Allow MessageFilters to restrict listening to specific message classes

ipc/ipc_channel_proxy.h

Index: ipc/ipc_channel_proxy.h
diff --git a/ipc/ipc_channel_proxy.h b/ipc/ipc_channel_proxy.h
index 1f5ecf450df7f7c6d8a486a3d4efb76a95e1f81e..3feb13778575b9357f161fd1a50d3ee81f349fa8 100644
--- a/ipc/ipc_channel_proxy.h
+++ b/ipc/ipc_channel_proxy.h
@@ -88,6 +88,13 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
     // the message be handled in the default way.
     virtual bool OnMessageReceived(const Message& message);
 
+    // Called to query the Message classes supported by the filter.  Return
+    // false to indicate that all message types should reach the filter, or true
+    // if the resulting contents of |supported_message_classes| may be used to
+    // selectively offer messages of a particular class to the filter.
+    virtual bool GetSupportedMessageClasses(
+        std::vector<uint32>* supported_message_classes) const;
+
    protected:
     virtual ~MessageFilter();
 
@@ -224,12 +231,22 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
     Listener* listener_;
 
     // List of filters.  This is only accessed on the IPC thread.
-    std::vector<scoped_refptr<MessageFilter> > filters_;
+    std::vector<scoped_refptr<MessageFilter> > all_filters_;

[piman, 2014/02/11 21:48:46]

Do we need this? Can't we just iterate over message_global_filters_ and
message_class_filters_ each time?

[jdduke (slow), 2014/02/11 23:01:48]

Well, there are a few operations where we iterate over each filter once and call
a particular function, e.g., |OnChannelError()|, |OnChannelClosed()|.  If we
don't store the list of all filters, we'd need to dynamically generate a unique
list of filters from those in  |message_class_filters_|.

     scoped_refptr<base::SingleThreadTaskRunner> ipc_task_runner_;
     scoped_ptr<Channel> channel_;
     std::string channel_id_;
     bool channel_connected_called_;
 
+    // List of global and selective filters; a given filter from |all_filters_|
+    // will exists in either |message_global_filters_| OR
+    // |message_class_filters_|, but not both.
+    std::vector<MessageFilter*> message_global_filters_;
+    // TODO(jdduke): Determine if base::SmallMap is a sensible choice here,
+    // or simply an array of length (LastIPCMsgStart + 1).

[epennerAtGoogle, 2014/02/10 23:55:47]

+1 to just a resized-vector, or something equivalent.

[piman, 2014/02/11 21:48:46]

An array sg.
Generally, hash_maps are preferred to maps if the order doesn't matter (usually
cheaper both in run-time and memory), but in this case, because the size is
static and the key space is compact, an array is even better.

[jdduke (slow), 2014/02/11 23:01:48]

Done.

[epennerAtGoogle, 2014/02/12 02:34:09]

Just FYI, I mentioned vector since it typically has bounds checking in debug
builds (at least IIRC - I haven't actually checked). If our other tools are good
enough to catch out-of-bounds these days, no worries (it's also pretty simple
code).

+    typedef std::map<uint32, std::vector<MessageFilter*> >
+        MessageClassFilterMap;
+    MessageClassFilterMap message_class_filters_;
+
     // Holds filters between the AddFilter call on the listerner thread and the
     // IPC thread when they're added to filters_.
     std::vector<scoped_refptr<MessageFilter> > pending_filters_;