mediaview: IPC definitions to watch for document changes.

components/arc/common/file_system.mojom

Index: components/arc/common/file_system.mojom
diff --git a/components/arc/common/file_system.mojom b/components/arc/common/file_system.mojom
index de13a030d0099265c5fd65fb27f39bfade747812..38c3d4d080b23dc57777bef2fd996caebb40dbd6 100644
--- a/components/arc/common/file_system.mojom
+++ b/components/arc/common/file_system.mojom
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Next MinVersion: 3
+// Next MinVersion: 4
 
 module arc.mojom;
 
@@ -29,7 +29,15 @@ struct Document {
   uint64 last_modified;
 };
 
-// Next method ID: 5
+// Next method ID: 1
+interface FileSystemHost {
+  // Called when a watched document was changed or deleted.
+  // If |deleted| is true, the watcher has been already removed and the host
+  // does not need to explicitly call RemoveWatcher().
+  [MinVersion=3] OnDocumentChanged@0(int64 watcher_id, bool deleted);

[Luis Héctor Chávez, 2017/02/22 17:29:31]

I'd prefer to replace |bool deleted| with an enum indicating the nature of the
change. Or a struct with even more information, but that depends on whether the
implementation will eagerly refresh metadata (struct would be preferred) or do
it lazily thus coalescing multiple changed notifications (enum is sufficient).

[Shuhei Takahashi, 2017/02/23 03:37:22]

Sure, let's use enum instead.

We are not going to do eager refreshing because the expected caller
(storage::WatcherManager) does not support such protocol.

+};
+
+// Next method ID: 8
 interface FileSystemInstance {
   // Notes about Android Documents Provider:
   //
@@ -47,6 +55,18 @@ interface FileSystemInstance {
   // https://developer.android.com/guide/topics/providers/document-provider.html
   // https://developer.android.com/reference/android/provider/DocumentsContract.html
 
+  // Installs a document watcher to watch updates of a document.
+  //
+  // On success, a positive unique integer is returned as a watcher ID and
+  // FileSystemHost.OnDocumentChanged() will be called with the watcher ID
+  // on document changes until the watcher is removed by RemoveWatcher().
+  // On failure, -1 is returned.
+  //
+  // It is allowed to install multiple watchers to the same document. In that
+  // case, different watcher IDs are returned.
+  [MinVersion=3] AddWatcher@6(string authority, string document_id) =>
+      (int64 watcher_id);
+
   // Queries child documents of the directory specified by |authority| and
   // |parent_document_id| in Documents Provider.
   // If such a directory does not exist, null is returned.
@@ -65,10 +85,16 @@ interface FileSystemInstance {
   // streams), -1 is returned.
   [MinVersion=1] GetFileSize@1(string url) => (int64 size);
 
+  // Establishes full-duplex communication with the host.
+  [MinVersion=3] Init@5(FileSystemHost host_ptr);
+
   // Asks the ContentResolver to get a FD to read the file specified by the
   // URL.
   [MinVersion=1] OpenFileToRead@2(string url) => (handle? fd);
 
+  // Uninstalls a document watcher.

[Luis Héctor Chávez, 2017/02/22 17:29:31]

Please document the semantics of uninstalling a document watcher that has been
deleted, given the wording of the comment above OnDocumentChanged() ("does not
need to explicitly call").

[Shuhei Takahashi, 2017/02/23 03:37:22]

I changed the comment of OnDocumentChanged():

  Before: the host does not need to explicitly call RemoveWatcher()
  After: the host should not call RemoveWatcher()

And updated the comments around here to be more explicit about semantics.

+  [MinVersion=3] RemoveWatcher@7(int64 watcher_id) => (bool success);
+
   // Requests MediaProvider to scan specified files.
   // When the specified file does not exist, the corresponding entry in
   // MediaProvider is removed.