From 568289aac70a6039b66b9819296722d392f06180 Mon Sep 17 00:00:00 2001
From: alwu <alwu@mozilla.com>
Date: Wed, 4 Mar 2020 18:38:43 +0000
Subject: [PATCH] Bug 1592037 - part1 : do not update empty metadata to media
 session controller. r=MeFisto94

If new coming metadata is `null` (when setting `MediaSession.metadata=null`) or an empty metadata [1], then we would like to reset the `Maybe` in `MediaSessionController` in order to use the default metadata when someone asks for the current metadata.

[1] https://w3c.github.io/mediasession/#empty-metadata

Differential Revision: https://phabricator.services.mozilla.com/D64844

--HG--
extra : moz-landing-system : lando
---
 .../mediasession/MediaSessionController.cpp   | 26 ++++++++++++++++---
 .../mediasession/MediaSessionController.h     |  3 ++-
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/dom/media/mediasession/MediaSessionController.cpp b/dom/media/mediasession/MediaSessionController.cpp
index cd96703a2e1a..2fbd45287dc4 100644
--- a/dom/media/mediasession/MediaSessionController.cpp
+++ b/dom/media/mediasession/MediaSessionController.cpp
@@ -25,6 +25,19 @@ mozilla::LazyLogModule gMediaSession("MediaSession");
 namespace mozilla {
 namespace dom {
 
+static bool IsMetadataEmpty(const Maybe<MediaMetadataBase>& aMetadata) {
+  // Media session's metadata is null.
+  if (!aMetadata) {
+    return true;
+  }
+
+  // All attirbutes in metadata are empty.
+  // https://w3c.github.io/mediasession/#empty-metadata
+  const MediaMetadataBase& metadata = *aMetadata;
+  return metadata.mTitle.IsEmpty() && metadata.mArtist.IsEmpty() &&
+         metadata.mAlbum.IsEmpty() && metadata.mArtwork.IsEmpty();
+}
+
 MediaSessionController::MediaSessionController(uint64_t aContextId)
     : mTopLevelBCId(aContextId) {
   MOZ_DIAGNOSTIC_ASSERT(XRE_IsParentProcess(),
@@ -51,13 +64,18 @@ void MediaSessionController::NotifySessionDestroyed(
   UpdateActiveMediaSessionContextId();
 }
 
-void MediaSessionController::UpdateMetadata(uint64_t aSessionContextId,
-                                            MediaMetadataBase& aMetadata) {
+void MediaSessionController::UpdateMetadata(
+    uint64_t aSessionContextId, const Maybe<MediaMetadataBase>& aMetadata) {
   if (!mMetadataMap.Contains(aSessionContextId)) {
     return;
   }
-  LOG("Update metadata for session %" PRId64, aSessionContextId);
-  mMetadataMap.GetValue(aSessionContextId)->emplace(aMetadata);
+  if (IsMetadataEmpty(aMetadata)) {
+    LOG("Reset metadata for session %" PRId64, aSessionContextId);
+    mMetadataMap.GetValue(aSessionContextId)->reset();
+  } else {
+    LOG("Update metadata for session %" PRId64, aSessionContextId);
+    mMetadataMap.GetValue(aSessionContextId)->emplace(*aMetadata);
+  }
 }
 
 void MediaSessionController::UpdateActiveMediaSessionContextId() {
diff --git a/dom/media/mediasession/MediaSessionController.h b/dom/media/mediasession/MediaSessionController.h
index f9a4753017a6..2ffd1f770b0a 100644
--- a/dom/media/mediasession/MediaSessionController.h
+++ b/dom/media/mediasession/MediaSessionController.h
@@ -46,7 +46,8 @@ class MediaSessionController {
 
   // Use this function to store the media metadata when media session updated
   // its metadata in the content process.
-  void UpdateMetadata(uint64_t aSessionContextId, MediaMetadataBase& aMetadata);
+  void UpdateMetadata(uint64_t aSessionContextId,
+                      const Maybe<MediaMetadataBase>& aMetadata);
 
   // Return active media session's metadata if active media session exists and
   // it has already set its metadata. Otherwise, return default media metadata