MSE-in-Workers: Switch getHandle() to simpler [SameObject] handle attr

Following discussion in the spec PR #306 [1], this change updates the
way to obtain a MediaSourceHandle to be via a "handle" attribute on the
MediaSource instance that is both readonly and always returns the same
object (or throws exception, if for instance, it is attempted to be read
from a main-thread-owned MediaSource instance instead of a dedicated-
worker-owned MediaSource instance).

Also included is the removal of the readyState check when attempting to
obtain this handle (since it is now never expected to be changeable; no
sequence of distinct handles is ever expected to be obtainable from a
worker MediaSource). Also removed is the prevention of retrieving such a
handle from an instance more than once.

Multiple tests are added or updated to ensure correct behavior.

[1] w3c/media-source#306

BUG=878133

Change-Id: Ic07095d6d1dc95b8e6be818027984600aa7ab334

Author: wolenetz

media-source/dedicated-worker/mediasource-worker-detach-element.js

@@ -32,7 +32,7 @@ util.mediaSource.addEventListener("sourceopen", () => {
                              err => { postMessage({ subject: messageSubject.ERROR, info: err }) } );
 }, { once : true });
 
-let handle = util.mediaSource.getHandle();
+let handle = util.mediaSource.handle;
 
 postMessage({ subject: messageSubject.HANDLE, info: handle }, { transfer: [handle] } );
 

media-source/dedicated-worker/mediasource-worker-duration.js

@@ -180,7 +180,7 @@ function processPhase(isResponseToAck = false) {
     case testPhase.kInitial:
       assert(Number.isNaN(util.mediaSource.duration), "Initial unattached MediaSource duration must be NaN, but instead is " + util.mediaSource.duration);
       phase = testPhase.kAttaching;
-      let handle = util.mediaSource.getHandle();
+      let handle = util.mediaSource.handle;
       postMessage({ subject: messageSubject.HANDLE, info: handle }, { transfer: [handle] } );
       break;
 

media-source/dedicated-worker/mediasource-worker-handle-transfer-to-main.js

@@ -5,6 +5,6 @@ importScripts('mediasource-message-util.js');
 // harness, and would confuse the test case message parsing there.
 
 // Just obtain a MediaSourceHandle and transfer it to creator of our context.
-let handle = new MediaSource().getHandle();
+let handle = new MediaSource().handle;
 postMessage(
     {subject: messageSubject.HANDLE, info: handle}, {transfer: [handle]});

media-source/dedicated-worker/mediasource-worker-handle-transfer.js

@@ -1,15 +1,15 @@
 importScripts('/resources/testharness.js');
 
 test(t => {
-  let handle = new MediaSource().getHandle();
+  let handle = new MediaSource().handle;
   assert_true(handle instanceof MediaSourceHandle);
   assert_throws_dom('DataCloneError', function() {
     postMessage(handle);
   }, 'serializing handle without transfer');
 }, 'MediaSourceHandle serialization without transfer must fail, tested in worker');
 
 test(t => {
-  let handle = new MediaSource().getHandle();
+  let handle = new MediaSource().handle;
   assert_true(handle instanceof MediaSourceHandle);
   assert_throws_dom('DataCloneError', function() {
     postMessage(handle, [handle, handle]);

media-source/dedicated-worker/mediasource-worker-handle.html

@@ -33,6 +33,17 @@
   });
 }, "Test main context receipt of postMessage'd MediaSourceHandle from DedicatedWorker MediaSource");
 
+test(t => {
+  assert_true(window.hasOwnProperty("MediaSourceHandle"), "window must have MediaSourceHandle visibility");
+
+  // Note, MSE spec may eventually describe how a main-thread MediaSource can
+  // attach to an HTMLMediaElement using a MediaSourceHandle. For now, we
+  // ensure that the implementation of this is not available.
+  assert_throws_dom('NotSupportedError', function() {
+    let h = new MediaSource().handle;
+  }, 'main thread MediaSource instance cannot (yet) create a usable MediaSourceHandle');
+}, "Test main-thread-owned MediaSource instance cannot create a MediaSourceHandle");
+
 if (MediaSource.hasOwnProperty("canConstructInDedicatedWorker") && MediaSource.canConstructInDedicatedWorker === true) {
   // If implementation claims support for MSE-in-Workers, then fetch and run
   // some tests directly in another dedicated worker and get their results

media-source/dedicated-worker/mediasource-worker-handle.js

@@ -13,9 +13,11 @@ test(t => {
 }, "MediaSource in DedicatedWorker context must have true-valued canConstructInDedicatedWorker if Window context had it");
 
 test(t => {
-  assert_true("getHandle" in MediaSource.prototype, "dedicated worker MediaSource must have getHandle");
+  assert_true(
+      'handle' in MediaSource.prototype,
+      'dedicated worker MediaSource must have handle in prototype');
   assert_true(self.hasOwnProperty("MediaSourceHandle"), "dedicated worker must have MediaSourceHandle visibility");
-}, "MediaSource prototype in DedicatedWorker context must have getHandle, and worker must have MediaSourceHandle");
+}, 'MediaSource prototype in DedicatedWorker context must have \'handle\', and worker must have MediaSourceHandle');
 
 test(t => {
   const ms = new MediaSource();
@@ -24,22 +26,45 @@ test(t => {
 
 test(t => {
   const ms = new MediaSource();
-  const handle = ms.getHandle();
-  assert_not_equals(handle, null, "must have a non-null getHandle result");
+  const handle = ms.handle;
+  assert_not_equals(handle, null, 'must have a non-null \'handle\' attribute');
   assert_true(handle instanceof MediaSourceHandle, "must be a MediaSourceHandle");
-}, "mediaSource.getHandle() in DedicatedWorker returns a MediaSourceHandle");
+}, 'mediaSource.handle in DedicatedWorker returns a MediaSourceHandle');
 
 test(t => {
-  const ms = new MediaSource();
-  const handle1 = ms.getHandle();
-  let handle2 = null;
-  assert_throws_dom("InvalidStateError", function()
-    {
-      handle2 = ms.getHandle();
-    }, "getting second handle from MediaSource instance");
-  assert_equals(handle2, null, "getting second handle from same MediaSource must have failed");
-  assert_not_equals(handle1, null, "must have a non-null result of the first getHandle");
-  assert_true(handle1 instanceof MediaSourceHandle, "first getHandle result must be a MediaSourceHandle");
-}, "mediaSource.getHandle() must not succeed more than precisely once for a MediaSource instance");
+  const msA = new MediaSource();
+  const msB = new MediaSource();
+  const handleA1 = msA.handle;
+  const handleA2 = msA.handle;
+  const handleA3 = msA['handle'];
+  const handleB1 = msB.handle;
+  const handleB2 = msB.handle;
+  assert_true(
+      handleA1 === handleA2 && handleB1 === handleB2 && handleA1 != handleB1,
+      'SameObject is observed for mediaSource.handle, and different MediaSource instances have different handles');
+  assert_true(
+      handleA1 === handleA3,
+      'SameObject is observed even when accessing handle differently');
+  assert_true(
+      handleA1 instanceof MediaSourceHandle &&
+          handleB1 instanceof MediaSourceHandle,
+      'handle property returns MediaSourceHandles');
+}, 'mediaSource.handle observes SameObject property correctly');
+
+test(t => {
+  const ms1 = new MediaSource();
+  const handle1 = ms1.handle;
+  const ms2 = new MediaSource();
+  const handle2 = ms2.handle;
+  assert_true(
+      handle1 !== handle2,
+      'distinct MediaSource instances must have distinct handles');
+
+  // Verify attempt to change value of the handle property does not succeed.
+  ms1.handle = handle2;
+  assert_true(
+      ms1.handle === handle1 && ms2.handle === handle2,
+      'MediaSource handle is readonly, so should not have changed');
+}, 'Attempt to set MediaSource handle property should fail to change it, since it is readonly');
 
 done();

media-source/dedicated-worker/mediasource-worker-play.js

@@ -9,8 +9,37 @@ onmessage = function(evt) {
 };
 
 let util = new MediaSourceWorkerUtil();
+let handle = util.mediaSource.handle;
+
+util.mediaSource.addEventListener('sourceopen', () => {
+  // Immediately re-verify the SameObject property of the handle we transferred.
+  if (handle !== util.mediaSource.handle) {
+    postMessage({
+      subject: messageSubject.ERROR,
+      info: 'mediaSource.handle changed from the original value'
+    });
+  }
+
+  // Also verify that transferring the already-transferred handle instance is
+  // prevented correctly.
+  try {
+    postMessage(
+        {
+          subject: messageSubject.ERROR,
+          info:
+              'This postMessage should fail: the handle has already been transferred',
+          extra_info: util.mediaSource.handle
+        },
+        {transfer: [util.mediaSource.handle]});
+  } catch (e) {
+    if (e.name != 'DataCloneError') {
+      postMessage({
+        subject: messageSubject.ERROR,
+        info: 'Expected handle retransfer exception did not occur'
+      });
+    }
+  }
 
-util.mediaSource.addEventListener("sourceopen", () => {
   sourceBuffer = util.mediaSource.addSourceBuffer(util.mediaMetadata.type);
   sourceBuffer.onerror = (err) => {
     postMessage({ subject: messageSubject.ERROR, info: err });
@@ -40,7 +69,6 @@ util.mediaSource.addEventListener("sourceopen", () => {
   };
   util.mediaLoadPromise.then(mediaData => { sourceBuffer.appendBuffer(mediaData); },
                              err => { postMessage({ subject: messageSubject.ERROR, info: err }) });
-}, { once : true });
+}, {once: true});
 
-let handle = util.mediaSource.getHandle();
 postMessage({ subject: messageSubject.HANDLE, info: handle }, { transfer: [handle] });