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

// Copyright 2016 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;

import com.google.common.annotations.VisibleForTesting;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.attribute.BasicFileAttributes;
import java.nio.file.attribute.DosFileAttributes;

/** Jury-rigged file system for Windows. */
@ThreadSafe
public class WindowsFileSystem extends JavaIoFileSystem {

  public static final LinkOption[] NO_OPTIONS = new LinkOption[0];
  public static final LinkOption[] NO_FOLLOW = new LinkOption[] {LinkOption.NOFOLLOW_LINKS};

  @Override
  protected void createSymbolicLink(Path linkPath, PathFragment targetFragment) throws IOException {
    // TODO(lberki): Add some JNI to create hard links/junctions instead of calling out to
    // cmd.exe
    File file = getIoFile(linkPath);
    try {
      File targetFile = new File(targetFragment.getPathString());
      if (targetFile.isDirectory()) {
        createDirectoryJunction(targetFile, file);
      } else {
        Files.copy(targetFile.toPath(), file.toPath());
      }
    } catch (java.nio.file.FileAlreadyExistsException e) {
      throw new IOException(linkPath + ERR_FILE_EXISTS);
    } catch (java.nio.file.AccessDeniedException e) {
      throw new IOException(linkPath + ERR_PERMISSION_DENIED);
    } catch (java.nio.file.NoSuchFileException e) {
      throw new FileNotFoundException(linkPath + ERR_NO_SUCH_FILE_OR_DIR);
    }
  }

  @Override
  public boolean supportsSymbolicLinksNatively() {
    return false;
  }

  @Override
  public boolean isFilePathCaseSensitive() {
    return false;
  }

  private void createDirectoryJunction(File sourceDirectory, File targetPath) throws IOException {
    StringBuilder cl = new StringBuilder("cmd.exe /c ");
    cl.append("mklink /J ");
    cl.append('"');
    cl.append(targetPath.getAbsolutePath());
    cl.append('"');
    cl.append(' ');
    cl.append('"');
    cl.append(sourceDirectory.getAbsolutePath());
    cl.append('"');
    Process process = Runtime.getRuntime().exec(cl.toString());
    try {
      process.waitFor();
      if (process.exitValue() != 0) {
        throw new IOException("Command failed " + cl);
      }
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      throw new IOException("Command failed ", e);
    }
  }

  @Override
  protected boolean fileIsSymbolicLink(File file) {
    try {
      if (file.isDirectory() && isJunction(file.toPath())) {
        return true;
      }
    } catch (IOException e) {
      // Did not work, try in another way
    }
    return super.fileIsSymbolicLink(file);
  }

  public static LinkOption[] symlinkOpts(boolean followSymlinks) {
    return followSymlinks ? NO_OPTIONS : NO_FOLLOW;
  }

  @Override
  protected FileStatus stat(Path path, boolean followSymlinks) throws IOException {
    File file = getIoFile(path);
    final BasicFileAttributes attributes;
    try {
      attributes =
          Files.readAttributes(
              file.toPath(), BasicFileAttributes.class, symlinkOpts(followSymlinks));
    } catch (java.nio.file.FileSystemException e) {
      throw new FileNotFoundException(path + ERR_NO_SUCH_FILE_OR_DIR);
    }

    final boolean isSymbolicLink = !followSymlinks && fileIsSymbolicLink(file);
    FileStatus status =
        new FileStatus() {
          @Override
          public boolean isFile() {
            return attributes.isRegularFile() || (isSpecialFile() && !isDirectory());
          }

          @Override
          public boolean isSpecialFile() {
            return attributes.isOther();
          }

          @Override
          public boolean isDirectory() {
            return attributes.isDirectory();
          }

          @Override
          public boolean isSymbolicLink() {
            return isSymbolicLink;
          }

          @Override
          public long getSize() throws IOException {
            return attributes.size();
          }

          @Override
          public long getLastModifiedTime() throws IOException {
            return attributes.lastModifiedTime().toMillis();
          }

          @Override
          public long getLastChangeTime() {
            // This is the best we can do with Java NIO...
            return attributes.lastModifiedTime().toMillis();
          }

          @Override
          public long getNodeId() {
            // TODO(bazel-team): Consider making use of attributes.fileKey().
            return -1;
          }
        };

    return status;
  }

  @Override
  protected boolean isDirectory(Path path, boolean followSymlinks) {
    if (!followSymlinks) {
      try {
        if (isJunction(getIoFile(path).toPath())) {
          return false;
        }
      } catch (IOException e) {
        return false;
      }
    }
    return super.isDirectory(path, followSymlinks);
  }

  /**
   * Returns true if the path refers to a directory junction, directory symlink, or regular symlink.
   *
   * <p>Directory junctions are symbolic links created with "mklink /J" where the target is a
   * directory or another directory junction. Directory junctions can be created without any user
   * privileges.
   *
   * <p>Directory symlinks are symbolic links created with "mklink /D" where the target is a
   * directory or another directory symlink. Note that directory symlinks can only be created by
   * Administrators.
   *
   * <p>Normal symlinks are symbolic links created with "mklink". Normal symlinks should not point
   * at directories, because even though "mklink" can create the link, it will not be a functional
   * one (the linked directory's contents cannot be listed). Only Administrators may create regular
   * symlinks.
   *
   * <p>This method returns true for all three types as long as their target is a directory (even if
   * they are dangling), though only directory junctions and directory symlinks are useful.
   */
  // TODO(laszlocsomor): fix https://github.com/bazelbuild/bazel/issues/1735 and use the JNI method
  // in WindowsFileOperations.
  @VisibleForTesting
  static boolean isJunction(java.nio.file.Path p) throws IOException {
    if (Files.exists(p, symlinkOpts(/* followSymlinks */ false))) {
      DosFileAttributes attributes =
          Files.readAttributes(p, DosFileAttributes.class, symlinkOpts(/* followSymlinks */ false));

      if (attributes.isRegularFile()) {
        return false;
      }

      if (attributes.isDirectory()) {
        return attributes.isOther();
      } else {
        return attributes.isSymbolicLink();
      }
    }
    return false;
  }
}