Fail quicker for 4xx responses in the key client, optional hit a different API path

synapse/crypto/keyclient.py

@@ -25,12 +25,15 @@ import logging
 
 logger = logging.getLogger(__name__)
 
+KEY_API_V1 = b"/_matrix/key/v1/"
+KEY_API_V2 = b"/_matrix/key/v2/local"
 
 @defer.inlineCallbacks
-def fetch_server_key(server_name, ssl_context_factory):
+def fetch_server_key(server_name, ssl_context_factory, path=KEY_API_V1):
     """Fetch the keys for a remote server."""
 
     factory = SynapseKeyClientFactory()
+    factory.path = path
     endpoint = matrix_federation_endpoint(
         reactor, server_name, ssl_context_factory, timeout=30
     )
@@ -42,13 +45,19 @@ def fetch_server_key(server_name, ssl_context_factory):
                 server_response, server_certificate = yield protocol.remote_key
                 defer.returnValue((server_response, server_certificate))
                 return
+        except SynapseKeyClientError as e:
+            logger.exception("Error getting key for %r" % (server_name,))
+            if e.status.startswith("4"):
+                # Don't retry for 4xx responses.
+                raise IOError("Cannot get key for %r" % server_name)
         except Exception as e:
             logger.exception(e)
-    raise IOError("Cannot get key for %s" % server_name)
+    raise IOError("Cannot get key for %r" % server_name)
 
 
 class SynapseKeyClientError(Exception):
     """The key wasn't retrieved from the remote server."""
+    status = None
     pass
 
 
@@ -66,17 +75,30 @@ class SynapseKeyClientProtocol(HTTPClient):
     def connectionMade(self):
         self.host = self.transport.getHost()
         logger.debug("Connected to %s", self.host)
-        self.sendCommand(b"GET", b"/_matrix/key/v1/")
+        self.sendCommand(b"GET", self.path)
         self.endHeaders()
         self.timer = reactor.callLater(
             self.timeout,
             self.on_timeout
         )
 
+    def errback(self, error):
+        if not self.remote_key.called:
+            self.remote_key.errback(error)
+
+    def callback(self, result):
+        if not self.remote_key.called:
+            self.remote_key.callback(result)
+
     def handleStatus(self, version, status, message):
         if status != b"200":
             # logger.info("Non-200 response from %s: %s %s",
             #            self.transport.getHost(), status, message)
+            error = SynapseKeyClientError("Non-200 response %r from %r" %
+                (status, self.host)
+            )
+            error.status = status
+            self.errback(error)
             self.transport.abortConnection()
 
     def handleResponse(self, response_body_bytes):
@@ -89,15 +111,18 @@ class SynapseKeyClientProtocol(HTTPClient):
             return
 
         certificate = self.transport.getPeerCertificate()
-        self.remote_key.callback((json_response, certificate))
+        self.callback((json_response, certificate))
         self.transport.abortConnection()
         self.timer.cancel()
 
     def on_timeout(self):
         logger.debug("Timeout waiting for response from %s", self.host)
-        self.remote_key.errback(IOError("Timeout waiting for response"))
+        self.errback(IOError("Timeout waiting for response"))
         self.transport.abortConnection()
 
 
 class SynapseKeyClientFactory(Factory):
-    protocol = SynapseKeyClientProtocol
+    def protocol(self):
+        protocol = SynapseKeyClientProtocol()
+        protocol.path = self.path
+        return protocol