Add experimental method to prepare connection in order to speed up su…

…bsequent ws connection (livekit#469)

* add method to prepare connection for speeding up subsequent first connection attempt

* changeset

* update comment

* mark as experimental

* update changeset

.changeset/smooth-dots-breathe.md

@@ -0,0 +1,5 @@
+---
+'livekit-client': patch
+---
+
+Add experimental method to prepare connection for speeding up subsequent first connection attempt

example/sample.ts

@@ -98,6 +98,11 @@ const appActions = {
  ): Promise<Room | undefined> => {
  const room = new Room(roomOptions);
 
+ startTime = Date.now();
+ await room.prepareConnection(url);
+ const prewarmTime = Date.now() - startTime;
+ appendLog(`prewarmed connection in ${prewarmTime}ms`);
+
  room
  .on(RoomEvent.ParticipantConnected, participantConnected)
  .on(RoomEvent.ParticipantDisconnected, participantDisconnected)
@@ -149,6 +154,8 @@ const appActions = {
  renderScreenShare(room);
  })
  .on(RoomEvent.SignalConnected, async () => {
+ const signalConnectionTime = Date.now() - startTime;
+ appendLog(`signal connection established in ${signalConnectionTime}ms`);
  if (shouldPublish) {
  await Promise.all([
  room.localParticipant.setCameraEnabled(true),
@@ -159,7 +166,6 @@ const appActions = {
  });
 
  try {
- startTime = Date.now();
  await room.connect(url, token, connectOptions);
  const elapsed = Date.now() - startTime;
  appendLog(

src/room/Room.ts

@@ -218,6 +218,18 @@ class Room extends (EventEmitter as new () => TypedEmitter<RoomEventCallbacks>)
  return DeviceManager.getInstance().getDevices(kind, requestPermissions);
  }
 
+ /**
+ * prepares the connection to the livekit server by sending a HEAD request in order to
+ * 1. speed up DNS resolution
+ * 2. speed up TLS setup
+ * on the actual connection request
+ * throws an error if server is not reachable after the request timeout
+ * @experimental
+ */
+ async prepareConnection(url: string) {
+ await fetch(`http${url.substring(2)}`, { method: 'HEAD' });
+ }
+
  connect = (url: string, token: string, opts?: RoomConnectOptions): Promise<void> => {
  if (this.state === ConnectionState.Connected) {
  // when the state is reconnecting or connected, this function returns immediately