getData(cb) {
    let data = EMPTY_BUFFER;

    if (this._payloadLength) {
      if (this._bufferedBytes < this._payloadLength) {
        this._loop = false;
        return;
      }

      data = this.consume(this._payloadLength);

      if (
        this._masked &&
        (this._mask[0] | this._mask[1] | this._mask[2] | this._mask[3]) !== 0
      ) {
        unmask(data, this._mask);
      }
    }

    if (this._opcode > 0x07) {
      this.controlMessage(data, cb);
      return;
    }

    if (this._compressed) {
      this._state = INFLATING;
      this.decompress(data, cb);
      return;
    }

    if (data.length) {
      //
      // This message is not compressed so its length is the sum of the payload
      // length of all fragments.
      //
      this._messageLength = this._totalPayloadLength;
      this._fragments.push(data);
    }

    this.dataMessage(cb);
  }
Reads data bytes.

@param {Function} cb Callback
@private