Refactor the FileSystem API to allow for different hash functions.

Refactor the FileSystem class to include the hash function as an
instance field. This allows us to have a different hash function
per FileSystem and removes technical debt, as currently that's
somewhat accomplished by a horrible hack that has a static method
to set the hash function for all FileSystem instances.

The FileSystem's default hash function remains MD5.

RELNOTES: None
PiperOrigin-RevId: 177479772

9 files changed, 136 insertions, 77 deletions

diff --git a/src/test/java/com/google/devtools/build/lib/remote/ByteStreamUploaderTest.java b/src/test/java/com/google/devtools/build/lib/remote/ByteStreamUploaderTest.java
index e809b74b7e..0b70f36623 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/ByteStreamUploaderTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/ByteStreamUploaderTest.java
@@ -26,6 +26,7 @@ import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.ListeningScheduledExecutorService;
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.devtools.build.lib.analysis.BlazeVersionInfo;
+import com.google.devtools.build.lib.vfs.FileSystem.HashFunction;
 import com.google.devtools.remoteexecution.v1test.Digest;
 import com.google.devtools.remoteexecution.v1test.RequestMetadata;
 import com.google.protobuf.ByteString;
@@ -75,6 +76,8 @@ import org.mockito.MockitoAnnotations;
 @RunWith(JUnit4.class)
 public class ByteStreamUploaderTest {
 
+  private static final DigestUtil DIGEST_UTIL = new DigestUtil(HashFunction.SHA256);
+
   private static final int CHUNK_SIZE = 10;
   private static final String INSTANCE_NAME = "foo";
 
@@ -99,7 +102,7 @@ public class ByteStreamUploaderTest {
     channel = InProcessChannelBuilder.forName(serverName).build();
     withEmptyMetadata =
         TracingMetadataUtils.contextWithMetadata(
-            "none", "none", Digests.unsafeActionKeyFromDigest(Digest.getDefaultInstance()));
+            "none", "none", DIGEST_UTIL.asActionKey(Digest.getDefaultInstance()));
     // Needs to be repeated in every test that uses the timeout setting, since the tests run
     // on different threads than the setUp.
     withEmptyMetadata.attach();
@@ -121,7 +124,7 @@ public class ByteStreamUploaderTest {
     byte[] blob = new byte[CHUNK_SIZE * 2 + 1];
     new Random().nextBytes(blob);
 
-    Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+    Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
 
     serviceRegistry.addService(new ByteStreamImplBase() {
           @Override
@@ -195,7 +198,7 @@ public class ByteStreamUploaderTest {
       int blobSize = rand.nextInt(CHUNK_SIZE * 10) + CHUNK_SIZE;
       byte[] blob = new byte[blobSize];
       rand.nextBytes(blob);
-      Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+      Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
       builders.add(chunker);
       blobsByHash.put(chunker.digest().getHash(), blob);
     }
@@ -281,7 +284,7 @@ public class ByteStreamUploaderTest {
     List<Chunker> builders = new ArrayList<>(toUpload.size());
     Map<String, Integer> uploadsFailed = new HashMap<>();
     for (String s : toUpload) {
-      Chunker chunker = new Chunker(s.getBytes(UTF_8), /* chunkSize=*/ 3);
+      Chunker chunker = new Chunker(s.getBytes(UTF_8), /* chunkSize=*/ 3, DIGEST_UTIL);
       builders.add(chunker);
       uploadsFailed.put(chunker.digest().getHash(), 0);
     }
@@ -342,7 +345,7 @@ public class ByteStreamUploaderTest {
     for (Chunker chunker : builders) {
       Context ctx =
           TracingMetadataUtils.contextWithMetadata(
-              "build-req-id", "command-id", Digests.unsafeActionKeyFromDigest(chunker.digest()));
+              "build-req-id", "command-id", DIGEST_UTIL.asActionKey(chunker.digest()));
       ctx.call(
           () -> {
             uploads.add(uploader.uploadBlobAsync(chunker));
@@ -367,7 +370,7 @@ public class ByteStreamUploaderTest {
         new ByteStreamUploader(INSTANCE_NAME, channel, null, 3, retrier, retryService);
 
     byte[] blob = new byte[CHUNK_SIZE * 10];
-    Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+    Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
 
     AtomicInteger numWriteCalls = new AtomicInteger();
     CountDownLatch blocker = new CountDownLatch(1);
@@ -426,7 +429,7 @@ public class ByteStreamUploaderTest {
         new ByteStreamUploader(INSTANCE_NAME, channel, null, 3, retrier, retryService);
 
     byte[] blob = new byte[CHUNK_SIZE];
-    Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+    Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
 
     serviceRegistry.addService(new ByteStreamImplBase() {
       @Override
@@ -477,10 +480,10 @@ public class ByteStreamUploaderTest {
     serviceRegistry.addService(service);
 
     byte[] blob1 = new byte[CHUNK_SIZE];
-    Chunker chunker1 = new Chunker(blob1, CHUNK_SIZE);
+    Chunker chunker1 = new Chunker(blob1, CHUNK_SIZE, DIGEST_UTIL);
 
     byte[] blob2 = new byte[CHUNK_SIZE + 1];
-    Chunker chunker2 = new Chunker(blob2, CHUNK_SIZE);
+    Chunker chunker2 = new Chunker(blob2, CHUNK_SIZE, DIGEST_UTIL);
 
     ListenableFuture<Void> f1 = uploader.uploadBlobAsync(chunker1);
     ListenableFuture<Void> f2 = uploader.uploadBlobAsync(chunker2);
@@ -519,7 +522,7 @@ public class ByteStreamUploaderTest {
     assertThat(retryService.isShutdown()).isTrue();
 
     byte[] blob = new byte[1];
-    Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+    Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
     try {
       uploader.uploadBlob(chunker);
       fail("Should have thrown an exception.");
@@ -560,7 +563,7 @@ public class ByteStreamUploaderTest {
     });
 
     byte[] blob = new byte[1];
-    Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+    Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
 
     uploader.uploadBlob(chunker);
   }
@@ -585,7 +588,7 @@ public class ByteStreamUploaderTest {
     });
 
     byte[] blob = new byte[1];
-    Chunker chunker = new Chunker(blob, CHUNK_SIZE);
+    Chunker chunker = new Chunker(blob, CHUNK_SIZE, DIGEST_UTIL);
 
     try {
       uploader.uploadBlob(chunker);
diff --git a/src/test/java/com/google/devtools/build/lib/remote/CasPathConverterTest.java b/src/test/java/com/google/devtools/build/lib/remote/CasPathConverterTest.java
index 5ba4ef0435..493041b5dd 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/CasPathConverterTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/CasPathConverterTest.java
@@ -17,6 +17,7 @@ import static com.google.common.truth.Truth.assertThat;
 
 import com.google.devtools.build.lib.remote.RemoteModule.CasPathConverter;
 import com.google.devtools.build.lib.vfs.FileSystem;
+import com.google.devtools.build.lib.vfs.FileSystem.HashFunction;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.inmemoryfs.InMemoryFileSystem;
@@ -34,12 +35,20 @@ public class CasPathConverterTest {
 
   @Test
   public void noOptionsShouldntCrash() {
+    converter.digestUtil = new DigestUtil(HashFunction.SHA256);
+    assertThat(converter.apply(fs.getPath("/foo"))).isNull();
+  }
+
+  @Test
+  public void noDigestUtilShouldntCrash() {
+    converter.options = Options.getDefaults(RemoteOptions.class);
     assertThat(converter.apply(fs.getPath("/foo"))).isNull();
   }
 
   @Test
   public void disabledRemote() {
     converter.options = Options.getDefaults(RemoteOptions.class);
+    converter.digestUtil = new DigestUtil(HashFunction.SHA256);
     assertThat(converter.apply(fs.getPath("/foo"))).isNull();
   }
 
@@ -48,6 +57,7 @@ public class CasPathConverterTest {
     OptionsParser parser = OptionsParser.newOptionsParser(RemoteOptions.class);
     parser.parse("--remote_cache=machine");
     converter.options = parser.getOptions(RemoteOptions.class);
+    converter.digestUtil = new DigestUtil(HashFunction.SHA256);
     Path path = fs.getPath("/foo");
     FileSystemUtils.writeContentAsLatin1(path, "foobar");
     assertThat(converter.apply(fs.getPath("/foo")))
@@ -59,6 +69,7 @@ public class CasPathConverterTest {
     OptionsParser parser = OptionsParser.newOptionsParser(RemoteOptions.class);
     parser.parse("--remote_cache=machine", "--remote_instance_name=projects/bazel");
     converter.options = parser.getOptions(RemoteOptions.class);
+    converter.digestUtil = new DigestUtil(HashFunction.SHA256);
     Path path = fs.getPath("/foo");
     FileSystemUtils.writeContentAsLatin1(path, "foobar");
     assertThat(converter.apply(fs.getPath("/foo")))
diff --git a/src/test/java/com/google/devtools/build/lib/remote/ChunkerTest.java b/src/test/java/com/google/devtools/build/lib/remote/ChunkerTest.java
index fd0cbade33..ed1ccf6ed2 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/ChunkerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/ChunkerTest.java
@@ -17,6 +17,7 @@ import static com.google.common.truth.Truth.assertThat;
 import static junit.framework.TestCase.fail;
 
 import com.google.devtools.build.lib.remote.Chunker.Chunk;
+import com.google.devtools.build.lib.vfs.FileSystem.HashFunction;
 import com.google.devtools.remoteexecution.v1test.Digest;
 import com.google.protobuf.ByteString;
 import java.io.ByteArrayInputStream;
@@ -36,14 +37,16 @@ import org.mockito.Mockito;
 @RunWith(JUnit4.class)
 public class ChunkerTest {
 
+  private final DigestUtil digestUtil = new DigestUtil(HashFunction.SHA256);
+
   @Test
   public void chunkingShouldWork() throws IOException {
     Random rand = new Random();
     byte[] expectedData = new byte[21];
     rand.nextBytes(expectedData);
-    Digest expectedDigest = Digests.computeDigest(expectedData);
+    Digest expectedDigest = digestUtil.compute(expectedData);
 
-    Chunker chunker = new Chunker(expectedData, 10);
+    Chunker chunker = new Chunker(expectedData, 10, digestUtil);
 
     ByteArrayOutputStream actualData = new ByteArrayOutputStream();
 
@@ -76,7 +79,7 @@ public class ChunkerTest {
   @Test
   public void nextShouldThrowIfNoMoreData() throws IOException {
     byte[] data = new byte[10];
-    Chunker chunker = new Chunker(data, 10);
+    Chunker chunker = new Chunker(data, 10, digestUtil);
 
     assertThat(chunker.hasNext()).isTrue();
     assertThat(chunker.next()).isNotNull();
@@ -94,7 +97,7 @@ public class ChunkerTest {
   @Test
   public void emptyData() throws Exception {
     byte[] data = new byte[0];
-    Chunker chunker = new Chunker(data);
+    Chunker chunker = new Chunker(data, digestUtil);
 
     assertThat(chunker.hasNext()).isTrue();
 
@@ -117,7 +120,7 @@ public class ChunkerTest {
   @Test
   public void reset() throws Exception {
     byte[] data = new byte[]{1, 2, 3};
-    Chunker chunker = new Chunker(data, 1);
+    Chunker chunker = new Chunker(data, 1, digestUtil);
 
     assertNextEquals(chunker, (byte) 1);
     assertNextEquals(chunker, (byte) 2);
@@ -144,9 +147,9 @@ public class ChunkerTest {
       in.set(Mockito.spy(new ByteArrayInputStream(data)));
       return in.get();
     };
-    Digest digest = Digests.computeDigest(data);
+    Digest digest = digestUtil.compute(data);
 
-    Chunker chunker = new Chunker(supplier, digest, 1);
+    Chunker chunker = new Chunker(supplier, digest, 1, digestUtil);
     assertThat(in.get()).isNull();
     assertNextEquals(chunker, (byte) 1);
     Mockito.verify(in.get(), Mockito.never()).close();
diff --git a/src/test/java/com/google/devtools/build/lib/remote/FakeActionInputFileCache.java b/src/test/java/com/google/devtools/build/lib/remote/FakeActionInputFileCache.java
index 565e5e927d..3f509684f2 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/FakeActionInputFileCache.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/FakeActionInputFileCache.java
@@ -32,9 +32,11 @@ import javax.annotation.Nullable;
 final class FakeActionInputFileCache implements ActionInputFileCache {
   private final Path execRoot;
   private final BiMap<ActionInput, String> cas = HashBiMap.create();
+  private final DigestUtil digestUtil;
 
   FakeActionInputFileCache(Path execRoot) {
     this.execRoot = execRoot;
+    this.digestUtil = new DigestUtil(execRoot.getFileSystem().getDigestFunction());
   }
 
   @Override
@@ -70,7 +72,7 @@ final class FakeActionInputFileCache implements ActionInputFileCache {
     Path inputFile = execRoot.getRelative(input.getExecPath());
     FileSystemUtils.createDirectoryAndParents(inputFile.getParentDirectory());
     FileSystemUtils.writeContentAsLatin1(inputFile, content);
-    Digest digest = Digests.computeDigest(inputFile);
+    Digest digest = digestUtil.compute(inputFile);
     setDigest(input, digest.getHash());
     return digest;
   }
diff --git a/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteCacheTest.java b/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteCacheTest.java
index 5cc03be824..5664ea37cc 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteCacheTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteCacheTest.java
@@ -29,7 +29,8 @@ import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.actions.ActionInputHelper;
 import com.google.devtools.build.lib.authandtls.AuthAndTLSOptions;
 import com.google.devtools.build.lib.authandtls.GrpcUtils;
-import com.google.devtools.build.lib.remote.Digests.ActionKey;
+import com.google.devtools.build.lib.clock.JavaClock;
+import com.google.devtools.build.lib.remote.DigestUtil.ActionKey;
 import com.google.devtools.build.lib.testutil.Scratch;
 import com.google.devtools.build.lib.util.io.FileOutErr;
 import com.google.devtools.build.lib.vfs.FileSystem;
@@ -75,6 +76,9 @@ import org.mockito.stubbing.Answer;
 /** Tests for {@link GrpcRemoteCache}. */
 @RunWith(JUnit4.class)
 public class GrpcRemoteCacheTest {
+
+  private static final DigestUtil DIGEST_UTIL = new DigestUtil(HashFunction.SHA256);
+
   private FileSystem fs;
   private Path execRoot;
   private FileOutErr outErr;
@@ -85,7 +89,6 @@ public class GrpcRemoteCacheTest {
 
   @Before
   public final void setUp() throws Exception {
-    FileSystem.setDigestFunctionForTesting(HashFunction.SHA1);
     // Use a mutable service registry for later registering the service impl for each test case.
     fakeServer =
         InProcessServerBuilder.forName(fakeServerName)
@@ -94,7 +97,7 @@ public class GrpcRemoteCacheTest {
             .build()
             .start();
     Chunker.setDefaultChunkSizeForTesting(1000); // Enough for everything to be one chunk.
-    fs = new InMemoryFileSystem();
+    fs = new InMemoryFileSystem(new JavaClock(), HashFunction.SHA256);
     execRoot = fs.getPath("/exec/root");
     FileSystemUtils.createDirectoryAndParents(execRoot);
     fakeFileCache = new FakeActionInputFileCache(execRoot);
@@ -106,7 +109,7 @@ public class GrpcRemoteCacheTest {
     outErr = new FileOutErr(stdout, stderr);
     Context withEmptyMetadata =
         TracingMetadataUtils.contextWithMetadata(
-            "none", "none", Digests.unsafeActionKeyFromDigest(Digest.getDefaultInstance()));
+            "none", "none", DIGEST_UTIL.asActionKey(Digest.getDefaultInstance()));
     withEmptyMetadata.attach();
   }
 
@@ -156,13 +159,14 @@ public class GrpcRemoteCacheTest {
             ImmutableList.of(new CallCredentialsInterceptor(creds))),
         creds,
         remoteOptions,
-        retrier);
+        retrier,
+        DIGEST_UTIL);
   }
 
   @Test
   public void testDownloadEmptyBlob() throws Exception {
     GrpcRemoteCache client = newClient();
-    Digest emptyDigest = Digests.computeDigest(new byte[0]);
+    Digest emptyDigest = DIGEST_UTIL.compute(new byte[0]);
     // Will not call the mock Bytestream interface at all.
     assertThat(client.downloadBlob(emptyDigest)).isEmpty();
   }
@@ -170,7 +174,7 @@ public class GrpcRemoteCacheTest {
   @Test
   public void testDownloadBlobSingleChunk() throws Exception {
     final GrpcRemoteCache client = newClient();
-    final Digest digest = Digests.computeDigestUtf8("abcdefg");
+    final Digest digest = DIGEST_UTIL.computeAsUtf8("abcdefg");
     serviceRegistry.addService(
         new ByteStreamImplBase() {
           @Override
@@ -187,7 +191,7 @@ public class GrpcRemoteCacheTest {
   @Test
   public void testDownloadBlobMultipleChunks() throws Exception {
     final GrpcRemoteCache client = newClient();
-    final Digest digest = Digests.computeDigestUtf8("abcdefg");
+    final Digest digest = DIGEST_UTIL.computeAsUtf8("abcdefg");
     serviceRegistry.addService(
         new ByteStreamImplBase() {
           @Override
@@ -208,9 +212,9 @@ public class GrpcRemoteCacheTest {
   @Test
   public void testDownloadAllResults() throws Exception {
     GrpcRemoteCache client = newClient();
-    Digest fooDigest = Digests.computeDigestUtf8("foo-contents");
-    Digest barDigest = Digests.computeDigestUtf8("bar-contents");
-    Digest emptyDigest = Digests.computeDigest(new byte[0]);
+    Digest fooDigest = DIGEST_UTIL.computeAsUtf8("foo-contents");
+    Digest barDigest = DIGEST_UTIL.computeAsUtf8("bar-contents");
+    Digest emptyDigest = DIGEST_UTIL.compute(new byte[0]);
     serviceRegistry.addService(
         new FakeImmutableCacheByteStreamImpl(fooDigest, "foo-contents", barDigest, "bar-contents"));
 
@@ -219,16 +223,16 @@ public class GrpcRemoteCacheTest {
     result.addOutputFilesBuilder().setPath("b/empty").setDigest(emptyDigest);
     result.addOutputFilesBuilder().setPath("a/bar").setDigest(barDigest).setIsExecutable(true);
     client.download(result.build(), execRoot, null);
-    assertThat(Digests.computeDigest(execRoot.getRelative("a/foo"))).isEqualTo(fooDigest);
-    assertThat(Digests.computeDigest(execRoot.getRelative("b/empty"))).isEqualTo(emptyDigest);
-    assertThat(Digests.computeDigest(execRoot.getRelative("a/bar"))).isEqualTo(barDigest);
+    assertThat(DIGEST_UTIL.compute(execRoot.getRelative("a/foo"))).isEqualTo(fooDigest);
+    assertThat(DIGEST_UTIL.compute(execRoot.getRelative("b/empty"))).isEqualTo(emptyDigest);
+    assertThat(DIGEST_UTIL.compute(execRoot.getRelative("a/bar"))).isEqualTo(barDigest);
     assertThat(execRoot.getRelative("a/bar").isExecutable()).isTrue();
   }
 
   @Test
   public void testUploadBlobCacheHitWithRetries() throws Exception {
     final GrpcRemoteCache client = newClient();
-    final Digest digest = Digests.computeDigestUtf8("abcdefg");
+    final Digest digest = DIGEST_UTIL.computeAsUtf8("abcdefg");
     serviceRegistry.addService(
         new ContentAddressableStorageImplBase() {
           private int numErrors = 4;
@@ -251,7 +255,7 @@ public class GrpcRemoteCacheTest {
   @Test
   public void testUploadBlobSingleChunk() throws Exception {
     final GrpcRemoteCache client = newClient();
-    final Digest digest = Digests.computeDigestUtf8("abcdefg");
+    final Digest digest = DIGEST_UTIL.computeAsUtf8("abcdefg");
     serviceRegistry.addService(
         new ContentAddressableStorageImplBase() {
           @Override
@@ -302,7 +306,7 @@ public class GrpcRemoteCacheTest {
       this.responseObserver = responseObserver;
       this.contents = contents;
       try {
-        chunker = new Chunker(contents.getBytes(UTF_8), chunkSizeBytes);
+        chunker = new Chunker(contents.getBytes(UTF_8), chunkSizeBytes, DIGEST_UTIL);
       } catch (IOException e) {
         fail("An error occurred:" + e);
       }
@@ -357,7 +361,7 @@ public class GrpcRemoteCacheTest {
 
   @Test
   public void testUploadBlobMultipleChunks() throws Exception {
-    final Digest digest = Digests.computeDigestUtf8("abcdef");
+    final Digest digest = DIGEST_UTIL.computeAsUtf8("abcdef");
     serviceRegistry.addService(
         new ContentAddressableStorageImplBase() {
           @Override
@@ -446,7 +450,7 @@ public class GrpcRemoteCacheTest {
           }
         });
 
-    ActionKey emptyKey = Digests.computeActionKey(Action.getDefaultInstance());
+    ActionKey emptyKey = DIGEST_UTIL.computeActionKey(Action.getDefaultInstance());
     Path fooFile = execRoot.getRelative("a/foo");
     Path barFile = execRoot.getRelative("bar");
     client.upload(emptyKey, execRoot, ImmutableList.<Path>of(fooFile, barFile), outErr, false);
@@ -464,7 +468,7 @@ public class GrpcRemoteCacheTest {
     final Path fooFile = execRoot.getRelative("a/foo");
     final Path barFile = execRoot.getRelative("bar");
     final Path bazFile = execRoot.getRelative("baz");
-    ActionKey actionKey = Digests.unsafeActionKeyFromDigest(fooDigest); // Could be any key.
+    ActionKey actionKey = DIGEST_UTIL.asActionKey(fooDigest); // Could be any key.
     barFile.setExecutable(true);
     serviceRegistry.addService(
         new ContentAddressableStorageImplBase() {
@@ -576,7 +580,7 @@ public class GrpcRemoteCacheTest {
   @Test
   public void testGetCachedActionResultWithRetries() throws Exception {
     final GrpcRemoteCache client = newClient();
-    ActionKey actionKey = Digests.unsafeActionKeyFromDigest(Digests.computeDigestUtf8("key"));
+    ActionKey actionKey = DIGEST_UTIL.asActionKey(DIGEST_UTIL.computeAsUtf8("key"));
     serviceRegistry.addService(
         new ActionCacheImplBase() {
           private int numErrors = 4;
diff --git a/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java b/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java
index 35bd1950e3..2e06805539 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java
@@ -38,6 +38,7 @@ import com.google.devtools.build.lib.actions.SpawnResult;
 import com.google.devtools.build.lib.analysis.BlazeVersionInfo;
 import com.google.devtools.build.lib.authandtls.AuthAndTLSOptions;
 import com.google.devtools.build.lib.authandtls.GrpcUtils;
+import com.google.devtools.build.lib.clock.JavaClock;
 import com.google.devtools.build.lib.exec.SpawnExecException;
 import com.google.devtools.build.lib.exec.SpawnInputExpander;
 import com.google.devtools.build.lib.exec.SpawnRunner.ProgressStatus;
@@ -102,6 +103,9 @@ import org.mockito.stubbing.Answer;
 /** Tests for {@link RemoteSpawnRunner} in combination with {@link GrpcRemoteExecutor}. */
 @RunWith(JUnit4.class)
 public class GrpcRemoteExecutionClientTest {
+
+  private static final DigestUtil DIGEST_UTIL = new DigestUtil(HashFunction.SHA256);
+
   private static final ArtifactExpander SIMPLE_ARTIFACT_EXPANDER =
       new ArtifactExpander() {
         @Override
@@ -176,7 +180,6 @@ public class GrpcRemoteExecutionClientTest {
 
   @Before
   public final void setUp() throws Exception {
-    FileSystem.setDigestFunctionForTesting(HashFunction.SHA1);
     String fakeServerName = "fake server for " + getClass();
     // Use a mutable service registry for later registering the service impl for each test case.
     fakeServer =
@@ -187,7 +190,7 @@ public class GrpcRemoteExecutionClientTest {
             .start();
 
     Chunker.setDefaultChunkSizeForTesting(1000); // Enough for everything to be one chunk.
-    fs = new InMemoryFileSystem();
+    fs = new InMemoryFileSystem(new JavaClock(), HashFunction.SHA256);
     execRoot = fs.getPath("/exec/root");
     FileSystemUtils.createDirectoryAndParents(execRoot);
     fakeFileCache = new FakeActionInputFileCache(execRoot);
@@ -236,7 +239,7 @@ public class GrpcRemoteExecutionClientTest {
     CallCredentials creds =
         GrpcUtils.newCallCredentials(Options.getDefaults(AuthAndTLSOptions.class));
     GrpcRemoteCache remoteCache =
-        new GrpcRemoteCache(channel, creds, options, retrier);
+        new GrpcRemoteCache(channel, creds, options, retrier, DIGEST_UTIL);
     client =
         new RemoteSpawnRunner(
             execRoot,
@@ -247,7 +250,8 @@ public class GrpcRemoteExecutionClientTest {
             "build-req-id",
             "command-id",
             remoteCache,
-            executor);
+            executor,
+            DIGEST_UTIL);
     inputDigest = fakeFileCache.createScratchInput(simpleSpawn.getInputFiles().get(0), "xyz");
   }
 
@@ -277,8 +281,8 @@ public class GrpcRemoteExecutionClientTest {
 
   @Test
   public void cacheHitWithOutput() throws Exception {
-    final Digest stdOutDigest = Digests.computeDigestUtf8("stdout");
-    final Digest stdErrDigest = Digests.computeDigestUtf8("stderr");
+    final Digest stdOutDigest = DIGEST_UTIL.computeAsUtf8("stdout");
+    final Digest stdErrDigest = DIGEST_UTIL.computeAsUtf8("stderr");
     serviceRegistry.addService(
         new ActionCacheImplBase() {
           @Override
@@ -326,7 +330,7 @@ public class GrpcRemoteExecutionClientTest {
   }
 
   private Answer<StreamObserver<WriteRequest>> blobWriteAnswer(final byte[] data) {
-    final Digest digest = Digests.computeDigest(data);
+    final Digest digest = DIGEST_UTIL.compute(data);
     return new Answer<StreamObserver<WriteRequest>>() {
       @Override
       public StreamObserver<WriteRequest> answer(InvocationOnMock invocation) {
@@ -444,7 +448,7 @@ public class GrpcRemoteExecutionClientTest {
                     .setValue("value")
                     .build())
             .build();
-    final Digest cmdDigest = Digests.computeDigest(command);
+    final Digest cmdDigest = DIGEST_UTIL.compute(command);
     BindableService cas =
         new ContentAddressableStorageImplBase() {
           @Override
@@ -633,7 +637,7 @@ public class GrpcRemoteExecutionClientTest {
                     .setValue("value")
                     .build())
             .build();
-    final Digest cmdDigest = Digests.computeDigest(command);
+    final Digest cmdDigest = DIGEST_UTIL.compute(command);
     serviceRegistry.addService(
         new ContentAddressableStorageImplBase() {
           private int numErrors = 4;
@@ -738,7 +742,7 @@ public class GrpcRemoteExecutionClientTest {
             responseObserver.onError(Status.NOT_FOUND.asRuntimeException());
           }
         });
-    Digest stdOutDigest = Digests.computeDigestUtf8("bla");
+    Digest stdOutDigest = DIGEST_UTIL.computeAsUtf8("bla");
     final ActionResult actionResult =
         ActionResult.newBuilder().setStdoutDigest(stdOutDigest).build();
     serviceRegistry.addService(
@@ -788,7 +792,7 @@ public class GrpcRemoteExecutionClientTest {
 
   @Test
   public void remotelyReExecuteOrphanedCachedActions() throws Exception {
-    final Digest stdOutDigest = Digests.computeDigestUtf8("stdout");
+    final Digest stdOutDigest = DIGEST_UTIL.computeAsUtf8("stdout");
     final ActionResult actionResult =
         ActionResult.newBuilder().setStdoutDigest(stdOutDigest).build();
     serviceRegistry.addService(
@@ -858,7 +862,9 @@ public class GrpcRemoteExecutionClientTest {
       fail("Expected an exception");
     } catch (ExecException expected) {
       assertThat(expected).hasMessageThat().contains("Missing digest");
-      assertThat(expected).hasMessageThat().contains("476d9ec701e2de6a6c37ab5211117a7cb8333a27");
+      assertThat(expected)
+          .hasMessageThat()
+          .contains(DIGEST_UTIL.computeAsUtf8("stdout").toString());
     }
   }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java
index 3295df658c..7ac5cfa190 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java
@@ -33,6 +33,7 @@ import com.google.devtools.build.lib.actions.ResourceSet;
 import com.google.devtools.build.lib.actions.SimpleSpawn;
 import com.google.devtools.build.lib.actions.SpawnResult;
 import com.google.devtools.build.lib.actions.SpawnResult.Status;
+import com.google.devtools.build.lib.clock.JavaClock;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.events.EventKind;
 import com.google.devtools.build.lib.events.Reporter;
@@ -42,10 +43,11 @@ import com.google.devtools.build.lib.exec.SpawnInputExpander;
 import com.google.devtools.build.lib.exec.SpawnRunner.ProgressStatus;
 import com.google.devtools.build.lib.exec.SpawnRunner.SpawnExecutionPolicy;
 import com.google.devtools.build.lib.exec.util.FakeOwner;
-import com.google.devtools.build.lib.remote.Digests.ActionKey;
+import com.google.devtools.build.lib.remote.DigestUtil.ActionKey;
 import com.google.devtools.build.lib.remote.TreeNodeRepository.TreeNode;
 import com.google.devtools.build.lib.util.io.FileOutErr;
 import com.google.devtools.build.lib.vfs.FileSystem;
+import com.google.devtools.build.lib.vfs.FileSystem.HashFunction;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -80,6 +82,7 @@ public class RemoteSpawnCacheTest {
       };
 
   private FileSystem fs;
+  private DigestUtil digestUtil;
   private Path execRoot;
   private SimpleSpawn simpleSpawn;
   private FakeActionInputFileCache fakeFileCache;
@@ -147,7 +150,8 @@ public class RemoteSpawnCacheTest {
   @Before
   public final void setUp() throws Exception {
     MockitoAnnotations.initMocks(this);
-    fs = new InMemoryFileSystem();
+    fs = new InMemoryFileSystem(new JavaClock(), HashFunction.SHA256);
+    digestUtil = new DigestUtil(HashFunction.SHA256);
     execRoot = fs.getPath("/exec/root");
     FileSystemUtils.createDirectoryAndParents(execRoot);
     fakeFileCache = new FakeActionInputFileCache(execRoot);
@@ -172,7 +176,14 @@ public class RemoteSpawnCacheTest {
     reporter.addHandler(eventHandler);
     cache =
         new RemoteSpawnCache(
-            execRoot, options, remoteCache, "build-req-id", "command-id", false, reporter);
+            execRoot,
+            options,
+            remoteCache,
+            "build-req-id",
+            "command-id",
+            false,
+            reporter,
+            digestUtil);
     fakeFileCache.createScratchInput(simpleSpawn.getInputFiles().get(0), "xyz");
   }
 
diff --git a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
index 5fec618cc8..31681906d8 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
@@ -38,6 +38,7 @@ import com.google.devtools.build.lib.actions.SimpleSpawn;
 import com.google.devtools.build.lib.actions.Spawn;
 import com.google.devtools.build.lib.actions.SpawnResult;
 import com.google.devtools.build.lib.actions.SpawnResult.Status;
+import com.google.devtools.build.lib.clock.JavaClock;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.events.EventKind;
 import com.google.devtools.build.lib.events.Reporter;
@@ -48,10 +49,11 @@ import com.google.devtools.build.lib.exec.SpawnRunner;
 import com.google.devtools.build.lib.exec.SpawnRunner.ProgressStatus;
 import com.google.devtools.build.lib.exec.SpawnRunner.SpawnExecutionPolicy;
 import com.google.devtools.build.lib.exec.util.FakeOwner;
-import com.google.devtools.build.lib.remote.Digests.ActionKey;
+import com.google.devtools.build.lib.remote.DigestUtil.ActionKey;
 import com.google.devtools.build.lib.util.ExitCode;
 import com.google.devtools.build.lib.util.io.FileOutErr;
 import com.google.devtools.build.lib.vfs.FileSystem;
+import com.google.devtools.build.lib.vfs.FileSystem.HashFunction;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -81,6 +83,7 @@ public class RemoteSpawnRunnerTest {
       ImmutableMap.of(ExecutionRequirements.NO_CACHE, "");
 
   private Path execRoot;
+  private DigestUtil digestUtil;
   private FakeActionInputFileCache fakeFileCache;
   private FileOutErr outErr;
 
@@ -96,8 +99,8 @@ public class RemoteSpawnRunnerTest {
   @Before
   public final void setUp() throws Exception {
     MockitoAnnotations.initMocks(this);
-
-    FileSystem fs = new InMemoryFileSystem();
+    digestUtil = new DigestUtil(HashFunction.SHA256);
+    FileSystem fs = new InMemoryFileSystem(new JavaClock(), HashFunction.SHA256);
     execRoot = fs.getPath("/exec/root");
     FileSystemUtils.createDirectoryAndParents(execRoot);
     fakeFileCache = new FakeActionInputFileCache(execRoot);
@@ -130,7 +133,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     ExecuteResponse succeeded = ExecuteResponse.newBuilder().setResult(
         ActionResult.newBuilder().setExitCode(0).build()).build();
@@ -186,7 +190,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            null);
+            null,
+            digestUtil);
 
     // Throw an IOException to trigger the local fallback.
     when(executor.executeRemotely(any(ExecuteRequest.class))).thenThrow(IOException.class);
@@ -237,7 +242,8 @@ public class RemoteSpawnRunnerTest {
                 "build-req-id",
                 "command-id",
                 cache,
-                null));
+                null,
+                digestUtil));
 
     Spawn spawn = newSimpleSpawn();
     SpawnExecutionPolicy policy = new FakeSpawnExecutionPolicy(spawn);
@@ -284,7 +290,8 @@ public class RemoteSpawnRunnerTest {
                 "build-req-id",
                 "command-id",
                 cache,
-                null));
+                null,
+                digestUtil));
 
     try {
       runner.exec(spawn, policy);
@@ -317,7 +324,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            null);
+            null,
+            digestUtil);
 
     Spawn spawn = newSimpleSpawn();
     SpawnExecutionPolicy policy = new FakeSpawnExecutionPolicy(spawn);
@@ -367,7 +375,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            null);
+            null,
+            digestUtil);
 
     Spawn spawn = newSimpleSpawn();
     SpawnExecutionPolicy policy = new FakeSpawnExecutionPolicy(spawn);
@@ -405,7 +414,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            null);
+            null,
+            digestUtil);
 
     Spawn spawn = newSimpleSpawn();
     SpawnExecutionPolicy policy = new FakeSpawnExecutionPolicy(spawn);
@@ -440,7 +450,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     when(cache.getCachedActionResult(any(ActionKey.class))).thenReturn(null);
     when(executor.executeRemotely(any(ExecuteRequest.class))).thenThrow(new IOException());
@@ -477,7 +488,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     ActionResult cachedResult = ActionResult.newBuilder().setExitCode(0).build();
     when(cache.getCachedActionResult(any(ActionKey.class))).thenReturn(cachedResult);
@@ -517,7 +529,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     ActionResult cachedResult = ActionResult.newBuilder().setExitCode(0).build();
     when(cache.getCachedActionResult(any(ActionKey.class))).thenReturn(null);
@@ -552,7 +565,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     ActionResult cachedResult = ActionResult.newBuilder().setExitCode(0).build();
     when(cache.getCachedActionResult(any(ActionKey.class))).thenReturn(null);
@@ -585,7 +599,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     ActionResult cachedResult = ActionResult.newBuilder().setExitCode(0).build();
     when(cache.getCachedActionResult(any(ActionKey.class))).thenReturn(null);
@@ -624,7 +639,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     when(cache.getCachedActionResult(any(ActionKey.class))).thenReturn(null);
     when(executor.executeRemotely(any(ExecuteRequest.class))).thenThrow(new IOException());
@@ -659,7 +675,8 @@ public class RemoteSpawnRunnerTest {
             "build-req-id",
             "command-id",
             cache,
-            executor);
+            executor,
+            digestUtil);
 
     when(cache.getCachedActionResult(any(ActionKey.class))).thenThrow(new IOException());
 
diff --git a/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java b/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java
index 94374f6364..9c0f43afc8 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java
@@ -21,13 +21,14 @@ import com.google.devtools.build.lib.actions.ActionInput;
 import com.google.devtools.build.lib.actions.ActionInputFileCache;
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.actions.Root;
+import com.google.devtools.build.lib.clock.BlazeClock;
 import com.google.devtools.build.lib.exec.SingleBuildFileCache;
 import com.google.devtools.build.lib.remote.TreeNodeRepository.TreeNode;
 import com.google.devtools.build.lib.testutil.Scratch;
-import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.FileSystem.HashFunction;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
+import com.google.devtools.build.lib.vfs.inmemoryfs.InMemoryFileSystem;
 import com.google.devtools.remoteexecution.v1test.Digest;
 import com.google.devtools.remoteexecution.v1test.Directory;
 import java.util.ArrayList;
@@ -42,13 +43,14 @@ import org.junit.runners.JUnit4;
 @RunWith(JUnit4.class)
 public class TreeNodeRepositoryTest {
   private Scratch scratch;
+  private DigestUtil digestUtil;
   private Root rootDir;
   private Path rootPath;
 
   @Before
   public final void setRootDir() throws Exception {
-    FileSystem.setDigestFunctionForTesting(HashFunction.SHA1);
-    scratch = new Scratch();
+    digestUtil = new DigestUtil(HashFunction.SHA256);
+    scratch = new Scratch(new InMemoryFileSystem(BlazeClock.instance(), HashFunction.SHA256));
     rootDir = Root.asDerivedRoot(scratch.dir("/exec/root"));
     rootPath = rootDir.getPath();
   }
@@ -56,7 +58,7 @@ public class TreeNodeRepositoryTest {
   private TreeNodeRepository createTestTreeNodeRepository() {
     ActionInputFileCache inputFileCache =
         new SingleBuildFileCache(rootPath.getPathString(), scratch.getFileSystem());
-    return new TreeNodeRepository(rootPath, inputFileCache);
+    return new TreeNodeRepository(rootPath, inputFileCache, digestUtil);
   }
 
   @Test