metamask-extension/app/scripts/inpage.js

const createPayload = require('web3-provider-engine/util/create-payload')
const StreamProvider = require('./lib/stream-provider.js')
const LocalMessageDuplexStream = require('./lib/local-message-stream.js')
const setupMultiplex = require('./lib/stream-utils.js').setupMultiplex
const RemoteStore = require('./lib/remote-store.js').RemoteStore
const Web3 = require('web3')

// rename on window
delete window.Web3
window.MetamaskWeb3 = Web3

const DEFAULT_RPC_URL = 'https://rpc.metamask.io/'


//
// setup plugin communication
//

// setup background connection
var pluginStream = new LocalMessageDuplexStream({
  name: 'inpage',
  target: 'contentscript',
})
var mx = setupMultiplex(pluginStream)
// connect features
var remoteProvider = new StreamProvider()
remoteProvider.pipe(mx.createStream('provider')).pipe(remoteProvider)
remoteProvider.on('error', console.error.bind(console))

var initState = JSON.parse(localStorage['MetaMask-Config'] || '{}')
var publicConfigStore = new RemoteStore(initState)
var storeStream = publicConfigStore.createStream()
storeStream.pipe(mx.createStream('publicConfig')).pipe(storeStream)

publicConfigStore.subscribe(function(state){
  localStorage['MetaMask-Config'] = JSON.stringify(state)
})


//
// global web3
//

var web3 = new Web3(remoteProvider)
window.web3 = web3
web3.setProvider = function(){
  console.log('MetaMask - overrode web3.setProvider')
}
console.log('MetaMask - injected web3')


//
// handle synchronous requests
//

global.publicConfigStore = publicConfigStore

// set web3 defaultAcount
publicConfigStore.subscribe(function(state){
  web3.eth.defaultAccount = state.selectedAddress
})

// setup sync http provider
var providerConfig = publicConfigStore.get('provider') || {}
var providerUrl = providerConfig.rpcTarget ? providerConfig.rpcTarget : DEFAULT_RPC_URL
var syncProvider = new Web3.providers.HttpProvider(providerUrl)
publicConfigStore.subscribe(function(state){
  if (!state.provider) return
  if (!state.provider.rpcTarget || state.provider.rpcTarget === providerUrl) return
  providerUrl = state.provider.rpcTarget
  syncProvider = new Web3.providers.HttpProvider(providerUrl)
})

// handle sync methods
remoteProvider.send = function(payload){
  var result = null
  switch (payload.method) {

    case 'eth_accounts':
      // read from localStorage
      var selectedAddress = publicConfigStore.get('selectedAddress')
      result = selectedAddress ? [selectedAddress] : []
      break

    case 'eth_coinbase':
      // read from localStorage
      var selectedAddress = publicConfigStore.get('selectedAddress')
      result = selectedAddress || '0x0000000000000000000000000000000000000000'
      break

    // fallback to normal rpc
    default:
      return syncProvider.send(payload)

  }

  // return the result
  return {
    id: payload.id,
    jsonrpc: payload.jsonrpc,
    result: result,
  }
}