lib: Folder marker is now a folder

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4341
LGTM: calmh

lib/fs/tempname.go

@@ -0,0 +1,59 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"crypto/md5"
+	"fmt"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+const (
+	WindowsTempPrefix = "~syncthing~"
+	UnixTempPrefix    = ".syncthing."
+)
+
+var TempPrefix string
+
+// Real filesystems usually handle 255 bytes. encfs has varying and
+// confusing file name limits. We take a safe way out and switch to hashing
+// quite early.
+const maxFilenameLength = 160 - len(UnixTempPrefix) - len(".tmp")
+
+func init() {
+	if runtime.GOOS == "windows" {
+		TempPrefix = WindowsTempPrefix
+	} else {
+		TempPrefix = UnixTempPrefix
+	}
+}
+
+// IsTemporary is true if the file name has the temporary prefix. Regardless
+// of the normally used prefix, the standard Windows and Unix temp prefixes
+// are always recognized as temp files.
+func IsTemporary(name string) bool {
+	name = filepath.Base(name)
+	if strings.HasPrefix(name, WindowsTempPrefix) ||
+		strings.HasPrefix(name, UnixTempPrefix) {
+		return true
+	}
+	return false
+}
+
+func TempName(name string) string {
+	tdir := filepath.Dir(name)
+	tbase := filepath.Base(name)
+	if len(tbase) > maxFilenameLength {
+		hash := md5.New()
+		hash.Write([]byte(name))
+		tbase = fmt.Sprintf("%x", hash.Sum(nil))
+	}
+	tname := fmt.Sprintf("%s%s.tmp", TempPrefix, tbase)
+	return filepath.Join(tdir, tname)
+}