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I'm trying to build a gRPC client for LND in C++, starting with the WalletBalance function. I've never used gRPC before, and I use make instead of cmake, but according to the documentation this is supposed to be possible. I am using the pkg-config files that get installed with gRPC, but they are not working.

Here is what I've successfully been able to do so far.

  1. Build gRPC
  2. Compile lightning.proto
  3. Compile lightning.pb.cc and lightning.grpc.pb.cc
  4. Link with lightning.pb.cc.o (but not lightning.grpc.pb.cc.o)

This is my cpp file:

#include <iostream>
#include <string>

#include <grpcpp/grpcpp.h>

#include "lightning.grpc.pb.h"
#include "lightning.pb.h"

using namespace std;
using namespace lnrpc;

using grpc::Channel;
using grpc::ClientContext;
using grpc::Status;

class LightningClient
{
private:
    unique_ptr<Lightning::Stub> stub_;

public:
    LightningClient (shared_ptr<grpc::Channel> channel) : stub_ (Lightning::NewStub (channel)) {}

    unsigned long WalletBalance (const string& user)
    {
        WalletBalanceRequest request;
        WalletBalanceResponse reply;
        ClientContext context;

        Status status = stub_->WalletBalance (&context, request, &reply);

        if (status.ok ())
            return reply.total_balance ();
        else
            cout << status.error_code () << ": " << status.error_message () << endl;

        return 0;
    }
};

int main (int argc, char *argv [])
{
    shared_ptr<grpc::Channel> channel;// = CreateChannel ("localhost:10009", grpc::InsecureChannelCredentials ());
    return 0;
}

This is my makefile:

lnd-grpc-client : lnd-grpc-client.o lightning.pb.cc.o lightning.grpc.pb.cc.o
    g++-10 -pthread -o lnd-grpc-client lnd-grpc-client.o lightning.pb.cc.o `pkg-config --libs --static protobuf`

lightning.grpc.pb.cc.o : lightning.grpc.pb.cc
    g++-10 -std=c++20 `pkg-config protobuf --cflags` -c -o lightning.grpc.pb.cc.o lightning.grpc.pb.cc

lightning.pb.cc.o : lightning.pb.cc
    g++-10 -std=c++20 `pkg-config protobuf --cflags` -c -o lightning.pb.cc.o lightning.pb.cc

lnd-grpc-client.o : lnd-grpc-client.cpp
    g++-10 -std=c++20 `pkg-config protobuf --cflags` -c -o lnd-grpc-client.o lnd-grpc-client.cpp

All of that compiles and links just fine. But I have the CreateChannel function commented out in my cpp file and I am not linking with lightning.grpc.pb.cc.o, both of which would be required if I am to get this working.

If I uncomment the CreateChannel function, it gives me a linker error saying undefined reference to 'grpc::InsecureChannelCredentials()'. But there does not seem to be any pkg-config that solves that problem.

If I try to link with lightning.grpc.pb.cc.o, I get hundreds of linker errors. I can't post all of them, but here are a few:

lightning.grpc.pb.cc:(.text._ZN4grpc5SliceD2Ev[_ZN4grpc5SliceD5Ev]+0x20): undefined reference to 'grpc_slice_unref'
/usr/bin/ld: lightning.grpc.pb.cc.o: in function 'grpc::Slice::Slice(unsigned long)':
lightning.grpc.pb.cc:(.text._ZN4grpc5SliceC2Em[_ZN4grpc5SliceC5Em]+0x32): undefined reference to 'grpc_slice_malloc'
/usr/bin/ld: lightning.grpc.pb.cc.o: in function 'grpc::SliceReferencingString(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
lightning.grpc.pb.cc:(.text._ZN4grpc22SliceReferencingStringERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN4grpc22SliceReferencingStringERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x50): undefined reference to 'grpc_slice_from_static_buffer'
/usr/bin/ld: lightning.grpc.pb.cc.o: in function 'grpc::ByteBuffer::ByteBuffer(grpc::Slice const*, unsigned long)':
lightning.grpc.pb.cc:(.text._ZN4grpc10ByteBufferC2EPKNS_5SliceEm[_ZN4grpc10ByteBufferC5EPKNS_5SliceEm]+0x27): undefined reference to 'grpc_raw_byte_buffer_create'
/usr/bin/ld: lightning.grpc.pb.cc.o: in function 'grpc::ByteBuffer::~ByteBuffer()':
lightning.grpc.pb.cc:(.text._ZN4grpc10ByteBufferD2Ev[_ZN4grpc10ByteBufferD5Ev]+0x27): undefined reference to 'grpc_byte_buffer_destroy'
/usr/bin/ld: lightning.grpc.pb.cc.o: in function 'grpc::ByteBuffer::Clear()':
lightning.grpc.pb.cc:(.text._ZN4grpc10ByteBuffer5ClearEv[_ZN4grpc10ByteBuffer5ClearEv]+0x27): undefined reference to 'grpc_byte_buffer_destroy'

I tried adding the grpc and grpc++ pkg-config files to my makefile's link command, but that did not solve the problem.

Has anyone actually built a gRPC client for LND in C++? If so, how do you know which libraries to link with and how do you link with them?

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