code: function onMessage(obj) {
      var id = obj.id;
      if (!self._matchesPrefix(id)) {
        debug('discarding unscoped message %s', id);
        return;
      }
      var cb = self._registry.get(id);
      if (cb) {
        process.nextTick(function () {
          debug('received message %s', id);
          // Ensure that the initial callback gets called asynchronously, even
          // for completely synchronous transports (otherwise the number of
          // pending requests will sometimes be inconsistent between stateful and
          // stateless transports).
          cb(null, Buffer.concat(obj.payload), self._adapter);
        });
      }
    }
docs: Callback used after a connection has been established.