Media Session: passing metadata from renderer/ to browser/.

content/public/common/media_metadata.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_PUBLIC_COMMON_MEDIA_METADATA_H_

[jochen (gone - plz use gerrit), 2015/12/14 12:38:30]

we is this in public, if you only use it from content?

[mlamouri (slow - plz ping), 2016/01/05 16:01:16]

This is going to be used by content embedders for UI purposes.

+#define CONTENT_PUBLIC_COMMON_MEDIA_METADATA_H_
+
+#include "base/strings/nullable_string16.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// The MediaMetadata is a structure carrying information associated to a
+// content::MediaSession.
+struct CONTENT_EXPORT MediaMetadata {
+  MediaMetadata();

[jochen (gone - plz use gerrit), 2015/12/14 12:38:30]

can you please add ctor args for all struct fields?

[mlamouri (slow - plz ping), 2016/01/05 16:01:17]

I think the issue of such a ctor is that it would be easy to swap strings by
mistake. What's the intent behind the request?

+  ~MediaMetadata();
+
+  // Returns whether this instance of MediaMetadata had no attribute set.
+  // A newly created MediaMetadata is always empty.
+  bool IsEmpty() const;
+
+  // Title associated to the MediaSession.
+  base::NullableString16 title;

[philipj_slow, 2015/12/14 14:09:24]

Rather than making every nullable, could we not use the empty string? The
web-exposed MediaMetadata does not have nullable members, so if we have just the
empty string to represent "missing" internally, that seems nice and simple.

[mlamouri (slow - plz ping), 2016/01/05 16:01:17]

Null will be used here to know whether a string was set or not. If we use empty
string, we wouldn't be able to know if a website set the author to "" or didn't
specify one. Content embedders might want to behave differently depending on
that.

[philipj_slow, 2016/01/18 12:31:43]

But the MediaMetadata interface assumes that "" is not a value that's meaningful
to set explicitly, as it's the default value for all of the dictionary members.
We'd have to change the IDL or use custom bindings to even know in
MediaMetadata.cpp whether the "" was explicitly passed or the default. If
content embedders did behave differently for these cases, the difference
couldn't be explained in terms of the spec.

Can we either stick with empty strings, and change the spec and implementation
if we find a reason to distinguish between explicit and default ""?

[mlamouri (slow - plz ping), 2016/01/19 14:20:09]

Ok. Done.

+
+  // Artist associated to the MediaSession.
+  base::NullableString16 artist;
+
+  // Album associated to the MediaSession.
+  base::NullableString16 album;
+
+  // Maximum length for all the strings inside the MediaMetadata when it is sent
+  // over IPC. The renderer process should truncate the strings before sending
+  // the MediaMetadata and the browser process must do the same when receiving
+  // it.
+  static const size_t kMaxIPCStringLength = 4 * 1024;

[jochen (gone - plz use gerrit), 2015/12/14 12:38:30]

can you move the definition to the cc file please?

[mlamouri (slow - plz ping), 2016/01/05 16:01:16]

Sure. I thought that given that we are now allowed to initialize non-static
members in headers it should be fine for static ones.

+};
+
+}  // namespace content
+
+#endif // CONTENT_PUBLIC_COMMON_MEDIA_METADATA_H_