receiver.js

'use strict';

const stream = require('stream');

const PerMessageDeflate = require('./permessage-deflate');
const bufferUtil = require('./buffer-util');
const validation = require('./validation');
const constants = require('./constants');

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;

/**
 * HyBi Receiver implementation.
 *
 * @extends stream.Writable
 */
class Receiver extends stream.Writable {
  /**
   * Creates a Receiver instance.
   *
   * @param {String} binaryType The type for binary data
   * @param {Object} extensions An object containing the negotiated extensions
   * @param {Number} maxPayload The maximum allowed message length
   */
  constructor(binaryType, extensions, maxPayload) {
    super();

    this._binaryType = binaryType || constants.BINARY_TYPES[0];
    this[constants.kWebSocket] = undefined;
    this._extensions = extensions || {};
    this._maxPayload = maxPayload | 0;

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

  /**
   * 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
   */
  _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] = buf.slice(n);
      return buf.slice(0, n);
    }

    const dst = Buffer.allocUnsafe(n);

    do {
      const buf = this._buffers[0];

      if (n >= buf.length) {
        this._buffers.shift().copy(dst, dst.length - n);
      } else {
        buf.copy(dst, dst.length - n, 0, n);
        this._buffers[0] = buf.slice(n);
      }

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

    return dst;
  }

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

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

    cb(err);
  }

  /**
   * Reads the first two bytes of a frame.
   *
   * @return {(RangeError|undefined)} A possible error
   * @private
   */
  getInfo() {
    if (this._bufferedBytes < 2) {
      this._loop = false;
      return;
    }

    const buf = this.consume(2);

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

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

    if (compressed && !this._extensions[PerMessageDeflate.extensionName]) {
      this._loop = false;
      return error(RangeError, 'RSV1 must be clear', true, 1002);
    }

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

    if (this._opcode === 0x00) {
      if (compressed) {
        this._loop = false;
        return error(RangeError, 'RSV1 must be clear', true, 1002);
      }

      if (!this._fragmented) {
        this._loop = false;
        return error(RangeError, 'invalid opcode 0', true, 1002);
      }

      this._opcode = this._fragmented;
    } else if (this._opcode === 0x01 || this._opcode === 0x02) {
      if (this._fragmented) {
        this._loop = false;
        return error(RangeError, `invalid opcode ${this._opcode}`, true, 1002);
      }

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

      if (compressed) {
        this._loop = false;
        return error(RangeError, 'RSV1 must be clear', true, 1002);
      }

      if (this._payloadLength > 0x7d) {
        this._loop = false;
        return error(
          RangeError,
          `invalid payload length ${this._payloadLength}`,
          true,
          1002
        );
      }
    } else {
      this._loop = false;
      return error(RangeError, `invalid opcode ${this._opcode}`, true, 1002);
    }

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

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

  /**
   * Gets extended payload length (7+16).
   *
   * @return {(RangeError|undefined)} A possible error
   * @private
   */
  getPayloadLength16() {
    if (this._bufferedBytes < 2) {
      this._loop = false;
      return;
    }

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

  /**
   * Gets extended payload length (7+64).
   *
   * @return {(RangeError|undefined)} A possible error
   * @private
   */
  getPayloadLength64() {
    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) {
      this._loop = false;
      return error(
        RangeError,
        'Unsupported WebSocket frame: payload length > 2^53 - 1',
        false,
        1009
      );
    }

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

  /**
   * Payload length has been read.
   *
   * @return {(RangeError|undefined)} A possible error
   * @private
   */
  haveLength() {
    if (this._payloadLength && this._opcode < 0x08) {
      this._totalPayloadLength += this._payloadLength;
      if (this._totalPayloadLength > this._maxPayload && this._maxPayload > 0) {
        this._loop = false;
        return error(RangeError, 'Max payload size exceeded', false, 1009);
      }
    }

    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
   * @return {(Error|RangeError|undefined)} A possible error
   * @private
   */
  getData(cb) {
    var data = constants.EMPTY_BUFFER;

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

      data = this.consume(this._payloadLength);
      if (this._masked) bufferUtil.unmask(data, this._mask);
    }

    if (this._opcode > 0x07) return this.controlMessage(data);

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

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

    return this.dataMessage();
  }

  /**
   * 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) {
          return cb(
            error(RangeError, 'Max payload size exceeded', false, 1009)
          );
        }

        this._fragments.push(buf);
      }

      const er = this.dataMessage();
      if (er) return cb(er);

      this.startLoop(cb);
    });
  }

  /**
   * Handles a data message.
   *
   * @return {(Error|undefined)} A possible error
   * @private
   */
  dataMessage() {
    if (this._fin) {
      const messageLength = this._messageLength;
      const fragments = this._fragments;

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

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

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

        this.emit('message', data);
      } else {
        const buf = toBuffer(fragments, messageLength);

        if (!validation.isValidUTF8(buf)) {
          this._loop = false;
          return error(Error, 'invalid UTF-8 sequence', true, 1007);
        }

        this.emit('message', buf.toString());
      }
    }

    this._state = GET_INFO;
  }

  /**
   * Handles a control message.
   *
   * @param {Buffer} data Data to handle
   * @return {(Error|RangeError|undefined)} A possible error
   * @private
   */
  controlMessage(data) {
    if (this._opcode === 0x08) {
      this._loop = false;

      if (data.length === 0) {
        this.emit('conclude', 1005, '');
        this.end();
      } else if (data.length === 1) {
        return error(RangeError, 'invalid payload length 1', true, 1002);
      } else {
        const code = data.readUInt16BE(0);

        if (!validation.isValidStatusCode(code)) {
          return error(RangeError, `invalid status code ${code}`, true, 1002);
        }

        const buf = data.slice(2);

        if (!validation.isValidUTF8(buf)) {
          return error(Error, 'invalid UTF-8 sequence', true, 1007);
        }

        this.emit('conclude', code, buf.toString());
        this.end();
      }

      this._state = GET_INFO;
      return;
    }

    if (this._opcode === 0x09) this.emit('ping', data);
    else this.emit('pong', data);

    this._state = GET_INFO;
  }
}

module.exports = Receiver;

/**
 * Builds an error object.
 *
 * @param {(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
 * @return {(Error|RangeError)} The error
 * @private
 */
function error(ErrorCtor, message, prefix, statusCode) {
  const err = new ErrorCtor(
    prefix ? `Invalid WebSocket frame: ${message}` : message
  );

  Error.captureStackTrace(err, error);
  err[constants.kStatusCode] = statusCode;
  return err;
}

/**
 * Makes a buffer from a list of fragments.
 *
 * @param {Buffer[]} fragments The list of fragments composing the message
 * @param {Number} messageLength The length of the message
 * @return {Buffer}
 * @private
 */
function toBuffer(fragments, messageLength) {
  if (fragments.length === 1) return fragments[0];
  if (fragments.length > 1) return bufferUtil.concat(fragments, messageLength);
  return constants.EMPTY_BUFFER;
}

/**
 * Converts a buffer to an `ArrayBuffer`.
 *
 * @param {Buffer} buf The buffer to convert
 * @return {ArrayBuffer} Converted buffer
 */
function toArrayBuffer(buf) {
  if (buf.byteLength === buf.buffer.byteLength) {
    return buf.buffer;
  }

  return buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength);
}