[android] check external database's read/write permissions asynchrono…

…usly

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/offline/OfflineManager.java

@@ -15,6 +15,7 @@
 import com.mapbox.mapboxsdk.log.Logger;
 import com.mapbox.mapboxsdk.net.ConnectivityReceiver;
 import com.mapbox.mapboxsdk.storage.FileSource;
+import com.mapbox.mapboxsdk.utils.FileUtils;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -235,20 +236,32 @@ public void run() {
    */
   public void mergeOfflineRegions(@NonNull String path, @NonNull final MergeOfflineRegionsCallback callback) {
     File src = new File(path);
-    if (!src.canRead()) {
-      // path not readable, abort
-      callback.onError("Secondary database needs to be located in a readable path.");
-      return;
-    }
+    new FileUtils.CheckFileReadPermissionTask(new FileUtils.OnCheckFileReadPermissionListener() {
+      @Override
+      public void onReadPermissionGranted() {
+        new FileUtils.CheckFileWritePermissionTask(new FileUtils.OnCheckFileWritePermissionListener() {
+          @Override
+          public void onWritePermissionGranted() {
+            // path writable, merge and update schema in place if necessary
+            mergeOfflineDatabaseFiles(src, callback, false);
+          }
 
-    if (src.canWrite()) {
-      // path writable, merge and update schema in place if necessary
-      mergeOfflineDatabaseFiles(src, callback, false);
-    } else {
-      // path not writable, copy the the file to temp directory, then merge and update schema on a copy if necessary
-      File dst = new File(FileSource.getInternalCachePath(context), src.getName());
-      new CopyTempDatabaseFileTask(this, callback).execute(src, dst);
-    }
+          @Override
+          public void onError() {
+            // path not writable, copy the the file to temp directory, then merge and update schema on a copy if
+            // necessary
+            File dst = new File(FileSource.getInternalCachePath(context), src.getName());
+            new CopyTempDatabaseFileTask(OfflineManager.this, callback).execute(src, dst);
+          }
+        }).execute(src);
+      }
+
+      @Override
+      public void onError() {
+        // path not readable, abort
+        callback.onError("Secondary database needs to be located in a readable path.");
+      }
+    }).execute(src);
   }
 
   private static final class CopyTempDatabaseFileTask extends AsyncTask<Object, Void, Object> {

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/utils/FileUtils.java

@@ -0,0 +1,121 @@
+package com.mapbox.mapboxsdk.utils;
+
+import android.os.AsyncTask;
+
+import java.io.File;
+import java.lang.ref.WeakReference;
+
+public class FileUtils {
+
+  /**
+   * Task checking whether app's process can read a file.
+   */
+  public static class CheckFileReadPermissionTask extends AsyncTask<File, Void, Boolean> {
+    private final WeakReference<OnCheckFileReadPermissionListener> listenerWeakReference;
+
+    public CheckFileReadPermissionTask(OnCheckFileReadPermissionListener listener) {
+      this.listenerWeakReference = new WeakReference<>(listener);
+    }
+
+    @Override
+    protected Boolean doInBackground(File... files) {
+      try {
+        return files[0].canRead();
+      } catch (Exception ex) {
+        return false;
+      }
+    }
+
+    @Override
+    protected void onCancelled() {
+      OnCheckFileReadPermissionListener listener = listenerWeakReference.get();
+      if (listener != null) {
+        listener.onError();
+      }
+    }
+
+    @Override
+    protected void onPostExecute(Boolean result) {
+      OnCheckFileReadPermissionListener listener = listenerWeakReference.get();
+      if (listener != null) {
+        if (result) {
+          listener.onReadPermissionGranted();
+        } else {
+          listener.onError();
+        }
+      }
+    }
+  }
+
+  /**
+   * Interface definition for a callback invoked when checking file's read permissions.
+   */
+  public interface OnCheckFileReadPermissionListener {
+
+    /**
+     * Invoked when app's process has a permission to read a file.
+     */
+    void onReadPermissionGranted();
+
+    /**
+     * Invoked when app's process doesn't have a permission to read a file or an error occurs.
+     */
+    void onError();
+  }
+
+  /**
+   * Task checking whether app's process can write to a file.
+   */
+  public static class CheckFileWritePermissionTask extends AsyncTask<File, Void, Boolean> {
+    private final WeakReference<OnCheckFileWritePermissionListener> listenerWeakReference;
+
+    public CheckFileWritePermissionTask(OnCheckFileWritePermissionListener listener) {
+      this.listenerWeakReference = new WeakReference<>(listener);
+    }
+
+    @Override
+    protected Boolean doInBackground(File... files) {
+      try {
+        return files[0].canWrite();
+      } catch (Exception ex) {
+        return false;
+      }
+    }
+
+    @Override
+    protected void onCancelled() {
+      OnCheckFileWritePermissionListener listener = listenerWeakReference.get();
+      if (listener != null) {
+        listener.onError();
+      }
+    }
+
+    @Override
+    protected void onPostExecute(Boolean result) {
+      OnCheckFileWritePermissionListener listener = listenerWeakReference.get();
+      if (listener != null) {
+        if (result) {
+          listener.onWritePermissionGranted();
+        } else {
+          listener.onError();
+        }
+      }
+    }
+  }
+
+  /**
+   * Interface definition for a callback invoked when checking file's write permissions.
+   */
+  public interface OnCheckFileWritePermissionListener {
+
+    /**
+     * Invoked when app's process has a permission to write to a file.
+     */
+    void onWritePermissionGranted();
+
+    /**
+     * Invoked when app's process doesn't have a permission to write to a file or an error occurs.
+     */
+    void onError();
+  }
+}