Use persistent WebTransport frame stream

server/index.js

@@ -65,6 +65,7 @@ const JPEG_EOI = Buffer.from([0xff, 0xd9]);
 const WT_STREAM_CONTROL_TO_CLIENT = 1;
 const WT_STREAM_FRAME = 2;
 const WT_STREAM_CONTROL_TO_SERVER = 3;
+const WT_FRAME_RECORD_HEADER_BYTES = 4;
 const BEST_EFFORT_RESUME_MAX_SECONDS = 30 * 24 * 60 * 60;
 const RECORDED_MEDIA_EXTENSIONS = new Set([
   '.avi',
@@ -2524,6 +2525,8 @@ class WebTransportFrameConnection extends EventEmitter {
     this._closedEmitted = false;
     this._controlStreamPromise = this.openControlStream();
     this._controlWrite = Promise.resolve();
+    this._frameStreamPromise = null;
+    this._frameWrite = Promise.resolve();
 
     this.session.closed().then((info) => {
       this.markClosed(info?.closeCode ?? 1000, info?.reason ?? '');
@@ -2554,7 +2557,11 @@ class WebTransportFrameConnection extends EventEmitter {
     }
 
     const packet = Buffer.isBuffer(data) ? data : Buffer.from(data);
-    this.writeFrame(packet).then(() => {
+    this._frameWrite = this._frameWrite
+      .catch(() => {})
+      .then(() => this.writeFrame(packet));
+
+    this._frameWrite.then(() => {
       done?.();
     }).catch((error) => {
       this.emitError(error);
@@ -2583,6 +2590,17 @@ class WebTransportFrameConnection extends EventEmitter {
     return stream;
   }
 
+  async openFrameStream() {
+    const stream = await this.session.openUni();
+    await stream.write(Buffer.from([WT_STREAM_FRAME]));
+    return stream;
+  }
+
+  getFrameStream() {
+    this._frameStreamPromise ??= this.openFrameStream();
+    return this._frameStreamPromise;
+  }
+
   async writeControl(data) {
     if (this.readyState !== WebSocket.OPEN) {
       return;
@@ -2597,17 +2615,20 @@ class WebTransportFrameConnection extends EventEmitter {
       throw new Error('WebTransport frame connection is closed.');
     }
 
-    this._bufferedAmount += packet.length;
+    if (packet.length > 0xffffffff) {
+      throw new Error('WebTransport frame packet is too large.');
+    }
+
+    const recordHeader = Buffer.allocUnsafe(WT_FRAME_RECORD_HEADER_BYTES);
+    recordHeader.writeUInt32LE(packet.length, 0);
+    this._bufferedAmount += WT_FRAME_RECORD_HEADER_BYTES + packet.length;
 
     try {
-      const stream = await this.session.openUni();
-      const payload = Buffer.allocUnsafe(packet.length + 1);
-      payload[0] = WT_STREAM_FRAME;
-      packet.copy(payload, 1);
-      await stream.write(payload);
-      await stream.finish();
+      const stream = await this.getFrameStream();
+      await stream.write(recordHeader);
+      await stream.write(packet);
     } finally {
-      this._bufferedAmount = Math.max(0, this._bufferedAmount - packet.length);
+      this._bufferedAmount = Math.max(0, this._bufferedAmount - WT_FRAME_RECORD_HEADER_BYTES - packet.length);
     }
   }