lnd/docs/grpc/c#.md

# 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/<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.



#### 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(<Tls_Cert_Location>);

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": <R_HASH>,
    "pay_req": <PAY_REQ>
}
$ lncli sendpayment --pay_req=<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<SendRequest> SendPayment()
{
    while (true)
    {
        SendRequest req = new SendRequest() {
            DestString = <DEST_PUB_KEY>,
            Amt = 100,
            PaymentHashString = <R_HASH>,
            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 <LND_DIR>/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("<LND_DIR>/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#.