Generate A Csharp Grpc Interface For Lnd

gRPC is an RPC framework from Google, whose aim is to be more efficient than JSON/HTTP. Intended as an alternative to REST, it is more efficient due to the use of Protocol Buffers and HTTP/2.

If you don’t wish to learn how to build a gRPC interface for lnd, you can install one from nuget and continue on to the next tutorial here. Otherwise, let’s continue!

In order to create a gRPC interface, you define a Service (end point definition), and both a request and response Message. These definitions are created in a .proto file, which will be used to generate the classes used in your chosen programming language. An example .proto file looks like the following:

syntax = "proto3";

package lnrpc;

service WalletUnlocker  {
      rpc UnlockWallet(UnlockWalletRequest) returns (UnlockWalletResponse) {}
}

message UnlockWalletRequest {
      bytes wallet_password = 1;
      int32 recovery_window = 2;
}

message UnlockWalletResponse {}

Prerequisites

• A unix terminal for Windows - this tutorial uses Cygwin

Setup and Installation

lnd uses the gRPC protocol for communication with clients like lncli.

gRPC is based on protocol buffers, and as such, you will need to compile the lnd proto file in C# before you can use it to communicate with lnd.

This assumes you are using a Windows machine, but it applies equally to Mac and Linux.

• Open Visual Studio, and create a new .net core console application called lnrpc at the root directory (Windows : C:/)

• Within Visual Studio, open nuget package manager and install Grpc.Tools (1.17.0 at time of writing)

• Open a Cygwin terminal and cd to your project folder:

  cd C:/lnrpc/lnrpc
  

• Create the necessary folder structure, and then fetch the lnd rpc.proto file:

  mkdir Grpc
  curl -o Grpc/rpc.proto -s https://raw.githubusercontent.com/lightningnetwork/lnd/master/lnrpc/rpc.proto
  

• Copy Google’s annotations.proto to the correct folder:

  mkdir Grpc/google
  mkdir Grpc/google/api
  curl -o Grpc/google/api/annotations.proto -s https://raw.githubusercontent.com/googleapis/googleapis/master/google/api/annotations.proto
  

• Copy Google’s http.proto to the correct folder:

  curl -o Grpc/google/api/http.proto -s https://raw.githubusercontent.com/googleapis/googleapis/master/google/api/http.proto
  

• Copy Google’s descriptor.proto to the correct folder:

  mkdir Grpc/google/protobuf
  curl -o Grpc/google/protobuf/descriptor.proto -s https://raw.githubusercontent.com/protocolbuffers/protobuf/master/src/google/protobuf/descriptor.proto
  

• Compile the proto file using protoc.exe from nuget package Grpc.Tools (remember to replace “YOUR_USER”, and possibly version “1.17.0” in both paths):

  # linux + mac nuget package location: ~/.nuget/packages
  cd Grpc
  C:/Users/<YOUR_USER>/.nuget/packages/grpc.tools/1.17.0/tools/windows_x64/protoc.exe --csharp_out . --grpc_out . rpc.proto --plugin=protoc-gen-grpc=C:/Users/<YOUR_USER>/.nuget/packages/grpc.tools/1.17.0/tools/windows_x64/grpc_csharp_plugin.exe
  

After following these steps, two files Rpc.cs and RpcGrpc.cs will be generated in the Grpc folder in your project.

Further steps

Continue on to the next tutorial, which explains how to use the files we just generated.

Written on August 30, 2018