Ethereum Transaction Batcher

A utility to batch Ethereum transactions in a single transaction.

Why use this?

• better user experience if you need do send (or re-send) many transactions
• save gas
• execute a sequence of transactions as an atomic transaction - if one fails, all do

Usage

Install the package npm install ethereum-transaction-batcher.

const Web3 = require('web3')
const Batcher = require('ethereum-transaction-batcher')

// the address where the helper contrat is deployed
const batcherAddress = '0x741A4dCaD4f72B83bE9103a383911d78362611cf'
const web3 = new Web3('http://localhost:8545/') // or another ethereum provider

batcher = new Batcher({web3, batcherAddress})

// create web3 transactions as you would normally
const tx1 = myContract.myMethod(myArg1, myarg2)

// call a function on a contract
const tx2 = {
  to: '0x11f4d0A3c12e86B4b5F39B213F7E19D048276DAe',
  data: '0x123454...',
}
// send some money to your friend
const tx3 =  {
  to: '0x11f4d0A3c12e86B4b5F39B213F7E19D048276DAe',
  value: '1000000000000000'
}

// send the transactions as a single transaction to the blockchain
// the batched transaction will fail if one of the subtransactions fail
const receipt = await batcher.sendTransaction([tx1, tx2, tx3])
console.log(receipt.events)

API

const batcher = new Batcher({
  web, // web3 instance, required
  batcherAdddress // address of batcher contract, optional if the network is main or rinkeby
})

A Batcher instance exposes a fucntion sendTransaction. The signature and behavior of the function is similar to the sendTransaction method in web3.js - the function can be called by providing it with a callback, if the callback is omitted it will return a Promise - but instead of taking a single transaction object as its first argument, it takes a list of transactions.

batcher.sendTransaction(
  transactions, // a list of web3-style transaction objects
  callback // optional, like in web3.js
)

The batcher.sendTransaction call will try to execute the entire list of transactions in the order that they are given. If one of them fails, the batched transaction fails atomically - i.e.\ none of the transactions will be executed.

sendTransaction behaves like web3.eth.sendTransaction - if a callback is provided, it will be called, if no callback is provided, it will return a promise that resolves to a transaction receipt.

The Contract

The solidity code is here.

Limitations

• The batched transactions will be sent from the Batcher contract - which means that transactions that require msg.sender to be (say) the account with which the batched transaction is signed, will fail. However, the batcher will work when for sending Ether in batch transactions.
• The batcher contract can only cal functions on existing contracts - it does not create new contracts

TODO

• use assembly call to save gas
• use assembly create to also allow for contract creation
• forward tokens, so that one can batch-send tokens as well as Ether

License

GNU GPL