use go module for dependencies (#594)

roomserver/auth/auth.go

@@ -0,0 +1,47 @@
+// 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 auth
+
+import "github.com/matrix-org/gomatrixserverlib"
+
+// IsServerAllowed returns true if there exists a event in authEvents
+// which allows server to view this event. That is true when a client on the server
+// can view the event. Otherwise returns false.
+func IsServerAllowed(
+	serverName gomatrixserverlib.ServerName,
+	authEvents []gomatrixserverlib.Event,
+) bool {
+	for _, ev := range authEvents {
+		membership, err := ev.Membership()
+		if err != nil || membership != "join" {
+			continue
+		}
+
+		stateKey := ev.StateKey()
+		if stateKey == nil {
+			continue
+		}
+
+		_, domain, err := gomatrixserverlib.SplitID('@', *stateKey)
+		if err != nil {
+			continue
+		}
+
+		if domain == serverName {
+			return true
+		}
+	}
+
+	// TODO: Check if history visibility is shared and if the server is currently in the room
+	return false
+}