Add joined hosts query APIs (#781)

This adds two joined hosts query APIs to the federation sender for use of other components.

federationsender/query/query.go

@@ -0,0 +1,55 @@
+package query
+
+import (
+	"context"
+
+	"github.com/matrix-org/dendrite/federationsender/api"
+	"github.com/matrix-org/dendrite/federationsender/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// FederationSenderQueryDatabase has the APIs needed to implement the query API.
+type FederationSenderQueryDatabase interface {
+	GetJoinedHosts(
+		ctx context.Context, roomID string,
+	) ([]types.JoinedHost, error)
+}
+
+// FederationSenderQueryAPI is an implementation of api.FederationSenderQueryAPI
+type FederationSenderQueryAPI struct {
+	DB FederationSenderQueryDatabase
+}
+
+// QueryJoinedHostsInRoom implements api.FederationSenderQueryAPI
+func (f *FederationSenderQueryAPI) QueryJoinedHostsInRoom(
+	ctx context.Context,
+	request *api.QueryJoinedHostsInRoomRequest,
+	response *api.QueryJoinedHostsInRoomResponse,
+) (err error) {
+	response.JoinedHosts, err = f.DB.GetJoinedHosts(ctx, request.RoomID)
+	return
+}
+
+// QueryJoinedHostServerNamesInRoom implements api.FederationSenderQueryAPI
+func (f *FederationSenderQueryAPI) QueryJoinedHostServerNamesInRoom(
+	ctx context.Context,
+	request *api.QueryJoinedHostServerNamesInRoomRequest,
+	response *api.QueryJoinedHostServerNamesInRoomResponse,
+) (err error) {
+	joinedHosts, err := f.DB.GetJoinedHosts(ctx, request.RoomID)
+	if err != nil {
+		return
+	}
+
+	serverNamesSet := make(map[gomatrixserverlib.ServerName]bool, len(joinedHosts))
+	for _, host := range joinedHosts {
+		serverNamesSet[host.ServerName] = true
+	}
+
+	response.ServerNames = make([]gomatrixserverlib.ServerName, 0, len(serverNamesSet))
+	for name := range serverNamesSet {
+		response.ServerNames = append(response.ServerNames, name)
+	}
+
+	return
+}