decode strips top-level __type_url.

[telackey]

It should be possible to "loop" a valid object through the codec, and the output be identical to the input. That is:

before = {
  __type_url: ‘my.Type’,
  payload: { _typeurl: ‘my.OtherType’, ..stuff.. }
}
after = codec.decode(codec.encode(before))
assert(after.equals(before))

But in practice, the top __type_url is stripped and after looks like:

{
  payload: { _typeurl: ‘my.OtherType’, ..stuff.. }
}

[tinchoz49]

This new codec-protobuf force you to have a root type for the encode/decode and type_url is only used for inner objects of type Any.

[tinchoz49]

Maybe if I know better what is the context to doing this we can find a workaround.

[telackey]

The first problem is just that it is unexpected, since an object should decode to the same thing it was before encoding.

In practical usage, it can show up a lot of ways, but the simplest is if I want to use a message I received in another message.

message A {
   a = 1;
   ...
}
message B {
   b = 1;
   Any payload = 2;
  ...
}

const a = { __type_url: 'my.A', a: 'a' }
send(codec.encode(a));

const incoming = codec.decode(a);
const b = {
  b: 'b',
  payload: incoming
};

send(codec.encode(b));  //ERROR missing __type_url.

In practice, this is problem for any of the 'Envelope' stuff. If you just want to see it break quickly, go here: https://github.com/wirelineio/incubator/blob/master/packages/credentials/src/party/party.test.js#L104

And add a codecLoop around pseudo.

[tinchoz49]

I understand. Yes, I think the problem here is related with having a rootTypeUrl is limiting us to use the codec-protobuf as normal encoder/decoder. Encode/decode any type of our schema.

I will prefer to always encode/decode using the __type_url as in your example and also returning it with the result.

And another thing, since we are in JavaScript I recomend to change __type_url to something like __typeurl like in apollo with the __typename

@richburdon