Merge pull request #28 from rthakohov/network-browsing-broadcast

Network browsing via broadcasting

app/src/main/java/com/google/android/sambadocumentsprovider/browsing/BrowsingException.java

@@ -17,8 +17,12 @@
 
 package com.google.android.sambadocumentsprovider.browsing;
 
-class BrowsingException extends Exception {
+public class BrowsingException extends Exception {
-  BrowsingException(String message) {
+  public BrowsingException(String message) {
     super("Browsing failed: " + message);
   }
+
+  public BrowsingException(String message, Throwable cause) {
+    super("Browsing failed: " + message, cause);
+  }
 }

app/src/main/java/com/google/android/sambadocumentsprovider/browsing/NetworkBrowser.java

@@ -22,30 +22,24 @@ import android.os.AsyncTask;
 import android.util.Log;
 
 import com.google.android.sambadocumentsprovider.TaskManager;
-import com.google.android.sambadocumentsprovider.base.DirectoryEntry;
 import com.google.android.sambadocumentsprovider.base.OnTaskFinishedCallback;
+import com.google.android.sambadocumentsprovider.browsing.broadcast.BroadcastBrowsingProvider;
 import com.google.android.sambadocumentsprovider.nativefacade.SmbClient;
-import com.google.android.sambadocumentsprovider.nativefacade.SmbDir;
 
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
-import java.util.concurrent.Future;
 
 public class NetworkBrowser {
   public static final Uri SMB_BROWSING_URI = Uri.parse("smb://");
 
   private static final String TAG = "NetworkBrowser";
-  
-  private final NetworkBrowsingProvider mMasterProvider;
-  private final TaskManager mTaskManager;
 
-  private final Map<Uri, Future> mTasks = new HashMap<>();
+  private final NetworkBrowsingProvider mMasterProvider;
+  private final NetworkBrowsingProvider mBroadcastProvider;
+  private final TaskManager mTaskManager;
 
   public NetworkBrowser(SmbClient client, TaskManager taskManager) {
     mMasterProvider = new MasterBrowsingProvider(client);
+    mBroadcastProvider = new BroadcastBrowsingProvider();
     mTaskManager = taskManager;
   }
 
@@ -58,7 +52,19 @@ public class NetworkBrowser {
   }
 
   private List<String> getServers() throws BrowsingException {
-    return mMasterProvider.getServers();
+    List<String> servers = null;
+
+    try {
+      servers = mMasterProvider.getServers();
+    } catch (BrowsingException e) {
+      Log.e(TAG, "Master browsing failed", e);
+    }
+
+    if (servers == null || servers.isEmpty()) {
+      return mBroadcastProvider.getServers();
+    }
+
+    return servers;
   }
 
   private class LoadServersTask extends AsyncTask<Void, Void, List<String>> {

app/src/main/java/com/google/android/sambadocumentsprovider/browsing/NetworkBrowsingProvider.java

@@ -19,7 +19,7 @@ package com.google.android.sambadocumentsprovider.browsing;
 
 import java.util.List;
 
-interface NetworkBrowsingProvider {
+public interface NetworkBrowsingProvider {
   /**
    * Returns unresolved host names.
    */

app/src/main/java/com/google/android/sambadocumentsprovider/browsing/broadcast/BroadcastBrowsingProvider.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.google.android.sambadocumentsprovider.browsing.broadcast;
+
+import android.util.Log;
+
+import com.google.android.sambadocumentsprovider.BuildConfig;
+import com.google.android.sambadocumentsprovider.browsing.BrowsingException;
+import com.google.android.sambadocumentsprovider.browsing.NetworkBrowsingProvider;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.SocketException;
+import java.net.SocketTimeoutException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+public class BroadcastBrowsingProvider implements NetworkBrowsingProvider {
+  private static final String TAG = "BroadcastBrowsing";
+  private static final int LISTENING_TIMEOUT = 3000; // 3 seconds.
+  private static final int NBT_PORT = 137;
+
+  private final ExecutorService mExecutor = Executors.newCachedThreadPool();
+
+  private int mTransId = 0;
+
+  @Override
+  public List<String> getServers() throws BrowsingException {
+    try {
+      List<Future<List<String>>> serverFutures = new ArrayList<>();
+
+      List<String> broadcastAddresses = BroadcastUtils.getBroadcastAddress();
+      for (String address : broadcastAddresses) {
+        mTransId++;
+        serverFutures.add(mExecutor.submit(new GetServersForInterfaceTask(address, mTransId)));
+      }
+
+      List<String> servers = new ArrayList<>();
+      for (Future<List<String>> future : serverFutures) {
+        servers.addAll(future.get());
+      }
+
+      return servers;
+    } catch (IOException | ExecutionException | InterruptedException e) {
+      Log.e(TAG, "Failed to get servers via broadcast", e);
+      throw new BrowsingException("Failed to get servers via broadcast", e);
+    }
+  }
+
+  private class GetServersForInterfaceTask implements Callable<List<String>> {
+    private final String mBroadcastAddress;
+    private final int mTransId;
+
+    GetServersForInterfaceTask(String broadcastAddress, int transId) {
+      mBroadcastAddress = broadcastAddress;
+      mTransId = transId;
+    }
+
+    @Override
+    public List<String> call() throws Exception {
+      try (DatagramSocket socket = new DatagramSocket()) {
+        InetAddress address = InetAddress.getByName(mBroadcastAddress);
+
+        sendNameQueryBroadcast(socket, address);
+
+        return listenForServers(socket);
+      }
+    }
+
+    private void sendNameQueryBroadcast(
+            DatagramSocket socket,
+            InetAddress address) throws IOException {
+      byte[] data = BroadcastUtils.createPacket(mTransId);
+      int dataLength = data.length;
+
+      DatagramPacket packet = new DatagramPacket(data, 0, dataLength, address, NBT_PORT);
+      socket.send(packet);
+
+      if (BuildConfig.DEBUG) Log.d(TAG, "Broadcast package sent");
+    }
+
+    private List<String> listenForServers(DatagramSocket socket) throws IOException {
+      List<String> servers = new ArrayList<>();
+
+      socket.setSoTimeout(LISTENING_TIMEOUT);
+
+      while (true) {
+        try {
+          byte[] buf = new byte[1024];
+          DatagramPacket packet = new DatagramPacket(buf, buf.length);
+
+          socket.receive(packet);
+
+          try {
+            servers.addAll(BroadcastUtils.extractServers(packet.getData(), mTransId));
+          } catch (BrowsingException e) {
+            Log.e(TAG, "Failed to parse incoming packet: ", e);
+          }
+        } catch (SocketTimeoutException e) {
+          break;
+        }
+      }
+
+      return servers;
+    }
+  }
+}

app/src/main/java/com/google/android/sambadocumentsprovider/browsing/broadcast/BroadcastUtils.java

@@ -0,0 +1,183 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.google.android.sambadocumentsprovider.browsing.broadcast;
+
+import android.util.Log;
+
+import com.google.android.sambadocumentsprovider.BuildConfig;
+import com.google.android.sambadocumentsprovider.browsing.BrowsingException;
+
+import java.net.InetAddress;
+import java.net.InterfaceAddress;
+import java.net.NetworkInterface;
+import java.net.SocketException;
+import java.nio.BufferUnderflowException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.List;
+
+class BroadcastUtils {
+  private static final String TAG = "BroadcastUtils";
+
+  private static final int FILE_SERVER_NODE_TYPE = 0x20;
+  private static final int SERVER_NAME_LENGTH = 15;
+  private static final String SERVER_NAME_CHARSET = "US-ASCII";
+
+  /**
+   * Generates a NetBIOS name query request.
+   * https://tools.ietf.org/html/rfc1002
+   * Section 4.2.12
+   */
+  static byte[] createPacket(int transId) {
+    ByteBuffer os = ByteBuffer.allocate(50);
+
+    char broadcastFlag = 0x0010;
+    char questionCount = 1;
+    char answerResourceCount = 0;
+    char authorityResourceCount = 0;
+    char additionalResourceCount = 0;
+
+    os.putChar((char) transId);
+    os.putChar(broadcastFlag);
+    os.putChar(questionCount);
+    os.putChar(answerResourceCount);
+    os.putChar(authorityResourceCount);
+    os.putChar(additionalResourceCount);
+
+    // Length of name. 16 bytes of name encoded to 32 bytes.
+    os.put((byte) 0x20);
+
+    // '*' character encodes to 2 bytes.
+    os.put((byte) 0x43);
+    os.put((byte) 0x4b);
+
+    // Write the remaining 15 nulls which encode to 30* 0x41
+    for (int i = 0; i < 30; i++) {
+      os.put((byte) 0x41);
+    }
+
+    // Length of next segment.
+    os.put((byte) 0);
+
+    // Question type: Node status
+    os.putChar((char) 0x21);
+
+    // Question class: Internet
+    os.putChar((char) 0x01);
+
+    return os.array();
+  }
+
+  /**
+   * Parses a positive response to NetBIOS name request query.
+   * https://tools.ietf.org/html/rfc1002
+   * Section 4.2.13
+   */
+  static List<String> extractServers(byte[] data, int expectedTransId) throws BrowsingException {
+    try {
+      ByteBuffer buffer = ByteBuffer.wrap(data).order(ByteOrder.BIG_ENDIAN);
+
+      int transId = buffer.getChar();
+      if (transId != expectedTransId) {
+        // This response is not to our broadcast.
+
+        if (BuildConfig.DEBUG) Log.d(TAG, "Irrelevant broadcast response");
+
+        return Collections.emptyList();
+      }
+
+      skipBytes(buffer, 2); // Skip flags.
+
+      skipBytes(buffer, 2); // No questions.
+      skipBytes(buffer, 2); // Skip answers count.
+      skipBytes(buffer, 2); // No authority resources.
+      skipBytes(buffer, 2); // No additional resources.
+
+      int nameLength = buffer.get();
+      skipBytes(buffer, nameLength);
+
+      skipBytes(buffer, 1);
+
+      int nodeStatus = buffer.getChar();
+      if (nodeStatus != 0x20 && nodeStatus != 0x21) {
+        throw new BrowsingException("Received negative response for the broadcast");
+      }
+
+      skipBytes(buffer, 2);
+      skipBytes(buffer, 4);
+      skipBytes(buffer, 2);
+
+      int addressListEntryCount = buffer.get();
+
+      List<String> servers = new ArrayList<>();
+      for (int i = 0; i < addressListEntryCount; i++) {
+        byte[] nameArray = new byte[SERVER_NAME_LENGTH];
+        buffer.get(nameArray, 0, SERVER_NAME_LENGTH);
+
+        final String serverName = new String(nameArray, Charset.forName(SERVER_NAME_CHARSET));
+        final int type = buffer.get();
+
+        if (type == FILE_SERVER_NODE_TYPE) {
+          servers.add(serverName);
+        }
+
+        skipBytes(buffer, 2);
+      }
+
+      return servers;
+    } catch (BufferUnderflowException e) {
+      Log.e(TAG, "Malformed incoming packet");
+
+      return Collections.emptyList();
+    }
+  }
+
+  static List<String> getBroadcastAddress() throws BrowsingException, SocketException {
+    Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
+
+    List<String> broadcastAddresses = new ArrayList<>();
+
+    while (interfaces.hasMoreElements()) {
+      NetworkInterface networkInterface = interfaces.nextElement();
+      if (networkInterface.isLoopback()) {
+        continue;
+      }
+
+      for (InterfaceAddress interfaceAddress :
+              networkInterface.getInterfaceAddresses()) {
+        InetAddress broadcast = interfaceAddress.getBroadcast();
+
+        if (broadcast != null) {
+          broadcastAddresses.add(broadcast.toString().substring(1));
+        }
+      }
+    }
+
+    return broadcastAddresses;
+  }
+
+  private static void skipBytes(ByteBuffer buffer, int bytes) {
+    for (int i = 0; i < bytes; i++) {
+      buffer.get();
+    }
+  }
+}

app/src/main/java/com/google/android/sambadocumentsprovider/provider/SambaDocumentsProvider.java

@@ -75,75 +75,75 @@ public class SambaDocumentsProvider extends DocumentsProvider {
   private static final String TAG = "SambaDocumentsProvider";
 
   private static final String[] DEFAULT_ROOT_PROJECTION = {
-      Root.COLUMN_ROOT_ID,
+          Root.COLUMN_ROOT_ID,
-      Root.COLUMN_DOCUMENT_ID,
+          Root.COLUMN_DOCUMENT_ID,
-      Root.COLUMN_TITLE,
+          Root.COLUMN_TITLE,
-      Root.COLUMN_FLAGS,
+          Root.COLUMN_FLAGS,
-      Root.COLUMN_ICON
+          Root.COLUMN_ICON
   };
 
   private static final String[] DEFAULT_DOCUMENT_PROJECTION = {
-      Document.COLUMN_DOCUMENT_ID,
+          Document.COLUMN_DOCUMENT_ID,
-      Document.COLUMN_DISPLAY_NAME,
+          Document.COLUMN_DISPLAY_NAME,
-      Document.COLUMN_FLAGS,
+          Document.COLUMN_FLAGS,
-      Document.COLUMN_MIME_TYPE,
+          Document.COLUMN_MIME_TYPE,
-      Document.COLUMN_SIZE,
+          Document.COLUMN_SIZE,
-      Document.COLUMN_LAST_MODIFIED,
+          Document.COLUMN_LAST_MODIFIED,
-      Document.COLUMN_ICON
+          Document.COLUMN_ICON
   };
 
   private final OnTaskFinishedCallback<Uri> mLoadDocumentCallback =
-      new OnTaskFinishedCallback<Uri>() {
+          new OnTaskFinishedCallback<Uri>() {
-        @Override
+            @Override
-        public void onTaskFinished(@Status int status, @Nullable Uri uri, Exception exception) {
+            public void onTaskFinished(@Status int status, @Nullable Uri uri, Exception exception) {
-          getContext().getContentResolver().notifyChange(toNotifyUri(uri), null, false);
+              getContext().getContentResolver().notifyChange(toNotifyUri(uri), null, false);
-        }
+            }
-      };
+          };
 
   private final OnTaskFinishedCallback<DocumentMetadata> mLoadChildrenCallback =
-      new OnTaskFinishedCallback<DocumentMetadata>() {
+          new OnTaskFinishedCallback<DocumentMetadata>() {
-        @Override
+            @Override
-        public void onTaskFinished(@Status int status, DocumentMetadata metadata,
+            public void onTaskFinished(@Status int status, DocumentMetadata metadata,
-            Exception exception) {
+                                       Exception exception) {
-          // Notify remote side that we get the list even though we don't have the stat yet.
+              // Notify remote side that we get the list even though we don't have the stat yet.
-          // If it failed we still should notify the remote side that the loading failed.
+              // If it failed we still should notify the remote side that the loading failed.
-          getContext().getContentResolver().notifyChange(
+              getContext().getContentResolver().notifyChange(
-              toNotifyUri(metadata.getUri()), null, false);
+                      toNotifyUri(metadata.getUri()), null, false);
-        }
+            }
-      };
+          };
 
   private final OnTaskFinishedCallback<String> mWriteFinishedCallback =
-      new OnTaskFinishedCallback<String>() {
+          new OnTaskFinishedCallback<String>() {
-        @Override
+            @Override
-        public void onTaskFinished(
+            public void onTaskFinished(
-            @Status int status, @Nullable String item, Exception exception) {
+                    @Status int status, @Nullable String item, Exception exception) {
-          final Uri uri = toUri(item);
+              final Uri uri = toUri(item);
-          try (final CacheResult result = mCache.get(uri)) {
+              try (final CacheResult result = mCache.get(uri)) {
-            if (result.getState() != CacheResult.CACHE_MISS) {
+                if (result.getState() != CacheResult.CACHE_MISS) {
-              result.getItem().reset();
+                  result.getItem().reset();
-            }
+                }
-          }
+              }
 
-          final Uri parentUri = DocumentMetadata.buildParentUri(uri);
+              final Uri parentUri = DocumentMetadata.buildParentUri(uri);
-          getContext().getContentResolver().notifyChange(toNotifyUri(parentUri), null, false);
+              getContext().getContentResolver().notifyChange(toNotifyUri(parentUri), null, false);
-        }
+            }
-      };
+          };
 
   private final OnTaskFinishedCallback<List<String>> mLoadSharesFinishedCallback =
-    new OnTaskFinishedCallback<List<String>>() {
+          new OnTaskFinishedCallback<List<String>>() {
-      @Override
+            @Override
-      public void onTaskFinished(
+            public void onTaskFinished(
-      @OnTaskFinishedCallback.Status int status,
+                    @OnTaskFinishedCallback.Status int status,
-      @Nullable List<String> item,
+                    @Nullable List<String> item,
-      @Nullable Exception exception) {
+                    @Nullable Exception exception) {
-        if (BuildConfig.DEBUG) Log.d(TAG, "Browsing callback");
+              if (BuildConfig.DEBUG) Log.d(TAG, "Browsing callback");
 
-        mBrowsingStorage = item;
+              mBrowsingStorage = item;
 
-        getContext().getContentResolver().notifyChange(
+              getContext().getContentResolver().notifyChange(
-                toNotifyUri(toUri(NetworkBrowser.SMB_BROWSING_URI.toString())), null, false);
+                      toNotifyUri(toUri(NetworkBrowser.SMB_BROWSING_URI.toString())), null, false);
-      }
+            }
-    };
+          };
 
   private final MountedShareChangeListener mShareChangeListener = new MountedShareChangeListener() {
     @Override
@@ -162,7 +162,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
   private StorageManager mStorageManager;
   private NetworkBrowser mNetworkBrowser;
 
-  private List<String> mBrowsingStorage = new ArrayList<>();
+  private List<String> mBrowsingStorage;
 
   @Override
   public boolean onCreate() {
@@ -189,11 +189,11 @@ public class SambaDocumentsProvider extends DocumentsProvider {
     MatrixCursor cursor = new MatrixCursor(projection, mShareManager.size());
 
     cursor.addRow(new Object[] {
-      NetworkBrowser.SMB_BROWSING_URI.toString(),
+            NetworkBrowser.SMB_BROWSING_URI.toString(),
-      NetworkBrowser.SMB_BROWSING_URI.toString(),
+            NetworkBrowser.SMB_BROWSING_URI.toString(),
-      getContext().getResources().getString(R.string.browsing_root_name),
+            getContext().getResources().getString(R.string.browsing_root_name),
-      0,
+            0,
-      R.drawable.ic_cloud,
+            R.drawable.ic_cloud,
     });
 
     for (String uri : mShareManager) {
@@ -211,11 +211,11 @@ public class SambaDocumentsProvider extends DocumentsProvider {
         name = metadata.getDisplayName();
 
         cursor.addRow(new Object[] {
-            toRootId(metadata),
+                toRootId(metadata),
-            toDocumentId(parsedUri),
+                toDocumentId(parsedUri),
-            name,
+                name,
-            Root.FLAG_SUPPORTS_CREATE | Root.FLAG_SUPPORTS_IS_CHILD,
+                Root.FLAG_SUPPORTS_CREATE | Root.FLAG_SUPPORTS_IS_CHILD,
-            R.drawable.ic_folder_shared
+                R.drawable.ic_folder_shared
         });
       }
 
@@ -273,7 +273,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
 
   @Override
   public Cursor queryChildDocuments(String documentId, String[] projection, String sortOrder)
-      throws FileNotFoundException {
+          throws FileNotFoundException {
     if (BuildConfig.DEBUG) Log.d(TAG, "Querying children documents under " + documentId);
     projection = (projection == null) ? DEFAULT_DOCUMENT_PROJECTION : projection;
 
@@ -304,7 +304,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
           mCache.throwLastExceptionIfAny(uri);
 
           final LoadDocumentTask task =
-              new LoadDocumentTask(uri, mClient, mCache, mLoadDocumentCallback);
+                  new LoadDocumentTask(uri, mClient, mCache, mLoadDocumentCallback);
           mTaskManager.runTask(uri, task);
           cursor.setLoadingTask(task);
 
@@ -321,7 +321,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
           final Map<Uri, DocumentMetadata> childrenMap = metadata.getChildren();
           if (childrenMap == null || result.getState() == CacheResult.CACHE_EXPIRED) {
             final LoadChildrenTask task =
-                new LoadChildrenTask(metadata, mClient, mCache, mLoadChildrenCallback);
+                    new LoadChildrenTask(metadata, mClient, mCache, mLoadChildrenCallback);
             mTaskManager.runTask(uri, task);
             cursor.setLoadingTask(task);
 
@@ -340,13 +340,13 @@ public class SambaDocumentsProvider extends DocumentsProvider {
             }
             if (!isLoading && !docMap.isEmpty()) {
               LoadStatTask task = new LoadStatTask(docMap, mClient,
-                  new OnTaskFinishedCallback<Map<Uri, DocumentMetadata>>() {
+                      new OnTaskFinishedCallback<Map<Uri, DocumentMetadata>>() {
-                    @Override
+                        @Override
-                    public void onTaskFinished(
+                        public void onTaskFinished(
-                        @Status int status, Map<Uri, DocumentMetadata> item, Exception exception) {
+                                @Status int status, Map<Uri, DocumentMetadata> item, Exception exception) {
-                      getContext().getContentResolver().notifyChange(notifyUri, null, false);
+                          getContext().getContentResolver().notifyChange(notifyUri, null, false);
-                    }
+                        }
-                  });
+                      });
               mTaskManager.runTask(uri, task);
               cursor.setLoadingTask(task);
 
@@ -381,7 +381,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
   }
 
   private Object[] getDocumentValues(
-      String[] projection, DocumentMetadata metadata) {
+          String[] projection, DocumentMetadata metadata) {
     Object[] row = new Object[projection.length];
     for (int i = 0; i < projection.length; ++i) {
       switch (projection[i]) {
@@ -461,7 +461,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
 
     final Uri uri = toUri(NetworkBrowser.SMB_BROWSING_URI.toString());
 
-    if (mBrowsingStorage.isEmpty()) {
+    if (mBrowsingStorage == null) {
       AsyncTask serversTask = mNetworkBrowser.getServersAsync(mLoadSharesFinishedCallback);
 
       Bundle extra = new Bundle();
@@ -475,7 +475,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
         cursor.addRow(getCursorRowForServer(projection, server));
       }
 
-      mBrowsingStorage.clear();
+      mBrowsingStorage = null;
     }
 
     return cursor;
@@ -483,15 +483,15 @@ public class SambaDocumentsProvider extends DocumentsProvider {
 
   @Override
   public String createDocument(String parentDocumentId, String mimeType, String displayName)
-      throws FileNotFoundException {
+          throws FileNotFoundException {
     try {
       final Uri parentUri = toUri(parentDocumentId);
 
       boolean isDir = Document.MIME_TYPE_DIR.equals(mimeType);
       final DirectoryEntry entry = new DirectoryEntry(
-          isDir ? DirectoryEntry.DIR : DirectoryEntry.FILE,
+              isDir ? DirectoryEntry.DIR : DirectoryEntry.FILE,
-          "", // comment
+              "", // comment
-          displayName);
+              displayName);
       final Uri uri = DocumentMetadata.buildChildUri(parentUri, entry);
 
       if (isDir) {
@@ -617,15 +617,15 @@ public class SambaDocumentsProvider extends DocumentsProvider {
 
   @Override
   public void removeDocument(String documentId, String parentDocumentId)
-      throws FileNotFoundException {
+          throws FileNotFoundException {
     // documentId is hierarchical. It can only have one parent.
     deleteDocument(documentId);
   }
 
   @Override
   public String moveDocument(
-      String sourceDocumentId, String sourceParentDocumentId, String targetParentDocumentId)
+          String sourceDocumentId, String sourceParentDocumentId, String targetParentDocumentId)
-    throws FileNotFoundException {
+          throws FileNotFoundException {
     try {
       final Uri uri = toUri(sourceDocumentId);
       final Uri targetParentUri = toUri(targetParentDocumentId);
@@ -637,19 +637,19 @@ public class SambaDocumentsProvider extends DocumentsProvider {
       final List<String> pathSegmentsOfSource = uri.getPathSegments();
       final List<String> pathSegmentsOfTargetParent = targetParentUri.getPathSegments();
       if (pathSegmentsOfSource.isEmpty() ||
-          pathSegmentsOfTargetParent.isEmpty() ||
+              pathSegmentsOfTargetParent.isEmpty() ||
-          !Objects.equals(pathSegmentsOfSource.get(0), pathSegmentsOfTargetParent.get(0))) {
+              !Objects.equals(pathSegmentsOfSource.get(0), pathSegmentsOfTargetParent.get(0))) {
         throw new UnsupportedOperationException("Instance move across shares are not supported.");
       }
 
       final Uri targetUri = DocumentMetadata
-          .buildChildUri(targetParentUri, uri.getLastPathSegment());
+              .buildChildUri(targetParentUri, uri.getLastPathSegment());
       mClient.rename(uri.toString(), targetUri.toString());
 
       revokeDocumentPermission(sourceDocumentId);
 
       getContext().getContentResolver()
-          .notifyChange(toNotifyUri(DocumentMetadata.buildParentUri(uri)), null, false);
+              .notifyChange(toNotifyUri(DocumentMetadata.buildParentUri(uri)), null, false);
       getContext().getContentResolver().notifyChange(toNotifyUri(targetParentUri), null, false);
 
       try (CacheResult result = mCache.get(uri)) {
@@ -672,7 +672,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
 
   @Override
   public ParcelFileDescriptor openDocument(String documentId, String mode,
-      CancellationSignal cancellationSignal) throws FileNotFoundException {
+                                           CancellationSignal cancellationSignal) throws FileNotFoundException {
     if (BuildConfig.DEBUG) Log.d(TAG, "Opening document " + documentId + " with mode " + mode);
 
     try {
@@ -680,7 +680,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
 
       if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
         OnTaskFinishedCallback<String> callback =
-            mode.contains("w") ? mWriteFinishedCallback : null;
+                mode.contains("w") ? mWriteFinishedCallback : null;
         return mClient.openProxyFile(
                 uri,
                 mode,
@@ -709,13 +709,13 @@ public class SambaDocumentsProvider extends DocumentsProvider {
     switch (mode) {
       case "r": {
         final ReadFileTask task = new ReadFileTask(
-            uri, mClient, pipe[1], mBufferPool);
+                uri, mClient, pipe[1], mBufferPool);
         mTaskManager.runIoTask(task);
       }
       return pipe[0];
       case "w": {
         final WriteFileTask task =
-            new WriteFileTask(uri, mClient, pipe[0], mBufferPool, mWriteFinishedCallback);
+                new WriteFileTask(uri, mClient, pipe[0], mBufferPool, mWriteFinishedCallback);
         mTaskManager.runIoTask(task);
         return pipe[1];
       }