Deserializing feed: missing optional fields return 0 value in node.js

[nselikoff]

Given a feed that does NOT have an optional field (e.g. vehicle speed), the value returned when getting this value is 0. So there's no way to differentiate "not included" from an actual value of zero.

const feed = realtime.transit_realtime.FeedMessage.decode(protobuf);
feed.entity.forEach((entity) => {
  if (entity.vehicle) {
    const speed = entity.vehicle.position.speed; // speed is 0
  }
});

This may be similar to #52

[barbeau]

@nselikoff Thanks for the report! In Java bindings there is a hasSpeed() method that you can call to determine if the field has been set, but I'm not as familiar with the Node.js bindings. I'm assuming there isn't an equivalent?

[nselikoff]

@barbeau good question - just looked and there is not a similar method. However, I found a workaround using realtime.transit_realtime.Position.toObject:

const feed = realtime.transit_realtime.FeedMessage.decode(protobuf);
feed.entity.forEach((entity) => {
  if (entity.vehicle) {
    // using `toObject` only adds properties that exist in the protobuf
    const position = realtime.transit_realtime.Position.toObject(entity.vehicle.position);
    // so speed will be undefined if not included in the protobuf
    const speed = position.speed; 
    // maybe you want it null
    // const speed = position.speed || null;
  }
});