/**
 * @fileoverview Utilities for mixed-content in Web Platform Tests.
 * @author burnik@google.com (Kristijan Burnik)
 * Disclaimer: Some methods of other authors are annotated in the corresponding
 *     method's JSDoc.
 */

// ===============================================================
// Types
// ===============================================================
// Objects of the following types are used to represent what kind of
// subresource requests should be sent with what kind of policies,
// from what kind of possibly nested source contexts.
// The objects are represented as JSON objects (not JavaScript/Python classes
// in a strict sense) to be passed between JavaScript/Python code.

// Note: So far this document covers:
// - resources/common.js : client-side test infra code
// - scope/ - server-side scripts that serves nested source contexts
// but doesn't cover:
// - tools/ - generator scripts that generates top-level HTML documents.
// There are some policies only handled by generators (e.g. mixed-content
// opt-ins) and not yet covered by the docs here.

/**
  @typedef PolicyDelivery
  @type {object}
  Referrer policy etc. can be applied/delivered in several ways.
  A PolicyDelivery object specifies what policy is delivered and how.

  @property {string} deliveryType
    Specifies how the policy is delivered.
    The valid deliveryType are:

     "attr"
        [A] DOM attributes e.g. referrerPolicy.

      "rel-noref"
        [A] <link rel="noreferrer"> (referrer-policy only).

      "http-rp"
        [B] HTTP response headers.

      "meta"
        [B] <meta> elements.

  @property {string} key
  @property {string} value
    Specifies what policy to be delivered. The valid keys are:

      "referrerPolicy"
        Referrer Policy
        https://w3c.github.io/webappsec-referrer-policy/
        Valid values are those listed in
        https://w3c.github.io/webappsec-referrer-policy/#referrer-policy
        (except that "" is represented as null/None)

  A PolicyDelivery can be specified in several ways:

  - (for [A]) Associated with an individual subresource request and
    specified in `Subresource.policies`,
    e.g. referrerPolicy attributes of DOM elements.
    This is handled in invokeRequest().

  - (for [B]) Associated with an nested environmental settings object and
    specified in `SourceContext.policies`,
    e.g. HTTP referrer-policy response headers of HTML/worker scripts.
    This is handled in server-side under /common/security-features/scope/.

  - (for [B]) Associated with the top-level HTML document.
    This is handled by the generators.d
*/

/**
  @typedef Subresource
  @type {object}
  A Subresource represents how a subresource request is sent.

  @property{SubresourceType} subresourceType
    How the subresource request is sent,
    e.g. "img-tag" for sending a request via <img src>.
    See the keys of `subresourceMap` for valid values.

  @property{string} url
    subresource's URL.
    Typically this is constructed by getRequestURLs() below.

  @property{PolicyDelivery} policyDeliveries
    Policies delivered specific to the subresource request.
*/

/**
  @typedef SourceContext
  @type {object}
  Requests can be possibly sent from various kinds of source contexts, i.e.
  fetch client's environment settings objects:
  top-level windows, iframes, or workers.
  A SourceContext object specifies one environment settings object, and
  an Array<SourceContext> specifies a possibly nested context,
  from the outer-most to inner-most environment settings objects.

  For example:
    [{sourceContextType: "srcdoc"}, {sourceContextType: "classic-worker"}]
  means that a subresource request is to be sent from
  a classic dedicated worker created from <iframe srcdoc>
  inside the top-level HTML document.
  Note: the top-level document is not included in the array and
  is assumed implicitly.

  SourceContext (or Array<SourceContext>) is set based on
  the fetch client's settings object that is used for the subresource request,
  NOT on module map settings object, and
  NOT on the inner-most settings object that appears in the test.
  For example, Array<SourceContext> is `[]` (indicating the top Window)
  for `worker.js`
  - When it is the root worker script: `new Worker('worker.js')`, or
  - When it is imported from the root worker script:
    `new Worker('top.js', {type: 'module'})`
    where `top.js` has `import 'worker.js'`.
  because the request for `worker.js` uses the Window as its fetch client's
  settings object, while a WorkerGlobalScope is created though.

  @property {string} sourceContextType
    Kind of the source context to be used.
    Valid values are the keys of `sourceContextMap` below.

  @property {Array<PolicyDelivery>} policyDeliveries
    A list of PolicyDelivery applied to the source context.
*/

// ===============================================================
// General utility functions
// ===============================================================

function timeoutPromise(t, ms) {
  return new Promise(resolve => { t.step_timeout(resolve, ms); });
}

/**
 * Normalizes the target port for use in a URL. For default ports, this is the
 *     empty string (omitted port), otherwise it's a colon followed by the port
 *     number. Ports 80, 443 and an empty string are regarded as default ports.
 * @param {number} targetPort The port to use
 * @return {string} The port portion for using as part of a URL.
 */
function getNormalizedPort(targetPort) {
  return ([80, 443, ""].indexOf(targetPort) >= 0) ? "" : ":" + targetPort;
}

/**
 * Creates a GUID.
 *     See: https://en.wikipedia.org/wiki/Globally_unique_identifier
 *     Original author: broofa (http://www.broofa.com/)
 *     Sourced from: http://stackoverflow.com/a/2117523/4949715
 * @return {string} A pseudo-random GUID.
 */
function guid() {
  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    var r = Math.random() * 16 | 0, v = c == 'x' ? r : (r & 0x3 | 0x8);
    return v.toString(16);
  });
}

/**
 * Initiates a new XHR via GET.
 * @param {string} url The endpoint URL for the XHR.
 * @param {string} responseType Optional - how should the response be parsed.
 *     Default is "json".
 *     See: https://xhr.spec.whatwg.org/#dom-xmlhttprequest-responsetype
 * @return {Promise} A promise wrapping the success and error events.
 */
function xhrRequest(url, responseType) {
  return new Promise(function(resolve, reject) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.responseType = responseType || "json";

    xhr.addEventListener("error", function() {
      reject(Error("Network Error"));
    });

    xhr.addEventListener("load", function() {
      if (xhr.status != 200)
        reject(Error(xhr.statusText));
      else
        resolve(xhr.response);
    });

    xhr.send();
  });
}

/**
 * Sets attributes on a given DOM element.
 * @param {DOMElement} element The element on which to set the attributes.
 * @param {object} An object with keys (serving as attribute names) and values.
 */
function setAttributes(el, attrs) {
  attrs = attrs || {}
  for (var attr in attrs) {
    if (attr !== 'src')
      el.setAttribute(attr, attrs[attr]);
  }
  // Workaround for Chromium: set <img>'s src attribute after all other
  // attributes to ensure the policy is applied.
  for (var attr in attrs) {
    if (attr === 'src')
      el.setAttribute(attr, attrs[attr]);
  }
}

/**
 * Binds to success and error events of an object wrapping them into a promise
 *     available through {@code element.eventPromise}. The success event
 *     resolves and error event rejects.
 * This method adds event listeners, and then removes all the added listeners
 * when one of listened event is fired.
 * @param {object} element An object supporting events on which to bind the
 *     promise.
 * @param {string} resolveEventName [="load"] The event name to bind resolve to.
 * @param {string} rejectEventName [="error"] The event name to bind reject to.
 */
function bindEvents(element, resolveEventName, rejectEventName) {
  element.eventPromise =
      bindEvents2(element, resolveEventName, element, rejectEventName);
}

// Returns a promise wrapping success and error events of objects.
// This is a variant of bindEvents that can accept separate objects for each
// events and two events to reject, and doesn't set `eventPromise`.
//
// When `resolveObject`'s `resolveEventName` event (default: "load") is
// fired, the promise is resolved with the event.
//
// When `rejectObject`'s `rejectEventName` event (default: "error") or
// `rejectObject2`'s `rejectEventName2` event (default: "error") is
// fired, the promise is rejected.
//
// `rejectObject2` is optional.
function bindEvents2(resolveObject, resolveEventName, rejectObject, rejectEventName, rejectObject2, rejectEventName2) {
  return new Promise(function(resolve, reject) {
    const actualResolveEventName = resolveEventName || "load";
    const actualRejectEventName = rejectEventName || "error";
    const actualRejectEventName2 = rejectEventName2 || "error";

    const resolveHandler = function(event) {
      cleanup();
      resolve(event);
    };

    const rejectHandler = function(event) {
      // Chromium starts propagating errors from worker.onerror to
      // window.onerror. This handles the uncaught exceptions in tests.
      event.preventDefault();
      cleanup();
      reject(event);
    };

    const cleanup = function() {
      resolveObject.removeEventListener(actualResolveEventName, resolveHandler);
      rejectObject.removeEventListener(actualRejectEventName, rejectHandler);
      if (rejectObject2) {
        rejectObject2.removeEventListener(actualRejectEventName2, rejectHandler);
      }
    };

    resolveObject.addEventListener(actualResolveEventName, resolveHandler);
    rejectObject.addEventListener(actualRejectEventName, rejectHandler);
    if (rejectObject2) {
      rejectObject2.addEventListener(actualRejectEventName2, rejectHandler);
    }
  });
}

/**
 * Creates a new DOM element.
 * @param {string} tagName The type of the DOM element.
 * @param {object} attrs A JSON with attributes to apply to the element.
 * @param {DOMElement} parent Optional - an existing DOM element to append to
 *     If not provided, the returned element will remain orphaned.
 * @param {boolean} doBindEvents Optional - Whether to bind to load and error
 *     events and provide the promise wrapping the events via the element's
 *     {@code eventPromise} property. Default value evaluates to false.
 * @return {DOMElement} The newly created DOM element.
 */
function createElement(tagName, attrs, parentNode, doBindEvents) {
  var element = document.createElement(tagName);

  if (doBindEvents)
    bindEvents(element);

  // We set the attributes after binding to events to catch any
  // event-triggering attribute changes. E.g. form submission.
  //
  // But be careful with images: unlike other elements they will start the load
  // as soon as the attr is set, even if not in the document yet, and sometimes
  // complete it synchronously, so the append doesn't have the effect we want.
  // So for images, we want to set the attrs after appending, whereas for other
  // elements we want to do it before appending.
  var isImg = (tagName == "img");
  if (!isImg)
    setAttributes(element, attrs);

  if (parentNode)
    parentNode.appendChild(element);

  if (isImg)
    setAttributes(element, attrs);

  return element;
}

function createRequestViaElement(tagName, attrs, parentNode) {
  return createElement(tagName, attrs, parentNode, true).eventPromise;
}

/**
 * Creates a new empty iframe and appends it to {@code document.body} .
 * @param {string} name The name and ID of the new iframe.
 * @param {boolean} doBindEvents Whether to bind load and error events.
 * @return {DOMElement} The newly created iframe.
 */
function createHelperIframe(name, doBindEvents) {
  return createElement("iframe",
                       {"name": name, "id": name},
                       document.body,
                       doBindEvents);
}

function wrapResult(server_data) {
  if (typeof(server_data) === "string") {
    throw server_data;
  }
  return {
    referrer: server_data.headers.referer,
    headers: server_data.headers
  }
}

// ===============================================================
// Subresources
// ===============================================================

/**
  @typedef RequestResult
  @type {object}
  Represents the result of sending an request.
  All properties are optional. See the comments for
  requestVia*() and invokeRequest() below to see which properties are set.

  @property {Array<Object<string, string>>} headers
    HTTP request headers sent to server.
  @property {string} referrer - Referrer.
  @property {string} location - The URL of the subresource.
  @property {string} sourceContextUrl
    the URL of the global object where the actual request is sent.
*/

/**
  requestVia*(url, additionalAttributes) functions send a subresource
  request from the current environment settings object.

  @param {string} url
    The URL of the subresource.
  @param {Object<string, string>} additionalAttributes
    Additional attributes set to DOM elements
    (element-initiated requests only).

  @returns {Promise} that are resolved with a RequestResult object
  on successful requests.

  - Category 1:
      `headers`: set.
      `referrer`: set via `document.referrer`.
      `location`: set via `document.location`.
      See `template/document.html.template`.
  - Category 2:
      `headers`: set.
      `referrer`: set to `headers.referer` by `wrapResult()`.
      `location`: not set.
  - Category 3:
      All the keys listed above are NOT set.
  `sourceContextUrl` is not set here.

  -------------------------------- -------- --------------------------
  Function name                    Category Used in
                                            -------- ------- ---------
                                            referrer mixed-  upgrade-
                                            policy   content insecure-
                                            policy   content request
  -------------------------------- -------- -------- ------- ---------
  requestViaAnchor                 1        Y        Y       -
  requestViaArea                   1        Y        Y       -
  requestViaAudio                  3        -        Y       -
  requestViaDedicatedWorker        2        Y        Y       Y
  requestViaFetch                  2        Y        Y       -
  requestViaForm                   3        -        Y       -
  requestViaIframe                 1        Y        Y       -
  requestViaImage                  2        Y        Y       -
  requestViaLinkPrefetch           3        -        Y       -
  requestViaLinkStylesheet         3        -        Y       -
  requestViaObject                 3        -        Y       -
  requestViaPicture                3        -        Y       -
  requestViaScript                 2        Y        Y       -
  requestViaSendBeacon             3        -        Y       -
  requestViaSharedWorker           2        Y        -       -
  requestViaVideo                  3        -        Y       -
  requestViaWebSocket              3        -        Y       -
  requestViaWorklet                3        -        Y       Y
  requestViaXhr                    2        Y        Y       -
  -------------------------------- -------- -------- ------- ---------
*/

/**
 * Creates a new iframe, binds load and error events, sets the src attribute and
 *     appends it to {@code document.body} .
 * @param {string} url The src for the iframe.
 * @return {Promise} The promise for success/error events.
 */
function requestViaIframe(url, additionalAttributes) {
  const iframe = createElement(
      "iframe",
      Object.assign({"src": url}, additionalAttributes),
      document.body,
      false);
  return bindEvents2(window, "message", iframe, "error", window, "error")
      .then(event => {
          if (event.source !== iframe.contentWindow)
            return Promise.reject(new Error('Unexpected event.source'));
          return event.data;
        });
}

/**
 * Creates a new image, binds load and error events, sets the src attribute and
 *     appends it to {@code document.body} .
 * @param {string} url The src for the image.
 * @return {Promise} The promise for success/error events.
 */
function requestViaImage(url, additionalAttributes) {
  const img = createElement(
      "img",
      // crossOrigin attribute is added to read the pixel data of the response.
      Object.assign({"src": url, "crossOrigin": "Anonymous"}, additionalAttributes),
      document.body, true);
  return img.eventPromise.then(() => wrapResult(decodeImageData(img)));
}

// Helper for requestViaImage().
function decodeImageData(img) {
  var canvas = document.createElement("canvas");
  var context = canvas.getContext('2d');
  context.drawImage(img, 0, 0);
  var imgData = context.getImageData(0, 0, img.clientWidth, img.clientHeight);
  const rgba = imgData.data;

  let decodedBytes = new Uint8ClampedArray(rgba.length);
  let decodedLength = 0;

  for (var i = 0; i + 12 <= rgba.length; i += 12) {
    // A single byte is encoded in three pixels. 8 pixel octets (among
    // 9 octets = 3 pixels * 3 channels) are used to encode 8 bits,
    // the most significant bit first, where `0` and `255` in pixel values
    // represent `0` and `1` in bits, respectively.
    // This encoding is used to avoid errors due to different color spaces.
    const bits = [];
    for (let j = 0; j < 3; ++j) {
      bits.push(rgba[i + j * 4 + 0]);
      bits.push(rgba[i + j * 4 + 1]);
      bits.push(rgba[i + j * 4 + 2]);
      // rgba[i + j * 4 + 3]: Skip alpha channel.
    }
    // The last one element is not used.
    bits.pop();

    // Decode a single byte.
    let byte = 0;
    for (let j = 0; j < 8; ++j) {
      byte <<= 1;
      if (bits[j] >= 128)
        byte |= 1;
    }

    // Zero is the string terminator.
    if (byte == 0)
      break;

    decodedBytes[decodedLength++] = byte;
  }

  // Remove trailing nulls from data.
  decodedBytes = decodedBytes.subarray(0, decodedLength);
  var string_data = (new TextDecoder("ascii")).decode(decodedBytes);

  return JSON.parse(string_data);
}

/**
 * Initiates a new XHR GET request to provided URL.
 * @param {string} url The endpoint URL for the XHR.
 * @return {Promise} The promise for success/error events.
 */
function requestViaXhr(url) {
  return xhrRequest(url).then(result => wrapResult(result));
}

/**
 * Initiates a new GET request to provided URL via the Fetch API.
 * @param {string} url The endpoint URL for the Fetch.
 * @return {Promise} The promise for success/error events.
 */
function requestViaFetch(url) {
  return fetch(url)
    .then(res => res.json())
    .then(j => wrapResult(j));
}

function dedicatedWorkerUrlThatFetches(url) {
  return `data:text/javascript,
    fetch('${url}')
      .then(r => r.json())
      .then(j => postMessage(j))
      .catch((e) => postMessage(e.message));`;
}

function workerUrlThatImports(url) {
  return `data:text/javascript,import '${url}';`;
}

/**
 * Creates a new Worker, binds message and error events wrapping them into.
 *     {@code worker.eventPromise} and posts an empty string message to start
 *     the worker.
 * @param {string} url The endpoint URL for the worker script.
 * @param {object} options The options for Worker constructor.
 * @return {Promise} The promise for success/error events.
 */
function requestViaDedicatedWorker(url, options) {
  var worker;
  try {
    worker = new Worker(url, options);
  } catch (e) {
    return Promise.reject(e);
  }
  worker.postMessage('');
  return bindEvents2(worker, "message", worker, "error")
    .then(event => wrapResult(event.data));
}

function requestViaSharedWorker(url) {
  var worker;
  try {
    worker = new SharedWorker(url);
  } catch(e) {
    return Promise.reject(e);
  }
  const promise = bindEvents2(worker.port, "message", worker, "error")
    .then(event => wrapResult(event.data));
  worker.port.start();
  return promise;
}

// Returns a reference to a worklet object corresponding to a given type.
function get_worklet(type) {
  if (type == 'animation')
    return CSS.animationWorklet;
  if (type == 'layout')
    return CSS.layoutWorklet;
  if (type == 'paint')
    return CSS.paintWorklet;
  if (type == 'audio')
    return new OfflineAudioContext(2,44100*40,44100).audioWorklet;

  throw new Error('unknown worklet type is passed.');
}

function requestViaWorklet(type, url) {
  try {
    return get_worklet(type).addModule(url);
  } catch (e) {
    return Promise.reject(e);
  }
}

/**
 * Sets the href attribute on a navigable DOM element and performs a navigation
 *     by clicking it. To avoid navigating away from the current execution
 *     context, a target attribute is set to point to a new helper iframe.
 * @param {DOMElement} navigableElement The navigable DOMElement
 * @param {string} url The href for the navigable element.
 * @return {Promise} The promise for success/error events.
 */
function requestViaNavigable(navigableElement, url) {
  var iframe = createHelperIframe(guid(), false);
  setAttributes(navigableElement,
                {"href": url,
                 "target": iframe.name});

  const promise =
    bindEvents2(window, "message", iframe, "error", window, "error")
      .then(event => {
          if (event.source !== iframe.contentWindow)
            return Promise.reject(new Error('Unexpected event.source'));
          return event.data;
        });
  navigableElement.click();
  return promise;
}

/**
 * Creates a new anchor element, appends it to {@code document.body} and
 *     performs the navigation.
 * @param {string} url The URL to navigate to.
 * @return {Promise} The promise for success/error events.
 */
function requestViaAnchor(url, additionalAttributes) {
  var a = createElement(
      "a",
      Object.assign({"innerHTML": "Link to resource"}, additionalAttributes),
      document.body);

  return requestViaNavigable(a, url);
}

/**
 * Creates a new area element, appends it to {@code document.body} and performs
 *     the navigation.
 * @param {string} url The URL to navigate to.
 * @return {Promise} The promise for success/error events.
 */
function requestViaArea(url, additionalAttributes) {
  var area = createElement(
      "area",
      Object.assign({}, additionalAttributes),
      document.body);

  // TODO(kristijanburnik): Append to map and add image.
  return requestViaNavigable(area, url);
}

/**
 * Creates a new script element, sets the src to url, and appends it to
 *     {@code document.body}.
 * @param {string} url The src URL.
 * @return {Promise} The promise for success/error events.
 */
function requestViaScript(url, additionalAttributes) {
  const script = createElement(
      "script",
      Object.assign({"src": url}, additionalAttributes),
      document.body,
      false);

  return bindEvents2(window, "message", script, "error", window, "error")
    .then(event => wrapResult(event.data));
}

/**
 * Creates a new form element, sets attributes, appends it to
 *     {@code document.body} and submits the form.
 * @param {string} url The URL to submit to.
 * @return {Promise} The promise for success/error events.
 */
function requestViaForm(url) {
  var iframe = createHelperIframe(guid());
  var form = createElement("form",
                           {"action": url,
                            "method": "POST",
                            "target": iframe.name},
                           document.body);
  bindEvents(iframe);
  form.submit();

  return iframe.eventPromise;
}

/**
 * Creates a new link element for a stylesheet, binds load and error events,
 *     sets the href to url and appends it to {@code document.head}.
 * @param {string} url The URL for a stylesheet.
 * @return {Promise} The promise for success/error events.
 */
function requestViaLinkStylesheet(url) {
  return createRequestViaElement("link",
                                 {"rel": "stylesheet", "href": url},
                                 document.head);
}

/**
 * Creates a new link element for a prefetch, binds load and error events, sets
 *     the href to url and appends it to {@code document.head}.
 * @param {string} url The URL of a resource to prefetch.
 * @return {Promise} The promise for success/error events.
 */
function requestViaLinkPrefetch(url) {
  var link = document.createElement('link');
  if (link.relList && link.relList.supports && link.relList.supports("prefetch")) {
    return createRequestViaElement("link",
                                   {"rel": "prefetch", "href": url},
                                   document.head);
  } else {
    return Promise.reject("This browser does not support 'prefetch'.");
  }
}

/**
 * Initiates a new beacon request.
 * @param {string} url The URL of a resource to prefetch.
 * @return {Promise} The promise for success/error events.
 */
async function requestViaSendBeacon(url) {
  function wait(ms) {
    return new Promise(resolve => step_timeout(resolve, ms));
  }
  if (!navigator.sendBeacon(url)) {
    // If mixed-content check fails, it should return false.
    throw new Error('sendBeacon() fails.');
  }
  // We don't have a means to see the result of sendBeacon() request
  // for sure. Let's wait for a while and let the generic test function
  // ask the server for the result.
  await wait(500);
  return 'allowed';
}

/**
 * Creates a new media element with a child source element, binds loadeddata and
 *     error events, sets attributes and appends to document.body.
 * @param {string} type The type of the media element (audio/video/picture).
 * @param {object} media_attrs The attributes for the media element.
 * @param {object} source_attrs The attributes for the child source element.
 * @return {DOMElement} The newly created media element.
 */
function createMediaElement(type, media_attrs, source_attrs) {
  var mediaElement = createElement(type, {});

  var sourceElement = createElement("source", {});

  mediaElement.eventPromise = new Promise(function(resolve, reject) {
    mediaElement.addEventListener("loadeddata", function (e) {
      resolve(e);
    });

    // Safari doesn't fire an `error` event when blocking mixed content.
    mediaElement.addEventListener("stalled", function(e) {
      reject(e);
    });

    sourceElement.addEventListener("error", function(e) {
      reject(e);
    });
  });

  setAttributes(mediaElement, media_attrs);
  setAttributes(sourceElement, source_attrs);

  mediaElement.appendChild(sourceElement);
  document.body.appendChild(mediaElement);

  return mediaElement;
}

/**
 * Creates a new video element, binds loadeddata and error events, sets
 *     attributes and source URL and appends to {@code document.body}.
 * @param {string} url The URL of the video.
 * @return {Promise} The promise for success/error events.
 */
function requestViaVideo(url) {
  return createMediaElement("video",
                            {},
                            {"src": url}).eventPromise;
}

/**
 * Creates a new audio element, binds loadeddata and error events, sets
 *     attributes and source URL and appends to {@code document.body}.
 * @param {string} url The URL of the audio.
 * @return {Promise} The promise for success/error events.
 */
function requestViaAudio(url) {
  return createMediaElement("audio",
                            {},
                            {"type": "audio/wav", "src": url}).eventPromise;
}

/**
 * Creates a new picture element, binds loadeddata and error events, sets
 *     attributes and source URL and appends to {@code document.body}. Also
 *     creates new image element appending it to the picture
 * @param {string} url The URL of the image for the source and image elements.
 * @return {Promise} The promise for success/error events.
 */
function requestViaPicture(url) {
  var picture = createMediaElement("picture", {}, {"srcset": url,
                                                "type": "image/png"});
  return createRequestViaElement("img", {"src": url}, picture);
}

/**
 * Creates a new object element, binds load and error events, sets the data to
 *     url, and appends it to {@code document.body}.
 * @param {string} url The data URL.
 * @return {Promise} The promise for success/error events.
 */
function requestViaObject(url) {
  return createRequestViaElement("object", {"data": url, "type": "text/html"}, document.body);
}

/**
 * Creates a new WebSocket pointing to {@code url} and sends a message string
 * "echo". The {@code message} and {@code error} events are triggering the
 * returned promise resolve/reject events.
 * @param {string} url The URL for WebSocket to connect to.
 * @return {Promise} The promise for success/error events.
 */
function requestViaWebSocket(url) {
  return new Promise(function(resolve, reject) {
    var websocket = new WebSocket(url);

    websocket.addEventListener("message", function(e) {
      resolve(e.data);
    });

    websocket.addEventListener("open", function(e) {
      websocket.send("echo");
    });

    websocket.addEventListener("error", function(e) {
      reject(e)
    });
  })
  .then(data => {
      return JSON.parse(data);
    });
}

/**
  @typedef SubresourceType
  @type {string}

  Represents how a subresource is sent.
  The keys of `subresourceMap` below are the valid values.
*/

// Subresource paths and invokers.
const subresourceMap = {
  "a-tag": {
    path: "/common/security-features/subresource/document.py",
    invoker: requestViaAnchor,
  },
  "area-tag": {
    path: "/common/security-features/subresource/document.py",
    invoker: requestViaArea,
  },
  "audio-tag": {
    path: "/common/security-features/subresource/audio.py",
    invoker: requestViaAudio,
  },
  "beacon-request": {
    path: "/common/security-features/subresource/empty.py",
    invoker: requestViaSendBeacon,
  },
  "fetch-request": {
    path: "/common/security-features/subresource/xhr.py",
    invoker: requestViaFetch,
  },
  "form-tag": {
    path: "/common/security-features/subresource/empty.py",
    invoker: requestViaForm,
  },
  "iframe-tag": {
    path: "/common/security-features/subresource/document.py",
    invoker: requestViaIframe,
  },
  "img-tag": {
    path: "/common/security-features/subresource/image.py",
    invoker: requestViaImage,
  },
  "link-css-tag": {
    path: "/common/security-features/subresource/empty.py",
    invoker: requestViaLinkStylesheet,
  },
  "link-prefetch-tag": {
    path: "/common/security-features/subresource/empty.py",
    invoker: requestViaLinkPrefetch,
  },
  "object-tag": {
    path: "/common/security-features/subresource/empty.py",
    invoker: requestViaObject,
  },
  "picture-tag": {
    path: "/common/security-features/subresource/image.py",
    invoker: requestViaPicture,
  },
  "script-tag": {
    path: "/common/security-features/subresource/script.py",
    invoker: requestViaScript,
  },
  "video-tag": {
    path: "/common/security-features/subresource/video.py",
    invoker: requestViaVideo,
  },
  "xhr-request": {
    path: "/common/security-features/subresource/xhr.py",
    invoker: requestViaXhr,
  },

  "worker-request": {
    path: "/common/security-features/subresource/worker.py",
    invoker: url => requestViaDedicatedWorker(url),
  },
  // TODO: Merge "module-worker" and "module-worker-top-level".
  "module-worker": {
    path: "/common/security-features/subresource/worker.py",
    invoker: url => requestViaDedicatedWorker(url, {type: "module"}),
  },
  "module-worker-top-level": {
    path: "/common/security-features/subresource/worker.py",
    invoker: url => requestViaDedicatedWorker(url, {type: "module"}),
  },
  "module-data-worker-import": {
    path: "/common/security-features/subresource/worker.py",
    invoker: url =>
        requestViaDedicatedWorker(workerUrlThatImports(url), {type: "module"}),
  },
  "shared-worker": {
    path: "/common/security-features/subresource/shared-worker.py",
    invoker: requestViaSharedWorker,
  },

  "websocket-request": {
    path: "/stash_responder",
    invoker: requestViaWebSocket,
  },
};
for (const workletType of ['animation', 'audio', 'layout', 'paint']) {
  subresourceMap[`worklet-${workletType}-top-level`] = {
      path: "/common/security-features/subresource/worker.py",
      invoker: url => requestViaWorklet(workletType, url)
    };
  subresourceMap[`worklet-${workletType}-data-import`] = {
      path: "/common/security-features/subresource/worker.py",
      invoker: url =>
          requestViaWorklet(workletType, workerUrlThatImports(url))
    };
}

/**
  @typedef RedirectionType
  @type {string}

  Represents what redirects should occur to the subresource request
  after initial request.
  See preprocess_redirection() in
  /common/security-features/subresource/subresource.py for valid values.
*/

/**
  Construct subresource (and related) URLs.

  @param {SubresourceType} subresourceType
  @param {OriginType} originType
  @param {RedirectionType} redirectionType
  @returns {object} with following properties:
    {string} testUrl
      The subresource request URL.
    {string} announceUrl
    {string} assertUrl
      The URLs to be used for detecting whether `testUrl` is actually sent
      to the server.
      1. Fetch `announceUrl` first,
      2. then possibly fetch `testUrl`, and
      3. finally fetch `assertUrl`.
         The fetch result of `assertUrl` should indicate whether
         `testUrl` is actually sent to the server or not.
*/
function getRequestURLs(subresourceType, originType, redirectionType) {
  const key = guid();
  const value = guid();

  // We use the same stash path for both HTTP/S and WS/S stash requests.
  const stashPath = encodeURIComponent("/mixed-content");

  const stashEndpoint = "/common/security-features/subresource/xhr.py?key=" +
                        key + "&path=" + stashPath;
  return {
    testUrl:
      getSubresourceOrigin(originType) +
        subresourceMap[subresourceType].path +
        "?redirection=" + encodeURIComponent(redirectionType) +
        "&action=purge&key=" + key +
        "&path=" + stashPath,
    announceUrl: stashEndpoint + "&action=put&value=" + value,
    assertUrl: stashEndpoint + "&action=take",
  };
}

// ===============================================================
// Source Context
// ===============================================================
// Requests can be sent from several source contexts,
// such as the main documents, iframes, workers, or so,
// possibly nested, and possibly with <meta>/http headers added.
// invokeRequest() and invokeFrom*() functions handles
// SourceContext-related setup in client-side.

/**
  invokeRequest() invokes a subresource request
  (specified as `subresource`)
  from a (possibly nested) environment settings object
  (specified as `sourceContextList`).

  For nested contexts, invokeRequest() calls an invokeFrom*() function
  that creates a nested environment settings object using
  /common/security-features/scope/, which calls invokeRequest()
  again inside the nested environment settings object.
  This cycle continues until all specified
  nested environment settings object are created, and
  finally invokeRequest() calls a requestVia*() function to start the
  subresource request from the inner-most environment settings object.

  @param {Subresource} subresource
  @param {Array<SourceContext>} sourceContextList

  @returns {Promise} A promise that is resolved with an RequestResult object.
  `sourceContextUrl` is always set. For whether other properties are set,
  see the comments for requestVia*() above.
*/
function invokeRequest(subresource, sourceContextList) {
  if (sourceContextList.length === 0) {
    // No further nested global objects. Send the subresource request here.

    const additionalAttributes = {};
    /** @type {PolicyDelivery} policyDelivery */
    for (const policyDelivery of (subresource.policyDeliveries || [])) {
      // Depending on the delivery method, extend the subresource element with
      // these attributes.
      if (policyDelivery.deliveryType === "attr") {
        additionalAttributes[policyDelivery.key] = policyDelivery.value;
      } else if (policyDelivery.deliveryType === "rel-noref") {
        additionalAttributes["rel"] = "noreferrer";
      }
    }

    return subresourceMap[subresource.subresourceType].invoker(
        subresource.url,
        additionalAttributes)
      .then(result => Object.assign(
          {sourceContextUrl: location.toString()},
          result));
  }

  // Defines invokers for each valid SourceContext.sourceContextType.
  const sourceContextMap = {
    "srcdoc": { // <iframe srcdoc></iframe>
      invoker: invokeFromIframe,
    },
    "iframe": { // <iframe src="same-origin-URL"></iframe>
      invoker: invokeFromIframe,
    },
    "classic-worker": {
      // Classic dedicated worker loaded from same-origin.
      invoker: invokeFromWorker.bind(undefined, false, {}),
    },
    "classic-data-worker": {
      // Classic dedicated worker loaded from data: URL.
      invoker: invokeFromWorker.bind(undefined, true, {}),
    },
    "module-worker": {
      // Module dedicated worker loaded from same-origin.
      invoker: invokeFromWorker.bind(undefined, false, {type: 'module'}),
    },
    "module-data-worker": {
      // Module dedicated worker loaded from data: URL.
      invoker: invokeFromWorker.bind(undefined, true, {type: 'module'}),
    },
  };

  return sourceContextMap[sourceContextList[0].sourceContextType].invoker(
      subresource, sourceContextList);
}

// Quick hack to expose invokeRequest when common.js is loaded either
// as a classic or module script.
self.invokeRequest = invokeRequest;

/**
  invokeFrom*() functions are helper functions with the same parameters
  and return values as invokeRequest(), that are tied to specific types
  of top-most environment settings objects.
  For example, invokeFromIframe() is the helper function for the cases where
  sourceContextList[0] is an iframe.
*/

/**
  @param {boolean} isDataUrl
    true if the worker script is loaded from data: URL.
    Otherwise, the script is loaded from same-origin.
  @param {object} workerOptions
    The `options` argument for Worker constructor.

  Other parameters and return values are the same as those of invokeRequest().
*/
function invokeFromWorker(isDataUrl, workerOptions,
                          subresource, sourceContextList) {
  const currentSourceContext = sourceContextList[0];
  let workerUrl =
    "/common/security-features/scope/worker.py?policyDeliveries=" +
    encodeURIComponent(JSON.stringify(
        currentSourceContext.policyDeliveries || []));
  if (workerOptions.type === 'module') {
    workerUrl += "&type=module";
  }

  let promise;
  if (isDataUrl) {
    promise = fetch(workerUrl)
      .then(r => r.text())
      .then(source => {
          return 'data:text/javascript;base64,' + btoa(source);
        });
  } else {
    promise = Promise.resolve(workerUrl);
  }

  return promise
    .then(url => {
      const worker = new Worker(url, workerOptions);
      worker.postMessage({subresource: subresource,
                          sourceContextList: sourceContextList.slice(1)});
      return bindEvents2(worker, "message", worker, "error", window, "error");
    })
    .then(event => {
        if (event.data.error)
          return Promise.reject(event.data.error);
        return event.data;
      });
}

function invokeFromIframe(subresource, sourceContextList) {
  const currentSourceContext = sourceContextList[0];
  const frameUrl =
    "/common/security-features/scope/document.py?policyDeliveries=" +
    encodeURIComponent(JSON.stringify(
        currentSourceContext.policyDeliveries || []));

  let promise;
  if (currentSourceContext.sourceContextType === 'srcdoc') {
    promise = fetch(frameUrl)
      .then(r => r.text())
      .then(srcdoc => {
          return createElement("iframe", {srcdoc: srcdoc}, document.body, true);
        });
  } else if (currentSourceContext.sourceContextType === 'iframe') {
    promise = Promise.resolve(
        createElement("iframe", {src: frameUrl}, document.body, true));
  }

  return promise
    .then(iframe => {
        return iframe.eventPromise
          .then(() => {
              const promise = bindEvents2(
                  window, "message", iframe, "error", window, "error");
              iframe.contentWindow.postMessage(
                  {subresource: subresource,
                   sourceContextList: sourceContextList.slice(1)},
                  "*");
              return promise;
            })
          .then(event => {
              if (event.data.error)
                return Promise.reject(event.data.error);
              return event.data;
            });
      });
}

// SanityChecker does nothing in release mode. See sanity-checker.js for debug
// mode.
function SanityChecker() {}
SanityChecker.prototype.checkScenario = function() {};
SanityChecker.prototype.setFailTimeout = function(test, timeout) {};
SanityChecker.prototype.checkSubresourceResult = function() {};