lib/fs: The interface and basicfs

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3748

lib/fs/filesystem.go

@@ -0,0 +1,77 @@
+// 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 http://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"errors"
+	"io"
+	"time"
+)
+
+type LinkTargetType int
+
+const (
+	LinkTargetFile LinkTargetType = iota
+	LinkTargetDirectory
+	LinkTargetUnknown
+)
+
+// The Filesystem interface abstracts access to the file system.
+type Filesystem interface {
+	ChangeSymlinkType(name string, tt LinkTargetType) error
+	Chmod(name string, mode FileMode) error
+	Chtimes(name string, atime time.Time, mtime time.Time) error
+	Create(name string) (File, error)
+	CreateSymlink(name, target string, tt LinkTargetType) error
+	DirNames(name string) ([]string, error)
+	Lstat(name string) (FileInfo, error)
+	Mkdir(name string, perm FileMode) error
+	Open(name string) (File, error)
+	ReadSymlink(name string) (string, LinkTargetType, error)
+	Remove(name string) error
+	Rename(oldname, newname string) error
+	Stat(name string) (FileInfo, error)
+	SymlinksSupported() bool
+	Walk(root string, walkFn WalkFunc) error
+}
+
+// The File interface abstracts access to a regular file, being a somewhat
+// smaller interface than os.File
+type File interface {
+	io.Reader
+	io.WriterAt
+	io.Closer
+	Truncate(size int64) error
+}
+
+// The FileInfo interface is almost the same as os.FileInfo, but with the
+// Sys method removed (as we don't want to expose whatever is underlying)
+// and with a couple of convenience methods added.
+type FileInfo interface {
+	// Standard things present in os.FileInfo
+	Name() string
+	Mode() FileMode
+	Size() int64
+	ModTime() time.Time
+	IsDir() bool
+	// Extensions
+	IsRegular() bool
+	IsSymlink() bool
+}
+
+// FileMode is similar to os.FileMode
+type FileMode uint32
+
+// DefaultFilesystem is the fallback to use when nothing explicitly has
+// been passed.
+var DefaultFilesystem Filesystem = new(BasicFilesystem)
+
+// SkipDir is used as a return value from WalkFuncs to indicate that
+// the directory named in the call is to be skipped. It is not returned
+// as an error by any function.
+var errSkipDir = errors.New("skip this directory")
+var SkipDir = errSkipDir // silences the lint warning...