Unmarshal response from streaming

[pavolloffay]

🚀 Feature

The streaming response is wrapped into result object (see #1254, applies for v1 and v2). This makes it impossible to unmarshal (via JSONPb) the response body into protoc generated objects (MyResponse) in this case. The response can be unmarshalled only if the "result" envelope is removed (e.g. string manipulation).

message MyResponse {
  string message = 1;
}

service QueryService {
  rpc Get(Request) returns (stream MyResponse) {}
}

The response body looks like:

{
  "result": {
    "message": "hello"
}

Is there a way we could improve this? I have tried to define a proto message (see below) that could be used to remove the envelope.

message ResultWrapper {
  bytes result = 1;
// google.protobuf.Any result = 1; // does not work either bc the JSON does not have type annotation https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/any.proto#L110
}

[johanbrandhorst]

An alternative way to unmarshal it is to wrap your response message type in the envelope type manually:

type Envelope struct {
    Result *yourpb.YourType `json:"result"`
    Error *statuspb.Status `json:"error"`
}

[pavolloffay]

Yes I ended up doing something like this in our tests.

type resultWrapper struct {
	Result json.RawMessage `json:"result"`
}

I am not sure if using the proto type in the envelope would work as expected bc JSONPb should be used for unmarshalling.

[johanbrandhorst]

You can use jsonpb with a custom type too. Another alternative is to generate the openapiv2 spec and then generate a client using that, it should be able to parse the streaming messages too.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Prabhjot-Sethi]

An alternative way to unmarshal it is to wrap your response message type in the envelope type manually:

type Envelope struct {
    Result *yourpb.YourType `json:"result"`
    Error *statuspb.Status `json:"error"`
}

Is there any documentation on how error reporting per entry works, can server control how and what error goes to client.
usually grpc only provides mechanism to report error while starting the stream

[johanbrandhorst]

gRPC generally supports returning an error at any point in the streaming, so the grpc-gateway must also be able to return an error at any point in the streaming.