Remote: Do not upload empty output to remote cache.

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

@@ -132,6 +132,32 @@ public ActionResult downloadActionResult(
     return getFromFuture(cacheProtocol.downloadActionResult(context, actionKey, inlineOutErr));
   }
 
+  /** Upload a local file to the remote cache. */
+  public ListenableFuture<Void> uploadFile(
+      RemoteActionExecutionContext context,
+      Digest digest,
+      Path file
+  ) {
+    if (digest.getSizeBytes() == 0) {
+      return COMPLETED_SUCCESS;
+    }
+
+    return cacheProtocol.uploadFile(context, digest, file);
+  }
+
+  /** Upload sequence of bytes to the remote cache. */
+  public ListenableFuture<Void> uploadBlob(
+      RemoteActionExecutionContext context,
+      Digest digest,
+      ByteString data
+  ) {
+    if (digest.getSizeBytes() == 0) {
+      return COMPLETED_SUCCESS;
+    }
+
+    return cacheProtocol.uploadBlob(context, digest, data);
+  }
+
   /**
    * Upload the result of a locally executed action to the remote cache.
    *
@@ -212,14 +238,14 @@ private void uploadOutputs(
     for (Digest digest : digestsToUpload) {
       Path file = digestToFile.get(digest);
       if (file != null) {
-        uploads.add(cacheProtocol.uploadFile(context, digest, file));
+        uploads.add(uploadFile(context, digest, file));
       } else {
         ByteString blob = digestToBlobs.get(digest);
         if (blob == null) {
           String message = "FindMissingBlobs call returned an unknown digest: " + digest;
           throw new IOException(message);
         }
-        uploads.add(cacheProtocol.uploadBlob(context, digest, blob));
+        uploads.add(uploadBlob(context, digest, blob));
       }
     }
 
@@ -588,7 +614,15 @@ public void onFailure(Throwable t) {
     return outerF;
   }
 
-  private List<ListenableFuture<FileMetadata>> downloadOutErr(
+  private ListenableFuture<Void> downloadBlob(RemoteActionExecutionContext context, Digest digest, OutputStream out) {
+    if (digest.getSizeBytes() == 0) {
+      return COMPLETED_SUCCESS;
+    }
+
+    return cacheProtocol.downloadBlob(context, digest, out);
+  }
+
+  public List<ListenableFuture<FileMetadata>> downloadOutErr(
       RemoteActionExecutionContext context, ActionResult result, OutErr outErr) {
     List<ListenableFuture<FileMetadata>> downloads = new ArrayList<>();
     if (!result.getStdoutRaw().isEmpty()) {
@@ -601,7 +635,7 @@ private List<ListenableFuture<FileMetadata>> downloadOutErr(
     } else if (result.hasStdoutDigest()) {
       downloads.add(
           Futures.transform(
-              cacheProtocol.downloadBlob(
+              downloadBlob(
                   context, result.getStdoutDigest(), outErr.getOutputStream()),
               (d) -> null,
               directExecutor()));
@@ -616,7 +650,7 @@ private List<ListenableFuture<FileMetadata>> downloadOutErr(
     } else if (result.hasStderrDigest()) {
       downloads.add(
           Futures.transform(
-              cacheProtocol.downloadBlob(
+              downloadBlob(
                   context, result.getStderrDigest(), outErr.getErrorStream()),
               (d) -> null,
               directExecutor()));

src/test/java/com/google/devtools/build/lib/remote/RemoteCacheTests.java

@@ -1304,6 +1304,27 @@ public void testDownloadEmptyBlobAndFile() throws Exception {
     assertThat(file.getFileSize()).isEqualTo(0);
   }
 
+  @Test
+  public void testDownloadEmptyOutErr() throws Exception {
+    // Test that downloading empty stdout/stderr does not try to perform a download.
+
+    InMemoryRemoteCache remoteCache = newRemoteCache();
+    Digest emptyDigest = digestUtil.compute(new byte[0]);
+    ActionResult.Builder result = ActionResult.newBuilder();
+    result.setStdoutDigest(emptyDigest);
+    result.setStderrDigest(emptyDigest);
+
+    RemoteCache.waitForBulkTransfer(
+        remoteCache.downloadOutErr(
+            context,
+            result.build(),
+            new FileOutErr(execRoot.getRelative("stdout"), execRoot.getRelative("stderr"))),
+        true);
+
+    assertThat(remoteCache.getNumSuccessfulDownloads()).isEqualTo(0);
+    assertThat(remoteCache.getNumFailedDownloads()).isEqualTo(0);
+  }
+
   @Test
   public void testDownloadFileWithSymlinkTemplate() throws Exception {
     // Test that when a symlink template is provided, we don't actually download files to disk.
@@ -1547,6 +1568,50 @@ public void testUploadDirectory() throws Exception {
     assertThat(remoteCache.findMissingDigests(context, toQuery)).isEmpty();
   }
 
+  @Test
+  public void testUploadEmptyBlobAndFile() throws Exception {
+    // Test that uploading an empty BLOB/file does not try to perform an upload.
+    InMemoryRemoteCache remoteCache = newRemoteCache();
+    Digest emptyDigest = fakeFileCache.createScratchInput(ActionInputHelper.fromPath("file"), "");
+    Path file = execRoot.getRelative("file");
+
+    Utils.getFromFuture(remoteCache.uploadBlob(context, emptyDigest, ByteString.EMPTY));
+    assertThat(remoteCache.findMissingDigests(context, ImmutableSet.of(emptyDigest)))
+        .containsExactly(emptyDigest);
+
+    Utils.getFromFuture(remoteCache.uploadFile(context, emptyDigest, file));
+    assertThat(remoteCache.findMissingDigests(context, ImmutableSet.of(emptyDigest)))
+        .containsExactly(emptyDigest);
+  }
+
+  @Test
+  public void testUploadEmptyOutputs() throws Exception {
+    // Test that uploading an empty output does not try to perform an upload.
+
+    // arrange
+    Digest emptyDigest =
+        fakeFileCache.createScratchInput(ActionInputHelper.fromPath("bar/test/wobble"), "");
+    Path file = execRoot.getRelative("bar/test/wobble");
+    InMemoryRemoteCache remoteCache = newRemoteCache();
+    Action action = Action.getDefaultInstance();
+    ActionKey actionDigest = digestUtil.computeActionKey(action);
+    Command cmd = Command.getDefaultInstance();
+
+    // act
+    remoteCache.upload(
+        context,
+        remotePathResolver,
+        actionDigest,
+        action,
+        cmd,
+        ImmutableList.of(file),
+        new FileOutErr(execRoot.getRelative("stdout"), execRoot.getRelative("stderr")));
+
+    // assert
+    assertThat(remoteCache.findMissingDigests(context, ImmutableSet.of(emptyDigest)))
+        .containsExactly(emptyDigest);
+  }
+
   @Test
   public void testUploadEmptyDirectory() throws Exception {
     // Test that uploading an empty directory works.