web3: Ethereum API for Haskell

Ethereum Haskell API

This is the Ethereum compatible Haskell API which implements the Generic JSON RPC spec.

Installation

$ git clone https://github.com/airalab/hs-web3 && cd hs-web3
$ stack setup
$ stack ghci

This library runs only paired with geth or parity Ethereum node, please start node first before using the library.

Web3 monad

Any Ethereum node communication wrapped with Web3 monadic type.

> import Network.Ethereum.Web3.Web3
> :t clientVersion
clientVersion :: Web3 Text

To run this computation used runWeb3' or runWeb3 functions.

> import Network.Ethereum.Web3
> runWeb3 clientVersion
Right "Parity//v1.4.5-beta-a028d04-20161126/x86_64-linux-gnu/rustc1.13.0"

Function runWeb3 use default Web3 provider at localhost:8545.

> :t runWeb3
runWeb3
  :: MonadIO m => Web3 a -> m (Either Web3Error a)

TemplateHaskell generator

Quasiquotation is used to parse contract ABI or load from JSON file. TemplateHaskell driven Haskell contract API generator can automatical create ABI encoding instances and contract method helpers.

> :set -XQuasiQuotes
> import Network.Ethereum.Contract.TH
> putStr [abiFrom|data/sample.json|]
Contract:
        Events:
                Action1(address,uint256)
                Action2(string,uint256)
        Methods:
                0x03de48b3 runA1()
                0x90126c7a runA2(string,uint256)

See example of usage below. Use -ddump-splices to see generated code during compilation or in GHCi.

{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE DeriveGeneric         #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE QuasiQuotes           #-}
module Main where

import           Data.Default                 (def)
import           Data.Text                    (unpack)
import           Text.Printf                  (printf)

import           Network.Ethereum.Contract.TH
import           Network.Ethereum.Web3        hiding (name)

[abiFrom|data/ERC20.json|]

main :: IO ()
main = do
    result <- runWeb3 $ do
        n <- name tokenCall
        s <- symbol tokenCall
        d <- decimals tokenCall
        return $ printf "Token %s with symbol %s and decimals %d"
                   (unpack n) (unpack s) (fromIntegral d :: Int)
    case result of
      Left error -> print error
      Right info -> putStrLn info
  where
    token :: Address
    token = "0xA2f4FCb0FDe2dD59f7a1873e121bc5623e3164Eb"

    tokenCall :: Call
    tokenCall = def { callTo = Just token }

Additional minimalistic example of JSON ABI code genration available in data/ERC20.hs.

Testing

Testing the web3 is split up into two suites: unit and live. The unit suite tests internal library facilities, while the live tests that the library adequately interacts with a Web3 provider.

One may simply run stack test to run both suites, or stack test web3:unit or stack test web3:live to run the test suites individually.

The unit suite has no external dependencies, while the live suite requires Truffle and jq to be available on your machine.

The live suite also requires a Web3 provider with Ethereum capabilities, as well as an unlocked account with ether to send transactions from. It uses Truffle to deploy testing contracts, generating ABIs for them in the process, then using said ABIs as part of a TemplateHaskell step in the suite. It is assumed that the provider is available at http://localhost:8545. If that's not the case, you must update truffle.js so that Truffle can deploy the contracts correctly, and pass the WEB3_PROVIDER=http://host:port environment variable when running the tests so that the web3 library can interact with the chain that's being tested against.