lightning/lnd_methods/onchain/subscribe_to_transactions.js

Lightning Network client library

const EventEmitter = require('events');

const {isLnd} = require('./../../lnd_requests');
const {rpcTxAsTransaction} = require('./../../lnd_responses');

const cancelError = 'Cancelled on client';
const {isArray} = Array;
const method = 'subscribeTransactions';
const type = 'default';

/** Subscribe to transactions

  Requires `onchain:read` permission

  `inputs` are not supported on LND 0.15.0 and below

  {
    lnd: <Authenticated LND API Object>
  }

  @throws
  <Error>

  @returns
  <EventEmitter Object>

  @event 'chain_transaction'
  {
    [block_id]: <Block Hash String>
    [confirmation_count]: <Confirmation Count Number>
    [confirmation_height]: <Confirmation Block Height Number>
    created_at: <Created ISO 8601 Date String>
    [fee]: <Fees Paid Tokens Number>
    id: <Transaction Id String>
    inputs: [{
      is_local: <Spent Outpoint is Local Bool>
      transaction_id: <Transaction Id Hex String>
      transaction_vout: <Transaction Output Index Number>
    }]
    is_confirmed: <Is Confirmed Bool>
    is_outgoing: <Transaction Outbound Bool>
    output_addresses: [<Address String>]
    tokens: <Tokens Including Fee Number>
    [transaction]: <Raw Transaction Hex String>
  }
*/
module.exports = ({lnd}) => {
  if (!isLnd({lnd, method, type})) {
    throw new Error('ExpectedAuthenticatedLndToSubscribeToTransactions');
  }

  const eventEmitter = new EventEmitter();
  const subscription = lnd[type][method]({});

  // Cancel the subscription when all listeners are removed
  eventEmitter.on('removeListener', () => {
    // Exit early when there are still listeners
    if (!!eventEmitter.listenerCount('chain_transaction')) {
      return;
    }

    subscription.cancel();

    return;
  });

  const emitErr = err => {
    if (!!err && err.details === cancelError) {
      subscription.removeAllListeners();
    }

    // Exit early when there are no listeners on error
    if (!eventEmitter.listenerCount('error')) {
      return;
    }

    if (isArray(err)) {
      return eventEmitter.emit('error', err);
    }

    return eventEmitter.emit('error', [503, 'UnexpectedChainTxSubErr', {err}]);
  };

  subscription.on('data', tx => {
    try {
      return eventEmitter.emit('chain_transaction', rpcTxAsTransaction(tx));
    } catch (err) {
      return emitErr([503, err.message]);
    }
  });

  subscription.on('end', () => eventEmitter.emit('end'));
  subscription.on('error', err => emitErr(err));
  subscription.on('status', status => eventEmitter.emit('status', status));

  return eventEmitter;
};