Factor out keyring initialisation (#329)

Take the keyring init from the client-api-server and the monolith out to a
shared file

src/github.com/matrix-org/dendrite/cmd/dendrite-client-api-server/main.go

@@ -98,13 +98,7 @@ func main() {
 		log.Panicf("Failed to setup key database(%q): %s", cfg.Database.ServerKey, err.Error())
 	}
 
-	keyRing := gomatrixserverlib.KeyRing{
+	keyRing := keydb.CreateKeyRing(federation.Client, keyDB)
-		KeyFetchers: []gomatrixserverlib.KeyFetcher{
-			// TODO: Use perspective key fetchers for production.
-			&gomatrixserverlib.DirectKeyFetcher{Client: federation.Client},
-		},
-		KeyDatabase: keyDB,
-	}
 
 	kafkaConsumer, err := sarama.NewConsumer(cfg.Kafka.Addresses, nil)
 	if err != nil {

src/github.com/matrix-org/dendrite/cmd/dendrite-monolith-server/main.go

@@ -194,13 +194,7 @@ func (m *monolith) setupFederation() {
 		m.cfg.Matrix.ServerName, m.cfg.Matrix.KeyID, m.cfg.Matrix.PrivateKey,
 	)
 
-	m.keyRing = gomatrixserverlib.KeyRing{
+	m.keyRing = keydb.CreateKeyRing(m.federation.Client, m.keyDB)
-		KeyFetchers: []gomatrixserverlib.KeyFetcher{
-			// TODO: Use perspective key fetchers for production.
-			&gomatrixserverlib.DirectKeyFetcher{Client: m.federation.Client},
-		},
-		KeyDatabase: m.keyDB,
-	}
 }
 
 func (m *monolith) setupKafka() {

src/github.com/matrix-org/dendrite/common/keydb/keyring.go

@@ -0,0 +1,32 @@
+// Copyright 2017 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.
+
+package keydb
+
+import "github.com/matrix-org/gomatrixserverlib"
+
+// CreateKeyRing creates and configures a KeyRing object.
+//
+// It creates the necessary key fetchers and collects them into a KeyRing
+// backed by the given KeyDatabase.
+func CreateKeyRing(client gomatrixserverlib.Client,
+	keyDB gomatrixserverlib.KeyDatabase) gomatrixserverlib.KeyRing {
+	return gomatrixserverlib.KeyRing{
+		KeyFetchers: []gomatrixserverlib.KeyFetcher{
+			// TODO: Use perspective key fetchers for production.
+			&gomatrixserverlib.DirectKeyFetcher{Client: client},
+		},
+		KeyDatabase: keyDB,
+	}
+}