GitHub PR - LTI Request for Page Information

Closes PLAT-4625

Test Plan:
- TBD: Pull Request from GitHub. Allows tool to query window and
  iframe size

Change-Id: I058dc55e1412c99aad3d0217816b57f2f7557f7a
Reviewed-on: https://gerrit.instructure.com/199596
Tested-by: Jenkins
Reviewed-by: Marc Phillips <mphillips@instructure.com>
QA-Review: Weston Dransfield <wdransfield@instructure.com>
Product-Review: Clint Furse <cfurse@instructure.com>

public/javascripts/lti/messages.js

@@ -74,6 +74,19 @@ export function ltiMessageHandler(e) {
       }
       break;
 
+      case 'lti.fetchWindowSize': {
+          const iframe = findDomForWindow(e.source);
+          if (iframe) {
+              message.height = window.innerHeight;
+              message.width = window.innerWidth;
+              message.offset = $('.tool_content_wrapper').offset();
+              const strMessage = JSON.stringify(message);
+
+              iframe.contentWindow.postMessage(strMessage, '*');
+          }
+          break;
+      }
+
       case 'lti.showModuleNavigation':
         if(message.show === true || message.show === false){
           $('.module-sequence-footer').toggle(message.show);

spec/javascripts/jsx/lti/messagesSpec.js

@@ -31,6 +31,10 @@ const resizeMessage = {
   height: finalHeight
 }
 
+const fetchWindowSize = {
+  subject: 'lti.fetchWindowSize'
+}
+
 const scrollMessage = {
   subject: 'lti.scrollToTop'
 }
@@ -109,6 +113,21 @@ QUnit.module('Messages', function (suiteHooks) {
     equal(iframe.height(), finalHeight)
   })
 
+  test('returns the hight and width of the page along with the iframe offset', () => {
+    ltiToolWrapperFixture.append(`
+      <div>
+        <h1 class="page-title">LTI resize test</h1>
+        <p><iframe style="width: 100%; height: ${intialHeight}px;" src="https://canvas.example.com/courses/4/external_tools/retrieve?display=borderless" width="100%" height="${intialHeight}px" allowfullscreen="allowfullscreen" webkitallowfullscreen="webkitallowfullscreen" mozallowfullscreen="mozallowfullscreen"></iframe></p>
+      </div>
+    `)
+    const iframe = $('iframe')
+
+    sinon.spy(iframe[0].contentWindow, 'postMessage')
+    notOk(iframe[0].contentWindow.postMessage.calledOnce)
+    ltiMessageHandler(postMessageEvent(fetchWindowSize, iframe[0].contentWindow))
+    ok(iframe[0].contentWindow.postMessage.calledOnce)
+  })
+
   test('hides the module navigation', () => {
     ltiToolWrapperFixture.append(`
       <div>