Post a Message from Java to JS

android_webview/common/aw_message_port_messages.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.
 
 // Multiply-included file, no traditional include guard.
 #include <vector>
 
 #include "base/basictypes.h"
 #include "ipc/ipc_message_macros.h"
 
 #define IPC_MESSAGE_START AwMessagePortMsgStart
 
 //-----------------------------------------------------------------------------
 // MessagePort messages
 // These are messages sent from the browser to the renderer process.
 
-// Tells the renderer to convert the sent message from a WebSerializeScript
-// format to a base::ListValue. Due to the complexities of renderer/browser
-// relation, this can only be done in renderer for now.
-IPC_MESSAGE_ROUTED3(AwMessagePortMsg_Message,
+// Normally the postmessages are exchanged between the renderers and the message
+// itself is opaque to the browser process. The format of the message is a
+// WebSerializesScriptValue.  A WebSerializedScriptValue is a blink structure
+// and can only be serialized/deserialized in renderer.

[mnaganov (inactive), 2015/01/27 13:30:17]

You may mention that we couldn't have Blink or V8 on the browser side due to
their reliance on static variables.

[sgurun-gerrit only, 2015/01/29 03:06:08]

Done.

+// For posting messages from Java (Webview) to JS, we pass the browser/renderer
+// boundary an extra time and convert the messages to a type that browser can
+// use. Since WebView is single-process this is not terribly expensive, but

[mnaganov (inactive), 2015/01/27 13:30:17]

I would argue with this statement. Using IPC takes its toll even for WebView due
to locking that is uses. Try conducting an experiment that sends, say, 10000
short messages and check how much time will you spend on that.

[sgurun-gerrit only, 2015/01/29 03:06:08]

Acknowledged. I am planning to add some perf tests in a next CL. Either way, I
don't feel like there is much to do at this moment. One possibility is
investigating a custom serializer/deserializer that does not depend on Blink,
but I am leaving it to later.

+// if we can do the conversion at the browser, then we can drop this code.
+
+// Tells the renderer to convert the message from a WebSerializeScript
+// format to a base::ListValue. This IPC is used for messages that are
+// incoming to Android webview from JS.
+IPC_MESSAGE_ROUTED3(AwMessagePortMsg_InMessage,

[mnaganov (inactive), 2015/01/27 13:30:17]

The terms "In" and "Out" doesn't clearly mark the origin or the recipient of the
message. There may be people around that place the Web platform in the center of
the universe, not WebView :)

How about naming the directions something like "WebToApp" and "AppToWeb" or
"WebToNative" and "NativeToWeb"?

[sgurun-gerrit only, 2015/01/29 03:06:08]

Done.

                     int /* recipient message port id */,
                     base::string16 /* message */,
                     std::vector<int> /* sent message port_ids */)
+
+// Tells the renderer to convert the message from a String16
+// format to a WebSerializedScriptValue. This IPC is used for messages that
+// are outgoing from Webview to JS.
+// TODO(sgurun) when we start supporting other types, use a ListValue instead
+// of string16
+IPC_MESSAGE_ROUTED3(AwMessagePortMsg_OutMessage,
+                    int /* recipient message port id */,
+                    base::string16 /* message */,
+                    std::vector<int> /* sent message port_ids */)
 
 //-----------------------------------------------------------------------------
 // These are messages sent from the renderer to the browser process.
 
-// Response to AwMessagePortMessage_ConvertMessage
-IPC_MESSAGE_ROUTED3(AwMessagePortHostMsg_ConvertedMessage,
+// Response to AwMessagePortMessage_InMessage
+IPC_MESSAGE_ROUTED3(AwMessagePortHostMsg_ConvertedInMessage,
                     int /* recipient message port id */,
                     base::ListValue /* converted message */,
                     std::vector<int> /* sent message port_ids */)
+
+// Response to AwMessagePortMessage_OutMessage
+IPC_MESSAGE_ROUTED3(AwMessagePortHostMsg_ConvertedOutMessage,
+                    int /* recipient message port id */,
+                    base::string16 /* converted message */,
+                    std::vector<int> /* sent message port_ids */)