ethereum-contracts

Robust Ethereum contracts wrapper for easier deployment, method invocation and automatic type conversion.


Keywords
ethereum, blockchain, contract, solidity, web3
License
MIT
Install
npm install ethereum-contracts@1.0.0

Documentation

ethereum-contracts

Build Status NPM module Twitter URL

Ethereum contracts wrapper which makes it easier to deploy contracts to the blockchain and invoke their methods.

Features:

  • Automatically converts method arguments and return values according to types in contract ABI.
  • Auto-fetches transaction receipts for sendTransaction calls.
  • Promise-ified asynchronous interface for easy use.
  • Errors are gracefully handled
  • Customizable logging, can be turned on/off at runtime
  • Works with any web3 instance
  • No dependencies - works in Node, Electron apps and browsers
  • Automated tests

Installation

$ npm install ethereum-contracts

Usage

Basic contract deployment:

import Web3 from 'web3';
import solc from 'solc';
import { ContractFactory } from 'ethereum-contracts';

const web3 = new Web3(/* connect to running Geth node */);

// create a new factory
const factory = new ContractFactory({
  web3: web3,
  /* Account from which to make transactions */
  account: web3.eth.coinbase,
  /* Default gas to use for any transaction */
  gas: 500000 
});

// compile our contract
const soliditySrc = readFile(...);
constant contractData = Object.values(solc.compile(soliditySrc, 1).contracts).pop();

// get Contract instance
const contract = factory.make({
  contract: contractData,
});

// Deploy it!
contract.deploy()
  .then((contractInstance) => {
    // deployed ok!
  })
  .catch(console.error);

The deploy() method returns a Promise which resolves to an instance of ContractInstance (require('ethereum-contracts').ContractInstance) representing an instance of the contract at its deployed address.

This instance exposes an API which by which you can methods within the deployed contract.

Note: If you get an error stating that your account is locked then you may need to unlock it first using web3.personal.unlockAccount().

Invoking contract methods locally

Suppose we have a simple contract code:

contract Local {
  function getOne() returns (uint8, string) {
    return (123, "ok");
  }
}

We can call getOne() on the local blockchain without having to send out a transaction:

console.log( contractInstance.localCall('getOne') );

/* [ 123, "ok" ] */

Invoking contract methods via Transaction

Let's say our contract is:

contract Counter {
  uint8 val;

  function increment(){
    val += 1;
  }
}

We can invoke increment() by sending a transaction to the blockchain, which returns a Promise:

contractInstance.sendCall('increment')
.then((txReceipt) => {
  // do something
})
.catch(console.error);

The txReceipt object returned above is the result of the call to web3.eth.getTransactionReceipt() for the corresponding transaction.

Passing in method arguments

Let's say we our contract is:

contract Counter {
  uint8 val;
  string label;

  function increment(uint8 amount, string newLabel) {
    val += amount;
    label = newLabel;
  }

  function isBigger(uint8 check) returns (bool) {
    return (check > val) ? true : false;
  }
}

We can pass in arguments for both local calls and transaction calls as key-value pairs (i.e. Object):

// local
let result = contractInstance.localCall('isBigger', {
  check: 5
})

// transaction
contractInstance.sendCall('increment', {
  amount: 10,
  newLabel: 'hello world'
});

Override account and gas

Whether deploying a contract or calling a method via transaction, the gas value and account from which the transaction is sent can be overridden on a per-call basis:

import { Contract } from 'ethereum-contracts';

contract = new Contract({
  web3: web3,
  contract: contractData,
  account: web3.eth.coinbase,
  gas: 500000
})

contract.deploy({}, {
  /* override account */
  account: '0xaa1a6e3e6ef20068f7f8d8c835d2d22fd5116444',
})
.then((contractInstance) => {
  return contractInstance.sendCall('increment', {}, {
    /* override gas */
    gas: 100000
  });
})

Browser usage

If you are not using a packaging manager and are instead importing ethereumContracts.js directly then the class is exposed on the global object as EthereumContracts. Thus, in the browser window context you would use it like this:

const contractFactory = new window.EthereumContracts.ContractFactory({
  web3: web3,
  account: web3.eth.coinbase,
  gas: 500000
});

Type conversions

When passing in method arguments the wrapper will try to type-cast each argument to the required target type as defined in the contract ABI.

Specifically, here is what it does for each type:

  • int/uint, int8/uint8, ..., int256/uint256 - input argument is converted to a number and then checked to ensure it is within the accepted range of numbers for the given type's boundaries. Note that Date instances get auto-converted to their millisecond representations.
  • string - input argument is converted to a string.
  • bool - if input argument is 0, false, "false", or "" it is passed on as false else it is passed on as true.
  • address - if input argument is a number it is converted to a hex representation with enough padding to ensure it is a valid address. Otherwise it is string-ified and checked using web3.isAddress().
  • byte, bytes, bytes, ..., bytes32 - input argument is converted to hex using web3.toHex().

For return values, the logic just ensures that int/uint values are returned as actual numbers and not BigNumber instances (as is usually returned by web3).

Example

Let's say our contructor has:

contract Test {
  constructor(uint256 val, bool flag, address addr) {}
}

If we deploy with the following arguments...

this.contract.deploy({
  val: new Date(2016,0,1,5,30,22),
  flag: 'false',
  addr: 234234
});

...the actual values passed to the constructor will be:

(1451597422000, false, '0x00000000000000000000000000000000000392fa')

Development

To build and run the tests:

$ npm install
$ npm test

To run tests with coverage:

$ npm run test-coverage

Contributions

Contributions welcome - see CONTRIBUTING.md

License

MIT - see LICENSE.md