# How to write a C# gRPC client for the Lightning Network Daemon This section enumerates what you need to do to write a client that communicates with `lnd` in C#. ### Prerequisites * .Net Core [SDK](https://dotnet.microsoft.com/download) * If using Windows, a unix terminal such as [Cygwin](https://www.cygwin.com/) ### 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. Create a new `.net core` console application called `lndclient` at your root directory (On Windows : `C:/`), and install `Grpc.Tools` (1.17.0 at time of writing) ```bash mkdir lndclient cd lndclient dotnet new console dotnet add package Grpc.Tools --version 1.17.0 ``` * Create the necessary folder structure, and then fetch the lnd [rpc.proto](https://github.com/lightningnetwork/lnd/blob/master/lnrpc/rpc.proto) file: ```bash mkdir Grpc curl -o Grpc/rpc.proto -s https://raw.githubusercontent.com/lightningnetwork/lnd/master/lnrpc/rpc.proto ``` * Copy Google's [annotations.proto](https://github.com/googleapis/googleapis/blob/master/google/api/annotations.proto) to the correct folder: ```bash 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](https://github.com/googleapis/googleapis/blob/master/google/api/http.proto) to the correct folder: ```bash curl -o Grpc/google/api/http.proto -s https://raw.githubusercontent.com/googleapis/googleapis/master/google/api/http.proto ``` * Copy Google's [descriptor.proto](https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/descriptor.proto) to the correct folder: ```bash 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` (possibly replace "YOUR_USER", version "1.17.0", or your OS in both paths): ```bash # linux + mac nuget package location: ~/.nuget/packages cd Grpc C:/Users//.nuget/packages/grpc.tools/1.17.0/tools/windows_x64/protoc.exe --csharp_out . --grpc_out . rpc.proto --plugin=protoc-gen-grpc=C:/Users//.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. #### Imports and Client Every time you use C# `gRPC`, you will have to import the generated rpc classes, and use `nuget` package manger to install `Grpc.Core` (1.17.0 at time of writing), `Google.Protobuf` (3.6.1), and `Google.Api.CommonProtos` (1.4.0). ```bash # from project root, install packages using nuget cd ../ dotnet add package Grpc.Core --version 1.17.0 dotnet add package Google.Protobuf --version 3.6.1 dotnet add package Google.Api.CommonProtos --version 1.4.0 ``` After installing these, use the code below to set up a channel and client to connect to your `lnd` node: ```c# using System.Collections.Generic; using System.IO; using System.Threading.Tasks; using Grpc.Core; using Lnrpc; ... // Due to updated ECDSA generated tls.cert we need to let gprc know that // we need to use that cipher suite otherwise there will be a handshake // error when we communicate with the lnd rpc server. System.Environment.SetEnvironmentVariable("GRPC_SSL_CIPHER_SUITES", "HIGH+ECDSA"); // Lnd cert is at AppData/Local/Lnd/tls.cert on Windows // ~/.lnd/tls.cert on Linux and ~/Library/Application Support/Lnd/tls.cert on Mac var cert = File.ReadAllText(); var sslCreds = new SslCredentials(cert); var channel = new Grpc.Core.Channel("localhost:10009", sslCreds); var client = new Lnrpc.Lightning.LightningClient(channel); ``` ### Examples Let's walk through some examples of C# `gRPC` clients. These examples assume that you have at least two `lnd` nodes running, the RPC location of one of which is at the default `localhost:10009`, with an open channel between the two nodes. #### Simple RPC ```c# // Retrieve and display the wallet balance // Use "WalletBalanceAsync" if in async context var response = client.WalletBalance(new WalletBalanceRequest()); Console.WriteLine(response); ``` #### Response-streaming RPC ```c# var request = new InvoiceSubscription(); using (var call = client.SubscribeInvoices(request)) { while (await call.ResponseStream.MoveNext()) { var invoice = call.ResponseStream.Current; Console.WriteLine(invoice.ToString()); } } ``` Now, create an invoice for your node at `localhost:10009` and send a payment to it from another node. ```bash $ lncli addinvoice --amt=100 { "r_hash": , "pay_req": } $ lncli sendpayment --pay_req= ``` Your console should now display the details of the recently satisfied invoice. #### Bidirectional-streaming RPC ```c# using (var call = client.SendPayment()) { var responseReaderTask = Task.Run(async () => { while (await call.ResponseStream.MoveNext()) { var payment = call.ResponseStream.Current; Console.WriteLine(payment.ToString()); } }); foreach (SendRequest sendRequest in SendPayment()) { await call.RequestStream.WriteAsync(sendRequest); } await call.RequestStream.CompleteAsync(); await responseReaderTask; } IEnumerable SendPayment() { while (true) { SendRequest req = new SendRequest() { DestString = , Amt = 100, PaymentHashString = , FinalCltvDelta = 144 }; yield return req; System.Threading.Thread.Sleep(2000); } } ``` This example will send a payment of 100 satoshis every 2 seconds. #### Using Macaroons To authenticate using macaroons you need to include the macaroon in the metadata of the request. ```c# // Lnd admin macaroon is at /data/chain/bitcoin/simnet/admin.macaroon on Windows // ~/.lnd/data/chain/bitcoin/simnet/admin.macaroon on Linux and ~/Library/Application Support/Lnd/data/chain/bitcoin/simnet/admin.macaroon on Mac byte[] macaroonBytes = File.ReadAllBytes("/data/chain/bitcoin/simnet/admin.macaroon"); var macaroon = BitConverter.ToString(macaroonBytes).Replace("-", ""); // hex format stripped of "-" chars ``` The simplest approach to use the macaroon is to include the metadata in each request as shown below. ```c# client.GetInfo(new GetInfoRequest(), new Metadata() { new Metadata.Entry("macaroon", macaroon) }); ``` However, this can get tiresome to do for each request, so to avoid explicitly including the macaroon we can update the credentials to include it automatically. ```c# // build ssl credentials using the cert the same as before var sslCreds = new SslCredentials(cert); // combine the cert credentials and the macaroon auth credentials using interceptors // so every call is properly encrypted and authenticated Task AddMacaroon(AuthInterceptorContext context, Metadata metadata) { metadata.Add(new Metadata.Entry("macaroon", macaroon)); return Task.CompletedTask; } var macaroonInterceptor = new AsyncAuthInterceptor(AddMacaroon); var combinedCreds = ChannelCredentials.Create(sslCreds, CallCredentials.FromInterceptor(macaroonInterceptor)); // finally pass in the combined credentials when creating a channel var channel = new Grpc.Core.Channel("localhost:10009", combinedCreds); var client = new Lnrpc.Lightning.LightningClient(channel); // now every call will be made with the macaroon already included client.GetInfo(new GetInfoRequest()); ``` ### Conclusion With the above, you should have all the `lnd` related `gRPC` dependencies installed locally in your project. In order to get up to speed with `protobuf` usage from C#, see [this official `protobuf` tutorial for C#](https://developers.google.com/protocol-buffers/docs/csharptutorial). Additionally, [this official gRPC resource](http://www.grpc.io/docs/tutorials/basic/csharp.html) provides more details around how to drive `gRPC` from C#.