internal/restic: Make FileType a uint8 instead of a string

The string form was presumably useful before the introduction of
layouts, but right now it just makes call sequences and garbage
collection more expensive (the latter because every string contains
a pointer to be scanned).

internal/restic/file.go

@@ -7,18 +7,38 @@ import (
 )
 
 // FileType is the type of a file in the backend.
-type FileType string
+type FileType uint8
 
 // These are the different data types a backend can store.
 const (
-	PackFile     FileType = "data" // use data, as packs are stored under /data in repo
-	KeyFile      FileType = "key"
-	LockFile     FileType = "lock"
-	SnapshotFile FileType = "snapshot"
-	IndexFile    FileType = "index"
-	ConfigFile   FileType = "config"
+	PackFile FileType = 1 + iota
+	KeyFile
+	LockFile
+	SnapshotFile
+	IndexFile
+	ConfigFile
 )
 
+func (t FileType) String() string {
+	s := "invalid"
+	switch t {
+	case PackFile:
+		// Spelled "data" instead of "pack" for historical reasons.
+		s = "data"
+	case KeyFile:
+		s = "key"
+	case LockFile:
+		s = "lock"
+	case SnapshotFile:
+		s = "snapshot"
+	case IndexFile:
+		s = "index"
+	case ConfigFile:
+		s = "config"
+	}
+	return s
+}
+
 // Handle is used to store and access data in a backend.
 type Handle struct {
 	Type              FileType
@@ -36,10 +56,6 @@ func (h Handle) String() string {
 
 // Valid returns an error if h is not valid.
 func (h Handle) Valid() error {
-	if h.Type == "" {
-		return errors.New("type is empty")
-	}
-
 	switch h.Type {
 	case PackFile:
 	case KeyFile:
@@ -48,7 +64,7 @@ func (h Handle) Valid() error {
 	case IndexFile:
 	case ConfigFile:
 	default:
-		return errors.Errorf("invalid Type %q", h.Type)
+		return errors.Errorf("invalid Type %d", h.Type)
 	}
 
 	if h.Type == ConfigFile {

internal/restic/file_test.go

@@ -1,20 +1,28 @@
 package restic
 
-import "testing"
+import (
+	"testing"
 
-var handleTests = []struct {
-	h     Handle
-	valid bool
-}{
-	{Handle{Name: "foo"}, false},
-	{Handle{Type: "foobar"}, false},
-	{Handle{Type: ConfigFile, Name: ""}, true},
-	{Handle{Type: PackFile, Name: ""}, false},
-	{Handle{Type: "", Name: "x"}, false},
-	{Handle{Type: LockFile, Name: "010203040506"}, true},
+	rtest "github.com/restic/restic/internal/test"
+)
+
+func TestHandleString(t *testing.T) {
+	rtest.Equals(t, "<data/foobar>", Handle{Type: PackFile, Name: "foobar"}.String())
+	rtest.Equals(t, "<lock/1>", Handle{Type: LockFile, Name: "1"}.String())
 }
 
 func TestHandleValid(t *testing.T) {
+	var handleTests = []struct {
+		h     Handle
+		valid bool
+	}{
+		{Handle{Name: "foo"}, false},
+		{Handle{Type: 0}, false},
+		{Handle{Type: ConfigFile, Name: ""}, true},
+		{Handle{Type: PackFile, Name: ""}, false},
+		{Handle{Type: LockFile, Name: "010203040506"}, true},
+	}
+
 	for i, test := range handleTests {
 		err := test.h.Valid()
 		if err != nil && test.valid {