metamask-extension/app/scripts/lib/stream-provider.js

const Duplex = require('readable-stream').Duplex
const inherits = require('util').inherits

module.exports = StreamProvider


inherits(StreamProvider, Duplex)

function StreamProvider(){
  Duplex.call(this, {
    objectMode: true,
  })

  this._payloads = {}
}

// public

StreamProvider.prototype.send = function(payload){
  throw new Error('StreamProvider - does not support synchronous RPC calls. called: "'+payload.method+'"')
}

StreamProvider.prototype.sendAsync = function(payload, callback){
  // console.log('StreamProvider - sending payload', payload)
  this._payloads[payload.id] = [payload, callback]
  // console.log('payload for plugin:', payload)
  this.push(payload)
}

// private

StreamProvider.prototype._onResponse = function(response){
  // console.log('StreamProvider - got response', payload)
  var data = this._payloads[response.id]
  if (!data) throw new Error('StreamProvider - Unknown response id')
  delete this._payloads[response.id]
  var payload = data[0]
  var callback = data[1]

  // logging
  var res = Array.isArray(response) ? response : [response]
  ;(Array.isArray(payload) ? payload : [payload]).forEach(function(payload, index){
    console.log('plugin response:', payload.id, payload.method, payload.params, '->', res[index].result)
  })

  callback(null, response)
}

// stream plumbing

StreamProvider.prototype._read = noop

StreamProvider.prototype._write = function(msg, encoding, cb){
  this._onResponse(msg)
  cb()
}

// util

function noop(){}