all: Convert folders to use filesystem abstraction

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4228

lib/fs/basicfs_unix.go

@@ -0,0 +1,57 @@
+// Copyright (C) 2016 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/.
+
+// +build !windows
+
+package fs
+
+import "os"
+
+func (BasicFilesystem) SymlinksSupported() bool {
+	return true
+}
+
+func (f *BasicFilesystem) CreateSymlink(target, name string) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	return os.Symlink(target, name)
+}
+
+func (f *BasicFilesystem) ReadSymlink(name string) (string, error) {
+	name, err := f.rooted(name)
+	if err != nil {
+		return "", err
+	}
+	return os.Readlink(name)
+}
+
+func (f *BasicFilesystem) MkdirAll(name string, perm FileMode) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	return os.MkdirAll(name, os.FileMode(perm))
+}
+
+// Unhide is a noop on unix, as unhiding files requires renaming them.
+// We still check that the relative path does not try to escape the root
+func (f *BasicFilesystem) Unhide(name string) error {
+	_, err := f.rooted(name)
+	return err
+}
+
+// Hide is a noop on unix, as hiding files requires renaming them.
+// We still check that the relative path does not try to escape the root
+func (f *BasicFilesystem) Hide(name string) error {
+	_, err := f.rooted(name)
+	return err
+}
+
+func (f *BasicFilesystem) Roots() ([]string, error) {
+	return []string{"/"}, nil
+}