rework post processing of files

Use groups of worker to make it faster and ensure encrypted files are
checksumed if required.

hash.go

@@ -51,12 +51,12 @@ func computeChecksum(path string, h hash.Hash) (string, error) {
 	return string(h.Sum(nil)), nil
 }
 
-func checksumFile(path string, algo string) error {
+func checksumFile(path string, algo string) (string, error) {
 	var h hash.Hash
 
 	switch algo {
 	case "none":
-		return nil
+		return "", nil
 	case "sha1":
 		h = sha1.New()
 	case "sha224":
@@ -68,19 +68,20 @@ func checksumFile(path string, algo string) error {
 	case "sha512":
 		h = sha512.New()
 	default:
-		return fmt.Errorf("unsupported hash algorithm: %s", algo)
+		return "", fmt.Errorf("unsupported hash algorithm: %s", algo)
 	}
 
 	i, err := os.Stat(path)
 	if err != nil {
-		return err
+		return "", err
 	}
 
-	l.Verbosef("create checksum file: %s.%s", path, algo)
-	o, err := os.Create(fmt.Sprintf("%s.%s", path, algo))
+	sumFile := fmt.Sprintf("%s.%s", path, algo)
+	l.Verbosef("create checksum file: %s", sumFile)
+	o, err := os.Create(sumFile)
 	if err != nil {
 		l.Errorln(err)
-		return err
+		return "", err
 	}
 	defer o.Close()
 
@@ -102,7 +103,7 @@ func checksumFile(path string, algo string) error {
 		})
 
 		if err != nil {
-			return fmt.Errorf("error walking the path %q: %v\n", path, err)
+			return "", fmt.Errorf("error walking the path %q: %v\n", path, err)
 		}
 	} else {
 
@@ -113,7 +114,7 @@ func checksumFile(path string, algo string) error {
 		r, _ := computeChecksum(path, h)
 		fmt.Fprintf(o, "%x  %s\n", r, path)
 	}
-	return nil
+	return sumFile, nil
 }
 
 func checksumFileList(paths []string, algo string, sumFilePrefix string) error {

hash_test.go

@@ -77,18 +77,18 @@ func TestChecksumFile(t *testing.T) {
 	}
 
 	// bad algo
-	if err := checksumFile("", "none"); err != nil {
+	if _, err := checksumFile("", "none"); err != nil {
 		t.Errorf("expected <nil>, got %q\n", err)
 	}
 
-	if err := checksumFile("", "other"); err == nil {
+	if _, err := checksumFile("", "other"); err == nil {
 		t.Errorf("expected err, got <nil>\n")
 	}
 
 	// test each algo with the file
 	for i, st := range tests {
 		t.Run(fmt.Sprintf("f%v", i), func(t *testing.T) {
-			if err := checksumFile("test", st.algo); err != nil {
+			if _, err := checksumFile("test", st.algo); err != nil {
 				t.Errorf("checksumFile returned: %v", err)
 			}
 
@@ -111,12 +111,12 @@ func TestChecksumFile(t *testing.T) {
 	// bad files
 	var e *os.PathError
 	l.logger.SetOutput(ioutil.Discard)
-	if err := checksumFile("", "sha1"); !errors.As(err, &e) {
+	if _, err := checksumFile("", "sha1"); !errors.As(err, &e) {
 		t.Errorf("expected an *os.PathError, got %q\n", err)
 	}
 
 	os.Chmod("test.sha1", 0444)
-	if err := checksumFile("test", "sha1"); !errors.As(err, &e) {
+	if _, err := checksumFile("test", "sha1"); !errors.As(err, &e) {
 		t.Errorf("expected an *os.PathError, got %q\n", err)
 	}
 	os.Chmod("test.sha1", 0644)
@@ -138,7 +138,7 @@ func TestChecksumFile(t *testing.T) {
 	// test each algo with the directory
 	for i, st := range tests {
 		t.Run(fmt.Sprintf("d%v", i), func(t *testing.T) {
-			if err := checksumFile("test.d", st.algo); err != nil {
+			if _, err := checksumFile("test.d", st.algo); err != nil {
 				t.Errorf("checksumFile returned: %v", err)
 			}