "r0.1.0",
+                "r0.2.0",
+                "r0.2.1",
+                "r0.3.0",
+                "v1.1",
+                "v1.2",
+                "v1.3",
+                "v1.4",
+                "v1.5",
+            ]
+        }
+
+    def render_OPTIONS(self, request: Request) -> bytes:
+        send_cors(request)
+        return b""