How to write a simple `lnd` client in Javascript using `node.js`

Setup and Installation

First, you'll need to initialize a simple nodejs project:

npm init (or npm init -f if you want to use the default values without prompt)

Then you need to install the Javascript grpc library dependency:

npm install grpc --save

You also need to copy the lnd rpc.proto file in your project directory (or at least somewhere reachable by your Javascript code).

The rpc.proto file is located in the lnrpc directory of the lnd sources.

In order to allow the auto code generated to compile the protos successfully, you'll need to comment out the following line:

//import "google/api/annotations.proto";

Imports and Client

Every time you work with Javascript gRPC, you will have to import grpc, load rpc.proto, and create a connection to your client like so:

var grpc = require('grpc');
var lnrpcDescriptor = grpc.load("rpc.proto");
var lnrpc = lnrpcDescriptor.lnrpc;
var lightning = new lnrpc.Lightning('localhost:10009', grpc.credentials.createInsecure());

Examples

Let's walk through some examples of Javascript gRPC clients.

Simple RPC

> lightning.getInfo({}, function(err, response) {
  	console.log('GetInfo:', response);
  });

You should get something like this in your console:

GetInfo: { identity_pubkey: '03c892e3f3f077ea1e381c081abb36491a2502bc43ed37ffb82e264224f325ff27',
  alias: '',
  num_pending_channels: 0,
  num_active_channels: 1,
  num_peers: 1,
  block_height: 1006,
  block_hash: '198ba1dc43b4190e507fa5c7aea07a74ec0009a9ab308e1736dbdab5c767ff8e',
  synced_to_chain: false,
  testnet: false,
  chains: [ 'bitcoin' ] }

Response-streaming RPC

var call = lightning.subscribeInvoices({});
call.on('data', function(invoice) {
    console.log(invoice);
})
.on('end', function() {
  // The server has finished sending
})
.on('status', function(status) {
  // Process status
  console.log("Current status" + status);
});

Now, create an invoice for your node at localhost:10009 and send a payment to it. Your Javascript console should display the details of the recently satisfied invoice.

Bidirectional-streaming RPC

This example has a few dependencies:

npm install --save async lodash bytebuffer

You can run the following in your shell or put it in a program and run it like node script.js

// Load some libraries specific to this example
var async = require('async');
var _ = require('lodash');
var ByteBuffer = require('bytebuffer');

var dest_pubkey = <RECEIVER_ID_PUBKEY>;
var dest_pubkey_bytes = ByteBuffer.fromHex(dest_pubkey);

// Set a listener on the bidirectional stream
var call = lightning.sendPayment();
call.on('data', function(payment) {
  console.log("Payment sent:");
  console.log(payment);
});
call.on('end', function() {
  // The server has finished
  console.log("END");
});

// You can send single payments like this
call.write({ dest: dest_pubkey_bytes, amt: 6969 });

// Or send a bunch of them like this
function paymentSender(destination, amount) {
  return function(callback) {
    console.log("Sending " + amount + " satoshis");
    console.log("To: " + destination);
    call.write({
      dest: destination,
      amt: amount
    });
    _.delay(callback, 2000);
  };
}
var payment_senders = [];
for (var i = 0; i < 10; i++) {
  payment_senders[i] = paymentSender(dest_pubkey_bytes, 100);
}
async.series(payment_senders, function() {
  call.end();
});

This example will send a payment of 100 satoshis every 2 seconds.

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 protofbuf usage from Javascript, see this official protobuf reference for Javascript. Additionally, this official gRPC resource provides more details around how to drive gRPC from node.js.

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How to write a simple lnd client in Javascript using node.js