Overview

This repository contains a transaction manager contract, allowing its owner to make multiple contract calls in one Ethereum transaction. This saves time, but what's most important it allows things like multi-step arbitrage to be executed in one transaction.

NOTE: this is great for testnets but it doesn't implement auth so anyone can invoke it. DO NOT USE ON MAINNET.

Contract deployment

The TxManager contract takes no parameters.

Use Dapp (https://github.com/dapphub/dapp) to build and deploy the contract:

dapp build
ETH_GAS=2000000 dapp create TxManager

Contract usage

The contract has only one public function:

function execute(bytes script) { … }

The script parameter is a byte array representing the sequence of contract calls to be made. It consists of multiple call records concatenated together, whereas each record is built as follows:

+-----------------+---------------------+-----------------------...------+
|     address     |   calldata length   |         calldata               |
|                 |                     |                                |
|   (20 bytes)    |      (32 bytes)     |                                |
+-----------------+---------------------+-----------------------...------+

For example, if you want to make one call to 0x11111222223333344444333332222211111122222, the script may look like this 111112222233333444443333322222111111222220000000000000000000000000000000000000000000000000000000000000024a39f1c6c0000000000000000000000000000000000000000000000000000000000000064, the last part of it being calldata encoded with:

$ seth calldata 'cork(uint256)' 100
0xa39f1c6c0000000000000000000000000000000000000000000000000000000000000064

The script parameter should be a concatenation of records of all calls to be made.

Typescript Example

import Web3 from "web3";

function padBytes(web3: Web3, calldata: string) {
  return web3.utils.padRight(calldata, Math.ceil(calldata.length / 32) * 32);
}

/**
 * We need to align build string so web3 will convert it to bytes later. This might be avoided if we build whole calldata manually but since we want to avoid it this is the only way. Also, this forced us to add additional check in tx-manager to skip ill formatted calldata
 */
export function buildCalls(
  web3: Web3,
  calls: { address: string; calldata: any }[]
) {
  let finalCalldata = "";
  for (const call of calls) {
    const calldata = call.calldata.encodeABI().slice(2);

    finalCalldata +=
      //tslint:disable-next-line
      call.address.slice(2) +
      web3.eth.abi.encodeParameter("uint256", calldata.length / 2).slice(2) +
      calldata;
  }

  return "0x" + padBytes(web3, finalCalldata);
}

const calls = [
  { address: spot.address, calldata: spot.methods.poke(ilkCode) },
  { address: jug.address, calldata: jug.methods.init(ilkCode) }
];
const calldata = buildCalls(web3, calls);

await txManager.methods.execute(calldata).send();