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InnerTx: SpendTx

Introduction

The whole script is located in the repository and this page explains in detail how to:

  • Create and sign a SpendTx for an account with the innerTx option.
  • Wrap the signed SpendTx in a PayingForTx, signing it using an account that pays the fees of the inner SpendTx and broadcasts it to the network.

Note:

  • This can be done for any transaction type!

1. Specify imports

You need to import Universal, Node and MemoryAccount Stamps from the SDK. Additionally you import the Crypto utility module to generate a new keypair. 

const { Universal, Node, MemoryAccount, Crypto } = require('@aeternity/aepp-sdk')
Note:

  • You need to have the SDK installed via npm i @aetenity/aepp-sdk -g to run that example code.

2. Define constants

The following constants are used in the subsequent code snippets. 

const PAYER_ACCOUNT_KEYPAIR = {
  publicKey: 'ak_2dATVcZ9KJU5a8hdsVtTv21pYiGWiPbmVcU1Pz72FFqpk9pSRR',
  secretKey: 'bf66e1c256931870908a649572ed0257876bb84e3cdf71efb12f56c7335fad54d5cf08400e988222f26eb4b02c8f89077457467211a6e6d955edb70749c6a33b'
}
const NODE_URL = 'https://testnet.aeternity.io'
const NEW_USER_KEYPAIR = Crypto.generateKeyPair()
const AMOUNT = 1;
Note:

  • The keypair of the account is pre-funded and only used for demonstration purpose
    • You can replace it with your own keypair (see Create a Keypair)
    • In case the account runs out of funds you can always request AE using the Faucet
  • The AMOUNT (in aettos) will be send to the new user and returned to the payer.

3. Open async codeblock

Most functions of the SDK return Promises, so the recommended way of dealing with subsequent actions is running them one by one using await. Therefore we are putting our logic into an async code block 

(async () => {

4. Create object instances

  const payerAccount = MemoryAccount({ keypair: PAYER_ACCOUNT_KEYPAIR })
  const newUserAccount = MemoryAccount({ keypair: NEW_USER_KEYPAIR })
  const node = await Node({ url: NODE_URL })
  const client = await Universal({
    nodes: [{ name: 'testnet', instance: node }],
    accounts: [payerAccount, newUserAccount],
  })
The Universal Stamp itself is asynchronous as it determines the node's version and rest interface automatically. Only once the Promise is fulfilled, you know you have a working object instance which is assigned to the client constant in this case.

Note:

  • Universal is not a constructor but a factory, which means it's not invoked with new.

5. Send 1 aetto from payer to new user

  const spendTxResult = await client.spend(AMOUNT, await newUserAccount.address(), { onAccount: payerAccount })
  console.log(spendTxResult)

6. Check balance of new user (before)

  const newUserBalanceBefore = await client.getBalance(await newUserAccount.address())
  console.log(`new user balance (before): ${newUserBalanceBefore}`)
Note:

  • The balance should now be 1

7. Create and sign SpendTx on behalf of new user

  const spendTx = await client.spendTx({
    senderId: await newUserAccount.address(),
    recipientId: await payerAccount.address(),
    amount: AMOUNT
  })
  const signedSpendTx = await client.signTransaction(spendTx, { onAccount: newUserAccount, innerTx: true })
Note:

  • The provided transaction option innerTx indicates that the transaction needs to be signed in a special way

7. Create, sign & broadcast the PayingForTx as payer

  const payForTx = await client.payForTransaction(signedSpendTx, { onAccount: payerAccount })
  console.log(payForTx)
Note:

  • Normally sending the whole balance (1 aetto) would not be possible as the new user would have to cover the transaction fee.

8. Check balance of new user (after)

  const newUserBalanceAfter = await client.getBalance(await newUserAccount.address())
  console.log(`new user balance (after): ${newUserBalanceAfter}`)
Note:

  • The balance should now be 0

9. Close and run async codeblock

Now you can close the async codeblock and execute it at the same time. 

})()