/**
   * Handles Socks v4 handshake response.
   * @param data
   */
  private handleSocks4FinalHandshakeResponse() {
    const data = this._receiveBuffer.get(8);

    if (data[1] !== Socks4Response.Granted) {
      this._closeSocket(
        `${ERRORS.Socks4ProxyRejectedConnection} - (${Socks4Response[data[1]]})`
      );
    } else {
      // Bind response
      if (SocksCommand[this._options.command] === SocksCommand.bind) {
        const buff = SmartBuffer.fromBuffer(data);
        buff.readOffset = 2;

        const remoteHost: SocksRemoteHost = {
          port: buff.readUInt16BE(),
          host: ip.fromLong(buff.readUInt32BE())
        };

        // If host is 0.0.0.0, set to proxy host.
        if (remoteHost.host === '0.0.0.0') {
          remoteHost.host = this._options.proxy.ipaddress;
        }
        this.state = SocksClientState.BoundWaitingForConnection;
        this.emit('bound', { socket: this._socket, remoteHost });

        // Connect response
      } else {
        this.state = SocksClientState.Established;
        this.removeInternalSocketHandlers();
        this.emit('established', { socket: this._socket });
      }
    }
  }

  /**
   * Parses a SOCKS UDP frame.
   * @param data
   */
  static parseUDPFrame(data: Buffer): SocksUDPFrameDetails {
    const buff = SmartBuffer.fromBuffer(data);
    buff.readOffset = 2;

    const frameNumber = buff.readUInt8();
    const hostType: Socks5HostType = buff.readUInt8();
    let remoteHost;

    if (hostType === Socks5HostType.IPv4) {
      remoteHost = ip.fromLong(buff.readUInt32BE());
    } else if (hostType === Socks5HostType.IPv6) {
      remoteHost = ip.toString(buff.readBuffer(16));
    } else {
      remoteHost = buff.readString(buff.readUInt8());
    }

    const remotePort = buff.readUInt16BE();

    return {
      frameNumber,
      remoteHost: {
        host: remoteHost,
        port: remotePort
      },
      data: buff.readBuffer()
    };
  }

  /**
   * Sends Socks v5 user & password auth handshake.
   *
   * Note: No auth and user/pass are currently supported.
   */
  private sendSocks5UserPassAuthentication() {
    const userId = this._options.proxy.userId || '';
    const password = this._options.proxy.password || '';

    const buff = new SmartBuffer();
    buff.writeUInt8(0x01);
    buff.writeUInt8(Buffer.byteLength(userId));
    buff.writeString(userId);
    buff.writeUInt8(Buffer.byteLength(password));
    buff.writeString(password);

    this._nextRequiredPacketBufferSize =
      SOCKS_INCOMING_PACKET_SIZES.Socks5UserPassAuthenticationResponse;
    this._socket.write(buff.toBuffer());
    this.state = SocksClientState.SentAuthentication;
  }

  /**
   * Sends initial Socks v5 handshake request.
   */
  private sendSocks5InitialHandshake() {
    const buff = new SmartBuffer();
    buff.writeUInt8(0x05);

    // We should only tell the proxy we support user/pass auth if auth info is actually provided.
    // Note: As of Tor v0.3.5.7+, if user/pass auth is an option from the client, by default it will always take priority.
    if (this._options.proxy.userId || this._options.proxy.password) {
      buff.writeUInt8(2);
      buff.writeUInt8(Socks5Auth.NoAuth);
      buff.writeUInt8(Socks5Auth.UserPass);
    } else {
      buff.writeUInt8(1);
      buff.writeUInt8(Socks5Auth.NoAuth);
    }

    this._nextRequiredPacketBufferSize =
      SOCKS_INCOMING_PACKET_SIZES.Socks5InitialHandshakeResponse;
    this._socket.write(buff.toBuffer());
    this.state = SocksClientState.SentInitialHandshake;
  }

  /**
   * Handles Socks v4 incoming connection request (BIND)
   * @param data
   */
  private handleSocks4IncomingConnectionResponse() {
    const data = this._receiveBuffer.get(8);

    if (data[1] !== Socks4Response.Granted) {
      this._closeSocket(
        `${ERRORS.Socks4ProxyRejectedIncomingBoundConnection} - (${
          Socks4Response[data[1]]
        })`
      );
    } else {
      const buff = SmartBuffer.fromBuffer(data);
      buff.readOffset = 2;

      const remoteHost: SocksRemoteHost = {
        port: buff.readUInt16BE(),
        host: ip.fromLong(buff.readUInt32BE())
      };

      this.state = SocksClientState.Established;
      this.removeInternalSocketHandlers();
      this.emit('established', { socket: this._socket, remoteHost });
    }
  }

  /**
   * Handles Socks v5 incoming connection request (BIND).
   */
  private handleSocks5IncomingConnectionResponse() {
    // Peek at available data (we need at least 5 bytes to get the hostname length)
    const header = this._receiveBuffer.peek(5);

    if (header[0] !== 0x05 || header[1] !== Socks5Response.Granted) {
      this._closeSocket(
        `${ERRORS.Socks5ProxyRejectedIncomingBoundConnection} - ${
          Socks5Response[header[1]]
        }`
      );
    } else {
      // Read address type
      const addressType = header[3];

      let remoteHost: SocksRemoteHost;
      let buff: SmartBuffer;

      // IPv4
      if (addressType === Socks5HostType.IPv4) {
        // Check if data is available.
        const dataNeeded = SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseIPv4;
        if (this._receiveBuffer.length < dataNeeded) {
          this._nextRequiredPacketBufferSize = dataNeeded;
          return;
        }

        buff = SmartBuffer.fromBuffer(
          this._receiveBuffer.get(dataNeeded).slice(4)
        );

        remoteHost = {
          host: ip.fromLong(buff.readUInt32BE()),
          port: buff.readUInt16BE()
        };

        // If given host is 0.0.0.0, assume remote proxy ip instead.
        if (remoteHost.host === '0.0.0.0') {
          remoteHost.host = this._options.proxy.ipaddress;
        }

        // Hostname
      } else if (addressType === Socks5HostType.Hostname) {
        const hostLength = header[4];
        const dataNeeded = SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseHostname(
          hostLength
        ); // header + host length + port

        // Check if data is available.
        if (this._receiveBuffer.length < dataNeeded) {
          this._nextRequiredPacketBufferSize = dataNeeded;
          return;
        }

        buff = SmartBuffer.fromBuffer(
          this._receiveBuffer.get(dataNeeded).slice(5) // Slice at 5 to skip host length
        );

        remoteHost = {
          host: buff.readString(hostLength),
          port: buff.readUInt16BE()
        };
        // IPv6
      } else if (addressType === Socks5HostType.IPv6) {
        // Check if data is available.
        const dataNeeded = SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseIPv6;
        if (this._receiveBuffer.length < dataNeeded) {
          this._nextRequiredPacketBufferSize = dataNeeded;
          return;
        }

        buff = SmartBuffer.fromBuffer(
          this._receiveBuffer.get(dataNeeded).slice(4)
        );

        remoteHost = {
          host: ip.toString(buff.readBuffer(16)),
          port: buff.readUInt16BE()
        };
      }

      this.state = SocksClientState.Established;
      this.removeInternalSocketHandlers();
      this.emit('established', { socket: this._socket, remoteHost });
    }
  }

  /**
   * Handles Socks v5 final handshake response.
   * @param data
   */
  private handleSocks5FinalHandshakeResponse() {
    // Peek at available data (we need at least 5 bytes to get the hostname length)
    const header = this._receiveBuffer.peek(5);

    if (header[0] !== 0x05 || header[1] !== Socks5Response.Granted) {
      this._closeSocket(
        `${ERRORS.InvalidSocks5FinalHandshakeRejected} - ${
          Socks5Response[header[1]]
        }`
      );
    } else {
      // Read address type
      const addressType = header[3];

      let remoteHost: SocksRemoteHost;
      let buff: SmartBuffer;

      // IPv4
      if (addressType === Socks5HostType.IPv4) {
        // Check if data is available.
        const dataNeeded = SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseIPv4;
        if (this._receiveBuffer.length < dataNeeded) {
          this._nextRequiredPacketBufferSize = dataNeeded;
          return;
        }

        buff = SmartBuffer.fromBuffer(
          this._receiveBuffer.get(dataNeeded).slice(4)
        );

        remoteHost = {
          host: ip.fromLong(buff.readUInt32BE()),
          port: buff.readUInt16BE()
        };

        // If given host is 0.0.0.0, assume remote proxy ip instead.
        if (remoteHost.host === '0.0.0.0') {
          remoteHost.host = this._options.proxy.ipaddress;
        }

        // Hostname
      } else if (addressType === Socks5HostType.Hostname) {
        const hostLength = header[4];
        const dataNeeded = SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseHostname(
          hostLength
        ); // header + host length + host + port

        // Check if data is available.
        if (this._receiveBuffer.length < dataNeeded) {
          this._nextRequiredPacketBufferSize = dataNeeded;
          return;
        }

        buff = SmartBuffer.fromBuffer(
          this._receiveBuffer.get(dataNeeded).slice(5) // Slice at 5 to skip host length
        );

        remoteHost = {
          host: buff.readString(hostLength),
          port: buff.readUInt16BE()
        };
        // IPv6
      } else if (addressType === Socks5HostType.IPv6) {
        // Check if data is available.
        const dataNeeded = SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseIPv6;
        if (this._receiveBuffer.length < dataNeeded) {
          this._nextRequiredPacketBufferSize = dataNeeded;
          return;
        }

        buff = SmartBuffer.fromBuffer(
          this._receiveBuffer.get(dataNeeded).slice(4)
        );

        remoteHost = {
          host: ip.toString(buff.readBuffer(16)),
          port: buff.readUInt16BE()
        };
      }

      // We have everything we need
      this.state = SocksClientState.ReceivedFinalResponse;

      // If using CONNECT, the client is now in the established state.
      if (SocksCommand[this._options.command] === SocksCommand.connect) {
        this.state = SocksClientState.Established;
        this.removeInternalSocketHandlers();
        this.emit('established', { socket: this._socket });
      } else if (SocksCommand[this._options.command] === SocksCommand.bind) {
        /* If using BIND, the Socks client is now in BoundWaitingForConnection state.
           This means that the remote proxy server is waiting for a remote connection to the bound port. */
        this.state = SocksClientState.BoundWaitingForConnection;
        this._nextRequiredPacketBufferSize =
          SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseHeader;
        this.emit('bound', { socket: this._socket, remoteHost });
        /*
//.........这里部分代码省略.........

  /**
   * Sends Socks v5 final handshake request.
   */
  private sendSocks5CommandRequest() {
    const buff = new SmartBuffer();

    buff.writeUInt8(0x05);
    buff.writeUInt8(SocksCommand[this._options.command]);
    buff.writeUInt8(0x00);

    // ipv4, ipv6, domain?
    if (net.isIPv4(this._options.destination.host)) {
      buff.writeUInt8(Socks5HostType.IPv4);
      buff.writeBuffer(ip.toBuffer(this._options.destination.host));
    } else if (net.isIPv6(this._options.destination.host)) {
      buff.writeUInt8(Socks5HostType.IPv6);
      buff.writeBuffer(ip.toBuffer(this._options.destination.host));
    } else {
      buff.writeUInt8(Socks5HostType.Hostname);
      buff.writeUInt8(this._options.destination.host.length);
      buff.writeString(this._options.destination.host);
    }
    buff.writeUInt16BE(this._options.destination.port);

    this._nextRequiredPacketBufferSize =
      SOCKS_INCOMING_PACKET_SIZES.Socks5ResponseHeader;
    this._socket.write(buff.toBuffer());
    this.state = SocksClientState.SentFinalHandshake;
  }

  /**
   * Sends initial Socks v4 handshake request.
   */
  private sendSocks4InitialHandshake() {
    const userId = this._options.proxy.userId || '';

    const buff = new SmartBuffer();
    buff.writeUInt8(0x04);
    buff.writeUInt8(SocksCommand[this._options.command]);
    buff.writeUInt16BE(this._options.destination.port);

    // Socks 4 (IPv4)
    if (net.isIPv4(this._options.destination.host)) {
      buff.writeBuffer(ip.toBuffer(this._options.destination.host));
      buff.writeStringNT(userId);
      // Socks 4a (hostname)
    } else {
      buff.writeUInt8(0x00);
      buff.writeUInt8(0x00);
      buff.writeUInt8(0x00);
      buff.writeUInt8(0x01);
      buff.writeStringNT(userId);
      buff.writeStringNT(this._options.destination.host);
    }

    this._nextRequiredPacketBufferSize =
      SOCKS_INCOMING_PACKET_SIZES.Socks4Response;
    this._socket.write(buff.toBuffer());
  }

  /**
   * Creates a SOCKS UDP Frame.
   * @param options
   */
  static createUDPFrame(options: SocksUDPFrameDetails): Buffer {
    const buff = new SmartBuffer();
    buff.writeUInt16BE(0);
    buff.writeUInt8(options.frameNumber || 0);

    // IPv4/IPv6/Hostname
    if (net.isIPv4(options.remoteHost.host)) {
      buff.writeUInt8(Socks5HostType.IPv4);
      buff.writeUInt32BE(ip.toLong(options.remoteHost.host));
    } else if (net.isIPv6(options.remoteHost.host)) {
      buff.writeUInt8(Socks5HostType.IPv6);
      buff.writeBuffer(ip.toBuffer(options.remoteHost.host));
    } else {
      buff.writeUInt8(Socks5HostType.Hostname);
      buff.writeUInt8(Buffer.byteLength(options.remoteHost.host));
      buff.writeString(options.remoteHost.host);
    }

    // Port
    buff.writeUInt16BE(options.remoteHost.port);

    // Data
    buff.writeBuffer(options.data);

    return buff.toBuffer();
  }