src/main/java/com/google/devtools/build/lib/vfs/DelegateFileSystem.java

// Copyright 2019 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.vfs;

/**
 * A file system that delegates all operations to {@code delegateFs} under the hood.
 *
 * <p>This is helpful when wanting to implement a file system on top of another file system as it
 * allows code patterns like: <code>
 * {@literal @}Override
 * protected long getFileSize(PathFragment path, boolean followSymlinks) throws IOException {
 *   if (!someCondition) {
 *     return super.getFileSize(path, followSymlinks);
 *   }
 *   return rpc.getFileSize(path, followSymlinks);
 * }
 * </code>
 *
 * <p>The implementation uses {@link PathTransformingDelegateFileSystem} with identity path
 * transformations ({@linkplain PathTransformingDelegateFileSystem#toDelegatePath(PathFragment)
 * toDelegatePath} and {@linkplain PathTransformingDelegateFileSystem#fromDelegatePath(PathFragment)
 * fromDelegatePath}).
 */
public abstract class DelegateFileSystem extends PathTransformingDelegateFileSystem {

  public DelegateFileSystem(FileSystem delegateFs) {
    super(delegateFs);
  }

  @Override
  protected final PathFragment toDelegatePath(PathFragment path) {
    return path;
  }

  @Override
  protected final PathFragment fromDelegatePath(PathFragment delegatePath) {
    return delegatePath;
  }
}