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

const Duplex = require('readable-stream').Duplex
const inherits = require('util').inherits
const noop = function () {}

module.exports = PortDuplexStream

inherits(PortDuplexStream, Duplex)

/**
 * Creates a stream that's both readable and writable.
 * The stream supports arbitrary objects.
 *
 * @class
 * @param {Object} port Remote Port object
 */
function PortDuplexStream (port) {
  Duplex.call(this, {
    objectMode: true,
  })
  this._port = port
  port.onMessage.addListener(this._onMessage.bind(this))
  port.onDisconnect.addListener(this._onDisconnect.bind(this))
}

/**
 * Callback triggered when a message is received from
 * the remote Port associated with this Stream.
 *
 * @private
 * @param {Object} msg - Payload from the onMessage listener of Port
 */
PortDuplexStream.prototype._onMessage = function (msg) {
  if (Buffer.isBuffer(msg)) {
    delete msg._isBuffer
    var data = new Buffer(msg)
    this.push(data)
  } else {
    this.push(msg)
  }
}

/**
 * Callback triggered when the remote Port
 * associated with this Stream disconnects.
 *
 * @private
 */
PortDuplexStream.prototype._onDisconnect = function () {
  this.destroy()
}

/**
 * Explicitly sets read operations to a no-op
 */
PortDuplexStream.prototype._read = noop


/**
 * Called internally when data should be written to
 * this writable stream.
 * 
 * @private
 * @param {*} msg Arbitrary object to write
 * @param {string} encoding Encoding to use when writing payload
 * @param {Function} cb Called when writing is complete or an error occurs
 */
PortDuplexStream.prototype._write = function (msg, encoding, cb) {
  try {
    if (Buffer.isBuffer(msg)) {
      var data = msg.toJSON()
      data._isBuffer = true
      this._port.postMessage(data)
    } else {
      this._port.postMessage(msg)
    }
  } catch (err) {
    return cb(new Error('PortDuplexStream - disconnected'))
  }
  cb()
}