Use ReLinker to load os-compat library

Author: cketti

SafeContentResolver-v14/build.gradle

@@ -20,5 +20,6 @@ android {
 
 dependencies {
     compile project(':SafeContentResolver')
+    compile 'com.getkeepsafe.relinker:relinker:1.2.1'
     compile 'com.android.support:support-annotations:23.2.0'
 }

SafeContentResolver-v14/src/main/java/de/cketti/safecontentresolver/Os.java

@@ -16,10 +16,56 @@
 package de.cketti.safecontentresolver;
 
 
+import android.content.Context;
+
+import com.getkeepsafe.relinker.MissingLibraryException;
+import com.getkeepsafe.relinker.ReLinker;
+
+
 class Os {
-    static {
-        System.loadLibrary("os-compat");
+    private static final String LIBRARY_NAME = "os-compat";
+
+    private static Context context;
+    private static boolean libraryNeedsLoading = true;
+    private static UnsupportedOperationException loadFailedException;
+
+
+    synchronized static void init(Context context) {
+        if (context == null) {
+            throw new NullPointerException("Argument 'context' must not be null");
+        }
+
+        // Only get the context here. Load the library before doing the actual work (hopefully in a background thread).
+        if (Os.context == null) {
+            Os.context = context.getApplicationContext();
+        }
+    }
+
+    static int fstat(int fileDescriptor) throws ErrnoException, UnsupportedOperationException {
+        synchronized (Os.class) {
+            if (context == null) {
+                throw new IllegalStateException("Call Os.init(Context) before attempting to call Os.fstat()");
+            }
+
+            if (libraryNeedsLoading) {
+                loadLibrary();
+            } else if (loadFailedException != null) {
+                throw loadFailedException;
+            }
+        }
+
+        return nativeFstat(fileDescriptor);
+    }
+
+    private static void loadLibrary() {
+        libraryNeedsLoading = false;
+        try {
+            ReLinker.loadLibrary(context, LIBRARY_NAME);
+        } catch (MissingLibraryException | UnsatisfiedLinkError e) {
+            loadFailedException = new UnsupportedOperationException("Failed to load native library " + LIBRARY_NAME, e);
+            throw loadFailedException;
+        }
     }
 
-    public static native int fstat(int fileDescriptor) throws ErrnoException;
+    private static native int nativeFstat(int fileDescriptor) throws ErrnoException;
 }

SafeContentResolver-v14/src/main/java/de/cketti/safecontentresolver/SafeContentResolverApi14.java

@@ -27,6 +27,7 @@
 class SafeContentResolverApi14 extends SafeContentResolver {
     SafeContentResolverApi14(Context context) {
         super(context);
+        Os.init(context);
     }
 
     @Override
@@ -35,7 +36,7 @@ protected int getFileUidOrThrow(@NonNull FileDescriptor fileDescriptor) throws F
             int systemFileDescriptor = extractSystemFileDescriptor(fileDescriptor);
 
             return Os.fstat(systemFileDescriptor);
-        } catch (ErrnoException e) {
+        } catch (ErrnoException | UnsupportedOperationException e) {
             throw new FileNotFoundException(e.getMessage());
         }
     }

SafeContentResolver-v14/src/main/jni/os-compat.c

@@ -29,7 +29,7 @@
 
 
 JNIEXPORT jint JNICALL
-Java_de_cketti_safecontentresolver_Os_fstat(JNIEnv *env, jclass type, jint fileDescriptor) {
+Java_de_cketti_safecontentresolver_Os_nativeFstat(JNIEnv *env, jclass type, jint fileDescriptor) {
     struct stat sb;
 
     int rc = TEMP_FAILURE_RETRY(fstat(fileDescriptor, &sb));