Wednesday, January 01, 2014

WebRTC app - C# / Xamarin - Part #2 - Attempt #2 - success using a JNI .so file from C# / Mono

This is a post in a series of postings

  1. WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library
  2. WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono
  3. WebRTC app - C# / Xamarin - Part #2 - Attempt #2 - success using a JNI .so file from C# / Mono
  4. WebRTC app - C# / Xamarin - (C# - JNI - C/C++) - Summary and GitHub repository
And finally the associated GitHub repository https://github.com/kenneththorman/webrtc-app-mono

In my previous posting WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono I wrote
This is pushing me in a direction that I initially hoped I could avoid (mainly due to my limited knowledge in the area), JNI.
There were a few reasons that I did not prefer to use a Java Binding Library in the solution. 
  • I would have an even more mixed source code base (C# calling jar/Java which is wrapping C/C++), I would have preferred to keep it at C# wrapping C/C++.
  • The upstream build process is packaging some of the compiled java classes that I need into jar files, but not all of them so now I manually need to add a build step to the build process.
  • I am not familiar with JNI

If we look at the files that are generated during the build process explained in this posting WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library we will see that the jars that we need to build the test android app supplied with the project are located in

~/WebRTCDemo/trunk/webrtc/video_engine/test/android/libs/

namely

audio_device_module_java.jar
video_capture_module_java.jar
video_render_module_java.jar

For each of these jars we need to create a Java Bindings Library that is using the relevant  jar as an input jar (actually 2 of the jars can go into the same Java Binding Library - video_capture_module_java.jar and video_render_module_java.jar since they share the same Java package/namespace). 


(It might be possible to add them all in one Java Binding Library but I encountered problems due to Visual Studios project setting of Default Namespace, which basically was affecting the namespace of the Java classes that I needed to invoke from C#. Since each of the jars contained classes from a different Java package, the easy work around was to add a Java Binding Library for each of the jars and make sure that the Visual Studio Default namespace matched the Java package name.)

Looking at the existing Java WebRTC demo app available in the folder

~/WebRTCDemo/trunk/webrtc/video_engine/test/android/src/org/webrtc/videoengineapp

you will find

IViEAndroidCallback.java
ViEAndroidJavaAPI.java
WebRTCDemo.java

The main file is called WebRTCDemo.java and contains code like the following

...
import org.webrtc.videoengine.ViERenderer;

import java.io.File;
import java.io.IOException;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.Enumeration;

public class WebRTCDemo extends TabActivity implements IViEAndroidCallback,
                                                       View.OnClickListener,
                                                       OnItemSelectedListener {
    private ViEAndroidJavaAPI vieAndroidAPI = null;

    // remote renderer
    private SurfaceView remoteSurfaceView = null;

    // local renderer and camera
    private SurfaceView svLocal = null;

    // channel number
    private int channel = -1;
    private int cameraId;
    private int voiceChannel = -1;
...



By looking at the code I could see there would be some problems, since the main activity is referencing 2 classes that are defined and located side by side with the main activity IViEAndroidCallback.java and ViEAndroidJavaAPI.java. In other words these are not available in a jar and especially the ViEAndroidJavaAPI.java ois the wrapper for the JNI native library so we cannot do this directly from C# according to Native library integration (posting #2).

In the beginning of this posting I outlined 3 reasons I preferred to avoid using JNI and Java Binding Libraries, one of them was
  •  The upstream build process is packaging some of the compiled java classes that I need into jar files, but not all of them so now I manually need to add a build step to the build process.
Anyhow this was fairly easy to remedy by manually creating a new jar containing the 2 files that was needed and then adding this new jar to a new Java Binding Library.
 
XXX@ubuntu:~/WebRTCDemo/trunk/webrtc/video_engine/test/android/bin/classes$
jar cvf ViEAndroidJavaAPI.jar
org/webrtc/videoengineapp/IViEAndroidCallback.class
org/webrtc/videoengineapp/ViEAndroidJavaAPI.class
added manifest
adding: org/webrtc/videoengineapp/IViEAndroidCallback.class(in = 218)
(out= 173)(deflated 20%)
adding: org/webrtc/videoengineapp/ViEAndroidJavaAPI.class(in = 2845)
(out= 1303)(deflated 54%)

Now I was able to use the native library without any exceptions occurring.
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