Loaders make it possible to easily access and load Ethereum smart contracts.

To interact with a contract, whether it's deployed on a local or remote network, you need the address of the deployed contract and its Application Binary Interface (ABI).

Loaders provide a simple way to get the address and ABI of a deployed contract, in a specific version, at a particular location (mainnet, testnet, or a local network). Within Tailor, this information is then parsed and used to form the Tailor instance.

In a nutshell, the loader is an abstraction that takes an argument (e.g. the name of a contract) and returns a definition (e.g. the address of the contract and its ABI) from a specific source (e.g. an http host).

How to use loaders

We imagine that the most useful case for developers will be for a loader to accept a contract address and return that contract's ABI from an http source such as Etherscan's API. Tailor provides several options for loading contract data.

Loading ABI from Etherscan with an address

Internally, Tailor is instantiating the Etherscan loader and calling its .load method with the provided query. The result of that (the contractData) is then handed over to the parser, which parses the data and tells Tailor what constants, events and methods are available on the contract.

import Tailor from '@colony/tailor';

// The default endpoint for Etherscan:
// https://api.etherscan.io/api?module=contract&action=getabi&address=%%ADDRESS%%

const client = Tailor.load({
  loader: 'etherscan',
  query: {
    contractAddress: '0xf000000000000000000000000000000000000000',
  },
  ...
});

We can also use EtherscanLoader to load contract data without creating a client instance.

import { EtherscanLoader } from '@colony/tailor';

// Create an instance of the loader
const loader = new EtherscanLoader();

// Get the contract data using the loader
const { abi, address, bytecode } = await loader.load({
  contractAddress: '0xf000000000000000000000000000000000000000',
});

Loading contractAddress and ABI from TrufflePig with a name

For local development, contracts are quite commonly deployed, destroyed, and re-deployed multiple times to a local test network. Colony's very own TrufflePig is a tool that was built to serve and load both the contractAddress and ABI when given a unique name for a specific contract.

import Tailor from '@colony/tailor';

// The default endpoint for TrufflePig:
// https://127.0.0.1:3030/contracts?name=%%NAME%%&address=%%ADDRESS%%&version=%%VERSION%%

const client = Tailor.load({
  loader: 'trufflepig',
  query: {
    contractName: 'ColonyNetwork',
  },
  ...
});

We can also use TrufflepigLoader to load contract data without creating a client instance.

import { TrufflepigLoader } from '@colony/tailor';

// Create an instance of the loader
const loader = new TrufflepigLoader();

// Get the contract data using the loader
const { abi, address, bytecode } = await loader.load({
  contractName: 'ColonyNetwork',
});

Loading from a custom data source using the transform property

It's possible that a custom data source will deliver your data in a format different than Etherscan or TrufflePig. For this, it's necessary to utilize the transform property, which can transform the raw output of the source. The default behavior of transform is to return the JSON object that is passed to it.

import Tailor from '@colony/tailor';

const client = Tailor.load({
  name: 'http',
  options: {
    endpoint: 'https://example.io/contracts?address=%%ADDRESS%%',
    transform(response, query) {
      return {
        address: query.contractAddress,
        abi: response.data.contractABI,
        bytecode: response.data.bytecode
      };
    },
  },
  ...
});

We can also use HttpLoader to load contract data without creating a client instance.

import { HttpLoader } from '@colony/tailor';

// Create an instance of the loader
const loader = new HttpLoader({
  endpoint: 'https://example.io/contracts?address=%%ADDRESS%%',
  transform(response, query) {
    return {
      address: query.contractAddress,
      abi: response.data.contractABI,
      bytecode: response.data.bytecode
    };
  },
});

// Get the contract data using the loader
const { abi, address, bytecode } = await loader.load({
  contractAddress: '0xf000000000000000000000000000000000000000'
});

Future/Imaginable loaders

Both the EtherscanLoader and TrufflepigLoader are modified versions of the more general HttpLoader. We plan to extend this functionality to load contract data from more data sources, such as:

• IPFS
• EthPM
• GitHub tagged releases
• Databases (including IndexedDB)
• Browser file API
• Swarm