Allow Soloader to work with system apps

Summary:
Fix to allow SoLoader to find .so deps when app is packaged as Prebuilt APK with Android AOSP Source
When an apk has .so files as part of the APK, the Android make system will generate the APK so as to allow .so files to be loaded directly.

Another option is to include the .so in system libs by updating the Android make file but that means that the files are shared across the OS and can cause conflicts with
applications that may want their own version of the .so

Possible fix for issue
#28

How to use:
  SoLoader.init(mContext, SOLOADER_DISABLE_BACKUP_SOSOURCE);
  SoLoader.setSystemLoadLibraryWrapper(
        new SystemLoadLibraryWrapper() {
          Override
          public void loadLibrary(String libName) {
            System.loadLibrary(libName);
          }
        });

Reviewed By: joelmccall

Differential Revision: D15082630

fbshipit-source-id: 68db389bc105929c6cba7a92285c5a3df947f51c

java/com/facebook/soloader/SoLoader.java

@@ -149,6 +149,8 @@ public class SoLoader {
   @GuardedBy("sSoSourcesLock")
   private static int sFlags;
 
+  private static boolean isSystemApp;
+
   static {
     boolean shouldSystrace = false;
     try {
@@ -177,6 +179,7 @@ private static void init(Context context, int flags, @Nullable SoFileLoader soFi
       throws IOException {
     StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskWrites();
     try {
+      isSystemApp = checkIfSystemApp(context);
       initSoLoader(soFileLoader);
       initSoSources(context, flags, soFileLoader);
     } finally {
@@ -239,12 +242,8 @@ private static void initSoSources(Context context, int flags, @Nullable SoFileLo
             Log.d(TAG, "adding exo package source: " + SO_STORE_NAME_MAIN);
             soSources.add(0, new ExoSoSource(context, SO_STORE_NAME_MAIN));
           } else {
-            ApplicationInfo applicationInfo = context.getApplicationInfo();
-            boolean isSystemApplication =
-                (applicationInfo.flags & ApplicationInfo.FLAG_SYSTEM) != 0
-                    && (applicationInfo.flags & ApplicationInfo.FLAG_UPDATED_SYSTEM_APP) == 0;
             int apkSoSourceFlags;
-            if (isSystemApplication) {
+            if (isSystemApp) {
               apkSoSourceFlags = 0;
             } else {
               apkSoSourceFlags = ApkSoSource.PREFER_ANDROID_LIBS_DIRECTORY;
@@ -429,6 +428,13 @@ private static Method getNativeLoadRuntimeMethod() {
     }
   }
 
+  private static boolean checkIfSystemApp(Context context) {
+    return (context != null)
+        && (context.getApplicationInfo().flags
+                & (ApplicationInfo.FLAG_SYSTEM | ApplicationInfo.FLAG_UPDATED_SYSTEM_APP))
+            != 0;
+  }
+
   /** Turn shared-library loading into a no-op. Useful in special circumstances. */
   public static void setInTestMode() {
     setSoSources(new SoSource[] {new NoopSoSource()});
@@ -545,6 +551,13 @@ public static boolean loadLibrary(String shortName, int loadFlags) throws Unsati
       sSoSourcesLock.readLock().unlock();
     }
 
+    // This is to account for the fact that we want to load .so files from the apk itself when it is
+    // a system app.
+    if (isSystemApp && sSystemLoadLibraryWrapper != null) {
+      sSystemLoadLibraryWrapper.loadLibrary(shortName);
+      return true;
+    }
+
     String mergedLibName = MergedSoMapping.mapLibName(shortName);
 
     String soName = mergedLibName != null ? mergedLibName : shortName;