Allow banning symlink action outputs from being uploaded to a remote cache.

This is mostly a roll-forward of 4465dae23de989f1452e93d0a88ac2a289103dd9, which
was reverted by fa36d2f48965b127e8fd397348d16e991135bfb6. The main difference is
that the new behavior is now gated behind the --noremote_allow_symlink_upload
flag.

https://docs.google.com/document/d/1gnOYszitgrLVet3sQk-TKGqIcpkkDsc6aw-izoo-d64
is a design proposal to support symlinks in the remote cache, which would render
this change moot. I'd like to be able to prevent incorrect cache behavior until
that change is implemented, though.

This fixes https://github.com/bazelbuild/bazel/issues/4840 (again).

Closes #5122.

Change-Id: I2136cfe82c2e1a8a9f5856e12a37d42cabd0e299
PiperOrigin-RevId: 195261827

10 files changed, 128 insertions, 98 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/exec/AbstractSpawnStrategy.java b/src/main/java/com/google/devtools/build/lib/exec/AbstractSpawnStrategy.java
index d8c42ff140..6745b1a96e 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/AbstractSpawnStrategy.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/AbstractSpawnStrategy.java
@@ -41,7 +41,6 @@ import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import java.io.IOException;
 import java.time.Duration;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.SortedMap;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -95,8 +94,7 @@ public abstract class AbstractSpawnStrategy implements SandboxedSpawnActionConte
           // Actual execution.
           spawnResult = spawnRunner.exec(spawn, context);
           if (cacheHandle.willStore()) {
-            cacheHandle.store(
-                spawnResult, listExistingOutputFiles(spawn, actionExecutionContext.getExecRoot()));
+            cacheHandle.store(spawnResult);
           }
         }
       }
@@ -144,19 +142,6 @@ public abstract class AbstractSpawnStrategy implements SandboxedSpawnActionConte
     return ImmutableList.of(spawnResult);
   }
 
-  private List<Path> listExistingOutputFiles(Spawn spawn, Path execRoot) {
-    ArrayList<Path> outputFiles = new ArrayList<>();
-    for (ActionInput output : spawn.getOutputFiles()) {
-      Path outputPath = execRoot.getRelative(output.getExecPathString());
-      // TODO(ulfjack): Store the actual list of output files in SpawnResult and use that instead
-      // of statting the files here again.
-      if (outputPath.exists()) {
-        outputFiles.add(outputPath);
-      }
-    }
-    return outputFiles;
-  }
-
   private final class SpawnExecutionContextImpl implements SpawnExecutionContext {
     private final Spawn spawn;
     private final ActionExecutionContext actionExecutionContext;
diff --git a/src/main/java/com/google/devtools/build/lib/exec/SpawnCache.java b/src/main/java/com/google/devtools/build/lib/exec/SpawnCache.java
index afc9d9376b..48bdaf5c81 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/SpawnCache.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/SpawnCache.java
@@ -19,10 +19,8 @@ import com.google.devtools.build.lib.actions.ExecutionStrategy;
 import com.google.devtools.build.lib.actions.Spawn;
 import com.google.devtools.build.lib.actions.SpawnResult;
 import com.google.devtools.build.lib.exec.SpawnRunner.SpawnExecutionContext;
-import com.google.devtools.build.lib.vfs.Path;
 import java.io.Closeable;
 import java.io.IOException;
-import java.util.Collection;
 import java.util.NoSuchElementException;
 
 /**
@@ -33,32 +31,31 @@ import java.util.NoSuchElementException;
  */
 public interface SpawnCache extends ActionContext {
   /** A no-op implementation that has no result, and performs no upload. */
-  public static CacheHandle NO_RESULT_NO_STORE = new CacheHandle() {
-    @Override
-    public boolean hasResult() {
-      return false;
-    }
-
-    @Override
-    public SpawnResult getResult() {
-      throw new NoSuchElementException();
-    }
-
-    @Override
-    public boolean willStore() {
-      return false;
-    }
-
-    @Override
-    public void store(SpawnResult result, Collection<Path> files)
-        throws InterruptedException, IOException {
-      // Do nothing.
-    }
-
-    @Override
-    public void close() {
-    }
-  };
+  public static CacheHandle NO_RESULT_NO_STORE =
+      new CacheHandle() {
+        @Override
+        public boolean hasResult() {
+          return false;
+        }
+
+        @Override
+        public SpawnResult getResult() {
+          throw new NoSuchElementException();
+        }
+
+        @Override
+        public boolean willStore() {
+          return false;
+        }
+
+        @Override
+        public void store(SpawnResult result) throws InterruptedException, IOException {
+          // Do nothing.
+        }
+
+        @Override
+        public void close() {}
+      };
 
   /**
    * Helper method to create a {@link CacheHandle} from a successful {@link SpawnResult} instance.
@@ -81,14 +78,12 @@ public interface SpawnCache extends ActionContext {
       }
 
       @Override
-      public void store(SpawnResult result, Collection<Path> files)
-          throws InterruptedException, IOException {
+      public void store(SpawnResult result) throws InterruptedException, IOException {
         throw new IllegalStateException();
       }
 
       @Override
-      public void close() {
-      }
+      public void close() {}
     };
   }
 
@@ -148,8 +143,7 @@ public interface SpawnCache extends ActionContext {
      * <p>If the current thread is interrupted, then this method should return as quickly as
      * possible with an {@link InterruptedException}.
      */
-    void store(SpawnResult result, Collection<Path> files)
-        throws InterruptedException, IOException;
+    void store(SpawnResult result) throws ExecException, InterruptedException, IOException;
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/remote/AbstractRemoteActionCache.java b/src/main/java/com/google/devtools/build/lib/remote/AbstractRemoteActionCache.java
index be81ad6cfe..009eddb991 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/AbstractRemoteActionCache.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/AbstractRemoteActionCache.java
@@ -15,13 +15,16 @@ package com.google.devtools.build.lib.remote;
 
 import com.google.devtools.build.lib.actions.EnvironmentalExecException;
 import com.google.devtools.build.lib.actions.ExecException;
+import com.google.devtools.build.lib.actions.UserExecException;
 import com.google.devtools.build.lib.concurrent.ThreadSafety;
 import com.google.devtools.build.lib.remote.TreeNodeRepository.TreeNode;
 import com.google.devtools.build.lib.remote.util.DigestUtil;
 import com.google.devtools.build.lib.util.io.FileOutErr;
 import com.google.devtools.build.lib.vfs.Dirent;
+import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
+import com.google.devtools.build.lib.vfs.Symlinks;
 import com.google.devtools.remoteexecution.v1test.ActionResult;
 import com.google.devtools.remoteexecution.v1test.Command;
 import com.google.devtools.remoteexecution.v1test.Digest;
@@ -45,9 +48,11 @@ import javax.annotation.Nullable;
 /** A cache for storing artifacts (input and output) as well as the output of running an action. */
 @ThreadSafety.ThreadSafe
 public abstract class AbstractRemoteActionCache implements AutoCloseable {
+  protected final RemoteOptions options;
   protected final DigestUtil digestUtil;
 
-  public AbstractRemoteActionCache(DigestUtil digestUtil) {
+  public AbstractRemoteActionCache(RemoteOptions options, DigestUtil digestUtil) {
+    this.options = options;
     this.digestUtil = digestUtil;
   }
 
@@ -93,7 +98,7 @@ public abstract class AbstractRemoteActionCache implements AutoCloseable {
       Collection<Path> files,
       FileOutErr outErr,
       boolean uploadAction)
-      throws IOException, InterruptedException;
+      throws ExecException, IOException, InterruptedException;
 
   /**
    * Download a remote blob to a local destination.
@@ -253,12 +258,12 @@ public abstract class AbstractRemoteActionCache implements AutoCloseable {
     }
   }
 
-  /**
-   * The UploadManifest is used to mutualize upload between the RemoteActionCache implementations.
-   */
-  public class UploadManifest {
+  /** UploadManifest adds output metadata to a {@link ActionResult}. */
+  static class UploadManifest {
+    private final DigestUtil digestUtil;
     private final ActionResult.Builder result;
     private final Path execRoot;
+    private final boolean allowSymlinks;
     private final Map<Digest, Path> digestToFile;
     private final Map<Digest, Chunker> digestToChunkers;
 
@@ -266,33 +271,45 @@ public abstract class AbstractRemoteActionCache implements AutoCloseable {
      * Create an UploadManifest from an ActionResult builder and an exec root. The ActionResult
      * builder is populated through a call to {@link #addFile(Digest, Path)}.
      */
-    public UploadManifest(ActionResult.Builder result, Path execRoot) {
+    public UploadManifest(
+        DigestUtil digestUtil, ActionResult.Builder result, Path execRoot, boolean allowSymlinks) {
+      this.digestUtil = digestUtil;
       this.result = result;
       this.execRoot = execRoot;
+      this.allowSymlinks = allowSymlinks;
 
       this.digestToFile = new HashMap<>();
       this.digestToChunkers = new HashMap<>();
     }
 
     /**
-     * Add a collection of files (and directories) to the UploadManifest. Adding a directory has the
+     * Add a collection of files or directories to the UploadManifest. Adding a directory has the
      * effect of 1) uploading a {@link Tree} protobuf message from which the whole structure of the
      * directory, including the descendants, can be reconstructed and 2) uploading all the
      * non-directory descendant files.
+     *
+     * <p>Attempting to a upload symlink results in a {@link
+     * com.google.build.lib.actions.ExecException}, since cachable actions shouldn't emit symlinks.
      */
-    public void addFiles(Collection<Path> files) throws IOException, InterruptedException {
+    public void addFiles(Collection<Path> files)
+        throws ExecException, IOException, InterruptedException {
       for (Path file : files) {
         // TODO(ulfjack): Maybe pass in a SpawnResult here, add a list of output files to that, and
         // rely on the local spawn runner to stat the files, instead of statting here.
-        if (!file.exists()) {
+        FileStatus stat = file.statIfFound(Symlinks.NOFOLLOW);
+        if (stat == null) {
           // We ignore requested results that have not been generated by the action.
           continue;
         }
-        if (file.isDirectory()) {
+        if (stat.isDirectory()) {
           addDirectory(file);
-        } else {
-          Digest digest = digestUtil.compute(file);
+        } else if (stat.isFile()) {
+          Digest digest = digestUtil.compute(file, stat.getSize());
           addFile(digest, file);
+        } else if (allowSymlinks && stat.isSymbolicLink()) {
+          addFile(digestUtil.compute(file), file);
+        } else {
+          illegalOutput(file);
         }
       }
     }
@@ -321,7 +338,7 @@ public abstract class AbstractRemoteActionCache implements AutoCloseable {
       digestToFile.put(digest, file);
     }
 
-    private void addDirectory(Path dir) throws IOException {
+    private void addDirectory(Path dir) throws ExecException, IOException {
       Tree.Builder tree = Tree.newBuilder();
       Directory root = computeDirectory(dir, tree);
       tree.setRoot(root);
@@ -340,7 +357,8 @@ public abstract class AbstractRemoteActionCache implements AutoCloseable {
       digestToChunkers.put(chunker.digest(), chunker);
     }
 
-    private Directory computeDirectory(Path path, Tree.Builder tree) throws IOException {
+    private Directory computeDirectory(Path path, Tree.Builder tree)
+        throws ExecException, IOException {
       Directory.Builder b = Directory.newBuilder();
 
       List<Dirent> sortedDirent = new ArrayList<>(path.readdir(TreeNodeRepository.SYMLINK_POLICY));
@@ -353,15 +371,28 @@ public abstract class AbstractRemoteActionCache implements AutoCloseable {
           Directory dir = computeDirectory(child, tree);
           b.addDirectoriesBuilder().setName(name).setDigest(digestUtil.compute(dir));
           tree.addChildren(dir);
-        } else {
+        } else if (dirent.getType() == Dirent.Type.FILE
+            || (dirent.getType() == Dirent.Type.SYMLINK && allowSymlinks)) {
           Digest digest = digestUtil.compute(child);
           b.addFilesBuilder().setName(name).setDigest(digest).setIsExecutable(child.isExecutable());
           digestToFile.put(digest, child);
+        } else {
+          illegalOutput(child);
         }
       }
 
       return b.build();
     }
+
+    private void illegalOutput(Path what) throws ExecException, IOException {
+      String kind = what.isSymbolicLink() ? "symbolic link" : "special file";
+      throw new UserExecException(
+          String.format(
+              "Output %s is a %s. Only regular files and directories may be "
+                  + "uploaded to a remote cache. "
+                  + "Change the file type or use --remote_allow_symlink_upload.",
+              what.relativeTo(execRoot), kind));
+    }
   }
 
   /** Release resources associated with the cache. The cache may not be used after calling this. */
diff --git a/src/main/java/com/google/devtools/build/lib/remote/GrpcRemoteCache.java b/src/main/java/com/google/devtools/build/lib/remote/GrpcRemoteCache.java
index 3f5a48176b..8f65021709 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/GrpcRemoteCache.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/GrpcRemoteCache.java
@@ -25,6 +25,7 @@ import com.google.common.collect.Iterables;
 import com.google.common.util.concurrent.ListeningScheduledExecutorService;
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.devtools.build.lib.actions.ActionInput;
+import com.google.devtools.build.lib.actions.ExecException;
 import com.google.devtools.build.lib.actions.MetadataProvider;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.remote.Retrier.RetryException;
@@ -65,7 +66,6 @@ import java.util.concurrent.TimeUnit;
 /** A RemoteActionCache implementation that uses gRPC calls to a remote cache server. */
 @ThreadSafe
 public class GrpcRemoteCache extends AbstractRemoteActionCache {
-  private final RemoteOptions options;
   private final CallCredentials credentials;
   private final Channel channel;
   private final RemoteRetrier retrier;
@@ -80,8 +80,7 @@ public class GrpcRemoteCache extends AbstractRemoteActionCache {
       RemoteOptions options,
       RemoteRetrier retrier,
       DigestUtil digestUtil) {
-    super(digestUtil);
-    this.options = options;
+    super(options, digestUtil);
     this.credentials = credentials;
     this.channel = channel;
     this.retrier = retrier;
@@ -240,7 +239,7 @@ public class GrpcRemoteCache extends AbstractRemoteActionCache {
       Collection<Path> files,
       FileOutErr outErr,
       boolean uploadAction)
-      throws IOException, InterruptedException {
+      throws ExecException, IOException, InterruptedException {
     ActionResult.Builder result = ActionResult.newBuilder();
     upload(execRoot, files, outErr, result);
     if (!uploadAction) {
@@ -266,8 +265,9 @@ public class GrpcRemoteCache extends AbstractRemoteActionCache {
   }
 
   void upload(Path execRoot, Collection<Path> files, FileOutErr outErr, ActionResult.Builder result)
-      throws IOException, InterruptedException {
-    UploadManifest manifest = new UploadManifest(result, execRoot);
+      throws ExecException, IOException, InterruptedException {
+    UploadManifest manifest =
+        new UploadManifest(digestUtil, result, execRoot, options.allowSymlinkUpload);
     manifest.addFiles(files);
 
     List<Chunker> filesToUpload = new ArrayList<>();
diff --git a/src/main/java/com/google/devtools/build/lib/remote/RemoteModule.java b/src/main/java/com/google/devtools/build/lib/remote/RemoteModule.java
index d9ab87a9f1..5453a98566 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/RemoteModule.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/RemoteModule.java
@@ -145,6 +145,7 @@ public final class RemoteModule extends BlazeModule {
       if (remoteOrLocalCache) {
         cache =
             new SimpleBlobStoreActionCache(
+                remoteOptions,
                 SimpleBlobStoreFactory.create(
                     remoteOptions,
                     GoogleAuthUtils.newCredentials(authAndTlsOptions),
diff --git a/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java b/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java
index e3b303db42..3431e95dac 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java
@@ -214,4 +214,19 @@ public final class RemoteOptions extends OptionsBase {
             + "LogEntry.writeDelimitedTo(OutputStream)."
   )
   public String experimentalRemoteGrpcLog;
+
+  @Option(
+    name = "remote_allow_symlink_upload",
+    defaultValue = "true",
+    category = "remote",
+    documentationCategory = OptionDocumentationCategory.EXECUTION_STRATEGY,
+    effectTags = {OptionEffectTag.EXECUTION},
+    help =
+        "If true, upload action symlink outputs to the remote cache. "
+            + "The remote cache currently doesn't support symlinks, "
+            + "so symlink outputs are converted into regular files. "
+            + "If this option is not enabled, "
+            + "otherwise cachable actions that output symlinks will fail."
+  )
+  public boolean allowSymlinkUpload;
 }
diff --git a/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnCache.java b/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnCache.java
index 2e31f83b48..ff83eb7a66 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnCache.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnCache.java
@@ -168,8 +168,8 @@ final class RemoteSpawnCache implements SpawnCache {
         }
 
         @Override
-        public void store(SpawnResult result, Collection<Path> files)
-            throws InterruptedException, IOException {
+        public void store(SpawnResult result)
+            throws ExecException, InterruptedException, IOException {
           if (options.experimentalGuardAgainstConcurrentChanges) {
             try {
               checkForConcurrentModifications();
@@ -183,6 +183,8 @@ final class RemoteSpawnCache implements SpawnCache {
                   && Status.SUCCESS.equals(result.status())
                   && result.exitCode() == 0;
           Context previous = withMetadata.attach();
+          Collection<Path> files =
+              RemoteSpawnRunner.resolveActionInputs(execRoot, spawn.getOutputFiles());
           try {
             remoteCache.upload(actionKey, execRoot, files, context.getFileOutErr(), uploadAction);
           } catch (IOException e) {
diff --git a/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnRunner.java b/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnRunner.java
index 9034e40c2e..fb28fffe96 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnRunner.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnRunner.java
@@ -16,6 +16,7 @@ package com.google.devtools.build.lib.remote;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Throwables;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.actions.ActionInput;
 import com.google.devtools.build.lib.actions.ActionInputFileCache;
@@ -441,12 +442,12 @@ class RemoteSpawnRunner implements SpawnRunner {
         return result;
       }
     }
-    List<Path> outputFiles = listExistingOutputFiles(execRoot, spawn);
+    boolean uploadAction =
+        Spawns.mayBeCached(spawn)
+            && Status.SUCCESS.equals(result.status())
+            && result.exitCode() == 0;
+    Collection<Path> outputFiles = resolveActionInputs(execRoot, spawn.getOutputFiles());
     try {
-      boolean uploadAction =
-          Spawns.mayBeCached(spawn)
-              && Status.SUCCESS.equals(result.status())
-              && result.exitCode() == 0;
       remoteCache.upload(actionKey, execRoot, outputFiles, context.getFileOutErr(), uploadAction);
     } catch (IOException e) {
       if (verboseFailures) {
@@ -470,16 +471,12 @@ class RemoteSpawnRunner implements SpawnRunner {
     }
   }
 
-  static List<Path> listExistingOutputFiles(Path execRoot, Spawn spawn) {
-    ArrayList<Path> outputFiles = new ArrayList<>();
-    for (ActionInput output : spawn.getOutputFiles()) {
-      Path outputPath = execRoot.getRelative(output.getExecPathString());
-      // TODO(ulfjack): Store the actual list of output files in SpawnResult and use that instead
-      // of statting the files here again.
-      if (outputPath.exists()) {
-        outputFiles.add(outputPath);
-      }
-    }
-    return outputFiles;
+  /** Resolve a collection of {@link com.google.build.lib.actions.ActionInput}s to {@link Path}s. */
+  static Collection<Path> resolveActionInputs(
+      Path execRoot, Collection<? extends ActionInput> actionInputs) {
+    return actionInputs
+        .stream()
+        .map((inp) -> execRoot.getRelative(inp.getExecPath()))
+        .collect(ImmutableList.toImmutableList());
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/remote/SimpleBlobStoreActionCache.java b/src/main/java/com/google/devtools/build/lib/remote/SimpleBlobStoreActionCache.java
index 2d4f4e9bbc..803946cc61 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/SimpleBlobStoreActionCache.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/SimpleBlobStoreActionCache.java
@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.remote;
 
 import com.google.devtools.build.lib.actions.ActionInput;
+import com.google.devtools.build.lib.actions.ExecException;
 import com.google.devtools.build.lib.actions.MetadataProvider;
 import com.google.devtools.build.lib.actions.cache.VirtualActionInput;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
@@ -55,8 +56,9 @@ public final class SimpleBlobStoreActionCache extends AbstractRemoteActionCache
 
   private final SimpleBlobStore blobStore;
 
-  public SimpleBlobStoreActionCache(SimpleBlobStore blobStore, DigestUtil digestUtil) {
-    super(digestUtil);
+  public SimpleBlobStoreActionCache(
+      RemoteOptions options, SimpleBlobStore blobStore, DigestUtil digestUtil) {
+    super(options, digestUtil);
     this.blobStore = blobStore;
   }
 
@@ -114,7 +116,7 @@ public final class SimpleBlobStoreActionCache extends AbstractRemoteActionCache
       Collection<Path> files,
       FileOutErr outErr,
       boolean uploadAction)
-      throws IOException, InterruptedException {
+      throws ExecException, IOException, InterruptedException {
     ActionResult.Builder result = ActionResult.newBuilder();
     upload(result, execRoot, files);
     if (outErr.getErrorPath().exists()) {
@@ -131,8 +133,9 @@ public final class SimpleBlobStoreActionCache extends AbstractRemoteActionCache
   }
 
   public void upload(ActionResult.Builder result, Path execRoot, Collection<Path> files)
-      throws IOException, InterruptedException {
-    UploadManifest manifest = new UploadManifest(result, execRoot);
+      throws ExecException, IOException, InterruptedException {
+    UploadManifest manifest =
+        new UploadManifest(digestUtil, result, execRoot, options.allowSymlinkUpload);
     manifest.addFiles(files);
 
     for (Map.Entry<Digest, Path> entry : manifest.getDigestToFile().entrySet()) {
diff --git a/src/main/java/com/google/devtools/build/lib/remote/util/DigestUtil.java b/src/main/java/com/google/devtools/build/lib/remote/util/DigestUtil.java
index afd31ccdeb..e4dc92a46f 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/util/DigestUtil.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/util/DigestUtil.java
@@ -60,9 +60,11 @@ public class DigestUtil {
   }
 
   public Digest compute(Path file) throws IOException {
-    long fileSize = file.getFileSize();
-    byte[] digest = DigestUtils.getDigestOrFail(file, fileSize);
-    return buildDigest(digest, fileSize);
+    return compute(file, file.getFileSize());
+  }
+
+  public Digest compute(Path file, long fileSize) throws IOException {
+    return buildDigest(DigestUtils.getDigestOrFail(file, fileSize), fileSize);
   }
 
   public Digest compute(VirtualActionInput input) throws IOException {