My suggestion is to introduce a new version of current messaging interface
instead of a whole new interface.
struct XW_MessagingInterface_2 {
void (*Register)(XW_Extension extension, XW_HandleMessageCallback
handle_message);
void (*PostMessage)(XW_Instance instance, const char* message);
void (*RegisterBinaryMessageCallback)(XW_Extension extension,
XW_HandleBinaryMessageCallback handle_message);
void (*PostBinaryMessage)(XW_Instance instance, const char* message,
const size_t size);
};
Thanks,
Zhenyu
On 7/16/15 15:25 , "Hu, Ningxin" <ningxin...@intel.com> wrote:
>Intent to Implement: Binary Messaging Interface for Crosswalk External
>Extension
>
>Description:
>Today's Crosswalk external extension API only provides text based
>messaging interface. However, coming use cases require the external
>extension native code to exchange binary data with JavaScript code. For
>example, an external extension wants to transfer the images stream from
>native to JavaScript in real-time (30FPS at least). With today's external
>extension messaging API, the extension has to encode the binary image
>data into text in native first, posts to JavaScript and then decodes from
>the text to binary data in JavaScript. The encoding, decoding (in
>JavaScript!) and increased message size leads to low performance.
>Experiment shows by using base64 to transfer VGA (640x480) images, this
>approach can only deliver less 10 FPS on mainstream PC.
>The binary messaging interface is proposed to added into Crosswalk
>external extension API. It allows native code to exchange binary data (a
>byte array) to JavaScript without unnecessary encoding/decoding.
>JavaScript receives an ArrayBuffer object and can access the binary data
>via different Typed Array View. Vice versa, JavaScript can send the
>binary data in an ArrayBuffer object to native, native code receives a
>byte array.
>Prototype shows 3X-8X (binary messaging vs. text messaging) performance
>speedup when transferring different size of data on both PC and mobile
>device. Initial data shows with binary messaging interface, an external
>extension is able to transfer VGA images at 60FPS on PC.
>
>Affected component: Crosswalk External Extension
>
>Related feature: https://crosswalk-project.org/jira/browse/XWALK-4615
>
>Target release: Crosswalk-17
>
>Implementation details:
>1. Interface change:
>For Crosswalk External Extension C API, a new interface
>XW_BinaryMessagingInterface_1 will be added. To keep API and ABI
>compatibility with existing external extension, a new file
>(extensions/public/XW_Extension_BinaryMessage.h) will be added to contain
>the XW_BinaryMessagingInterface_1 interface. The
>XW_BinaryMessagingInterface_1 looks like:
>
>//////////////////////////////////////////////////////////////////////////
>/////////////////
>#ifdef __cplusplus
>extern "C" {
>#endif
>
>#define XW_BINARY_MESSAGING_INTERFACE_1 "XW_BinaryMessagingInterface_1"
>#define XW_BINARY_MESSAGING_INTERFACE XW_BINARY_MESSAGING_INTERFACE_1
>
>typedef void (*XW_HandleBinaryMessageCallback)(XW_Instance instance,
>
> const char* message,
>
> const size_t size);
>
>struct XW_BinaryMessagingInterface_1 {
> void (*Register)(XW_Extension extension,
> XW_HandleBinaryMessageCallback
>handle_message);
>
> void (*PostMessage)(XW_Instance instance, const char* message, const
>size_t size);
>};
>
>typedef struct XW_BinaryMessagingInterface_1 XW_BinaryMessagingInterface;
>
>#ifdef __cplusplus
>} // extern "C"
>#endif
>//////////////////////////////////////////////////////////////////////////
>////////////////
>
>If the C extension wants to use binary messaging, it needs to query the
>"XW_BinaryMessagingInterface_1" interface and use the PostMessage method
>to post binary data to JavaScript. On other hand, it needs to register a
>XW_HandleBinaryMessageCallback to receive binary data from JavaScript.
>
>For Crosswalk external extension Android Java API, two methods will be
>added into XWalkExtensionClient interface:
>
>//////////////////////////////////////////////////////////////////////////
>///////////////
>
>public void onBinaryMessage(int extensionInstanceID, byte[] message);
>
>public final void postBinaryMessage(int instanceID, byte[] message);
>
>//////////////////////////////////////////////////////////////////////////
>//////////////
>
>Java extension which inherits XWalkExtensionClient can use
>postBinaryMesssage to post binary data to JavaScript and implements
>onBinaryMessage to receive binary data from JavaScript.
>
>No new APIs will be added into Crosswalk extension JavaScript API. When
>native external extension posts binary message, the JavaScript message
>listener receives an ArrayBuffer object.
>When JavaScript invokes extension.postMessage with an ArrayBuffer object
>as argument, the native binary message listener is invoked.
>
>This proposal doesn't cover binary messaging support in SyncMessage, as
>there is no obvious use case.
>
>Sample code:
>An external extension wants to transfer image data to JavaScript. To
>transfer structured data, the extension can use simple custom binary
>message format as this sample shows. Or it can leverage more
>sophisticated binary format, e.g. Google's Protocol Buffer
>(https://developers.google.com/protocol-buffers/).
>C++:
>//////////////////////////////////////////////////////////////////////////
>/////////////
>// image binary format
>// uint32_t width;
>// uint32_t height;
>// char data[width * height * 4];
>
>static const XW_BinaryMessagingInterface* g_binary_messaging =
> get_interface(XW_BINARY_MESSAGING_INTERFACE);
>.....
>size_t buffer_size = sizeof(uint32_t) + sizeof(uint32_t) +
>width*height*4*sizeof(char);
>char* buffer = new char[buffer_size ];
>uint32_t* uint32_array = reinterpret_cast<uint32_t*>(buffer);
>uint32_array[0] = image.width();
>uint32_array[1] = image.height();
>char* data = buffer + 2 * sizeof(uint32_t);
>image.CopyImageData(data);
>g_binary_messaging->postMessage(instance, buffer, buffer_size);
>delete[] buffer;
>//////////////////////////////////////////////////////////////////////////
>/////////////
>
>JavaScript:
>//////////////////////////////////////////////////////////////////////////
>/////////////
>extension.setMessageListener(function(msg) {
> if (msg instaceof ArrayBuffer) {
> var uint32_view = new Uint32Array(msg);
> var width = uint32_view[0];
> var height = uint32_view[1];
> var data = new Uint8Array(msg, 8, width*height*4);
> ....
> }
>}
>//////////////////////////////////////////////////////////////////////////
>////////////
>
>Details:
>It doesn't require to modify Crosswalk Core Extension code
>(XWalkExtensionModule), as V8ValueConverter already supports to convert a
>base::BinaryValue object to V8 ArrayBuffer object and vice versa.
>
>It mainly requires to modify the external extension components, to expose
>the binary interface and convert the binary data to base::BinaryValue and
>vice versa.
>
>For C external extension, files to be modified:
>extensions/common/xwalk_external_adapter.cc
>extensions/common/xwalk_external_adapter.h
>extensions/common/xwalk_external_extension.cc
>extensions/common/xwalk_external_extension.h
>extensions/common/xwalk_external_instance.cc
>extensions/common/xwalk_external_instance.h
>extensions/extensions.gyp
>
>new file:
>extensions/public/XW_Extension_BinaryMessage.h
>
>For Java external extension, files to be modified:
>app/android/runtime_client/src/org/xwalk/app/runtime/extension/XWalkCoreEx
>tensionBridge.java
>app/android/runtime_client/src/org/xwalk/app/runtime/extension/XWalkExtens
>ionClient.java
>app/android/runtime_client/src/org/xwalk/app/runtime/extension/XWalkExtens
>ionContextClient.java
>app/android/runtime_client/src/org/xwalk/app/runtime/extension/XWalkRuntim
>eExtensionBridge.java
>app/android/runtime_client/src/org/xwalk/app/runtime/extension/XWalkRuntim
>eExtensionManager.java
>extensions/android/java/src/org/xwalk/core/internal/extensions/XWalkExtens
>ionAndroid.java
>extensions/common/android/xwalk_extension_android.cc
>extensions/common/android/xwalk_extension_android.h
>runtime/android/core_internal/src/org/xwalk/core/internal/XWalkExtensionIn
>ternal.java
>
>
>Thanks,
>-ningxin
>
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