Build Fee Delegation Example
Table of Contents
- 1. Introduction
- 2. How fee delegation works
- 2.1 Transaction signing by the sender
- 2.2 Transaction signing by the fee payer
- 3. Simple server and client for fee delegation
- 3.1 Sender's client
- 3.2 Fee payer's server
- 4. Run example
- 4.1 Run
feepayer_server.js
- 4.2 Run
sender_client.js
- 4.3 Check
feepayer_server.js
- 4.4 Kaia scope
- 4.1 Run
1. Introduction
This tutorial helps you to write a simple server-client example using caver-js SDK to illustrate how fee delegated value transfer transaction works in Kaia. This tutorial and the example code is using the Kairos testnet.
2. How fee delegation works
Let's skim through how fee delegation works.
2.1 Transaction signing by the sender
Sender
always should sign the transaction before sending a transaction.
To sign a transaction, use signTransaction which signs a transaction with given private key.
// using the event emitterconst senderAddress = "SENDER_ADDRESS";const senderPrivateKey = "SENDER_PRIVATEKEY";const toAddress = "TO_ADDRESS";const { rawTransaction: senderRawTransaction } = await caver.kaia.accounts.signTransaction({ type: 'FEE_DELEGATED_VALUE_TRANSFER', from: senderAddress, to: toAddress, gas: '300000', value: caver.utils.toPeb('1', 'KAIA'),}, senderPrivateKey)
If there are no errors, then senderRawTransaction
will have a signed transaction which is signed by the senderPrivateKey
.
Now, you need to send the senderRawTransaction
to the fee payer. There will be various ways to implement this. In this tutorial, we will provide you a simple server-client code as an example of sending a senderRawTransaction
to the fee payer.
2.2 Transaction signing by the fee payer
When fee payer
receives the senderRawTransaction
, fee payer
signs the senderRawTransaction
again with their private key and sends the transaction to Kaia. The below code snippet illustrates the process. kaia.sendTransaction
method signs the transaction with the given account's private key before sending the transaction. Before running the code, please replace "FEEPAYER_ADDRESS"
and "PRIVATE_KEY"
with the actual values.
Note that when the fee payer
submits the transaction to Kaia on behalf of the sender
, the senderRawTransaction
type must be a FEE_DELEATED
type of transaction. In the below example, sendTransaction(FEE_DELEGATED_VALUE_TRANSFER) method is invoked, because the original senderRawTransaction
generated by the sender was TxTypeFeeDelegatedValueTransfer.
const feePayerAddress = "FEEPAYER_ADDRESS";const feePayerPrivateKey = "PRIVATE_KEY"caver.kaia.accounts.wallet.add(feePayerPrivateKey, feePayerAddress);caver.kaia.sendTransaction({ senderRawTransaction: senderRawTransaction, feePayer: feePayerAddress,}).on('transactionHash', function(hash){ ...}).on('receipt', function(receipt){ ...}).on('error', console.error); // If an out-of-gas error, the second parameter is the receipt.
3. Simple server and client for fee delegation
Let's write a simple server and client using above fee delegation code.
3.1 Environment setup
We will use npm
and caver-js to setup environment for this example as below.
$ mkdir example$ cd example$ npm init$ npm install caver-js@latest
3.1 Sender's client
First, we are going to write a sender_client.js
as below.
In the example, please replace "SENDER_ADDRESS"
, "SENDER_PRIVATEKEY"
and "TO_ADDRESS"
with the actual values.
var net = require('net');var client = new net.Socket();const Caver = require('caver-js');const caver = new Caver('https://public-en-kairos.node.kaia.io');const senderAddress = "SENDER_ADDRESS";const senderPrivateKey = "SENDER_PRIVATEKEY";const toAddress = "TO_ADDRESS";sendFeeDelegateTx = async() => { // sign transaction with private key of sender const { rawTransaction: senderRawTransaction } = await caver.kaia.accounts.signTransaction({ type: 'FEE_DELEGATED_VALUE_TRANSFER', from: senderAddress, to: toAddress, gas: '300000', value: caver.utils.toPeb('0.00001', 'KAIA'), }, senderPrivateKey) // send signed raw transaction to fee payer's server client.connect(1337, '127.0.0.1', function() { console.log('Connected to fee delegated service'); }); client.write(senderRawTransaction); client.on('data', function(data) { console.log('Received data from server: ' + data); }); client.on('close', function() { console.log('Connection closed'); });}sendFeeDelegateTx();
The above code signs a fee delegated value transfer transaction with senderPrivateKey
and sends the signed senderRawTransaction
to the fee payer's server which is running on port 1337
on 127.0.0.1
, i.e. localhost.
3.2 Fee payer's server
Now let's write the fee payer's server, feepayer_server.js
, which signs received senderRawTransaction
with feePayerPrivateKey
and sends it to Kairos testnet.
In the below example, please replace "FEEPAYER_ADDRESS"
and "FEEPAYER_PRIVATEKEY"
with actual values.
const Caver = require('caver-js');const caver = new Caver('https://public-en-kairos.node.kaia.io');const feePayerAddress = "FEEPAYER_ADDRESS";const feePayerPrivateKey = "FEEPAYER_PRIVATEKEY";// add fee payer accountcaver.kaia.accounts.wallet.add(feePayerPrivateKey, feePayerAddress);var net = require('net');feePayerSign = (senderRawTransaction, socket) => { // fee payer caver.kaia.sendTransaction({ senderRawTransaction: senderRawTransaction, feePayer: feePayerAddress, }) .on('transactionHash', function(hash){ console.log('transactionHash', hash); }) .on('receipt', function(receipt){ console.log('receipt', receipt); socket.write('Tx hash is '+ receipt.transactionHash); socket.write('Sender Tx hash is '+ receipt.senderTxHash); }) .on('error', console.error); // If an out-of-gas error, the second parameter is the receipt.}var server = net.createServer(function(socket) { console.log('Client is connected ...'); socket.write('This is fee delegating service'); socket.write('Fee payer is ' + feePayerAddress); socket.on('data', function(data) { console.log('Received data from client:', data.toString()); feePayerSign(data.toString(), socket); });});server.listen(1337, '127.0.0.1');console.log('Fee delegate service started ...');
The server listens on port 1337
.
When there is incoming data
, it signs the data
with feePayerPrivateKey
and sends it to the Kaia blockchain. It assumes that the data
is senderRawTransaction
from the sender_client.js
.
4. Run example
Prepare two terminals, one for sender_client.js
and another for feepayer_server.js
.
4.1 Run feepayer_server.js
Below the command will start the fee payer's server.
$ node feepayer_server.jsFee delegate service started ...
The server starts and is now listening on port 1337.
4.2 Run sender_client.js
Let's run sender_client.js
to send a fee delegated transaction.
$ node sender_client.jsSigned a fee delegated value transfer transaction.Sending a signed transaction to fee delegated service.Connected to fee delegated serviceReceived data from server: This is fee delegating serviceReceived data from server: Fee payer is 0x2645BA5Be42FfEe907ca8e9d88f6Ee6dAd8c1410Received data from server: Tx hash is 0xd99086aa8188255d4ee885d9f1933b6cc062085c1196731ba599b2fb8f2dbbd7Received data from server: Sender Tx hash is 0xe1f630547f287177a0e92198b1c67212b24fc1ad5a1f0b1f94fd6f980281fdba
It will sign a transaction with the sender
private key and send the signed transaction to the fee delegated service (i.e., fee payer's server). Then it will receive the response from the fee delegate service including the Fee payer
address, Tx hash
, and Sender Tx hash
. Tx hash
is hash of a transaction submitted to the Kaia network, while Sender Tx hash
is hash of a transaction without the fee payer's address and signature. For more details, please take a look at SenderTxHash.
4.3 Check feepayer_server.js
On the server's console, you will see below outputs. It prints the transaction receipt from the Kaia.
$ node feepayer_server.jsFee delegate service started ...Client is connected ...Received data from client: 0x09f88b3a8505d21dba00830493e094fc83add44939ef818ce62dacea23697fa17257838609184e72a000940ecc24157e38b1997aace56f32ccb381b16e1710f847f8458207f5a0e636e67d01acc1f368db5e60290721e9059b13b0bf74af6d46391cc48bd31a81a0135118878be87f808e064f64fa4f13d6dc5bd9888b154ecd17f02980063b9e4280c4c3018080transactionHash { messageHash: '0xa4cd7d479d19251a1981086431eff5514c5edf61731a6e5271b2a137a156f7e7', v: '0x07f6', r: '0xdb9c3a5b75c20f15cba9bc28eebcaff58701f57d4a226e7e3cb2bc4544b3c96c', s: '0x7646e929aa6467fa1c849f3abf37054df4cb08e6ee160f6375517ae2609f4b11', rawTransaction: '0x09f8e33a8505d21dba00830493e094fc83add44939ef818ce62dacea23697fa17257838609184e72a000940ecc24157e38b1997aace56f32ccb381b16e1710f847f8458207f5a0e636e67d01acc1f368db5e60290721e9059b13b0bf74af6d46391cc48bd31a81a0135118878be87f808e064f64fa4f13d6dc5bd9888b154ecd17f02980063b9e42942645ba5be42ffee907ca8e9d88f6ee6dad8c1410f847f8458207f6a0db9c3a5b75c20f15cba9bc28eebcaff58701f57d4a226e7e3cb2bc4544b3c96ca07646e929aa6467fa1c849f3abf37054df4cb08e6ee160f6375517ae2609f4b11', txHash: '0xd99086aa8188255d4ee885d9f1933b6cc062085c1196731ba599b2fb8f2dbbd7' }transactionHash 0xd99086aa8188255d4ee885d9f1933b6cc062085c1196731ba599b2fb8f2dbbd7receipt { blockHash: '0x1c61f03d2f0eba86c0f58ee7d1be8e8e425f47e9c46433474bd11c5a3f0528b2', blockNumber: 3175653, contractAddress: null, feePayer: '0x2645ba5be42ffee907ca8e9d88f6ee6dad8c1410', feePayerSignatures: [ { V: '0x7f6', R: '0xdb9c3a5b75c20f15cba9bc28eebcaff58701f57d4a226e7e3cb2bc4544b3c96c', S: '0x7646e929aa6467fa1c849f3abf37054df4cb08e6ee160f6375517ae2609f4b11' } ], from: '0x0ecc24157e38b1997aace56f32ccb381b16e1710', gas: '0x493e0', gasPrice: '0x5d21dba00', gasUsed: 31000, logs: [], logsBloom: '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000', nonce: '0x3a', senderTxHash: '0xe1f630547f287177a0e92198b1c67212b24fc1ad5a1f0b1f94fd6f980281fdba', signatures: [ { V: '0x7f5', R: '0xe636e67d01acc1f368db5e60290721e9059b13b0bf74af6d46391cc48bd31a81', S: '0x135118878be87f808e064f64fa4f13d6dc5bd9888b154ecd17f02980063b9e42' } ], status: true, to: '0xfc83add44939ef818ce62dacea23697fa1725783', transactionHash: '0xd99086aa8188255d4ee885d9f1933b6cc062085c1196731ba599b2fb8f2dbbd7', transactionIndex: 0, type: 'TxTypeFeeDelegatedValueTransfer', typeInt: 9, value: '0x9184e72a000' }
4.4 Kaia scope
You can also find the above transaction on the Kaiascope.
It shows that the transaction is TxTypeFeeDelegatedValueTransfer
and Fee payer
is 0x2645ba5be42ffee907ca8e9d88f6ee6dad8c1410
or feepayerAddress
that you entered, while From
is a different address which should be the senderAddress
in above example.