MetaMaskSigner / Web3Signer for ethers.js

Web3Provider.js

import { providers } from 'ethers';
import Eth from 'ethjs';

class Web3Provider extends providers.Provider {
  constructor() {
    super();
    // https://github.com/MetaMask/faq/blob/master/detecting_metamask.md#web3-deprecation
    if (typeof window.web3 == 'undefined' || typeof window.web3.currentProvider == 'undefined') {
      throw new Error('Web3Provider can just be used with a web3 currentProvider injected');
    }
    this.eth = new Eth(window.web3.currentProvider);
  }
  async perform(method, params) {
    switch (method) {
      case 'getGasPrice': {
        const gasPriceBn = await this.eth.gasPrice();
        // Converting to string for now as this is the only format both BN libs understand
        return gasPriceBn.toString();
      }
      case 'getTransactionCount':
        return this.eth.getTransactionCount(params.address, params.blockTag);
      default:
        return Promise.reject(new Error('Not implemented'));
    }
  }
}

export default Web3Provider;

Web3Signer.js

import Web3Provider from './Web3Provider';

const ethersTxToWeb3 = (tx, from) => ({
  from,
  to: tx.to,
  value: tx.value ? tx.value.toString() : '0',
  gas: tx.gasLimit.toString(),
  gasPrice: tx.gasPrice.toString(),
  data: tx.data,
  nonce: tx.nonce,
});

class Web3Signer {
  constructor() {
    this.provider = new Web3Provider();
  }
  async getAddress() {
    // https://github.com/MetaMask/faq/blob/master/DEVELOPERS.md#raising_hand-account-list-reflects-user-preference
    const accounts = await this.provider.eth.accounts();
    return accounts[0];
  }
  async sign(tx) {
    const from = await this.getAddress();
    const web3Tx = ethersTxToWeb3(tx, from);
    return this.provider.eth.sendTransaction(web3Tx);
  }
}

export default Web3Signer;