content: /*
   * Copyright (C) 2006 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.content;
  
  import static android.Manifest.permission.INTERACT_ACROSS_USERS;
  import static android.app.AppOpsManager.MODE_ALLOWED;
  import static android.app.AppOpsManager.MODE_DEFAULT;
  import static android.app.AppOpsManager.MODE_ERRORED;
  import static android.app.AppOpsManager.MODE_IGNORED;
  import static android.content.pm.PackageManager.PERMISSION_GRANTED;
  import static android.os.Trace.TRACE_TAG_DATABASE;
  
  import android.annotation.NonNull;
  import android.annotation.Nullable;
  import android.annotation.UnsupportedAppUsage;
  import android.app.AppOpsManager;
  import android.content.pm.PathPermission;
  import android.content.pm.ProviderInfo;
  import android.content.res.AssetFileDescriptor;
  import android.content.res.Configuration;
  import android.database.Cursor;
  import android.database.MatrixCursor;
  import android.database.SQLException;
  import android.net.Uri;
  import android.os.AsyncTask;
  import android.os.Binder;
  import android.os.Build;
  import android.os.Bundle;
  import android.os.CancellationSignal;
  import android.os.IBinder;
  import android.os.ICancellationSignal;
  import android.os.ParcelFileDescriptor;
  import android.os.Process;
  import android.os.RemoteException;
  import android.os.Trace;
  import android.os.UserHandle;
  import android.os.storage.StorageManager;
  import android.text.TextUtils;
  import android.util.Log;
  
  import com.android.internal.annotations.VisibleForTesting;
  
  import java.io.File;
  import java.io.FileDescriptor;
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Objects;
  
  /**
   * Content providers are one of the primary building blocks of Android applications, providing
   * content to applications. They encapsulate data and provide it to applications through the single
   * {@link ContentResolver} interface. A content provider is only required if you need to share
   * data between multiple applications. For example, the contacts data is used by multiple
   * applications and must be stored in a content provider. If you don't need to share data amongst
   * multiple applications you can use a database directly via
   * {@link android.database.sqlite.SQLiteDatabase}.
   *
   * <p>When a request is made via
   * a {@link ContentResolver} the system inspects the authority of the given URI and passes the
   * request to the content provider registered with the authority. The content provider can interpret
   * the rest of the URI however it wants. The {@link UriMatcher} class is helpful for parsing
   * URIs.</p>
   *
   * <p>The primary methods that need to be implemented are:
   * <ul>
   *   <li>{@link #onCreate} which is called to initialize the provider</li>
   *   <li>{@link #query} which returns data to the caller</li>
   *   <li>{@link #insert} which inserts new data into the content provider</li>
   *   <li>{@link #update} which updates existing data in the content provider</li>
   *   <li>{@link #delete} which deletes data from the content provider</li>
   *   <li>{@link #getType} which returns the MIME type of data in the content provider</li>
   * </ul></p>
   *
   * <p class="caution">Data access methods (such as {@link #insert} and
   * {@link #update}) may be called from many threads at once, and must be thread-safe.
   * Other methods (such as {@link #onCreate}) are only called from the application
   * main thread, and must avoid performing lengthy operations.  See the method
   * descriptions for their expected thread behavior.</p>
   *
   * <p>Requests to {@link ContentResolver} are automatically forwarded to the appropriate
   * ContentProvider instance, so subclasses don't have to worry about the details of
   * cross-process calls.</p>
   *
   * <div class="special reference">
   * <h3>Developer Guides</h3>
   * <p>For more information about using content providers, read the
   * <a href="{@docRoot}guide/topics/providers/content-providers.html">Content Providers</a>
   * developer guide.</p>
   * </div>
   */
  public abstract class ContentProvider implements ContentInterface, ComponentCallbacks2 {
  
      private static final String TAG = "ContentProvider";
  
      /*
       * Note: if you add methods to ContentProvider, you must add similar methods to
       *       MockContentProvider.
       */
  
      @UnsupportedAppUsage
      private Context mContext = null;
      private int mMyUid;
  
      // Since most Providers have only one authority, we keep both a String and a String[] to improve
      // performance.
      @UnsupportedAppUsage
      private String mAuthority;
      @UnsupportedAppUsage
      private String[] mAuthorities;
      @UnsupportedAppUsage
      private String mReadPermission;
      @UnsupportedAppUsage
      private String mWritePermission;
      @UnsupportedAppUsage
      private PathPermission[] mPathPermissions;
      private boolean mExported;
      private boolean mNoPerms;
      private boolean mSingleUser;
  
      private ThreadLocal<String> mCallingPackage;
  
      private Transport mTransport = new Transport();
  
      /**
       * Construct a ContentProvider instance.  Content providers must be
       * <a href="{@docRoot}guide/topics/manifest/provider-element.html">declared
       * in the manifest</a>, accessed with {@link ContentResolver}, and created
       * automatically by the system, so applications usually do not create
       * ContentProvider instances directly.
       *
       * <p>At construction time, the object is uninitialized, and most fields and
       * methods are unavailable.  Subclasses should initialize themselves in
       * {@link #onCreate}, not the constructor.
       *
       * <p>Content providers are created on the application main thread at
       * application launch time.  The constructor must not perform lengthy
       * operations, or application startup will be delayed.
       */
      public ContentProvider() {
      }
  
      /**
       * Constructor just for mocking.
       *
       * @param context A Context object which should be some mock instance (like the
       * instance of {@link android.test.mock.MockContext}).
       * @param readPermission The read permision you want this instance should have in the
       * test, which is available via {@link #getReadPermission()}.
       * @param writePermission The write permission you want this instance should have
       * in the test, which is available via {@link #getWritePermission()}.
       * @param pathPermissions The PathPermissions you want this instance should have
       * in the test, which is available via {@link #getPathPermissions()}.
       * @hide
       */
      @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023)
      public ContentProvider(
              Context context,
              String readPermission,
              String writePermission,
              PathPermission[] pathPermissions) {
          mContext = context;
          mReadPermission = readPermission;
          mWritePermission = writePermission;
          mPathPermissions = pathPermissions;
      }
  
      /**
       * Given an IContentProvider, try to coerce it back to the real
       * ContentProvider object if it is running in the local process.  This can
       * be used if you know you are running in the same process as a provider,
       * and want to get direct access to its implementation details.  Most
       * clients should not nor have a reason to use it.
       *
       * @param abstractInterface The ContentProvider interface that is to be
       *              coerced.
       * @return If the IContentProvider is non-{@code null} and local, returns its actual
       * ContentProvider instance.  Otherwise returns {@code null}.
       * @hide
       */
      @UnsupportedAppUsage
      public static ContentProvider coerceToLocalContentProvider(
              IContentProvider abstractInterface) {
          if (abstractInterface instanceof Transport) {
              return ((Transport)abstractInterface).getContentProvider();
          }
          return null;
      }
  
      /**
       * Binder object that deals with remoting.
       *
       * @hide
       */
      class Transport extends ContentProviderNative {
          volatile AppOpsManager mAppOpsManager = null;
          volatile int mReadOp = AppOpsManager.OP_NONE;
          volatile int mWriteOp = AppOpsManager.OP_NONE;
          volatile ContentInterface mInterface = ContentProvider.this;
  
          ContentProvider getContentProvider() {
              return ContentProvider.this;
          }
  
          @Override
          public String getProviderName() {
              return getContentProvider().getClass().getName();
          }
  
          @Override
          public Cursor query(String callingPkg, Uri uri, @Nullable String[] projection,
                  @Nullable Bundle queryArgs, @Nullable ICancellationSignal cancellationSignal) {
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              if (enforceReadPermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  // The caller has no access to the data, so return an empty cursor with
                  // the columns in the requested order. The caller may ask for an invalid
                  // column and we would not catch that but this is not a problem in practice.
                  // We do not call ContentProvider#query with a modified where clause since
                  // the implementation is not guaranteed to be backed by a SQL database, hence
                  // it may not handle properly the tautology where clause we would have created.
                  if (projection != null) {
                      return new MatrixCursor(projection, 0);
                  }
  
                  // Null projection means all columns but we have no idea which they are.
                  // However, the caller may be expecting to access them my index. Hence,
                  // we have to execute the query as if allowed to get a cursor with the
                  // columns. We then use the column names to return an empty cursor.
                  Cursor cursor;
                  final String original = setCallingPackage(callingPkg);
                  try {
                      cursor = mInterface.query(
                              uri, projection, queryArgs,
                              CancellationSignal.fromTransport(cancellationSignal));
                  } catch (RemoteException e) {
                      throw e.rethrowAsRuntimeException();
                  } finally {
                      setCallingPackage(original);
                  }
                  if (cursor == null) {
                      return null;
                  }
  
                  // Return an empty cursor for all columns.
                  return new MatrixCursor(cursor.getColumnNames(), 0);
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "query");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.query(
                          uri, projection, queryArgs,
                          CancellationSignal.fromTransport(cancellationSignal));
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public String getType(Uri uri) {
              // getCallingPackage() isn't available in getType(), as the javadoc states.
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              Trace.traceBegin(TRACE_TAG_DATABASE, "getType");
              try {
                  return mInterface.getType(uri);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public Uri insert(String callingPkg, Uri uri, ContentValues initialValues) {
              uri = validateIncomingUri(uri);
              int userId = getUserIdFromUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              if (enforceWritePermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  final String original = setCallingPackage(callingPkg);
                  try {
                      return rejectInsert(uri, initialValues);
                  } finally {
                      setCallingPackage(original);
                  }
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "insert");
              final String original = setCallingPackage(callingPkg);
              try {
                  return maybeAddUserId(mInterface.insert(uri, initialValues), userId);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public int bulkInsert(String callingPkg, Uri uri, ContentValues[] initialValues) {
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              if (enforceWritePermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  return 0;
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "bulkInsert");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.bulkInsert(uri, initialValues);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public ContentProviderResult[] applyBatch(String callingPkg, String authority,
                  ArrayList<ContentProviderOperation> operations)
                  throws OperationApplicationException {
              validateIncomingAuthority(authority);
              int numOperations = operations.size();
              final int[] userIds = new int[numOperations];
              for (int i = 0; i < numOperations; i++) {
                  ContentProviderOperation operation = operations.get(i);
                  Uri uri = operation.getUri();
                  userIds[i] = getUserIdFromUri(uri);
                  uri = validateIncomingUri(uri);
                  uri = maybeGetUriWithoutUserId(uri);
                  // Rebuild operation if we changed the Uri above
                  if (!Objects.equals(operation.getUri(), uri)) {
                      operation = new ContentProviderOperation(operation, uri);
                      operations.set(i, operation);
                  }
                  if (operation.isReadOperation()) {
                      if (enforceReadPermission(callingPkg, uri, null)
                              != AppOpsManager.MODE_ALLOWED) {
                          throw new OperationApplicationException("App op not allowed", 0);
                      }
                  }
                  if (operation.isWriteOperation()) {
                      if (enforceWritePermission(callingPkg, uri, null)
                              != AppOpsManager.MODE_ALLOWED) {
                          throw new OperationApplicationException("App op not allowed", 0);
                      }
                  }
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "applyBatch");
              final String original = setCallingPackage(callingPkg);
              try {
                  ContentProviderResult[] results = mInterface.applyBatch(authority,
                          operations);
                  if (results != null) {
                      for (int i = 0; i < results.length ; i++) {
                          if (userIds[i] != UserHandle.USER_CURRENT) {
                              // Adding the userId to the uri.
                              results[i] = new ContentProviderResult(results[i], userIds[i]);
                          }
                      }
                  }
                  return results;
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public int delete(String callingPkg, Uri uri, String selection, String[] selectionArgs) {
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              if (enforceWritePermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  return 0;
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "delete");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.delete(uri, selection, selectionArgs);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public int update(String callingPkg, Uri uri, ContentValues values, String selection,
                  String[] selectionArgs) {
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              if (enforceWritePermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  return 0;
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "update");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.update(uri, values, selection, selectionArgs);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public ParcelFileDescriptor openFile(
                  String callingPkg, Uri uri, String mode, ICancellationSignal cancellationSignal,
                  IBinder callerToken) throws FileNotFoundException {
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              enforceFilePermission(callingPkg, uri, mode, callerToken);
              Trace.traceBegin(TRACE_TAG_DATABASE, "openFile");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.openFile(
                          uri, mode, CancellationSignal.fromTransport(cancellationSignal));
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public AssetFileDescriptor openAssetFile(
                  String callingPkg, Uri uri, String mode, ICancellationSignal cancellationSignal)
                  throws FileNotFoundException {
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              enforceFilePermission(callingPkg, uri, mode, null);
              Trace.traceBegin(TRACE_TAG_DATABASE, "openAssetFile");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.openAssetFile(
                          uri, mode, CancellationSignal.fromTransport(cancellationSignal));
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public Bundle call(String callingPkg, String authority, String method, @Nullable String arg,
                  @Nullable Bundle extras) {
              validateIncomingAuthority(authority);
              Bundle.setDefusable(extras, true);
              Trace.traceBegin(TRACE_TAG_DATABASE, "call");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.call(authority, method, arg, extras);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public String[] getStreamTypes(Uri uri, String mimeTypeFilter) {
              // getCallingPackage() isn't available in getType(), as the javadoc states.
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              Trace.traceBegin(TRACE_TAG_DATABASE, "getStreamTypes");
              try {
                  return mInterface.getStreamTypes(uri, mimeTypeFilter);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public AssetFileDescriptor openTypedAssetFile(String callingPkg, Uri uri, String mimeType,
                  Bundle opts, ICancellationSignal cancellationSignal) throws FileNotFoundException {
              Bundle.setDefusable(opts, true);
              uri = validateIncomingUri(uri);
              uri = maybeGetUriWithoutUserId(uri);
              enforceFilePermission(callingPkg, uri, "r", null);
              Trace.traceBegin(TRACE_TAG_DATABASE, "openTypedAssetFile");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.openTypedAssetFile(
                          uri, mimeType, opts, CancellationSignal.fromTransport(cancellationSignal));
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public ICancellationSignal createCancellationSignal() {
              return CancellationSignal.createTransport();
          }
  
          @Override
          public Uri canonicalize(String callingPkg, Uri uri) {
              uri = validateIncomingUri(uri);
              int userId = getUserIdFromUri(uri);
              uri = getUriWithoutUserId(uri);
              if (enforceReadPermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  return null;
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "canonicalize");
              final String original = setCallingPackage(callingPkg);
              try {
                  return maybeAddUserId(mInterface.canonicalize(uri), userId);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public Uri uncanonicalize(String callingPkg, Uri uri) {
              uri = validateIncomingUri(uri);
              int userId = getUserIdFromUri(uri);
              uri = getUriWithoutUserId(uri);
              if (enforceReadPermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  return null;
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "uncanonicalize");
              final String original = setCallingPackage(callingPkg);
              try {
                  return maybeAddUserId(mInterface.uncanonicalize(uri), userId);
              } catch (RemoteException e) {
                  throw e.rethrowAsRuntimeException();
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          @Override
          public boolean refresh(String callingPkg, Uri uri, Bundle args,
                  ICancellationSignal cancellationSignal) throws RemoteException {
              uri = validateIncomingUri(uri);
              uri = getUriWithoutUserId(uri);
              if (enforceReadPermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
                  return false;
              }
              Trace.traceBegin(TRACE_TAG_DATABASE, "refresh");
              final String original = setCallingPackage(callingPkg);
              try {
                  return mInterface.refresh(uri, args,
                          CancellationSignal.fromTransport(cancellationSignal));
              } finally {
                  setCallingPackage(original);
                  Trace.traceEnd(TRACE_TAG_DATABASE);
              }
          }
  
          private void enforceFilePermission(String callingPkg, Uri uri, String mode,
                  IBinder callerToken) throws FileNotFoundException, SecurityException {
              if (mode != null && mode.indexOf('w') != -1) {
                  if (enforceWritePermission(callingPkg, uri, callerToken)
                          != AppOpsManager.MODE_ALLOWED) {
                      throw new FileNotFoundException("App op not allowed");
                  }
              } else {
                  if (enforceReadPermission(callingPkg, uri, callerToken)
                          != AppOpsManager.MODE_ALLOWED) {
                      throw new FileNotFoundException("App op not allowed");
                  }
              }
          }
  
          private int enforceReadPermission(String callingPkg, Uri uri, IBinder callerToken)
                  throws SecurityException {
              final int mode = enforceReadPermissionInner(uri, callingPkg, callerToken);
              if (mode != MODE_ALLOWED) {
                  return mode;
              }
  
              return noteProxyOp(callingPkg, mReadOp);
          }
  
          private int enforceWritePermission(String callingPkg, Uri uri, IBinder callerToken)
                  throws SecurityException {
              final int mode = enforceWritePermissionInner(uri, callingPkg, callerToken);
              if (mode != MODE_ALLOWED) {
                  return mode;
              }
  
              return noteProxyOp(callingPkg, mWriteOp);
          }
  
          private int noteProxyOp(String callingPkg, int op) {
              if (op != AppOpsManager.OP_NONE) {
                  int mode = mAppOpsManager.noteProxyOp(op, callingPkg);
                  return mode == MODE_DEFAULT ? MODE_IGNORED : mode;
              }
  
              return AppOpsManager.MODE_ALLOWED;
          }
      }
  
      boolean checkUser(int pid, int uid, Context context) {
          return UserHandle.getUserId(uid) == context.getUserId()
                  || mSingleUser
                  || context.checkPermission(INTERACT_ACROSS_USERS, pid, uid)
                  == PERMISSION_GRANTED;
      }
  
      /**
       * Verify that calling app holds both the given permission and any app-op
       * associated with that permission.
       */
      private int checkPermissionAndAppOp(String permission, String callingPkg,
              IBinder callerToken) {
          if (getContext().checkPermission(permission, Binder.getCallingPid(), Binder.getCallingUid(),
                  callerToken) != PERMISSION_GRANTED) {
              return MODE_ERRORED;
          }
  
          return mTransport.noteProxyOp(callingPkg, AppOpsManager.permissionToOpCode(permission));
      }
  
      /** {@hide} */
      protected int enforceReadPermissionInner(Uri uri, String callingPkg, IBinder callerToken)
              throws SecurityException {
          final Context context = getContext();
          final int pid = Binder.getCallingPid();
          final int uid = Binder.getCallingUid();
          String missingPerm = null;
          int strongestMode = MODE_ALLOWED;
  
          if (UserHandle.isSameApp(uid, mMyUid)) {
              return MODE_ALLOWED;
          }
  
          if (mExported && checkUser(pid, uid, context)) {
              final String componentPerm = getReadPermission();
              if (componentPerm != null) {
                  final int mode = checkPermissionAndAppOp(componentPerm, callingPkg, callerToken);
                  if (mode == MODE_ALLOWED) {
                      return MODE_ALLOWED;
                  } else {
                      missingPerm = componentPerm;
                      strongestMode = Math.max(strongestMode, mode);
                  }
              }
  
              // track if unprotected read is allowed; any denied
              // <path-permission> below removes this ability
              boolean allowDefaultRead = (componentPerm == null);
  
              final PathPermission[] pps = getPathPermissions();
              if (pps != null) {
                  final String path = uri.getPath();
                  for (PathPermission pp : pps) {
                      final String pathPerm = pp.getReadPermission();
                      if (pathPerm != null && pp.match(path)) {
                          final int mode = checkPermissionAndAppOp(pathPerm, callingPkg, callerToken);
                          if (mode == MODE_ALLOWED) {
                              return MODE_ALLOWED;
                          } else {
                              // any denied <path-permission> means we lose
                              // default <provider> access.
                              allowDefaultRead = false;
                              missingPerm = pathPerm;
                              strongestMode = Math.max(strongestMode, mode);
                          }
                      }
                  }
              }
  
              // if we passed <path-permission> checks above, and no default
              // <provider> permission, then allow access.
              if (allowDefaultRead) return MODE_ALLOWED;
          }
  
          // last chance, check against any uri grants
          final int callingUserId = UserHandle.getUserId(uid);
          final Uri userUri = (mSingleUser && !UserHandle.isSameUser(mMyUid, uid))
                  ? maybeAddUserId(uri, callingUserId) : uri;
          if (context.checkUriPermission(userUri, pid, uid, Intent.FLAG_GRANT_READ_URI_PERMISSION,
                  callerToken) == PERMISSION_GRANTED) {
              return MODE_ALLOWED;
          }
  
          // If the worst denial we found above was ignored, then pass that
          // ignored through; otherwise we assume it should be a real error below.
          if (strongestMode == MODE_IGNORED) {
              return MODE_IGNORED;
          }
  
          final String suffix;
          if (android.Manifest.permission.MANAGE_DOCUMENTS.equals(mReadPermission)) {
              suffix = " requires that you obtain access using ACTION_OPEN_DOCUMENT or related APIs";
          } else if (mExported) {
              suffix = " requires " + missingPerm + ", or grantUriPermission()";
          } else {
              suffix = " requires the provider be exported, or grantUriPermission()";
          }
          throw new SecurityException("Permission Denial: reading "
                  + ContentProvider.this.getClass().getName() + " uri " + uri + " from pid=" + pid
                  + ", uid=" + uid + suffix);
      }
  
      /** {@hide} */
      protected int enforceWritePermissionInner(Uri uri, String callingPkg, IBinder callerToken)
              throws SecurityException {
          final Context context = getContext();
          final int pid = Binder.getCallingPid();
          final int uid = Binder.getCallingUid();
          String missingPerm = null;
          int strongestMode = MODE_ALLOWED;
  
          if (UserHandle.isSameApp(uid, mMyUid)) {
              return MODE_ALLOWED;
          }
  
          if (mExported && checkUser(pid, uid, context)) {
              final String componentPerm = getWritePermission();
              if (componentPerm != null) {
                  final int mode = checkPermissionAndAppOp(componentPerm, callingPkg, callerToken);
                  if (mode == MODE_ALLOWED) {
                      return MODE_ALLOWED;
                  } else {
                      missingPerm = componentPerm;
                      strongestMode = Math.max(strongestMode, mode);
                  }
              }
  
              // track if unprotected write is allowed; any denied
              // <path-permission> below removes this ability
              boolean allowDefaultWrite = (componentPerm == null);
  
              final PathPermission[] pps = getPathPermissions();
              if (pps != null) {
                  final String path = uri.getPath();
                  for (PathPermission pp : pps) {
                      final String pathPerm = pp.getWritePermission();
                      if (pathPerm != null && pp.match(path)) {
                          final int mode = checkPermissionAndAppOp(pathPerm, callingPkg, callerToken);
                          if (mode == MODE_ALLOWED) {
                              return MODE_ALLOWED;
                          } else {
                              // any denied <path-permission> means we lose
                              // default <provider> access.
                              allowDefaultWrite = false;
                              missingPerm = pathPerm;
                              strongestMode = Math.max(strongestMode, mode);
                          }
                      }
                  }
              }
  
              // if we passed <path-permission> checks above, and no default
              // <provider> permission, then allow access.
              if (allowDefaultWrite) return MODE_ALLOWED;
          }
  
          // last chance, check against any uri grants
          if (context.checkUriPermission(uri, pid, uid, Intent.FLAG_GRANT_WRITE_URI_PERMISSION,
                  callerToken) == PERMISSION_GRANTED) {
              return MODE_ALLOWED;
          }
  
          // If the worst denial we found above was ignored, then pass that
          // ignored through; otherwise we assume it should be a real error below.
          if (strongestMode == MODE_IGNORED) {
              return MODE_IGNORED;
          }
  
          final String failReason = mExported
                  ? " requires " + missingPerm + ", or grantUriPermission()"
                  : " requires the provider be exported, or grantUriPermission()";
          throw new SecurityException("Permission Denial: writing "
                  + ContentProvider.this.getClass().getName() + " uri " + uri + " from pid=" + pid
                  + ", uid=" + uid + failReason);
      }
  
      /**
       * Retrieves the Context this provider is running in.  Only available once
       * {@link #onCreate} has been called -- this will return {@code null} in the
       * constructor.
       */
      public final @Nullable Context getContext() {
          return mContext;
      }
  
      /**
       * Set the calling package, returning the current value (or {@code null})
       * which can be used later to restore the previous state.
       */
      private String setCallingPackage(String callingPackage) {
          final String original = mCallingPackage.get();
          mCallingPackage.set(callingPackage);
          onCallingPackageChanged();
          return original;
      }
  
      /**
       * Return the package name of the caller that initiated the request being
       * processed on the current thread. The returned package will have been
       * verified to belong to the calling UID. Returns {@code null} if not
       * currently processing a request.
       * <p>
       * This will always return {@code null} when processing
       * {@link #getType(Uri)} or {@link #getStreamTypes(Uri, String)} requests.
       *
       * @see Binder#getCallingUid()
       * @see Context#grantUriPermission(String, Uri, int)
       * @throws SecurityException if the calling package doesn't belong to the
       *             calling UID.
       */
      public final @Nullable String getCallingPackage() {
          final String pkg = mCallingPackage.get();
          if (pkg != null) {
              mTransport.mAppOpsManager.checkPackage(Binder.getCallingUid(), pkg);
          }
          return pkg;
      }
  
      /** {@hide} */
      public final @Nullable String getCallingPackageUnchecked() {
          return mCallingPackage.get();
      }
  
      /** {@hide} */
      public void onCallingPackageChanged() {
      }
  
      /**
       * Opaque token representing the identity of an incoming IPC.
       */
      public final class CallingIdentity {
          /** {@hide} */
          public final long binderToken;
          /** {@hide} */
          public final String callingPackage;
  
          /** {@hide} */
          public CallingIdentity(long binderToken, String callingPackage) {
              this.binderToken = binderToken;
              this.callingPackage = callingPackage;
          }
      }
  
      /**
       * Reset the identity of the incoming IPC on the current thread.
       * <p>
       * Internally this calls {@link Binder#clearCallingIdentity()} and also
       * clears any value stored in {@link #getCallingPackage()}.
       *
       * @return Returns an opaque token that can be used to restore the original
       *         calling identity by passing it to
       *         {@link #restoreCallingIdentity}.
       */
      public final @NonNull CallingIdentity clearCallingIdentity() {
          return new CallingIdentity(Binder.clearCallingIdentity(), setCallingPackage(null));
      }
  
      /**
       * Restore the identity of the incoming IPC on the current thread back to a
       * previously identity that was returned by {@link #clearCallingIdentity}.
       * <p>
       * Internally this calls {@link Binder#restoreCallingIdentity(long)} and
       * also restores any value stored in {@link #getCallingPackage()}.
       */
      public final void restoreCallingIdentity(@NonNull CallingIdentity identity) {
          Binder.restoreCallingIdentity(identity.binderToken);
          mCallingPackage.set(identity.callingPackage);
      }
  
      /**
       * Change the authorities of the ContentProvider.
       * This is normally set for you from its manifest information when the provider is first
       * created.
       * @hide
       * @param authorities the semi-colon separated authorities of the ContentProvider.
       */
      protected final void setAuthorities(String authorities) {
          if (authorities != null) {
              if (authorities.indexOf(';') == -1) {
                  mAuthority = authorities;
                  mAuthorities = null;
              } else {
                  mAuthority = null;
                  mAuthorities = authorities.split(";");
              }
          }
      }
  
      /** @hide */
      protected final boolean matchesOurAuthorities(String authority) {
          if (mAuthority != null) {
              return mAuthority.equals(authority);
          }
          if (mAuthorities != null) {
              int length = mAuthorities.length;
              for (int i = 0; i < length; i++) {
                  if (mAuthorities[i].equals(authority)) return true;
              }
          }
          return false;
      }
  
  
      /**
       * Change the permission required to read data from the content
       * provider.  This is normally set for you from its manifest information
       * when the provider is first created.
       *
       * @param permission Name of the permission required for read-only access.
       */
      protected final void setReadPermission(@Nullable String permission) {
          mReadPermission = permission;
      }
  
      /**
       * Return the name of the permission required for read-only access to
       * this content provider.  This method can be called from multiple
       * threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       */
      public final @Nullable String getReadPermission() {
          return mReadPermission;
      }
  
      /**
       * Change the permission required to read and write data in the content
       * provider.  This is normally set for you from its manifest information
       * when the provider is first created.
       *
       * @param permission Name of the permission required for read/write access.
       */
      protected final void setWritePermission(@Nullable String permission) {
          mWritePermission = permission;
      }
  
      /**
       * Return the name of the permission required for read/write access to
       * this content provider.  This method can be called from multiple
       * threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       */
      public final @Nullable String getWritePermission() {
          return mWritePermission;
      }
  
      /**
       * Change the path-based permission required to read and/or write data in
       * the content provider.  This is normally set for you from its manifest
       * information when the provider is first created.
       *
       * @param permissions Array of path permission descriptions.
       */
      protected final void setPathPermissions(@Nullable PathPermission[] permissions) {
          mPathPermissions = permissions;
      }
  
      /**
       * Return the path-based permissions required for read and/or write access to
       * this content provider.  This method can be called from multiple
       * threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       */
      public final @Nullable PathPermission[] getPathPermissions() {
          return mPathPermissions;
      }
  
      /** @hide */
      @UnsupportedAppUsage
      public final void setAppOps(int readOp, int writeOp) {
          if (!mNoPerms) {
              mTransport.mReadOp = readOp;
              mTransport.mWriteOp = writeOp;
          }
      }
  
      /** @hide */
      public AppOpsManager getAppOpsManager() {
          return mTransport.mAppOpsManager;
      }
  
      /** @hide */
      public final void setTransportLoggingEnabled(boolean enabled) {
          if (enabled) {
              mTransport.mInterface = new LoggingContentInterface(getClass().getSimpleName(), this);
          } else {
              mTransport.mInterface = this;
          }
      }
  
      /**
       * Implement this to initialize your content provider on startup.
       * This method is called for all registered content providers on the
       * application main thread at application launch time.  It must not perform
       * lengthy operations, or application startup will be delayed.
       *
       * <p>You should defer nontrivial initialization (such as opening,
       * upgrading, and scanning databases) until the content provider is used
       * (via {@link #query}, {@link #insert}, etc).  Deferred initialization
       * keeps application startup fast, avoids unnecessary work if the provider
       * turns out not to be needed, and stops database errors (such as a full
       * disk) from halting application launch.
       *
       * <p>If you use SQLite, {@link android.database.sqlite.SQLiteOpenHelper}
       * is a helpful utility class that makes it easy to manage databases,
       * and will automatically defer opening until first use.  If you do use
       * SQLiteOpenHelper, make sure to avoid calling
       * {@link android.database.sqlite.SQLiteOpenHelper#getReadableDatabase} or
       * {@link android.database.sqlite.SQLiteOpenHelper#getWritableDatabase}
       * from this method.  (Instead, override
       * {@link android.database.sqlite.SQLiteOpenHelper#onOpen} to initialize the
       * database when it is first opened.)
       *
       * @return true if the provider was successfully loaded, false otherwise
       */
      public abstract boolean onCreate();
  
      /**
       * {@inheritDoc}
       * This method is always called on the application main thread, and must
       * not perform lengthy operations.
       *
       * <p>The default content provider implementation does nothing.
       * Override this method to take appropriate action.
       * (Content providers do not usually care about things like screen
       * orientation, but may want to know about locale changes.)
       */
      @Override
      public void onConfigurationChanged(Configuration newConfig) {
      }
  
      /**
       * {@inheritDoc}
       * This method is always called on the application main thread, and must
       * not perform lengthy operations.
       *
       * <p>The default content provider implementation does nothing.
       * Subclasses may override this method to take appropriate action.
       */
      @Override
      public void onLowMemory() {
      }
  
      @Override
      public void onTrimMemory(int level) {
      }
  
      /**
       * Implement this to handle query requests from clients.
       *
       * <p>Apps targeting {@link android.os.Build.VERSION_CODES#O} or higher should override
       * {@link #query(Uri, String[], Bundle, CancellationSignal)} and provide a stub
       * implementation of this method.
       *
       * <p>This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       * <p>
       * Example client call:<p>
       * <pre>// Request a specific record.
       * Cursor managedCursor = managedQuery(
                  ContentUris.withAppendedId(Contacts.People.CONTENT_URI, 2),
                  projection,    // Which columns to return.
                  null,          // WHERE clause.
                  null,          // WHERE clause value substitution
                  People.NAME + " ASC");   // Sort order.</pre>
       * Example implementation:<p>
       * <pre>// SQLiteQueryBuilder is a helper class that creates the
          // proper SQL syntax for us.
          SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder();
  
          // Set the table we're querying.
          qBuilder.setTables(DATABASE_TABLE_NAME);
  
          // If the query ends in a specific record number, we're
          // being asked for a specific record, so set the
          // WHERE clause in our query.
          if((URI_MATCHER.match(uri)) == SPECIFIC_MESSAGE){
              qBuilder.appendWhere("_id=" + uri.getPathLeafId());
          }
  
          // Make the query.
          Cursor c = qBuilder.query(mDb,
                  projection,
                  selection,
                  selectionArgs,
                  groupBy,
                  having,
                  sortOrder);
          c.setNotificationUri(getContext().getContentResolver(), uri);
          return c;</pre>
       *
       * @param uri The URI to query. This will be the full URI sent by the client;
       *      if the client is requesting a specific record, the URI will end in a record number
       *      that the implementation should parse and add to a WHERE or HAVING clause, specifying
       *      that _id value.
       * @param projection The list of columns to put into the cursor. If
       *      {@code null} all columns are included.
       * @param selection A selection criteria to apply when filtering rows.
       *      If {@code null} then all rows are included.
       * @param selectionArgs You may include ?s in selection, which will be replaced by
       *      the values from selectionArgs, in order that they appear in the selection.
       *      The values will be bound as Strings.
       * @param sortOrder How the rows in the cursor should be sorted.
       *      If {@code null} then the provider is free to define the sort order.
       * @return a Cursor or {@code null}.
       */
      public abstract @Nullable Cursor query(@NonNull Uri uri, @Nullable String[] projection,
              @Nullable String selection, @Nullable String[] selectionArgs,
              @Nullable String sortOrder);
  
      /**
       * Implement this to handle query requests from clients with support for cancellation.
       *
       * <p>Apps targeting {@link android.os.Build.VERSION_CODES#O} or higher should override
       * {@link #query(Uri, String[], Bundle, CancellationSignal)} instead of this method.
       *
       * <p>This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       * <p>
       * Example client call:<p>
       * <pre>// Request a specific record.
       * Cursor managedCursor = managedQuery(
                  ContentUris.withAppendedId(Contacts.People.CONTENT_URI, 2),
                  projection,    // Which columns to return.
                  null,          // WHERE clause.
                  null,          // WHERE clause value substitution
                  People.NAME + " ASC");   // Sort order.</pre>
       * Example implementation:<p>
       * <pre>// SQLiteQueryBuilder is a helper class that creates the
          // proper SQL syntax for us.
          SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder();
  
          // Set the table we're querying.
          qBuilder.setTables(DATABASE_TABLE_NAME);
  
          // If the query ends in a specific record number, we're
          // being asked for a specific record, so set the
          // WHERE clause in our query.
          if((URI_MATCHER.match(uri)) == SPECIFIC_MESSAGE){
              qBuilder.appendWhere("_id=" + uri.getPathLeafId());
          }
  
          // Make the query.
          Cursor c = qBuilder.query(mDb,
                  projection,
                  selection,
                  selectionArgs,
                  groupBy,
                  having,
                  sortOrder);
          c.setNotificationUri(getContext().getContentResolver(), uri);
          return c;</pre>
       * <p>
       * If you implement this method then you must also implement the version of
       * {@link #query(Uri, String[], String, String[], String)} that does not take a cancellation
       * signal to ensure correct operation on older versions of the Android Framework in
       * which the cancellation signal overload was not available.
       *
       * @param uri The URI to query. This will be the full URI sent by the client;
       *      if the client is requesting a specific record, the URI will end in a record number
       *      that the implementation should parse and add to a WHERE or HAVING clause, specifying
       *      that _id value.
       * @param projection The list of columns to put into the cursor. If
       *      {@code null} all columns are included.
       * @param selection A selection criteria to apply when filtering rows.
       *      If {@code null} then all rows are included.
       * @param selectionArgs You may include ?s in selection, which will be replaced by
       *      the values from selectionArgs, in order that they appear in the selection.
       *      The values will be bound as Strings.
       * @param sortOrder How the rows in the cursor should be sorted.
       *      If {@code null} then the provider is free to define the sort order.
       * @param cancellationSignal A signal to cancel the operation in progress, or {@code null} if none.
       * If the operation is canceled, then {@link android.os.OperationCanceledException} will be thrown
       * when the query is executed.
       * @return a Cursor or {@code null}.
       */
      public @Nullable Cursor query(@NonNull Uri uri, @Nullable String[] projection,
              @Nullable String selection, @Nullable String[] selectionArgs,
              @Nullable String sortOrder, @Nullable CancellationSignal cancellationSignal) {
          return query(uri, projection, selection, selectionArgs, sortOrder);
      }
  
      /**
       * Implement this to handle query requests where the arguments are packed into a {@link Bundle}.
       * Arguments may include traditional SQL style query arguments. When present these
       * should be handled  according to the contract established in
       * {@link #query(Uri, String[], String, String[], String, CancellationSignal)}.
       *
       * <p>Traditional SQL arguments can be found in the bundle using the following keys:
       * <li>{@link android.content.ContentResolver#QUERY_ARG_SQL_SELECTION}
       * <li>{@link android.content.ContentResolver#QUERY_ARG_SQL_SELECTION_ARGS}
       * <li>{@link android.content.ContentResolver#QUERY_ARG_SQL_SORT_ORDER}
       *
       * <p>This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>
       * Example client call:<p>
       * <pre>// Request 20 records starting at row index 30.
         Bundle queryArgs = new Bundle();
         queryArgs.putInt(ContentResolver.QUERY_ARG_OFFSET, 30);
         queryArgs.putInt(ContentResolver.QUERY_ARG_LIMIT, 20);
  
         Cursor cursor = getContentResolver().query(
                  contentUri,    // Content Uri is specific to individual content providers.
                  projection,    // String[] describing which columns to return.
                  queryArgs,     // Query arguments.
                  null);         // Cancellation signal.</pre>
       *
       * Example implementation:<p>
       * <pre>
  
          int recordsetSize = 0x1000;  // Actual value is implementation specific.
          queryArgs = queryArgs != null ? queryArgs : Bundle.EMPTY;  // ensure queryArgs is non-null
  
          int offset = queryArgs.getInt(ContentResolver.QUERY_ARG_OFFSET, 0);
          int limit = queryArgs.getInt(ContentResolver.QUERY_ARG_LIMIT, Integer.MIN_VALUE);
  
          MatrixCursor c = new MatrixCursor(PROJECTION, limit);
  
          // Calculate the number of items to include in the cursor.
          int numItems = MathUtils.constrain(recordsetSize - offset, 0, limit);
  
          // Build the paged result set....
          for (int i = offset; i < offset + numItems; i++) {
              // populate row from your data.
          }
  
          Bundle extras = new Bundle();
          c.setExtras(extras);
  
          // Any QUERY_ARG_* key may be included if honored.
          // In an actual implementation, include only keys that are both present in queryArgs
          // and reflected in the Cursor output. For example, if QUERY_ARG_OFFSET were included
          // in queryArgs, but was ignored because it contained an invalid value (like –273),
          // then QUERY_ARG_OFFSET should be omitted.
          extras.putStringArray(ContentResolver.EXTRA_HONORED_ARGS, new String[] {
              ContentResolver.QUERY_ARG_OFFSET,
              ContentResolver.QUERY_ARG_LIMIT
          });
  
          extras.putInt(ContentResolver.EXTRA_TOTAL_COUNT, recordsetSize);
  
          cursor.setNotificationUri(getContext().getContentResolver(), uri);
  
          return cursor;</pre>
       * <p>
       * See {@link #query(Uri, String[], String, String[], String, CancellationSignal)}
       * for implementation details.
       *
       * @param uri The URI to query. This will be the full URI sent by the client.
       * @param projection The list of columns to put into the cursor.
       *            If {@code null} provide a default set of columns.
       * @param queryArgs A Bundle containing all additional information necessary for the query.
       *            Values in the Bundle may include SQL style arguments.
       * @param cancellationSignal A signal to cancel the operation in progress,
       *            or {@code null}.
       * @return a Cursor or {@code null}.
       */
      @Override
      public @Nullable Cursor query(@NonNull Uri uri, @Nullable String[] projection,
              @Nullable Bundle queryArgs, @Nullable CancellationSignal cancellationSignal) {
          queryArgs = queryArgs != null ? queryArgs : Bundle.EMPTY;
  
          // if client doesn't supply an SQL sort order argument, attempt to build one from
          // QUERY_ARG_SORT* arguments.
          String sortClause = queryArgs.getString(ContentResolver.QUERY_ARG_SQL_SORT_ORDER);
          if (sortClause == null && queryArgs.containsKey(ContentResolver.QUERY_ARG_SORT_COLUMNS)) {
              sortClause = ContentResolver.createSqlSortClause(queryArgs);
          }
  
          return query(
                  uri,
                  projection,
                  queryArgs.getString(ContentResolver.QUERY_ARG_SQL_SELECTION),
                  queryArgs.getStringArray(ContentResolver.QUERY_ARG_SQL_SELECTION_ARGS),
                  sortClause,
                  cancellationSignal);
      }
  
      /**
       * Implement this to handle requests for the MIME type of the data at the
       * given URI.  The returned MIME type should start with
       * <code>vnd.android.cursor.item</code> for a single record,
       * or <code>vnd.android.cursor.dir/</code> for multiple items.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>Note that there are no permissions needed for an application to
       * access this information; if your content provider requires read and/or
       * write permissions, or is not exported, all applications can still call
       * this method regardless of their access permissions.  This allows them
       * to retrieve the MIME type for a URI when dispatching intents.
       *
       * @param uri the URI to query.
       * @return a MIME type string, or {@code null} if there is no type.
       */
      @Override
      public abstract @Nullable String getType(@NonNull Uri uri);
  
      /**
       * Implement this to support canonicalization of URIs that refer to your
       * content provider.  A canonical URI is one that can be transported across
       * devices, backup/restore, and other contexts, and still be able to refer
       * to the same data item.  Typically this is implemented by adding query
       * params to the URI allowing the content provider to verify that an incoming
       * canonical URI references the same data as it was originally intended for and,
       * if it doesn't, to find that data (if it exists) in the current environment.
       *
       * <p>For example, if the content provider holds people and a normal URI in it
       * is created with a row index into that people database, the cananical representation
       * may have an additional query param at the end which specifies the name of the
       * person it is intended for.  Later calls into the provider with that URI will look
       * up the row of that URI's base index and, if it doesn't match or its entry's
       * name doesn't match the name in the query param, perform a query on its database
       * to find the correct row to operate on.</p>
       *
       * <p>If you implement support for canonical URIs, <b>all</b> incoming calls with
       * URIs (including this one) must perform this verification and recovery of any
       * canonical URIs they receive.  In addition, you must also implement
       * {@link #uncanonicalize} to strip the canonicalization of any of these URIs.</p>
       *
       * <p>The default implementation of this method returns null, indicating that
       * canonical URIs are not supported.</p>
       *
       * @param url The Uri to canonicalize.
       *
       * @return Return the canonical representation of <var>url</var>, or null if
       * canonicalization of that Uri is not supported.
       */
      @Override
      public @Nullable Uri canonicalize(@NonNull Uri url) {
          return null;
      }
  
      /**
       * Remove canonicalization from canonical URIs previously returned by
       * {@link #canonicalize}.  For example, if your implementation is to add
       * a query param to canonicalize a URI, this method can simply trip any
       * query params on the URI.  The default implementation always returns the
       * same <var>url</var> that was passed in.
       *
       * @param url The Uri to remove any canonicalization from.
       *
       * @return Return the non-canonical representation of <var>url</var>, return
       * the <var>url</var> as-is if there is nothing to do, or return null if
       * the data identified by the canonical representation can not be found in
       * the current environment.
       */
      @Override
      public @Nullable Uri uncanonicalize(@NonNull Uri url) {
          return url;
      }
  
      /**
       * Implement this to support refresh of content identified by {@code uri}. By default, this
       * method returns false; providers who wish to implement this should return true to signal the
       * client that the provider has tried refreshing with its own implementation.
       * <p>
       * This allows clients to request an explicit refresh of content identified by {@code uri}.
       * <p>
       * Client code should only invoke this method when there is a strong indication (such as a user
       * initiated pull to refresh gesture) that the content is stale.
       * <p>
       * Remember to send {@link ContentResolver#notifyChange(Uri, android.database.ContentObserver)}
       * notifications when content changes.
       *
       * @param uri The Uri identifying the data to refresh.
       * @param args Additional options from the client. The definitions of these are specific to the
       *            content provider being called.
       * @param cancellationSignal A signal to cancel the operation in progress, or {@code null} if
       *            none. For example, if you called refresh on a particular uri, you should call
       *            {@link CancellationSignal#throwIfCanceled()} to check whether the client has
       *            canceled the refresh request.
       * @return true if the provider actually tried refreshing.
       */
      @Override
      public boolean refresh(Uri uri, @Nullable Bundle args,
              @Nullable CancellationSignal cancellationSignal) {
          return false;
      }
  
      /**
       * @hide
       * Implementation when a caller has performed an insert on the content
       * provider, but that call has been rejected for the operation given
       * to {@link #setAppOps(int, int)}.  The default implementation simply
       * returns a dummy URI that is the base URI with a 0 path element
       * appended.
       */
      public Uri rejectInsert(Uri uri, ContentValues values) {
          // If not allowed, we need to return some reasonable URI.  Maybe the
          // content provider should be responsible for this, but for now we
          // will just return the base URI with a dummy '0' tagged on to it.
          // You shouldn't be able to read if you can't write, anyway, so it
          // shouldn't matter much what is returned.
          return uri.buildUpon().appendPath("0").build();
      }
  
      /**
       * Implement this to handle requests to insert a new row.
       * As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
       * after inserting.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       * @param uri The content:// URI of the insertion request. This must not be {@code null}.
       * @param values A set of column_name/value pairs to add to the database.
       *     This must not be {@code null}.
       * @return The URI for the newly inserted item.
       */
      @Override
      public abstract @Nullable Uri insert(@NonNull Uri uri, @Nullable ContentValues values);
  
      /**
       * Override this to handle requests to insert a set of new rows, or the
       * default implementation will iterate over the values and call
       * {@link #insert} on each of them.
       * As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
       * after inserting.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * @param uri The content:// URI of the insertion request.
       * @param values An array of sets of column_name/value pairs to add to the database.
       *    This must not be {@code null}.
       * @return The number of values that were inserted.
       */
      @Override
      public int bulkInsert(@NonNull Uri uri, @NonNull ContentValues[] values) {
          int numValues = values.length;
          for (int i = 0; i < numValues; i++) {
              insert(uri, values[i]);
          }
          return numValues;
      }
  
      /**
       * Implement this to handle requests to delete one or more rows.
       * The implementation should apply the selection clause when performing
       * deletion, allowing the operation to affect multiple rows in a directory.
       * As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
       * after deleting.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>The implementation is responsible for parsing out a row ID at the end
       * of the URI, if a specific row is being deleted. That is, the client would
       * pass in <code>content://contacts/people/22</code> and the implementation is
       * responsible for parsing the record number (22) when creating a SQL statement.
       *
       * @param uri The full URI to query, including a row ID (if a specific record is requested).
       * @param selection An optional restriction to apply to rows when deleting.
       * @return The number of rows affected.
       * @throws SQLException
       */
      @Override
      public abstract int delete(@NonNull Uri uri, @Nullable String selection,
              @Nullable String[] selectionArgs);
  
      /**
       * Implement this to handle requests to update one or more rows.
       * The implementation should update all rows matching the selection
       * to set the columns according to the provided values map.
       * As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
       * after updating.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * @param uri The URI to query. This can potentially have a record ID if this
       * is an update request for a specific record.
       * @param values A set of column_name/value pairs to update in the database.
       *     This must not be {@code null}.
       * @param selection An optional filter to match rows to update.
       * @return the number of rows affected.
       */
      @Override
      public abstract int update(@NonNull Uri uri, @Nullable ContentValues values,
              @Nullable String selection, @Nullable String[] selectionArgs);
  
      /**
       * Override this to handle requests to open a file blob.
       * The default implementation always throws {@link FileNotFoundException}.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>This method returns a ParcelFileDescriptor, which is returned directly
       * to the caller.  This way large data (such as images and documents) can be
       * returned without copying the content.
       *
       * <p>The returned ParcelFileDescriptor is owned by the caller, so it is
       * their responsibility to close it when done.  That is, the implementation
       * of this method should create a new ParcelFileDescriptor for each call.
       * <p>
       * If opened with the exclusive "r" or "w" modes, the returned
       * ParcelFileDescriptor can be a pipe or socket pair to enable streaming
       * of data. Opening with the "rw" or "rwt" modes implies a file on disk that
       * supports seeking.
       * <p>
       * If you need to detect when the returned ParcelFileDescriptor has been
       * closed, or if the remote process has crashed or encountered some other
       * error, you can use {@link ParcelFileDescriptor#open(File, int,
       * android.os.Handler, android.os.ParcelFileDescriptor.OnCloseListener)},
       * {@link ParcelFileDescriptor#createReliablePipe()}, or
       * {@link ParcelFileDescriptor#createReliableSocketPair()}.
       * <p>
       * If you need to return a large file that isn't backed by a real file on
       * disk, such as a file on a network share or cloud storage service,
       * consider using
       * {@link StorageManager#openProxyFileDescriptor(int, android.os.ProxyFileDescriptorCallback, android.os.Handler)}
       * which will let you to stream the content on-demand.
       *
       * <p class="note">For use in Intents, you will want to implement {@link #getType}
       * to return the appropriate MIME type for the data returned here with
       * the same URI.  This will allow intent resolution to automatically determine the data MIME
       * type and select the appropriate matching targets as part of its operation.</p>
       *
       * <p class="note">For better interoperability with other applications, it is recommended
       * that for any URIs that can be opened, you also support queries on them
       * containing at least the columns specified by {@link android.provider.OpenableColumns}.
       * You may also want to support other common columns if you have additional meta-data
       * to supply, such as {@link android.provider.MediaStore.MediaColumns#DATE_ADDED}
       * in {@link android.provider.MediaStore.MediaColumns}.</p>
       *
       * @param uri The URI whose file is to be opened.
       * @param mode Access mode for the file.  May be "r" for read-only access,
       * "rw" for read and write access, or "rwt" for read and write access
       * that truncates any existing file.
       *
       * @return Returns a new ParcelFileDescriptor which you can use to access
       * the file.
       *
       * @throws FileNotFoundException Throws FileNotFoundException if there is
       * no file associated with the given URI or the mode is invalid.
       * @throws SecurityException Throws SecurityException if the caller does
       * not have permission to access the file.
       *
       * @see #openAssetFile(Uri, String)
       * @see #openFileHelper(Uri, String)
       * @see #getType(android.net.Uri)
       * @see ParcelFileDescriptor#parseMode(String)
       */
      public @Nullable ParcelFileDescriptor openFile(@NonNull Uri uri, @NonNull String mode)
              throws FileNotFoundException {
          throw new FileNotFoundException("No files supported by provider at "
                  + uri);
      }
  
      /**
       * Override this to handle requests to open a file blob.
       * The default implementation always throws {@link FileNotFoundException}.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>This method returns a ParcelFileDescriptor, which is returned directly
       * to the caller.  This way large data (such as images and documents) can be
       * returned without copying the content.
       *
       * <p>The returned ParcelFileDescriptor is owned by the caller, so it is
       * their responsibility to close it when done.  That is, the implementation
       * of this method should create a new ParcelFileDescriptor for each call.
       * <p>
       * If opened with the exclusive "r" or "w" modes, the returned
       * ParcelFileDescriptor can be a pipe or socket pair to enable streaming
       * of data. Opening with the "rw" or "rwt" modes implies a file on disk that
       * supports seeking.
       * <p>
       * If you need to detect when the returned ParcelFileDescriptor has been
       * closed, or if the remote process has crashed or encountered some other
       * error, you can use {@link ParcelFileDescriptor#open(File, int,
       * android.os.Handler, android.os.ParcelFileDescriptor.OnCloseListener)},
       * {@link ParcelFileDescriptor#createReliablePipe()}, or
       * {@link ParcelFileDescriptor#createReliableSocketPair()}.
       *
       * <p class="note">For use in Intents, you will want to implement {@link #getType}
       * to return the appropriate MIME type for the data returned here with
       * the same URI.  This will allow intent resolution to automatically determine the data MIME
       * type and select the appropriate matching targets as part of its operation.</p>
       *
       * <p class="note">For better interoperability with other applications, it is recommended
       * that for any URIs that can be opened, you also support queries on them
       * containing at least the columns specified by {@link android.provider.OpenableColumns}.
       * You may also want to support other common columns if you have additional meta-data
       * to supply, such as {@link android.provider.MediaStore.MediaColumns#DATE_ADDED}
       * in {@link android.provider.MediaStore.MediaColumns}.</p>
       *
       * @param uri The URI whose file is to be opened.
       * @param mode Access mode for the file. May be "r" for read-only access,
       *            "w" for write-only access, "rw" for read and write access, or
       *            "rwt" for read and write access that truncates any existing
       *            file.
       * @param signal A signal to cancel the operation in progress, or
       *            {@code null} if none. For example, if you are downloading a
       *            file from the network to service a "rw" mode request, you
       *            should periodically call
       *            {@link CancellationSignal#throwIfCanceled()} to check whether
       *            the client has canceled the request and abort the download.
       *
       * @return Returns a new ParcelFileDescriptor which you can use to access
       * the file.
       *
       * @throws FileNotFoundException Throws FileNotFoundException if there is
       * no file associated with the given URI or the mode is invalid.
       * @throws SecurityException Throws SecurityException if the caller does
       * not have permission to access the file.
       *
       * @see #openAssetFile(Uri, String)
       * @see #openFileHelper(Uri, String)
       * @see #getType(android.net.Uri)
       * @see ParcelFileDescriptor#parseMode(String)
       */
      @Override
      public @Nullable ParcelFileDescriptor openFile(@NonNull Uri uri, @NonNull String mode,
              @Nullable CancellationSignal signal) throws FileNotFoundException {
          return openFile(uri, mode);
      }
  
      /**
       * This is like {@link #openFile}, but can be implemented by providers
       * that need to be able to return sub-sections of files, often assets
       * inside of their .apk.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>If you implement this, your clients must be able to deal with such
       * file slices, either directly with
       * {@link ContentResolver#openAssetFileDescriptor}, or by using the higher-level
       * {@link ContentResolver#openInputStream ContentResolver.openInputStream}
       * or {@link ContentResolver#openOutputStream ContentResolver.openOutputStream}
       * methods.
       * <p>
       * The returned AssetFileDescriptor can be a pipe or socket pair to enable
       * streaming of data.
       *
       * <p class="note">If you are implementing this to return a full file, you
       * should create the AssetFileDescriptor with
       * {@link AssetFileDescriptor#UNKNOWN_LENGTH} to be compatible with
       * applications that cannot handle sub-sections of files.</p>
       *
       * <p class="note">For use in Intents, you will want to implement {@link #getType}
       * to return the appropriate MIME type for the data returned here with
       * the same URI.  This will allow intent resolution to automatically determine the data MIME
       * type and select the appropriate matching targets as part of its operation.</p>
       *
       * <p class="note">For better interoperability with other applications, it is recommended
       * that for any URIs that can be opened, you also support queries on them
       * containing at least the columns specified by {@link android.provider.OpenableColumns}.</p>
       *
       * @param uri The URI whose file is to be opened.
       * @param mode Access mode for the file.  May be "r" for read-only access,
       * "w" for write-only access (erasing whatever data is currently in
       * the file), "wa" for write-only access to append to any existing data,
       * "rw" for read and write access on any existing data, and "rwt" for read
       * and write access that truncates any existing file.
       *
       * @return Returns a new AssetFileDescriptor which you can use to access
       * the file.
       *
       * @throws FileNotFoundException Throws FileNotFoundException if there is
       * no file associated with the given URI or the mode is invalid.
       * @throws SecurityException Throws SecurityException if the caller does
       * not have permission to access the file.
       *
       * @see #openFile(Uri, String)
       * @see #openFileHelper(Uri, String)
       * @see #getType(android.net.Uri)
       */
      public @Nullable AssetFileDescriptor openAssetFile(@NonNull Uri uri, @NonNull String mode)
              throws FileNotFoundException {
          ParcelFileDescriptor fd = openFile(uri, mode);
          return fd != null ? new AssetFileDescriptor(fd, 0, -1) : null;
      }
  
      /**
       * This is like {@link #openFile}, but can be implemented by providers
       * that need to be able to return sub-sections of files, often assets
       * inside of their .apk.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * <p>If you implement this, your clients must be able to deal with such
       * file slices, either directly with
       * {@link ContentResolver#openAssetFileDescriptor}, or by using the higher-level
       * {@link ContentResolver#openInputStream ContentResolver.openInputStream}
       * or {@link ContentResolver#openOutputStream ContentResolver.openOutputStream}
       * methods.
       * <p>
       * The returned AssetFileDescriptor can be a pipe or socket pair to enable
       * streaming of data.
       *
       * <p class="note">If you are implementing this to return a full file, you
       * should create the AssetFileDescriptor with
       * {@link AssetFileDescriptor#UNKNOWN_LENGTH} to be compatible with
       * applications that cannot handle sub-sections of files.</p>
       *
       * <p class="note">For use in Intents, you will want to implement {@link #getType}
       * to return the appropriate MIME type for the data returned here with
       * the same URI.  This will allow intent resolution to automatically determine the data MIME
       * type and select the appropriate matching targets as part of its operation.</p>
       *
       * <p class="note">For better interoperability with other applications, it is recommended
       * that for any URIs that can be opened, you also support queries on them
       * containing at least the columns specified by {@link android.provider.OpenableColumns}.</p>
       *
       * @param uri The URI whose file is to be opened.
       * @param mode Access mode for the file.  May be "r" for read-only access,
       * "w" for write-only access (erasing whatever data is currently in
       * the file), "wa" for write-only access to append to any existing data,
       * "rw" for read and write access on any existing data, and "rwt" for read
       * and write access that truncates any existing file.
       * @param signal A signal to cancel the operation in progress, or
       *            {@code null} if none. For example, if you are downloading a
       *            file from the network to service a "rw" mode request, you
       *            should periodically call
       *            {@link CancellationSignal#throwIfCanceled()} to check whether
       *            the client has canceled the request and abort the download.
       *
       * @return Returns a new AssetFileDescriptor which you can use to access
       * the file.
       *
       * @throws FileNotFoundException Throws FileNotFoundException if there is
       * no file associated with the given URI or the mode is invalid.
       * @throws SecurityException Throws SecurityException if the caller does
       * not have permission to access the file.
       *
       * @see #openFile(Uri, String)
       * @see #openFileHelper(Uri, String)
       * @see #getType(android.net.Uri)
       */
      @Override
      public @Nullable AssetFileDescriptor openAssetFile(@NonNull Uri uri, @NonNull String mode,
              @Nullable CancellationSignal signal) throws FileNotFoundException {
          return openAssetFile(uri, mode);
      }
  
      /**
       * Convenience for subclasses that wish to implement {@link #openFile}
       * by looking up a column named "_data" at the given URI.
       *
       * @param uri The URI to be opened.
       * @param mode The file mode.  May be "r" for read-only access,
       * "w" for write-only access (erasing whatever data is currently in
       * the file), "wa" for write-only access to append to any existing data,
       * "rw" for read and write access on any existing data, and "rwt" for read
       * and write access that truncates any existing file.
       *
       * @return Returns a new ParcelFileDescriptor that can be used by the
       * client to access the file.
       */
      protected final @NonNull ParcelFileDescriptor openFileHelper(@NonNull Uri uri,
              @NonNull String mode) throws FileNotFoundException {
          Cursor c = query(uri, new String[]{"_data"}, null, null, null);
          int count = (c != null) ? c.getCount() : 0;
          if (count != 1) {
              // If there is not exactly one result, throw an appropriate
              // exception.
              if (c != null) {
                  c.close();
              }
              if (count == 0) {
                  throw new FileNotFoundException("No entry for " + uri);
              }
              throw new FileNotFoundException("Multiple items at " + uri);
          }
  
          c.moveToFirst();
          int i = c.getColumnIndex("_data");
          String path = (i >= 0 ? c.getString(i) : null);
          c.close();
          if (path == null) {
              throw new FileNotFoundException("Column _data not found.");
          }
  
          int modeBits = ParcelFileDescriptor.parseMode(mode);
          return ParcelFileDescriptor.open(new File(path), modeBits);
      }
  
      /**
       * Called by a client to determine the types of data streams that this
       * content provider supports for the given URI.  The default implementation
       * returns {@code null}, meaning no types.  If your content provider stores data
       * of a particular type, return that MIME type if it matches the given
       * mimeTypeFilter.  If it can perform type conversions, return an array
       * of all supported MIME types that match mimeTypeFilter.
       *
       * @param uri The data in the content provider being queried.
       * @param mimeTypeFilter The type of data the client desires.  May be
       * a pattern, such as *&#47;* to retrieve all possible data types.
       * @return Returns {@code null} if there are no possible data streams for the
       * given mimeTypeFilter.  Otherwise returns an array of all available
       * concrete MIME types.
       *
       * @see #getType(Uri)
       * @see #openTypedAssetFile(Uri, String, Bundle)
       * @see ClipDescription#compareMimeTypes(String, String)
       */
      @Override
      public @Nullable String[] getStreamTypes(@NonNull Uri uri, @NonNull String mimeTypeFilter) {
          return null;
      }
  
      /**
       * Called by a client to open a read-only stream containing data of a
       * particular MIME type.  This is like {@link #openAssetFile(Uri, String)},
       * except the file can only be read-only and the content provider may
       * perform data conversions to generate data of the desired type.
       *
       * <p>The default implementation compares the given mimeType against the
       * result of {@link #getType(Uri)} and, if they match, simply calls
       * {@link #openAssetFile(Uri, String)}.
       *
       * <p>See {@link ClipData} for examples of the use and implementation
       * of this method.
       * <p>
       * The returned AssetFileDescriptor can be a pipe or socket pair to enable
       * streaming of data.
       *
       * <p class="note">For better interoperability with other applications, it is recommended
       * that for any URIs that can be opened, you also support queries on them
       * containing at least the columns specified by {@link android.provider.OpenableColumns}.
       * You may also want to support other common columns if you have additional meta-data
       * to supply, such as {@link android.provider.MediaStore.MediaColumns#DATE_ADDED}
       * in {@link android.provider.MediaStore.MediaColumns}.</p>
       *
       * @param uri The data in the content provider being queried.
       * @param mimeTypeFilter The type of data the client desires.  May be
       * a pattern, such as *&#47;*, if the caller does not have specific type
       * requirements; in this case the content provider will pick its best
       * type matching the pattern.
       * @param opts Additional options from the client.  The definitions of
       * these are specific to the content provider being called.
       *
       * @return Returns a new AssetFileDescriptor from which the client can
       * read data of the desired type.
       *
       * @throws FileNotFoundException Throws FileNotFoundException if there is
       * no file associated with the given URI or the mode is invalid.
       * @throws SecurityException Throws SecurityException if the caller does
       * not have permission to access the data.
       * @throws IllegalArgumentException Throws IllegalArgumentException if the
       * content provider does not support the requested MIME type.
       *
       * @see #getStreamTypes(Uri, String)
       * @see #openAssetFile(Uri, String)
       * @see ClipDescription#compareMimeTypes(String, String)
       */
      public @Nullable AssetFileDescriptor openTypedAssetFile(@NonNull Uri uri,
              @NonNull String mimeTypeFilter, @Nullable Bundle opts) throws FileNotFoundException {
          if ("*/*".equals(mimeTypeFilter)) {
              // If they can take anything, the untyped open call is good enough.
              return openAssetFile(uri, "r");
          }
          String baseType = getType(uri);
          if (baseType != null && ClipDescription.compareMimeTypes(baseType, mimeTypeFilter)) {
              // Use old untyped open call if this provider has a type for this
              // URI and it matches the request.
              return openAssetFile(uri, "r");
          }
          throw new FileNotFoundException("Can't open " + uri + " as type " + mimeTypeFilter);
      }
  
  
      /**
       * Called by a client to open a read-only stream containing data of a
       * particular MIME type.  This is like {@link #openAssetFile(Uri, String)},
       * except the file can only be read-only and the content provider may
       * perform data conversions to generate data of the desired type.
       *
       * <p>The default implementation compares the given mimeType against the
       * result of {@link #getType(Uri)} and, if they match, simply calls
       * {@link #openAssetFile(Uri, String)}.
       *
       * <p>See {@link ClipData} for examples of the use and implementation
       * of this method.
       * <p>
       * The returned AssetFileDescriptor can be a pipe or socket pair to enable
       * streaming of data.
       *
       * <p class="note">For better interoperability with other applications, it is recommended
       * that for any URIs that can be opened, you also support queries on them
       * containing at least the columns specified by {@link android.provider.OpenableColumns}.
       * You may also want to support other common columns if you have additional meta-data
       * to supply, such as {@link android.provider.MediaStore.MediaColumns#DATE_ADDED}
       * in {@link android.provider.MediaStore.MediaColumns}.</p>
       *
       * @param uri The data in the content provider being queried.
       * @param mimeTypeFilter The type of data the client desires.  May be
       * a pattern, such as *&#47;*, if the caller does not have specific type
       * requirements; in this case the content provider will pick its best
       * type matching the pattern.
       * @param opts Additional options from the client.  The definitions of
       * these are specific to the content provider being called.
       * @param signal A signal to cancel the operation in progress, or
       *            {@code null} if none. For example, if you are downloading a
       *            file from the network to service a "rw" mode request, you
       *            should periodically call
       *            {@link CancellationSignal#throwIfCanceled()} to check whether
       *            the client has canceled the request and abort the download.
       *
       * @return Returns a new AssetFileDescriptor from which the client can
       * read data of the desired type.
       *
       * @throws FileNotFoundException Throws FileNotFoundException if there is
       * no file associated with the given URI or the mode is invalid.
       * @throws SecurityException Throws SecurityException if the caller does
       * not have permission to access the data.
       * @throws IllegalArgumentException Throws IllegalArgumentException if the
       * content provider does not support the requested MIME type.
       *
       * @see #getStreamTypes(Uri, String)
       * @see #openAssetFile(Uri, String)
       * @see ClipDescription#compareMimeTypes(String, String)
       */
      @Override
      public @Nullable AssetFileDescriptor openTypedAssetFile(@NonNull Uri uri,
              @NonNull String mimeTypeFilter, @Nullable Bundle opts,
              @Nullable CancellationSignal signal) throws FileNotFoundException {
          return openTypedAssetFile(uri, mimeTypeFilter, opts);
      }
  
      /**
       * Interface to write a stream of data to a pipe.  Use with
       * {@link ContentProvider#openPipeHelper}.
       */
      public interface PipeDataWriter<T> {
          /**
           * Called from a background thread to stream data out to a pipe.
           * Note that the pipe is blocking, so this thread can block on
           * writes for an arbitrary amount of time if the client is slow
           * at reading.
           *
           * @param output The pipe where data should be written.  This will be
           * closed for you upon returning from this function.
           * @param uri The URI whose data is to be written.
           * @param mimeType The desired type of data to be written.
           * @param opts Options supplied by caller.
           * @param args Your own custom arguments.
           */
          public void writeDataToPipe(@NonNull ParcelFileDescriptor output, @NonNull Uri uri,
                  @NonNull String mimeType, @Nullable Bundle opts, @Nullable T args);
      }
  
      /**
       * A helper function for implementing {@link #openTypedAssetFile}, for
       * creating a data pipe and background thread allowing you to stream
       * generated data back to the client.  This function returns a new
       * ParcelFileDescriptor that should be returned to the caller (the caller
       * is responsible for closing it).
       *
       * @param uri The URI whose data is to be written.
       * @param mimeType The desired type of data to be written.
       * @param opts Options supplied by caller.
       * @param args Your own custom arguments.
       * @param func Interface implementing the function that will actually
       * stream the data.
       * @return Returns a new ParcelFileDescriptor holding the read side of
       * the pipe.  This should be returned to the caller for reading; the caller
       * is responsible for closing it when done.
       */
      public @NonNull <T> ParcelFileDescriptor openPipeHelper(final @NonNull Uri uri,
              final @NonNull String mimeType, final @Nullable Bundle opts, final @Nullable T args,
              final @NonNull PipeDataWriter<T> func) throws FileNotFoundException {
          try {
              final ParcelFileDescriptor[] fds = ParcelFileDescriptor.createPipe();
  
              AsyncTask<Object, Object, Object> task = new AsyncTask<Object, Object, Object>() {
                  @Override
                  protected Object doInBackground(Object... params) {
                      func.writeDataToPipe(fds[1], uri, mimeType, opts, args);
                      try {
                          fds[1].close();
                      } catch (IOException e) {
                          Log.w(TAG, "Failure closing pipe", e);
                      }
                      return null;
                  }
              };
              task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Object[])null);
  
              return fds[0];
          } catch (IOException e) {
              throw new FileNotFoundException("failure making pipe");
          }
      }
  
      /**
       * Returns true if this instance is a temporary content provider.
       * @return true if this instance is a temporary content provider
       */
      protected boolean isTemporary() {
          return false;
      }
  
      /**
       * Returns the Binder object for this provider.
       *
       * @return the Binder object for this provider
       * @hide
       */
      @UnsupportedAppUsage
      public IContentProvider getIContentProvider() {
          return mTransport;
      }
  
      /**
       * Like {@link #attachInfo(Context, android.content.pm.ProviderInfo)}, but for use
       * when directly instantiating the provider for testing.
       * @hide
       */
      @UnsupportedAppUsage
      public void attachInfoForTesting(Context context, ProviderInfo info) {
          attachInfo(context, info, true);
      }
  
      /**
       * After being instantiated, this is called to tell the content provider
       * about itself.
       *
       * @param context The context this provider is running in
       * @param info Registered information about this content provider
       */
      public void attachInfo(Context context, ProviderInfo info) {
          attachInfo(context, info, false);
      }
  
      private void attachInfo(Context context, ProviderInfo info, boolean testing) {
          mNoPerms = testing;
          mCallingPackage = new ThreadLocal<>();
  
          /*
           * Only allow it to be set once, so after the content service gives
           * this to us clients can't change it.
           */
          if (mContext == null) {
              mContext = context;
              if (context != null && mTransport != null) {
                  mTransport.mAppOpsManager = (AppOpsManager) context.getSystemService(
                          Context.APP_OPS_SERVICE);
              }
              mMyUid = Process.myUid();
              if (info != null) {
                  setReadPermission(info.readPermission);
                  setWritePermission(info.writePermission);
                  setPathPermissions(info.pathPermissions);
                  mExported = info.exported;
                  mSingleUser = (info.flags & ProviderInfo.FLAG_SINGLE_USER) != 0;
                  setAuthorities(info.authority);
              }
              ContentProvider.this.onCreate();
          }
      }
  
      /**
       * Override this to handle requests to perform a batch of operations, or the
       * default implementation will iterate over the operations and call
       * {@link ContentProviderOperation#apply} on each of them.
       * If all calls to {@link ContentProviderOperation#apply} succeed
       * then a {@link ContentProviderResult} array with as many
       * elements as there were operations will be returned.  If any of the calls
       * fail, it is up to the implementation how many of the others take effect.
       * This method can be called from multiple threads, as described in
       * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html#Threads">Processes
       * and Threads</a>.
       *
       * @param operations the operations to apply
       * @return the results of the applications
       * @throws OperationApplicationException thrown if any operation fails.
       * @see ContentProviderOperation#apply
       */
      @Override
      public @NonNull ContentProviderResult[] applyBatch(@NonNull String authority,
              @NonNull ArrayList<ContentProviderOperation> operations)
                      throws OperationApplicationException {
          return applyBatch(operations);
      }
  
      public @NonNull ContentProviderResult[] applyBatch(
              @NonNull ArrayList<ContentProviderOperation> operations)
                      throws OperationApplicationException {
          final int numOperations = operations.size();
          final ContentProviderResult[] results = new ContentProviderResult[numOperations];
          for (int i = 0; i < numOperations; i++) {
              results[i] = operations.get(i).apply(this, results, i);
          }
          return results;
      }
  
      /**
       * Call a provider-defined method.  This can be used to implement
       * interfaces that are cheaper and/or unnatural for a table-like
       * model.
       *
       * <p class="note"><strong>WARNING:</strong> The framework does no permission checking
       * on this entry into the content provider besides the basic ability for the application
       * to get access to the provider at all.  For example, it has no idea whether the call
       * being executed may read or write data in the provider, so can't enforce those
       * individual permissions.  Any implementation of this method <strong>must</strong>
       * do its own permission checks on incoming calls to make sure they are allowed.</p>
       *
       * @param method method name to call.  Opaque to framework, but should not be {@code null}.
       * @param arg provider-defined String argument.  May be {@code null}.
       * @param extras provider-defined Bundle argument.  May be {@code null}.
       * @return provider-defined return value.  May be {@code null}, which is also
       *   the default for providers which don't implement any call methods.
       */
      @Override
      public @Nullable Bundle call(@NonNull String authority, @NonNull String method,
              @Nullable String arg, @Nullable Bundle extras) {
          return call(method, arg, extras);
      }
  
      public @Nullable Bundle call(@NonNull String method, @Nullable String arg,
              @Nullable Bundle extras) {
          return null;
      }
  
      /**
       * Implement this to shut down the ContentProvider instance. You can then
       * invoke this method in unit tests.
       *
       * <p>
       * Android normally handles ContentProvider startup and shutdown
       * automatically. You do not need to start up or shut down a
       * ContentProvider. When you invoke a test method on a ContentProvider,
       * however, a ContentProvider instance is started and keeps running after
       * the test finishes, even if a succeeding test instantiates another
       * ContentProvider. A conflict develops because the two instances are
       * usually running against the same underlying data source (for example, an
       * sqlite database).
       * </p>
       * <p>
       * Implementing shutDown() avoids this conflict by providing a way to
       * terminate the ContentProvider. This method can also prevent memory leaks
       * from multiple instantiations of the ContentProvider, and it can ensure
       * unit test isolation by allowing you to completely clean up the test
       * fixture before moving on to the next test.
       * </p>
       */
      public void shutdown() {
          Log.w(TAG, "implement ContentProvider shutdown() to make sure all database " +
                  "connections are gracefully shutdown");
      }
  
      /**
       * Print the Provider's state into the given stream.  This gets invoked if
       * you run "adb shell dumpsys activity provider &lt;provider_component_name&gt;".
       *
       * @param fd The raw file descriptor that the dump is being sent to.
       * @param writer The PrintWriter to which you should dump your state.  This will be
       * closed for you after you return.
       * @param args additional arguments to the dump request.
       */
      public void dump(FileDescriptor fd, PrintWriter writer, String[] args) {
          writer.println("nothing to dump");
      }
  
      private void validateIncomingAuthority(String authority) throws SecurityException {
          if (!matchesOurAuthorities(getAuthorityWithoutUserId(authority))) {
              String message = "The authority " + authority + " does not match the one of the "
                      + "contentProvider: ";
              if (mAuthority != null) {
                  message += mAuthority;
              } else {
                  message += Arrays.toString(mAuthorities);
              }
              throw new SecurityException(message);
          }
      }
  
      /** @hide */
      @VisibleForTesting
      public Uri validateIncomingUri(Uri uri) throws SecurityException {
          String auth = uri.getAuthority();
          if (!mSingleUser) {
              int userId = getUserIdFromAuthority(auth, UserHandle.USER_CURRENT);
              if (userId != UserHandle.USER_CURRENT && userId != mContext.getUserId()) {
                  throw new SecurityException("trying to query a ContentProvider in user "
                          + mContext.getUserId() + " with a uri belonging to user " + userId);
              }
          }
          validateIncomingAuthority(auth);
  
          // Normalize the path by removing any empty path segments, which can be
          // a source of security issues.
          final String encodedPath = uri.getEncodedPath();
          if (encodedPath != null && encodedPath.indexOf("//") != -1) {
              final Uri normalized = uri.buildUpon()
                      .encodedPath(encodedPath.replaceAll("//+", "/")).build();
              Log.w(TAG, "Normalized " + uri + " to " + normalized
                      + " to avoid possible security issues");
              return normalized;
          } else {
              return uri;
          }
      }
  
      /** @hide */
      private Uri maybeGetUriWithoutUserId(Uri uri) {
          if (mSingleUser) {
              return uri;
          }
          return getUriWithoutUserId(uri);
      }
  
      /** @hide */
      public static int getUserIdFromAuthority(String auth, int defaultUserId) {
          if (auth == null) return defaultUserId;
          int end = auth.lastIndexOf('@');
          if (end == -1) return defaultUserId;
          String userIdString = auth.substring(0, end);
          try {
              return Integer.parseInt(userIdString);
          } catch (NumberFormatException e) {
              Log.w(TAG, "Error parsing userId.", e);
              return UserHandle.USER_NULL;
          }
      }
  
      /** @hide */
      public static int getUserIdFromAuthority(String auth) {
          return getUserIdFromAuthority(auth, UserHandle.USER_CURRENT);
      }
  
      /** @hide */
      public static int getUserIdFromUri(Uri uri, int defaultUserId) {
          if (uri == null) return defaultUserId;
          return getUserIdFromAuthority(uri.getAuthority(), defaultUserId);
      }
  
      /** @hide */
      public static int getUserIdFromUri(Uri uri) {
          return getUserIdFromUri(uri, UserHandle.USER_CURRENT);
      }
  
      /**
       * Removes userId part from authority string. Expects format:
       * userId@some.authority
       * If there is no userId in the authority, it symply returns the argument
       * @hide
       */
      public static String getAuthorityWithoutUserId(String auth) {
          if (auth == null) return null;
          int end = auth.lastIndexOf('@');
          return auth.substring(end+1);
      }
  
      /** @hide */
      public static Uri getUriWithoutUserId(Uri uri) {
          if (uri == null) return null;
          Uri.Builder builder = uri.buildUpon();
          builder.authority(getAuthorityWithoutUserId(uri.getAuthority()));
          return builder.build();
      }
  
      /** @hide */
      public static boolean uriHasUserId(Uri uri) {
          if (uri == null) return false;
          return !TextUtils.isEmpty(uri.getUserInfo());
      }
  
      /** @hide */
      @UnsupportedAppUsage
      public static Uri maybeAddUserId(Uri uri, int userId) {
          if (uri == null) return null;
          if (userId != UserHandle.USER_CURRENT
                  && ContentResolver.SCHEME_CONTENT.equals(uri.getScheme())) {
              if (!uriHasUserId(uri)) {
                  //We don't add the user Id if there's already one
                  Uri.Builder builder = uri.buildUpon();
                  builder.encodedAuthority("" + userId + "@" + uri.getEncodedAuthority());
                  return builder.build();
              }
          }
          return uri;
      }
  }
  