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libspiffy

8 · React to events

Some events answer a request, and ask hands those to you. Others report something that happened on its own: a balance changed, an invoice was paid, a block confirmed a transaction. You follow those with coordinator.on<E>(). In this last step you listen for them, mine the payment, and watch both wallets settle.

Listen

Section titled “Listen”

Add this right after initializing, before step 3, so it hears everything:

bin/first_payment.dart (after step 2)
  // Step 8: listen for what happens without being asked.
  final subscriptions = [
    coordinator.on<BalanceUpdatedEvent>().listen((e) =>
        print('  [${e.walletId}] balance now ${e.totalBalance} sats')),
    coordinator.on<TransactionConfirmedEvent>().listen((e) =>
        print('  [${e.walletId}] ${e.txid} confirmed at ${e.blockHeight}')),
    coordinator.on<InvoicePaidEvent>().listen((e) =>
        print('  [${e.walletId}] invoice ${e.invoiceId} paid: '
            '${e.amountReceived} sats in ${e.txid}')),
  ];

on<E>({walletId}) gives you one kind of event, for one wallet if you name it. BalanceUpdatedEvent is announced whenever a balance changes, so you don’t need to poll GetBalanceQuery.

Mine the payment and wait for both confirmations

Section titled “Mine the payment and wait for both confirmations”
bin/first_payment.dart (step 8)
  // Step 8: mine the payment. Each wallet confirms it on its own once the
  // proof arrives and matches the header it synced.
  await printBalance(coordinator, 'alice'); // inputs held: 0 until it settles
  await waitForArcade(payment.txid, {'SEEN_ON_NETWORK', 'SEEN_MULTIPLE_NODES'});
  final confirmations = [
    for (final walletId in ['alice', 'bob'])
      coordinator
          .on<TransactionConfirmedEvent>(walletId: walletId)
          .firstWhere((e) => e.txid == payment.txid)
          .timeout(const Duration(minutes: 3)),
  ];
  await mineBlock();
  await Future.wait(confirmations);


  await printBalance(coordinator, 'alice');
  await printBalance(coordinator, 'bob');


  for (final s in subscriptions) {
    await s.cancel();
  }

You start waiting for the confirmations before mining, so one that arrives quickly isn’t missed. Each wallet confirms the payment independently: ARC reports it MINED with its merkle path, and the wallet checks that path against the header it synced. On localnet this took about a minute.

The whole run

Section titled “The whole run”
libspiffy is up; headers at 0
Created alice (root address mgK27BXo3QodQsiRa8gBLF46jYnsY78Yvm)
Created bob (root address mxSu1TZsACrkLcoUDBVjwqDj7qHdYwM2nQ)
Alice receives at mu343b2opCEdXpDRT4wXjnC8qHfee5SqkB
Faucet sent 1000000 sats in a80c33b869c4ef6d0f33698bc48a0c3eb0bd9ed6d9d84786a59ac5c996e8a77c
Mined at height 486
  [alice] balance now 1000000 sats
alice: 1000000 sats (confirmed 1000000, unconfirmed 0)
  [alice] a80c33b869c4ef6d0f33698bc48a0c3eb0bd9ed6d9d84786a59ac5c996e8a77c confirmed at 486
Bob invoices 100000 sats to mvd5qb56orNeWYdutrXpub9YR1yAJbrUKr
  [alice] balance now 0 sats
Alice built c5013d51885cc8e9115b2bdd1865c35866d77e165c6cc25dd564d13f0fa489f5: 533 BEEF bytes, 1 ancestors
  [alice] balance now 0 sats
  [bob] balance now 0 sats
  [bob] balance now 100000 sats
Bob: valid=true broadcasted=true networkStatus=SEEN_ON_NETWORK
  [bob] invoice d2fb82ed-424b-4477-9a65-fc8e9394947a paid: 100000 sats in c5013d51885cc8e9115b2bdd1865c35866d77e165c6cc25dd564d13f0fa489f5
alice: 0 sats (confirmed 0, unconfirmed 0)
  [alice] balance now 0 sats
  [alice] balance now 899977 sats
  [bob] c5013d51885cc8e9115b2bdd1865c35866d77e165c6cc25dd564d13f0fa489f5 confirmed at 487
  [bob] balance now 100000 sats
  [alice] c5013d51885cc8e9115b2bdd1865c35866d77e165c6cc25dd564d13f0fa489f5 confirmed at 487
alice: 899977 sats (confirmed 899977, unconfirmed 0)
  [alice] balance now 899977 sats
bob: 100000 sats (confirmed 100000, unconfirmed 0)

Alice paid 100,000 sats and a 23-sat fee, and kept 899,977 in change. Bob has 100,000, confirmed against his own headers. Neither wallet trusted the other or a server for any of it.

Where to go next

Section titled “Where to go next”