Function transform

packages/engine.io-parser/lib/index.ts:51–77

(packet: Packet, controller)

export function createPacketEncoderStream(): any {
  return new TransformStream({
    transform(packet: Packet, controller) {
      encodePacketToBinary(packet, (encodedPacket) => {
        const payloadLength = encodedPacket.length;
        let header;
        // inspired by the WebSocket format: https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_servers#decoding_payload_length
        if (payloadLength < 126) {
          header = new Uint8Array(1);
          new DataView(header.buffer).setUint8(0, payloadLength);
        } else if (payloadLength < 65536) {
          header = new Uint8Array(3);
          const view = new DataView(header.buffer);
          view.setUint8(0, 126);
          view.setUint16(1, payloadLength);
        } else {
          header = new Uint8Array(9);
          const view = new DataView(header.buffer);
          view.setUint8(0, 127);
          view.setBigUint64(1, BigInt(payloadLength));
        }
        // first bit indicates whether the payload is plain text (0) or binary (1)
        if (packet.data && typeof packet.data !== "string") {
          header[0] |= 0x80;
        }
        controller.enqueue(header);
        controller.enqueue(encodedPacket);
      });
    },
  });
}