Fee Delegation

Gas fees are usually paid by the address that signs the transaction. VeChain's fee delegation allows you to pass on this payment to another wallet, which can either reside as private key in your realm or shielded by a web service.

To use fee delegation, you can need to:

1. Enable it while building the transaction object

2. Provide information about the delegator during transaction signing

Enable Fee Delegation

To enable fee delegation as feature, you need to set isDelegated to true while building the transaction body:

const tx = await thor.transactions.buildTransactionBody(clauses, gas,
  { isDelegated: true }
);

Sign with Fee Delegation

To get the fee delegator involved, you'll pass either delegatorPrivateKey or delegatorUrl to the signing wallet:

const walletWithUrlSponsor = new ProviderInternalBaseWallet(
  [{ privateKey, address: senderAddress }],
  {
    delegator: {
      delegatorUrl: 'https://sponsor-testnet.vechain.energy/by/90',
    },
  }
);

const walletWithAccountSponsor = new ProviderInternalBaseWallet(
  [{ privateKey, address: senderAddress }],
  {
    delegator: {
      delegatorPrivateKey: delegatorAccount.privateKey,
    },
  }
);

Example Project

Sign as Delegator Service

To shield your private key for paying gas fees into a backend service, you can setup a web-service that receives a raw transaction and co-signs it to confirm gas payment (based on VIP-201).

The process requires you to rebuilt a transaction object from a hex encoded version:

const transactionToSign = TransactionHandler.decode(
  Buffer.from(req.body.raw.slice(2), 'hex')
);

Afterwards a unique hash is calculated for the given transaction, only valid if a specific origin will sign it:

const delegatedHash = transactionToSign.getSignatureHash(req.body.origin);

The resulting hash is signed and then returned as hex string for further processing on the client side:

const signature = `0x${Buffer.from(
    secp256k1.sign(delegatedHash, delegatorPrivateKey)
  ).toString('hex')}`;

Example Project