"proto: no coders for int" printed whenever a gRPC error is returned over grpc-gateway.

[johanbrandhorst]

I've been able to reproduce this using the very example server suggested in the main README.md. Steps to reproduce:

1. Compile grpc-gateway-out and go_out of the example echo service.
2. Using the example server implementation, use go run to start the server. It will complain about not being able to connect to your backend gRPC server, but that's fine.
3. Send a simple cURL request to the HTTP API

curl -X POST http://localhost:8080/v1/example/echo

In the console of the grpc-gateway server you will get the proto: no coders for int message.

The source of the message is in https://github.com/golang/protobuf/blob/4bd1920723d7b7c925de087aa32e2187708897f7/proto/properties.go#L349.

The reason for it being printed appears to be that grpc-gateway creates an error struct with a Code of type int.

See

grpc-gateway/runtime/errors.go

Line 67 in 84398b9

Code int `protobuf:"bytes,2,name=code" json:"code"`

.

This issue has been encountered in several places downstream already: gogo/protobuf#178 and cockroachdb/cockroach#10484 at the least.

[tmc]

PR #256 addresses this.