Tricks to communicate between pages while writing test cases

Here are some techniques I’ve used while writing Gecko test cases. It’s quite handy for people to create complicate test cases across multiple frames or processes.

To IFrame

postMessage: You can pass the message between non-OOP iframes that not in the same origin, using postMessage and addEventListener('message', callback).

outer.html

var iframe = document.getElementById('iframe');
iframe.src = 'inner.html';

window.addEventListener('message', function(evt) { /* handle the message from inner.html */ });
iframe.onload = function() { iframe.contentWindow.postMessage('some-js-value', window.location.origin) };

inner.html

window.addEventListener('message', function(evt) {
  // handle the message from outer.html
  if (evt.data === 'some-js-value') {
    event.source.postMessage('something-else', window.location.origin);
  }
}

URL Query String: You can pass the information in URL while opening a page in iframe, using encodeURIComponent and decodeURIComponent.

outer.html

var iframe = document.getElementById('iframe');
iframe.src = 'inner.html?' + encodeURIComponent('some string or json string');

inner.html

var queryString = decodeURIComponent(window.location.search.substring(1));
// use JSON.parse(queryString) if passing a json string

To Parent Process

loadChromeScript: You can load a specified js file into B2G process and you can use sendAsyncMessage to pass information between chrome process and content process.

test.html

var script = SpecialPowers.loadChromeScript(SimpleTest.getTestFileURL('chrome-script.js');
script.addMessageListener('some-command', function(data) {
  // handle the message from chrome-script.js
});
script.sendAsyncMessage('some-message', 'some js value');
script.destroy();

chrome-script.js

addMessageHandler('some-message', function(data) {
  // handle the message from test.html
  sendAsyncMessage('some-command', 'some other js value');
});

window.alert/window.prompt: If you create a content process in your testcase, you can use window.alert or window.prompt to initiate a IPC from content process to parent process by handling mozbrowsershowmodalprompt event.

outer.html

function callback() {
  var iframe = document.createElement('iframe');
  SpecialPowers.wrap(iframe).mozbrowser = true;

  iframe.addEventListener('mozbrowsershowmodalprompt', function(e) {
    // handle the message from inner.html
    var message = e.detail.message;
    var initValue = e.detail.initValue; // init value from prompt.
    e.detail.returenValue = 'some string'; // return value for prompt.

    e.preventDefault(); // cause the alert to block.
    e.detail.unblock(); // Now unblock the iframe and check that the script completed.

  });

  iframe.src = 'inner.html';
}

// necessary permission and preference for creating a remote iframe
SpecialPowers.addPermission("browser", true, document);
SpecialPowers.pushPrefEnv({
  "set": [
    ["network.disable.ipc.security", true],
    ["dom.ipc.tabs.disabled", false],
    ["dom.ipc.browser_frames.oop_by_default", true],
    ["dom.mozBrowserFramesEnabled", true],
    ["browser.pagethumbnails.capturing_disabled", true]
  ]
}, callback);

inner.html

window.alert('some string or json string');
var retValue = window.prompt('some thing need return', 'some init value');

To Child Process

hashchange: You can pass the information by changing the URL hash for the iframe, using encodeURIComponent and decodeURIComponent.

outer.html

var iframe = document.getElementById('iframe');
iframe.src = 'inner.html#' + encodeURIComponent('some string or json string');

inner.html

window.addEventListener('hashchange', function() {
  var queryString = decodeURIComponent(window.location.hash.substring(1));
  // use JSON.parse(queryString) if passing a json string
});