static _makePairingChannel()

in src/index.js [71:108]
32 lines of code
2 McCabe index (conditional complexity)

  static _makePairingChannel(wsUri, ConnectionClass, psk) {
    const socket = new WebSocket(wsUri);
    return new Promise((resolve, reject) => {
      // eslint-disable-next-line prefer-const
      let stopListening;
      const onConnectionError = async () => {
        stopListening();
        reject(new Error('Error while creating the pairing channel'));
      };
      const onFirstMessage = async event => {
        stopListening();
        try {
          // The channelserver echos back the channel id, and we use it as an
          // additional input to the TLS handshake via the "psk id" field.
          const {channelid: channelId} = JSON.parse(event.data);
          const pskId = utf8ToBytes(channelId);
          const connection = await ConnectionClass.create(psk, pskId, data => {
            // Send data by forwarding it via the channelserver websocket.
            // The TLS connection gives us `data` as raw bytes, but channelserver
            // expects b64urlsafe strings, because it wraps them in a JSON object envelope.
            socket.send(bytesToBase64url(data));
          });
          const instance = new this(channelId, psk, socket, connection);
          resolve(instance);
        } catch (err) {
          reject(err);
        }
      };
      stopListening = () => {
        socket.removeEventListener('close', onConnectionError);
        socket.removeEventListener('error', onConnectionError);
        socket.removeEventListener('message', onFirstMessage);
      };
      socket.addEventListener('close', onConnectionError);
      socket.addEventListener('error', onConnectionError);
      socket.addEventListener('message', onFirstMessage);
    });
  }