[7.1.0] Avoid exception-based control flow in RAFS#getDigest and RAFS#getFastDigest.

src/main/java/com/google/devtools/build/lib/remote/RemoteActionFileSystem.java

@@ -90,21 +90,21 @@ public class RemoteActionFileSystem extends AbstractFileSystemWithCustomStat {
 
  @Nullable private ActionExecutionMetadata action = null;
 
- /** Describes how to handle symlinks when calling {@link #statUnchecked}. */
+ /** Describes how to handle symlinks when calling {@link #statInternal}. */
  private enum FollowMode {
- /** Dereference the entire path. This is equivalent to {@link Symlinks.FOLLOW}. */
+ /** Canonicalize the entire path. This is equivalent to {@link Symlinks.FOLLOW}. */
  FOLLOW_ALL,
- /** Dereference the parent path. This is equivalent to {@link Symlinks.NOFOLLOW}. */
+ /** Canonicalize the parent path. This is equivalent to {@link Symlinks.NOFOLLOW}. */
  FOLLOW_PARENT,
- /** Do not dereference. This is only used internally to resolve symlinks efficiently. */
+ /** Do not canonicalize. This is only used internally to resolve symlinks efficiently. */
  FOLLOW_NONE
  };
 
- /** Describes which sources to consider when statting a file. */
+ /** Describes which sources to consider when calling {@link #statInternal}. */
  private enum StatSources {
- /** Consider all sources (action input map, in-memory filesystem and local filesystem). */
+ /** Consider all sources (action input map, remote output tree and local filesystem). */
  ALL,
- /** Consider only in-memory sources (action input map and in-memory filesystem). */
+ /** Consider only in-memory sources (action input map and remote output tree). */
  IN_MEMORY_ONLY,
  }
 
@@ -267,13 +267,9 @@ boolean isRemote(Path path) throws IOException {
 
  private boolean isRemote(PathFragment path) throws IOException {
  // Files in the local filesystem are non-remote by definition, so stat only in-memory sources.
- try {
- var status = statUnchecked(path, FollowMode.FOLLOW_ALL, StatSources.IN_MEMORY_ONLY);
- return (status instanceof FileStatusWithMetadata)
- && ((FileStatusWithMetadata) status).getMetadata().isRemote();
- } catch (FileNotFoundException e) {
- return false;
- }
+ var status = statInternal(path, FollowMode.FOLLOW_ALL, StatSources.IN_MEMORY_ONLY);
+ return (status instanceof FileStatusWithMetadata)
+ && ((FileStatusWithMetadata) status).getMetadata().isRemote();
  }
 
  public void updateContext(ActionExecutionMetadata action) {
@@ -365,18 +361,15 @@ public byte[] getxattr(PathFragment path, String name, boolean followSymlinks)
  }
 
  @Override
+ @Nullable
  protected byte[] getFastDigest(PathFragment path) throws IOException {
  path = resolveSymbolicLinks(path).asFragment();
  // Try to obtain a fast digest through a stat. This is only possible for in-memory files.
  // The parent path has already been canonicalized by resolveSymbolicLinks, so FOLLOW_NONE is
  // effectively the same as FOLLOW_PARENT, but more efficient.
- try {
- var status = statUnchecked(path, FollowMode.FOLLOW_NONE, StatSources.IN_MEMORY_ONLY);
- if (status instanceof FileStatusWithDigest) {
- return ((FileStatusWithDigest) status).getDigest();
- }
- } catch (FileNotFoundException e) {
- // Intentionally ignored.
+ var status = statInternal(path, FollowMode.FOLLOW_NONE, StatSources.IN_MEMORY_ONLY);
+ if (status instanceof FileStatusWithDigest) {
+ return ((FileStatusWithDigest) status).getDigest();
  }
  return localFs.getPath(path).getFastDigest();
  }
@@ -387,13 +380,9 @@ protected byte[] getDigest(PathFragment path) throws IOException {
  // Try to obtain a fast digest through a stat. This is only possible for in-memory files.
  // The parent path has already been canonicalized by resolveSymbolicLinks, so FOLLOW_NONE is
  // effectively the same as FOLLOW_PARENT, but more efficient.
- try {
- var status = statUnchecked(path, FollowMode.FOLLOW_NONE, StatSources.IN_MEMORY_ONLY);
- if (status instanceof FileStatusWithDigest) {
- return ((FileStatusWithDigest) status).getDigest();
- }
- } catch (FileNotFoundException e) {
- // Intentionally ignored.
+ var status = statInternal(path, FollowMode.FOLLOW_NONE, StatSources.IN_MEMORY_ONLY);
+ if (status instanceof FileStatusWithDigest) {
+ return ((FileStatusWithDigest) status).getDigest();
  }
  return localFs.getPath(path).getDigest();
  }
@@ -529,7 +518,10 @@ protected PathFragment resolveOneLink(PathFragment path) throws IOException {
  //
  // The parent path has already been canonicalized, so FOLLOW_NONE is effectively the same as
  // FOLLOW_PARENT, but much more efficient as it doesn't call stat recursively.
- var stat = statUnchecked(path, FollowMode.FOLLOW_NONE, StatSources.ALL);
+ var stat = statInternal(path, FollowMode.FOLLOW_NONE, StatSources.ALL);
+ if (stat == null) {
+ throw new FileNotFoundException(path.getPathString() + " (No such file or directory)");
+ }
  return stat.isSymbolicLink() ? readSymbolicLink(path) : null;
  }
 
@@ -554,34 +546,45 @@ protected boolean exists(PathFragment path, boolean followSymlinks) {
  }
  }
 
+ @Override
+ protected FileStatus stat(PathFragment path, boolean followSymlinks) throws IOException {
+ FileStatus stat = statIfFound(path, followSymlinks);
+ if (stat == null) {
+ throw new FileNotFoundException(path.getPathString() + " (No such file or directory)");
+ }
+ return stat;
+ }
+
  @Nullable
  @Override
  protected FileStatus statIfFound(PathFragment path, boolean followSymlinks) throws IOException {
- try {
- return stat(path, followSymlinks);
- } catch (FileNotFoundException e) {
- return null;
- }
+ return statInternal(
+ path, followSymlinks ? FollowMode.FOLLOW_ALL : FollowMode.FOLLOW_PARENT, StatSources.ALL);
  }
 
  @Nullable
  @Override
  protected FileStatus statNullable(PathFragment path, boolean followSymlinks) {
  try {
- return stat(path, followSymlinks);
+ return statIfFound(path, followSymlinks);
  } catch (IOException e) {
  return null;
  }
  }
 
- @Override
- protected FileStatus stat(PathFragment path, boolean followSymlinks) throws IOException {
- return statUnchecked(
- path, followSymlinks ? FollowMode.FOLLOW_ALL : FollowMode.FOLLOW_PARENT, StatSources.ALL);
- }
-
- private FileStatus statUnchecked(
- PathFragment path, FollowMode followMode, StatSources statSources) throws IOException {
+ /**
+ * Internal stat implementation.
+ *
+ * @param path the path to stat
+ * @param followMode whether and how to canonicalize the path
+ * @param statSources which sources to consider
+ * @return the file status on success, or null if the file was not found in any of the sources
+ * under consideration
+ * @throws IOException if an error other than file not found occurred
+ */
+ @Nullable
+ private FileStatus statInternal(PathFragment path, FollowMode followMode, StatSources statSources)
+ throws IOException {
  // Canonicalize the path.
  if (followMode == FollowMode.FOLLOW_ALL) {
  path = resolveSymbolicLinks(path).asFragment();
@@ -611,10 +614,10 @@ private FileStatus statUnchecked(
  }
 
  if (statSources == StatSources.ALL) {
- return localFs.getPath(path).stat(Symlinks.NOFOLLOW);
+ return localFs.getPath(path).statIfFound(Symlinks.NOFOLLOW);
  }
 
- throw new FileNotFoundException(path.getPathString() + " (No such file or directory)");
+ return null;
  }
 
  private static FileStatusWithMetadata statFromMetadata(FileArtifactValue m) {

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

@@ -331,6 +331,7 @@ public byte[] getxattr(PathFragment path, String name, boolean followSymlinks)
  * filesystem doesn't support them. This digest should be suitable for detecting changes to the
  * file.
  */
+ @Nullable
  protected byte[] getFastDigest(PathFragment path) throws IOException {
  return null;
  }