metamask-extension/app/scripts/inpage.js

const XHR = window.XMLHttpRequest
const fauxJax = require('faux-jax')
fauxJax.install()
const Web3 = require('web3')
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 RPC_URL = 'https://rawtestrpc.metamask.io/'


//
// setup plugin communication
//

var pluginStream = new LocalMessageDuplexStream({
  name: 'inpage',
  target: 'contentscript',
})
var remoteProvider = new StreamProvider()
remoteProvider.pipe(pluginStream).pipe(remoteProvider)

pluginStream.on('error', console.error.bind(console))
remoteProvider.on('error', console.error.bind(console))


//
// handle synchronous requests
//

// handle accounts cache
var accountsCache = []
setInterval(populateAccountsCache, 4000)
function populateAccountsCache(){
  remoteProvider.sendAsync(createPayload({
    method: 'eth_accounts',
    params: [],
    note: 'from metamask inpage provider',
  }), function(err, response){
    if (err) return console.error('MetaMask - Error polling accounts')
    // update localStorage
    var accounts = response.result
    if (accounts.toString() !== accountsCache.toString()) {
      accountsCache = accounts
      localStorage['MetaMask-Accounts'] = JSON.stringify(accounts)
    }
  })
}

// handle synchronous methods via standard http provider
var syncProvider = new Web3.providers.HttpProvider(RPC_URL)
remoteProvider.send = function(payload){
  var result = null
  switch (payload.method) {
    
    case 'eth_accounts':
      // read from localStorage
      accountsCache = JSON.parse(localStorage['MetaMask-Accounts'] || '[]')
      result = accountsCache
      break

    case 'eth_coinbase':
      // read from localStorage
      accountsCache = JSON.parse(localStorage['MetaMask-Accounts'] || '[]')
      result = accountsCache[0] || '0x0000000000000000000000000000000000000000'
      break

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

  }

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

//
// global web3
//

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


//
// intercept local node requests
//


console.log('MetaMask - intercepting localhost:8545 requests')

fauxJax.on('request', function(req){
  // check if local node request
  if (req.requestURL.indexOf('localhost:8545') !== -1) {
    var rpcReq = JSON.parse(req.requestBody)
    if (req.async) {
      remoteProvider.sendAsync(rpcReq, function(err, result){
        // console.log('intercepted request (async):', rpcReq, result)
        handleResult(result)
      })
    } else {
      var result = remoteProvider.send(rpcReq)
      // console.log('intercepted request (sync):', rpcReq, result)
      handleResult(result)
    }
  } else {
    // console.log('request continuing normally:', req.requestURL)
    continueRequestNormally(req)
  }

  function handleResult(result){
    var serializedResult = JSON.stringify(result)
    req.respond(200, {
      'content-type': 'application/json',
    }, serializedResult)
  }
})

function continueRequestNormally(req){
  var xhr = new XHR()
  // set target url and method
  xhr.open(req.requestMethod, req.requestURL, req.async)
  // set headers
  Object.keys(req.requestHeaders || {}).forEach(function(headerKey){
    xhr.setRequestHeader(headerKey, req.requestHeaders[headerKey])
  })
  // send and call completion handler
  if (req.async) {
    xhr.onload = copyResult
    xhr.send(req.requestBody)
  } else {
    xhr.send(req.requestBody)
    copyResult()
  }

  function copyResult() {
    var headers = extractResponseHeaders(xhr.getAllResponseHeaders())
    req.respond(xhr.status, headers, xhr.response)
  }
}

function extractResponseHeaders(rawHeaders){
  var headers = {}
  var headerKeyValues = rawHeaders.split('\r\n').filter(Boolean)
  headerKeyValues.forEach(function(keyValue){
    var data = keyValue.split(': ')
    headers[data[0]] = data[1]
  })
  return headers
}