move Backend interface to backend package

internal/backend/file.go

@@ -0,0 +1,79 @@
+package backend
+
+import (
+	"fmt"
+
+	"github.com/restic/restic/internal/errors"
+)
+
+// FileType is the type of a file in the backend.
+type FileType uint8
+
+// These are the different data types a backend can store.
+const (
+	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
+	IsMetadata bool
+	Name       string
+}
+
+func (h Handle) String() string {
+	name := h.Name
+	if len(name) > 10 {
+		name = name[:10]
+	}
+	return fmt.Sprintf("<%s/%s>", h.Type, name)
+}
+
+// Valid returns an error if h is not valid.
+func (h Handle) Valid() error {
+	switch h.Type {
+	case PackFile:
+	case KeyFile:
+	case LockFile:
+	case SnapshotFile:
+	case IndexFile:
+	case ConfigFile:
+	default:
+		return errors.Errorf("invalid Type %d", h.Type)
+	}
+
+	if h.Type == ConfigFile {
+		return nil
+	}
+
+	if h.Name == "" {
+		return errors.New("invalid Name")
+	}
+
+	return nil
+}