Inserting downstream trailers when upstream has no trailers

[snowp]

I was playing around with a filter that bridge grpc -> http/1.1 (opposite direction to the bridge that already exists in envoy) and I couldn't figure out how to insert trailers into a downstream h/2 response when the upstream response is h/1.1. It seems like the encodeTrailers cb is not invoked (presumably because the h/1.1 response doesn't have any trailers).

Hopefully I'm missing something and this is already doable. If not, would it be reasonable to add this functionality?

[mattklein123]

Unfortunately I don't think this is possible today. Have a look how addEncodedData() is implemented. We would want to add something similar along the lines of addEncodedTrailers(). I don't think it would be that hard to implement.