gRPC responses doesn't support setting up custom headers

[vronin]

Proposal

gRPC supports setting custom response HTTP headers.

I attempted to implement this based on an example in the README, specifically the section on setting up headers:

{
  "request" : {
    "urlPath" : "/com.example.grpc.GreetingService/greeting",
    "method" : "POST",
    "bodyPatterns" : [{
      "equalToJson" : "{ \"name\":  \"Tom\" }"
    }]
  },
  "response" : {
    "status" : 200,
    "body" : "{\n  \"greeting\": \"Hi Tom\"\n}",
    "headers" : {
      "grpc-status-name" : "OK"
    }
  }
}

I modified the headers key and value to include a custom header. While the header tag was accepted (i.e., WireMock didn't throw any errors), it doesn't appear in the response.

I reviewed the wiremock-grpc-extension codebase but couldn't locate code or tests handling this behavior. That said, I might have missed something since I'm not very familiar with the codebase.

Supporting custom headers in gRPC responses would be useful.

BTW. Please let me know if I am missing anything.

Reproduction steps

1. Create a mapping with custom headers in the response tag.
2. Have a client doing gRPC call (resulting in UnaryServerCall)
3. Check the response headers on the client side.
4. Observed headers:
   • content-type: application/grpc
   • grpc-encoding: identity
   • grpc-accept-encoding: gzip
   • grpc-status: 0

However, custom headers are not present in the response.

References

No response