Gas vouchers

Vouchers, issued by any actor empower users with gas-free interactions, enabling them to send messages to specific programs seamlessly.

An example of using vouchers is shown in the Battleship game. Users without tokens on their balance can make moves by sending messages to a program using a voucher.

Issue a voucher

Use api.voucher.issue method to issue a new voucher for a user to be used to pay for sending messages to program_id program.

  import { VoucherIssued } from '@gear-js/api';

  const programId = '0x..';
  const account = '0x...';
  const tx = api.voucher.issue(account, programId, 10000);
  tx.signAndSend(account, (events) => {
    const voucherIssuedEvent = events.events.filter(({event: {method}}) => method === 'VoucherIssued') as VoucherIssued;
    console.log(voucherIssuedEvent.toJSON());
  })

Check voucher

Use api.voucher.exists method to check that the voucher exists for a particular user and program:

const voucherExists = await api.voucher.exists(programId, accountId);

Send a message using voucher

To send message with voucher you can use api.voucher.call method:

  const messageTx = api.message.send({
    destination: destination,
    payload: somePayload,
    gasLimit: 10000000,
    value: 1000
  }, meta);

  const voucherTx = api.voucher.call({ SendMessage: messageTx });
  await voucherTx.signAndSend(account, (events) => {
    console.log(events.toHuman());
  });

Send a reply using voucher

Sending a reply with issued voucher works similar to sending message with voucher:

  const messageTx = api.message.sendReply(...);

  const voucherTx = api.voucher.call({ SendReply: messageTx });
  await voucherTx.signAndSend(account, (events) => {
    console.log(events.toHuman());
  });