backend: skip hash calculation when the hashType is None - fixes #8518

When hashType is None `local` backend still runs expensive logic that reads the entire file content to produce an empty string.

backend/local/local.go

@@ -1090,6 +1090,10 @@ func (o *Object) Remote() string {
 
 // Hash returns the requested hash of a file as a lowercase hex string
 func (o *Object) Hash(ctx context.Context, r hash.Type) (string, error) {
+	if r == hash.None {
+		return "", nil
+	}
+
 	// Check that the underlying file hasn't changed
 	o.fs.objectMetaMu.RLock()
 	oldtime := o.modTime

backend/local/local_internal_test.go

@@ -204,6 +204,23 @@ func TestSymlinkError(t *testing.T) {
 	assert.Equal(t, errLinksAndCopyLinks, err)
 }
 
+func TestHashWithTypeNone(t *testing.T) {
+	ctx := context.Background()
+	r := fstest.NewRun(t)
+	const filePath = "file.txt"
+	r.WriteFile(filePath, "content", time.Now())
+	f := r.Flocal.(*Fs)
+
+	// Get the object
+	o, err := f.NewObject(ctx, filePath)
+	require.NoError(t, err)
+
+	// Test the hash is as we expect
+	h, err := o.Hash(ctx, hash.None)
+	require.Empty(t, h)
+	require.NoError(t, err)
+}
+
 // Test hashes on updating an object
 func TestHashOnUpdate(t *testing.T) {
 	ctx := context.Background()

cmd/serve/s3/utils.go

@@ -45,6 +45,10 @@ func getFileHashByte(node any, hashType hash.Type) []byte {
 }
 
 func getFileHash(node any, hashType hash.Type) string {
+	if hashType == hash.None {
+		return ""
+	}
+
 	var o fs.Object
 
 	switch b := node.(type) {