fix: remove misleading error messages on successful syncs (#3619)

See: https://github.com/project-zot/zot/issues/3560#issuecomment-3594856118
What happens is:
- syncRef skips the image ("skipping image because it's already synced")
- syncReferrers doesn't sync anything
- CommitAll is still called even though nothing was synced
- The temp directory exists but is empty (no index.json, no blobs)
- CommitAll fails because index.json is missing

Let's ensure we properly check for errors, and skip the log messages if some of the cases.

Signed-off-by: Andrei Aaron <andreifdaaron@gmail.com>

pkg/extensions/sync/destination.go

@@ -92,13 +92,36 @@ func (registry *DestinationRegistry) CommitAll(repo string, imageReference ref.R
 
 	defer os.RemoveAll(tempImageStore.RootDir())
 
-	registry.log.Info().Str("syncTempDir", path.Join(tempImageStore.RootDir(), repo)).Str("repository", repo).
+	repoDir := path.Join(tempImageStore.RootDir(), repo)
+
+	// Check if directory is empty before attempting to get index
+	entries, err := os.ReadDir(repoDir)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			// Directory doesn't exist - nothing to commit (image was skipped)
+			return nil
+		}
+
+		// Other directory read errors should be reported
+		registry.log.Error().Str("errorType", common.TypeOf(err)).
+			Err(err).Str("dir", repoDir).Str("repo", repo).
+			Msg("failed to read temp sync dir")
+
+		return err
+	}
+
+	// If directory is empty, nothing was synced (e.g., image was skipped)
+	if len(entries) == 0 {
+		return nil
+	}
+
+	registry.log.Info().Str("syncTempDir", repoDir).Str("repository", repo).
 		Msg("pushing synced local image to local registry")
 
 	index, err := storageCommon.GetIndex(tempImageStore, repo, registry.log)
 	if err != nil {
 		registry.log.Error().Str("errorType", common.TypeOf(err)).
-			Err(err).Str("dir", path.Join(tempImageStore.RootDir(), repo)).Str("repo", repo).
+			Err(err).Str("dir", repoDir).Str("repo", repo).
 			Msg("failed to get repo index from temp sync dir")
 
 		return err

pkg/extensions/sync/sync_internal_test.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"path"
 	"strings"
 	"testing"
 	"time"
@@ -995,6 +996,87 @@ func TestDestinationRegistry(t *testing.T) {
 				So(err, ShouldBeNil)
 			})
 		})
+
+		Convey("CommitAll with non-existent directory", func() {
+			// Create a registry and get an image reference
+			registry := NewDestinationRegistry(storeController, storeController, nil, log)
+			imageReference, err := registry.GetImageReference("nonexistent-repo", "1.0")
+			So(err, ShouldBeNil)
+
+			// Remove the directory to simulate it not existing
+			tempImageStore := getImageStoreFromImageReference("nonexistent-repo", imageReference, log)
+			repoDir := path.Join(tempImageStore.RootDir(), "nonexistent-repo")
+			err = os.RemoveAll(repoDir)
+			So(err, ShouldBeNil)
+
+			// CommitAll should return nil when directory doesn't exist (image was skipped)
+			err = registry.CommitAll("nonexistent-repo", imageReference)
+			So(err, ShouldBeNil)
+		})
+
+		Convey("CommitAll with empty directory", func() {
+			// Create a registry and get an image reference
+			registry := NewDestinationRegistry(storeController, storeController, nil, log)
+			imageReference, err := registry.GetImageReference("empty-repo", "1.0")
+			So(err, ShouldBeNil)
+
+			// Create an empty directory (no index.json, no blobs)
+			tempImageStore := getImageStoreFromImageReference("empty-repo", imageReference, log)
+			repoDir := path.Join(tempImageStore.RootDir(), "empty-repo")
+			err = os.MkdirAll(repoDir, 0o755)
+			So(err, ShouldBeNil)
+
+			// CommitAll should return nil when directory is empty (image was skipped)
+			err = registry.CommitAll("empty-repo", imageReference)
+			So(err, ShouldBeNil)
+		})
+
+		Convey("CommitAll with directory containing files but no index.json", func() {
+			// Create a registry and get an image reference
+			registry := NewDestinationRegistry(storeController, storeController, nil, log)
+			imageReference, err := registry.GetImageReference("inconsistent-repo", "1.0")
+			So(err, ShouldBeNil)
+
+			// Create a directory with some files but no index.json (inconsistent state)
+			tempImageStore := getImageStoreFromImageReference("inconsistent-repo", imageReference, log)
+			repoDir := path.Join(tempImageStore.RootDir(), "inconsistent-repo")
+			err = os.MkdirAll(repoDir, 0o755)
+			So(err, ShouldBeNil)
+
+			// Create a dummy file to make directory non-empty
+			dummyFile := path.Join(repoDir, "dummy.txt")
+			err = os.WriteFile(dummyFile, []byte("dummy"), 0o644)
+			So(err, ShouldBeNil)
+
+			// CommitAll should return an error when directory is not empty but index.json is missing
+			err = registry.CommitAll("inconsistent-repo", imageReference)
+			So(err, ShouldNotBeNil)
+			So(errors.Is(err, zerr.ErrRepoNotFound), ShouldBeTrue)
+		})
+
+		Convey("CommitAll with ReadDir error (non-ErrNotExist)", func() {
+			// Create a registry and get an image reference
+			registry := NewDestinationRegistry(storeController, storeController, nil, log)
+			imageReference, err := registry.GetImageReference("error-repo", "1.0")
+			So(err, ShouldBeNil)
+
+			// Get the repo directory path
+			tempImageStore := getImageStoreFromImageReference("error-repo", imageReference, log)
+			repoDir := path.Join(tempImageStore.RootDir(), "error-repo")
+
+			// Create a file at the repoDir path instead of a directory
+			// This will cause os.ReadDir to fail with an error that is NOT os.ErrNotExist
+			err = os.MkdirAll(path.Dir(repoDir), 0o755)
+			So(err, ShouldBeNil)
+
+			err = os.WriteFile(repoDir, []byte("not a directory"), 0o644)
+			So(err, ShouldBeNil)
+
+			// CommitAll should return the ReadDir error (not ErrNotExist)
+			err = registry.CommitAll("error-repo", imageReference)
+			So(err, ShouldNotBeNil)
+			So(errors.Is(err, os.ErrNotExist), ShouldBeFalse)
+		})
 	})
 }