Return non protobuf format from a ::grpc::Server

[cur...@gmail.com]

im trying to find an example of calling ServerBuilder::RegisterService with a custom Service that can read / write raw data. 

My use case is that i need an extra endpoint that does some metric reporting that responds with a custom format when pulled. 

Ideally i would like to reuse the server part of GRPC (in addition to some grpc native Services) for serving this custom endpoint.

Thanks!

Curtis

[Curtis Mahieu]

I can get close to having it work by looking at how Flatbuffer support was added by doing something like this:

//Header file:

struct Thing1{

};

struct Thing2 : public Thing1 {

};

namespace helloworld {

// The greeting service definition.

class Greeter GRPC_FINAL {

public:

  class Service : public ::grpc::Service {

   public:

    Service();

    virtual ~Service() = default;

    virtual ::grpc::Status SayHello(::grpc::ServerContext*, const Thing1*, Thing2*){

        return ::grpc::Status::OK;

    }

  };

};

}  // namespace helloworld

namespace grpc {

    template<class T>

    class SerializationTraits<T, typename std::enable_if<std::is_base_of<Thing1, T>::value>::type> {

    public:

        // The type we're passing here is a BufferRef, which is already serialized

        // FlatBuffer data, which then gets passed to GRPC.

        static grpc::Status Serialize(const T &,

                                      grpc_byte_buffer **buffer,

                                      bool *own_buffer) {

            auto slice = gpr_slice_from_static_string("Hello!World!");

           // *buffer = grpc_raw_byte_buffer_create(&slice, 1);  <- This line make its not work at all!!!!!!

            grpc_slice_unref(slice);

            *own_buffer = true;

            return grpc::Status();

        }

        // There is no de-serialization step in FlatBuffers, so we just receive

        // the data from GRPC.

        static grpc::Status Deserialize(grpc_byte_buffer *buffer, T *) {

            grpc_byte_buffer_destroy(buffer);

            return grpc::Status();

        }

    };

}  // namespace grpc;

namespace helloworld {

    Greeter::Service::Service() {

        AddMethod(new ::grpc::RpcServiceMethod(

                "/bob",

                ::grpc::RpcMethod::NORMAL_RPC,

                new ::grpc::RpcMethodHandler<Greeter::Service, Thing1, Thing2>(std::mem_fn(&Greeter::Service::SayHello), this)));

    }

}  // namespace helloworld

if i use the grpc_cli tool i can get an empty message back when the *buffer line is disabled: 

grpc_cli call localhost:8080 /bob --binary_input=true --infile=frame.bin --outfile=out.bin

Method name not found

connecting to localhost:8080

Rpc succeeded with OK status

but then its enabled i get this:

grpc_cli call localhost:8080 /bob --binary_input=true --infile=./frame.bin --outfile=./out.bin 

Method name not found

connecting to localhost:8080

Method name not found

I can see in the debugger that its going to the entire flow like i expect for both cases, but how do i get it to echo back the raw data????