receiver.js

'use strict';

const { Writable } = require('stream');

const PerMessageDeflate = require('./permessage-deflate');
const {
  BINARY_TYPES,
  EMPTY_BUFFER,
  kStatusCode,
  kWebSocket
} = require('./constants');
const { concat, toArrayBuffer, unmask } = require('./buffer-util');
const { isValidStatusCode, isValidUTF8 } = require('./validation');

const FastBuffer = Buffer[Symbol.species];

const GET_INFO = 0;
const GET_PAYLOAD_LENGTH_16 = 1;
const GET_PAYLOAD_LENGTH_64 = 2;
const GET_MASK = 3;
const GET_DATA = 4;
const INFLATING = 5;
const DEFER_EVENT = 6;

/**
 * HyBi Receiver implementation.
 *
 * @extends Writable
 */
class Receiver extends Writable {
  /**
   * Creates a Receiver instance.
   *
   * @param {Object} [options] Options object
   * @param {Boolean} [options.allowSynchronousEvents=false] Specifies whether
   *     any of the `'message'`, `'ping'`, and `'pong'` events can be emitted
   *     multiple times in the same tick
   * @param {String} [options.binaryType=nodebuffer] The type for binary data
   * @param {Object} [options.extensions] An object containing the negotiated
   *     extensions
   * @param {Boolean} [options.isServer=false] Specifies whether to operate in
   *     client or server mode
   * @param {Number} [options.maxPayload=0] The maximum allowed message length
   * @param {Boolean} [options.skipUTF8Validation=false] Specifies whether or
   *     not to skip UTF-8 validation for text and close messages
   */
  constructor(options = {}) {
    super();

    this._allowSynchronousEvents = !!options.allowSynchronousEvents;
    this._binaryType = options.binaryType || BINARY_TYPES[0];
    this._extensions = options.extensions || {};
    this._isServer = !!options.isServer;
    this._maxPayload = options.maxPayload | 0;
    this._skipUTF8Validation = !!options.skipUTF8Validation;
    this[kWebSocket] = undefined;

    this._bufferedBytes = 0;
    this._buffers = [];

    this._compressed = false;
    this._payloadLength = 0;
    this._mask = undefined;
    this._fragmented = 0;
    this._masked = false;
    this._fin = false;
    this._opcode = 0;

    this._totalPayloadLength = 0;
    this._messageLength = 0;
    this._fragments = [];

    this._errored = false;
    this._loop = false;
    this._state = GET_INFO;
  }

  /**
   * Implements `Writable.prototype._write()`.
   *
   * @param {Buffer} chunk The chunk of data to write
   * @param {String} encoding The character encoding of `chunk`
   * @param {Function} cb Callback
   * @private
   */
  _write(chunk, encoding, cb) {
    if (this._opcode === 0x08 && this._state == GET_INFO) return cb();

    this._bufferedBytes += chunk.length;
    this._buffers.push(chunk);
    this.startLoop(cb);
  }

  /**
   * Consumes `n` bytes from the buffered data.
   *
   * @param {Number} n The number of bytes to consume
   * @return {Buffer} The consumed bytes
   * @private
   */
  consume(n) {
    this._bufferedBytes -= n;

    if (n === this._buffers[0].length) return this._buffers.shift();

    if (n < this._buffers[0].length) {
      const buf = this._buffers[0];
      this._buffers[0] = new FastBuffer(
        buf.buffer,
        buf.byteOffset + n,
        buf.length - n
      );

      return new FastBuffer(buf.buffer, buf.byteOffset, n);
    }

    const dst = Buffer.allocUnsafe(n);

    do {
      const buf = this._buffers[0];
      const offset = dst.length - n;

      if (n >= buf.length) {
        dst.set(this._buffers.shift(), offset);
      } else {
        dst.set(new Uint8Array(buf.buffer, buf.byteOffset, n), offset);
        this._buffers[0] = new FastBuffer(
          buf.buffer,
          buf.byteOffset + n,
          buf.length - n
        );
      }

      n -= buf.length;
    } while (n > 0);

    return dst;
  }

  /**
   * Starts the parsing loop.
   *
   * @param {Function} cb Callback
   * @private
   */
  startLoop(cb) {
    this._loop = true;

    do {
      switch (this._state) {
        case GET_INFO:
          this.getInfo(cb);
          break;
        case GET_PAYLOAD_LENGTH_16:
          this.getPayloadLength16(cb);
          break;
        case GET_PAYLOAD_LENGTH_64:
          this.getPayloadLength64(cb);
          break;
        case GET_MASK:
          this.getMask();
          break;
        case GET_DATA:
          this.getData(cb);
          break;
        case INFLATING:
        case DEFER_EVENT:
          this._loop = false;
          return;
      }
    } while (this._loop);

    if (!this._errored) cb();
  }

  /**
   * Reads the first two bytes of a frame.
   *
   * @param {Function} cb Callback
   * @private
   */
  getInfo(cb) {
    if (this._bufferedBytes < 2) {
      this._loop = false;
      return;
    }

    const buf = this.consume(2);

    if ((buf[0] & 0x30) !== 0x00) {
      const error = this.createError(
        RangeError,
        'RSV2 and RSV3 must be clear',
        true,
        1002,
        'WS_ERR_UNEXPECTED_RSV_2_3'
      );

      cb(error);
      return;
    }

    const compressed = (buf[0] & 0x40) === 0x40;

    if (compressed && !this._extensions[PerMessageDeflate.extensionName]) {
      const error = this.createError(
        RangeError,
        'RSV1 must be clear',
        true,
        1002,
        'WS_ERR_UNEXPECTED_RSV_1'
      );

      cb(error);
      return;
    }

    this._fin = (buf[0] & 0x80) === 0x80;
    this._opcode = buf[0] & 0x0f;
    this._payloadLength = buf[1] & 0x7f;

    if (this._opcode === 0x00) {
      if (compressed) {
        const error = this.createError(
          RangeError,
          'RSV1 must be clear',
          true,
          1002,
          'WS_ERR_UNEXPECTED_RSV_1'
        );

        cb(error);
        return;
      }

      if (!this._fragmented) {
        const error = this.createError(
          RangeError,
          'invalid opcode 0',
          true,
          1002,
          'WS_ERR_INVALID_OPCODE'
        );

        cb(error);
        return;
      }

      this._opcode = this._fragmented;
    } else if (this._opcode === 0x01 || this._opcode === 0x02) {
      if (this._fragmented) {
        const error = this.createError(
          RangeError,
          `invalid opcode ${this._opcode}`,
          true,
          1002,
          'WS_ERR_INVALID_OPCODE'
        );

        cb(error);
        return;
      }

      this._compressed = compressed;
    } else if (this._opcode > 0x07 && this._opcode < 0x0b) {
      if (!this._fin) {
        const error = this.createError(
          RangeError,
          'FIN must be set',
          true,
          1002,
          'WS_ERR_EXPECTED_FIN'
        );

        cb(error);
        return;
      }

      if (compressed) {
        const error = this.createError(
          RangeError,
          'RSV1 must be clear',
          true,
          1002,
          'WS_ERR_UNEXPECTED_RSV_1'
        );

        cb(error);
        return;
      }

      if (
        this._payloadLength > 0x7d ||
        (this._opcode === 0x08 && this._payloadLength === 1)
      ) {
        const error = this.createError(
          RangeError,
          `invalid payload length ${this._payloadLength}`,
          true,
          1002,
          'WS_ERR_INVALID_CONTROL_PAYLOAD_LENGTH'
        );

        cb(error);
        return;
      }
    } else {
      const error = this.createError(
        RangeError,
        `invalid opcode ${this._opcode}`,
        true,
        1002,
        'WS_ERR_INVALID_OPCODE'
      );

      cb(error);
      return;
    }

    if (!this._fin && !this._fragmented) this._fragmented = this._opcode;
    this._masked = (buf[1] & 0x80) === 0x80;

    if (this._isServer) {
      if (!this._masked) {
        const error = this.createError(
          RangeError,
          'MASK must be set',
          true,
          1002,
          'WS_ERR_EXPECTED_MASK'
        );

        cb(error);
        return;
      }
    } else if (this._masked) {
      const error = this.createError(
        RangeError,
        'MASK must be clear',
        true,
        1002,
        'WS_ERR_UNEXPECTED_MASK'
      );

      cb(error);
      return;
    }

    if (this._payloadLength === 126) this._state = GET_PAYLOAD_LENGTH_16;
    else if (this._payloadLength === 127) this._state = GET_PAYLOAD_LENGTH_64;
    else this.haveLength(cb);
  }

  /**
   * Gets extended payload length (7+16).
   *
   * @param {Function} cb Callback
   * @private
   */
  getPayloadLength16(cb) {
    if (this._bufferedBytes < 2) {
      this._loop = false;
      return;
    }

    this._payloadLength = this.consume(2).readUInt16BE(0);
    this.haveLength(cb);
  }

  /**
   * Gets extended payload length (7+64).
   *
   * @param {Function} cb Callback
   * @private
   */
  getPayloadLength64(cb) {
    if (this._bufferedBytes < 8) {
      this._loop = false;
      return;
    }

    const buf = this.consume(8);
    const num = buf.readUInt32BE(0);

    //
    // The maximum safe integer in JavaScript is 2^53 - 1. An error is returned
    // if payload length is greater than this number.
    //
    if (num > Math.pow(2, 53 - 32) - 1) {
      const error = this.createError(
        RangeError,
        'Unsupported WebSocket frame: payload length > 2^53 - 1',
        false,
        1009,
        'WS_ERR_UNSUPPORTED_DATA_PAYLOAD_LENGTH'
      );

      cb(error);
      return;
    }

    this._payloadLength = num * Math.pow(2, 32) + buf.readUInt32BE(4);
    this.haveLength(cb);
  }

  /**
   * Payload length has been read.
   *
   * @param {Function} cb Callback
   * @private
   */
  haveLength(cb) {
    if (this._payloadLength && this._opcode < 0x08) {
      this._totalPayloadLength += this._payloadLength;
      if (this._totalPayloadLength > this._maxPayload && this._maxPayload > 0) {
        const error = this.createError(
          RangeError,
          'Max payload size exceeded',
          false,
          1009,
          'WS_ERR_UNSUPPORTED_MESSAGE_LENGTH'
        );

        cb(error);
        return;
      }
    }

    if (this._masked) this._state = GET_MASK;
    else this._state = GET_DATA;
  }

  /**
   * Reads mask bytes.
   *
   * @private
   */
  getMask() {
    if (this._bufferedBytes < 4) {
      this._loop = false;
      return;
    }

    this._mask = this.consume(4);
    this._state = GET_DATA;
  }

  /**
   * Reads data bytes.
   *
   * @param {Function} cb Callback
   * @private
   */
  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);
  }

  /**
   * Decompresses data.
   *
   * @param {Buffer} data Compressed data
   * @param {Function} cb Callback
   * @private
   */
  decompress(data, cb) {
    const perMessageDeflate = this._extensions[PerMessageDeflate.extensionName];

    perMessageDeflate.decompress(data, this._fin, (err, buf) => {
      if (err) return cb(err);

      if (buf.length) {
        this._messageLength += buf.length;
        if (this._messageLength > this._maxPayload && this._maxPayload > 0) {
          const error = this.createError(
            RangeError,
            'Max payload size exceeded',
            false,
            1009,
            'WS_ERR_UNSUPPORTED_MESSAGE_LENGTH'
          );

          cb(error);
          return;
        }

        this._fragments.push(buf);
      }

      this.dataMessage(cb);
      if (this._state === GET_INFO) this.startLoop(cb);
    });
  }

  /**
   * Handles a data message.
   *
   * @param {Function} cb Callback
   * @private
   */
  dataMessage(cb) {
    if (!this._fin) {
      this._state = GET_INFO;
      return;
    }

    const messageLength = this._messageLength;
    const fragments = this._fragments;

    this._totalPayloadLength = 0;
    this._messageLength = 0;
    this._fragmented = 0;
    this._fragments = [];

    if (this._opcode === 2) {
      let data;

      if (this._binaryType === 'nodebuffer') {
        data = concat(fragments, messageLength);
      } else if (this._binaryType === 'arraybuffer') {
        data = toArrayBuffer(concat(fragments, messageLength));
      } else {
        data = fragments;
      }

      //
      // If the state is `INFLATING`, it means that the frame data was
      // decompressed asynchronously, so there is no need to defer the event
      // as it will be emitted asynchronously anyway.
      //
      if (this._state === INFLATING || this._allowSynchronousEvents) {
        this.emit('message', data, true);
        this._state = GET_INFO;
      } else {
        this._state = DEFER_EVENT;
        setImmediate(() => {
          this.emit('message', data, true);
          this._state = GET_INFO;
          this.startLoop(cb);
        });
      }
    } else {
      const buf = concat(fragments, messageLength);

      if (!this._skipUTF8Validation && !isValidUTF8(buf)) {
        const error = this.createError(
          Error,
          'invalid UTF-8 sequence',
          true,
          1007,
          'WS_ERR_INVALID_UTF8'
        );

        cb(error);
        return;
      }

      if (this._state === INFLATING || this._allowSynchronousEvents) {
        this.emit('message', buf, false);
        this._state = GET_INFO;
      } else {
        this._state = DEFER_EVENT;
        setImmediate(() => {
          this.emit('message', buf, false);
          this._state = GET_INFO;
          this.startLoop(cb);
        });
      }
    }
  }

  /**
   * Handles a control message.
   *
   * @param {Buffer} data Data to handle
   * @return {(Error|RangeError|undefined)} A possible error
   * @private
   */
  controlMessage(data, cb) {
    if (this._opcode === 0x08) {
      if (data.length === 0) {
        this._loop = false;
        this.emit('conclude', 1005, EMPTY_BUFFER);
        this.end();
      } else {
        const code = data.readUInt16BE(0);

        if (!isValidStatusCode(code)) {
          const error = this.createError(
            RangeError,
            `invalid status code ${code}`,
            true,
            1002,
            'WS_ERR_INVALID_CLOSE_CODE'
          );

          cb(error);
          return;
        }

        const buf = new FastBuffer(
          data.buffer,
          data.byteOffset + 2,
          data.length - 2
        );

        if (!this._skipUTF8Validation && !isValidUTF8(buf)) {
          const error = this.createError(
            Error,
            'invalid UTF-8 sequence',
            true,
            1007,
            'WS_ERR_INVALID_UTF8'
          );

          cb(error);
          return;
        }

        this._loop = false;
        this.emit('conclude', code, buf);
        this.end();
      }

      this._state = GET_INFO;
      return;
    }

    if (this._allowSynchronousEvents) {
      this.emit(this._opcode === 0x09 ? 'ping' : 'pong', data);
      this._state = GET_INFO;
    } else {
      this._state = DEFER_EVENT;
      setImmediate(() => {
        this.emit(this._opcode === 0x09 ? 'ping' : 'pong', data);
        this._state = GET_INFO;
        this.startLoop(cb);
      });
    }
  }

  /**
   * Builds an error object.
   *
   * @param {function(new:Error|RangeError)} ErrorCtor The error constructor
   * @param {String} message The error message
   * @param {Boolean} prefix Specifies whether or not to add a default prefix to
   *     `message`
   * @param {Number} statusCode The status code
   * @param {String} errorCode The exposed error code
   * @return {(Error|RangeError)} The error
   * @private
   */
  createError(ErrorCtor, message, prefix, statusCode, errorCode) {
    this._loop = false;
    this._errored = true;

    const err = new ErrorCtor(
      prefix ? `Invalid WebSocket frame: ${message}` : message
    );

    Error.captureStackTrace(err, this.createError);
    err.code = errorCode;
    err[kStatusCode] = statusCode;
    return err;
  }
}

module.exports = Receiver;