Transcoding HTTP request fails if accept header is "*/*

[the-destro]

Describe the bug
When exposing an endpoint via transcoding the accept header seems to require "application/json". This makes it a challenge when you are, say, adding a health check route and you don't have control over what the service sends as a request header.

To Reproduce

a minimal service definition

message HealthCheckRequest {
}

message HealthCheckResponse {
}

service Health {
  rpc Check(HealthCheckRequest) returns (HealthCheckResponse){
    option (google.api.http) = {
      get: "/_health"
    };
  }
}

2025-09-08T15:25:42.607 [error] ** (GRPC.Server.Adapters.ReportException) Exception raised while handling /_health:
** (GRPC.RPCError) Message is malformed.

[sleipnir]

Describe the bug When exposing an endpoint via transcoding the accept header seems to require "application/json". This makes it a challenge when you are, say, adding a health check route and you don't have control over what the service sends as a request header.

To Reproduce

a minimal service definition

message HealthCheckRequest {
}

message HealthCheckResponse {
}

service Health {
  rpc Check(HealthCheckRequest) returns (HealthCheckResponse){
    option (google.api.http) = {
      get: "/_health"
    };
  }
}

2025-09-08T15:25:42.607 [error] ** (GRPC.Server.Adapters.ReportException) Exception raised while handling /_health:
** (GRPC.RPCError) Message is malformed.

Hello, how are you?
The error doesn't seem to be related to what you said. How did you arrive at that conclusion about the Accept header? What does the request look like?

[sleipnir]

@the-destro Have you enabled transcoding on your server? See an example of a project that uses transcoding for health checks.https://github.com/eigr/spawn/blob/e1a0690bbe9559948c2088ba8feeb2c7ab5688a4/lib/_generated/spawn/actors/healthcheck.pb.ex#L730C5-L730C25

[sleipnir]

@the-destro I created a patch that can fix this, I'm waiting for the review to go ahead with it or not.

[sleipnir]

Close this by #436

[the-destro]

Thank you!