mitm.html

<!--
	mitm.html is the lite "man in the middle"

	This is only meant to signal the opener's messageChannel to
	the service worker - when that is done this mitm can be closed
    but it's better to keep it alive since this also stops the sw
    from restarting

	The service worker is capable of intercepting all request and fork their
	own "fake" response - wish we are going to craft
	when the worker then receives a stream then the worker will tell the opener
	to open up a link that will start the download
-->
<script>
// This will prevent the sw from restarting
let keepAlive = () => {
  keepAlive = () => {}
  var ping = location.href.substr(0, location.href.lastIndexOf('/')) + '/ping'
  var interval = setInterval(() => {
    if (sw) {
      sw.postMessage('ping')
    } else {
      fetch(ping).then(res => res.text(!res.ok && clearInterval(interval)))
    }
  }, 10000)
}

// message event is the first thing we need to setup a listner for
// don't want the opener to do a random timeout - instead they can listen for
// the ready event
// but since we need to wait for the Service Worker registration, we store the
// message for later
let messages = []
window.onmessage = evt => messages.push(evt)

let sw = null
let scope = ''

function registerWorker() {
  return navigator.serviceWorker.getRegistration('./').then(swReg => {
    return swReg || navigator.serviceWorker.register('sw.js', { scope: './' })
  }).then(swReg => {
    const swRegTmp = swReg.installing || swReg.waiting

    scope = swReg.scope

    return (sw = swReg.active) || new Promise(resolve => {
      swRegTmp.addEventListener('statechange', fn = () => {
        if (swRegTmp.state === 'activated') {
          swRegTmp.removeEventListener('statechange', fn)
          sw = swReg.active
          resolve()
        }
      })
    })
  })
}

// Now that we have the Service Worker registered we can process messages
function onMessage (event) {
  let { data, ports, origin } = event

  // It's important to have a messageChannel, don't want to interfere
  // with other simultaneous downloads
  if (!ports || !ports.length) {
    throw new TypeError("[StreamSaver] You didn't send a messageChannel")
  }

  if (typeof data !== 'object') {
    throw new TypeError("[StreamSaver] You didn't send a object")
  }

  // the default public service worker for StreamSaver is shared among others.
  // so all download links needs to be prefixed to avoid any other conflict
  data.origin = origin

  // if we ever (in some feature versoin of streamsaver) would like to
  // redirect back to the page of who initiated a http request
  data.referrer = data.referrer || document.referrer || origin

  // pass along version for possible backwards compatibility in sw.js
  data.streamSaverVersion = new URLSearchParams(location.search).get('version')

  if (data.streamSaverVersion === '1.2.0') {
    console.warn('[StreamSaver] please update streamsaver')
  }

  /** @since v2.0.0 */
  if (!data.headers) {
    console.warn("[StreamSaver] pass `data.headers` that you would like to pass along to the service worker\nit should be a 2D array or a key/val object that fetch's Headers api accepts")
  } else {
    // test if it's correct
    // should thorw a typeError if not
    new Headers(data.headers)
  }

  /** @since v2.0.0 */
  if (typeof data.filename === 'string') {
    console.warn("[StreamSaver] You shouldn't send `data.filename` anymore. It should be included in the Content-Disposition header option")
    // Do what File constructor do with fileNames
    data.filename = data.filename.replace(/\//g, ':')
  }

  /** @since v2.0.0 */
  if (data.size) {
    console.warn("[StreamSaver] You shouldn't send `data.size` anymore. It should be included in the content-length header option")
  }

  /** @since v2.0.0 */
  if (data.readableStream) {
    console.warn("[StreamSaver] You should send the readableStream in the messageChannel, not throught mitm")
  }

  /** @since v2.0.0 */
  if (!data.pathname) {
    console.warn("[StreamSaver] Please send `data.pathname` (eg: /pictures/summer.jpg)")
    data.pathname = Math.random().toString().slice(-6) + '/' + data.filename
  }

  // remove all leading slashes
  data.pathname = data.pathname.replace(/^\/+/g, '')

  // remove protocol
  let org = origin.replace(/(^\w+:|^)\/\//, '')

  // set the absolute pathname to the download url.
  data.url = new URL(`${scope + org}/${data.pathname}`).toString()

  if (!data.url.startsWith(`${scope + org}/`)) {
    throw new TypeError('[StreamSaver] bad `data.pathname`')
  }

  // This sends the message data as well as transferring
  // messageChannel.port2 to the service worker. The service worker can
  // then use the transferred port to reply via postMessage(), which
  // will in turn trigger the onmessage handler on messageChannel.port1.

  const transferable = data.readableStream
    ? [ ports[0], data.readableStream ]
    : [ ports[0] ]

  if (!(data.readableStream || data.transferringReadable)) {
    keepAlive()
  }

  return sw.postMessage(data, transferable)
}

if (window.opener) {
  // The opener can't listen to onload event, so we need to help em out!
  // (telling them that we are ready to accept postMessage's)
  window.opener.postMessage('StreamSaver::loadedPopup', '*')
}

if (navigator.serviceWorker) {
  registerWorker().then(() => {
    window.onmessage = onMessage
    messages.forEach(window.onmessage)
  })
} else {
  // FF can ping sw with fetch from a secure hidden iframe
  // shouldn't really be possible?
  keepAlive()
}

</script>