Function createPacketDecoderStream

packages/engine.io-parser/lib/index.ts:113–197

(
  maxPayload: number,
  binaryType: BinaryType,
)

}

export function createPacketDecoderStream(
  maxPayload: number,
  binaryType: BinaryType,
): any {
  if (!TEXT_DECODER) {
    TEXT_DECODER = new TextDecoder();
  }
  const chunks: Uint8Array[] = [];
  let state = State.READ_HEADER;
  let expectedLength = -1;
  let isBinary = false;

  return new TransformStream({
    transform(chunk: Uint8Array, controller) {
      chunks.push(chunk);
      while (true) {
        if (state === State.READ_HEADER) {
          if (totalLength(chunks) < 1) {
            break;
          }
          const header = concatChunks(chunks, 1);
          isBinary = (header[0] & 0x80) === 0x80;
          expectedLength = header[0] & 0x7f;
          if (expectedLength < 126) {
            state = State.READ_PAYLOAD;
          } else if (expectedLength === 126) {
            state = State.READ_EXTENDED_LENGTH_16;
          } else {
            state = State.READ_EXTENDED_LENGTH_64;
          }
        } else if (state === State.READ_EXTENDED_LENGTH_16) {
          if (totalLength(chunks) < 2) {
            break;
          }
          const headerArray = concatChunks(chunks, 2);
          expectedLength = new DataView(
            headerArray.buffer,
            headerArray.byteOffset,
            headerArray.length,
          ).getUint16(0);
          state = State.READ_PAYLOAD;
        } else if (state === State.READ_EXTENDED_LENGTH_64) {
          if (totalLength(chunks) < 8) {
            break;
          }
          const headerArray = concatChunks(chunks, 8);

          const view = new DataView(
            headerArray.buffer,
            headerArray.byteOffset,
            headerArray.length,
          );

          const n = view.getUint32(0);

          if (n > Math.pow(2, 53 - 32) - 1) {
            // the maximum safe integer in JavaScript is 2^53 - 1
            controller.enqueue(ERROR_PACKET);