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lib/fs: The interface and basicfs

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GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3748
This commit is contained in:
Jakob Borg 2016-11-24 12:07:14 +00:00 committed by Audrius Butkevicius
parent 3cde608eda
commit fc1430aa92
5 changed files with 492 additions and 0 deletions
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96
lib/fs/basicfs.go Normal file
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// 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 (
"os"
"time"
)
// The BasicFilesystem implements all aspects by delegating to package os.
type BasicFilesystem struct {
}
func NewBasicFilesystem() *BasicFilesystem {
return new(BasicFilesystem)
}
func (f *BasicFilesystem) Chmod(name string, mode FileMode) error {
return os.Chmod(name, os.FileMode(mode))
}
func (f *BasicFilesystem) Chtimes(name string, atime time.Time, mtime time.Time) error {
return os.Chtimes(name, atime, mtime)
}
func (f *BasicFilesystem) Mkdir(name string, perm FileMode) error {
return os.Mkdir(name, os.FileMode(perm))
}
func (f *BasicFilesystem) Lstat(name string) (FileInfo, error) {
fi, err := os.Lstat(name)
if err != nil {
return nil, err
}
return fsFileInfo{fi}, err
}
func (f *BasicFilesystem) Remove(name string) error {
return os.Remove(name)
}
func (f *BasicFilesystem) Rename(oldpath, newpath string) error {
return os.Rename(oldpath, newpath)
}
func (f *BasicFilesystem) Stat(name string) (FileInfo, error) {
fi, err := os.Stat(name)
if err != nil {
return nil, err
}
return fsFileInfo{fi}, err
}
func (f *BasicFilesystem) DirNames(name string) ([]string, error) {
fd, err := os.OpenFile(name, os.O_RDONLY, 0777)
if err != nil {
return nil, err
}
defer fd.Close()
names, err := fd.Readdirnames(-1)
if err != nil {
return nil, err
}
return names, nil
}
func (f *BasicFilesystem) Open(name string) (File, error) {
return os.Open(name)
}
func (f *BasicFilesystem) Create(name string) (File, error) {
return os.Create(name)
}
// fsFileInfo implements the fs.FileInfo interface on top of an os.FileInfo.
type fsFileInfo struct {
os.FileInfo
}
func (e fsFileInfo) Mode() FileMode {
return FileMode(e.FileInfo.Mode())
}
func (e fsFileInfo) IsRegular() bool {
return e.FileInfo.Mode().IsRegular()
}
func (e fsFileInfo) IsSymlink() bool {
return e.FileInfo.Mode()&os.ModeSymlink == os.ModeSymlink
}

43
lib/fs/basicfs_symlink_unix.go Normal file
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// 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/.
// +build !windows
package fs
import "os"
var symlinksSupported = true
func DisableSymlinks() {
symlinksSupported = false
}
func (BasicFilesystem) SymlinksSupported() bool {
return symlinksSupported
}
func (BasicFilesystem) CreateSymlink(name, target string, _ LinkTargetType) error {
return os.Symlink(target, name)
}
func (BasicFilesystem) ChangeSymlinkType(_ string, _ LinkTargetType) error {
return nil
}
func (BasicFilesystem) ReadSymlink(path string) (string, LinkTargetType, error) {
tt := LinkTargetUnknown
if stat, err := os.Stat(path); err == nil {
if stat.IsDir() {
tt = LinkTargetDirectory
} else {
tt = LinkTargetFile
}
}
path, err := os.Readlink(path)
return path, tt, err
}

195
lib/fs/basicfs_symlink_windows.go Normal file
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// Copyright (C) 2014 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/.
// +build windows
package fs
import (
"os"
"path/filepath"
"github.com/syncthing/syncthing/lib/osutil"
"syscall"
"unicode/utf16"
"unsafe"
)
const (
win32FsctlGetReparsePoint = 0x900a8
win32FileFlagOpenReparsePoint = 0x00200000
win32SymbolicLinkFlagDirectory = 0x1
)
var (
modkernel32 = syscall.NewLazyDLL("kernel32.dll")
procDeviceIoControl = modkernel32.NewProc("DeviceIoControl")
procCreateSymbolicLink = modkernel32.NewProc("CreateSymbolicLinkW")
symlinksSupported = false
)
func init() {
defer func() {
if err := recover(); err != nil {
// Ensure that the supported flag is disabled when we hit an
// error, even though it should already be. Also, silently swallow
// the error since it's fine for a system not to support symlinks.
symlinksSupported = false
}
}()
// Needs administrator privileges.
// Let's check that everything works.
// This could be done more officially:
// http://stackoverflow.com/questions/2094663/determine-if-windows-process-has-privilege-to-create-symbolic-link
// But I don't want to define 10 more structs just to look this up.
base := os.TempDir()
path := filepath.Join(base, "symlinktest")
defer os.Remove(path)
err := DefaultFilesystem.CreateSymlink(path, base, LinkTargetDirectory)
if err != nil {
return
}
stat, err := osutil.Lstat(path)
if err != nil || stat.Mode()&os.ModeSymlink == 0 {
return
}
target, tt, err := DefaultFilesystem.ReadSymlink(path)
if err != nil || osutil.NativeFilename(target) != base || tt != LinkTargetDirectory {
return
}
symlinksSupported = true
}
func DisableSymlinks() {
symlinksSupported = false
}
func (BasicFilesystem) SymlinksSupported() bool {
return symlinksSupported
}
func (BasicFilesystem) ReadSymlink(path string) (string, LinkTargetType, error) {
ptr, err := syscall.UTF16PtrFromString(path)
if err != nil {
return "", LinkTargetUnknown, err
}
handle, err := syscall.CreateFile(ptr, 0, syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE, nil, syscall.OPEN_EXISTING, syscall.FILE_FLAG_BACKUP_SEMANTICS|win32FileFlagOpenReparsePoint, 0)
if err != nil || handle == syscall.InvalidHandle {
return "", LinkTargetUnknown, err
}
defer syscall.Close(handle)
var ret uint16
var data reparseData
r1, _, err := syscall.Syscall9(procDeviceIoControl.Addr(), 8, uintptr(handle), win32FsctlGetReparsePoint, 0, 0, uintptr(unsafe.Pointer(&data)), unsafe.Sizeof(data), uintptr(unsafe.Pointer(&ret)), 0, 0)
if r1 == 0 {
return "", LinkTargetUnknown, err
}
tt := LinkTargetUnknown
if attr, err := syscall.GetFileAttributes(ptr); err == nil {
if attr&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
tt = LinkTargetDirectory
} else {
tt = LinkTargetFile
}
}
return osutil.NormalizedFilename(data.printName()), tt, nil
}
func (BasicFilesystem) CreateSymlink(path, target string, tt LinkTargetType) error {
srcp, err := syscall.UTF16PtrFromString(path)
if err != nil {
return err
}
trgp, err := syscall.UTF16PtrFromString(osutil.NativeFilename(target))
if err != nil {
return err
}
// Sadly for Windows we need to specify the type of the symlink,
// whether it's a directory symlink or a file symlink.
// If the flags doesn't reveal the target type, try to evaluate it
// ourselves, and worst case default to the symlink pointing to a file.
mode := 0
if tt == LinkTargetUnknown {
path := target
if !filepath.IsAbs(target) {
path = filepath.Join(filepath.Dir(path), target)
}
stat, err := os.Stat(path)
if err == nil && stat.IsDir() {
mode = win32SymbolicLinkFlagDirectory
}
} else if tt == LinkTargetDirectory {
mode = win32SymbolicLinkFlagDirectory
}
r0, _, err := syscall.Syscall(procCreateSymbolicLink.Addr(), 3, uintptr(unsafe.Pointer(srcp)), uintptr(unsafe.Pointer(trgp)), uintptr(mode))
if r0 == 1 {
return nil
}
return err
}
func (fs BasicFilesystem) ChangeSymlinkType(path string, tt LinkTargetType) error {
target, existingTargetType, err := fs.ReadSymlink(path)
if err != nil {
return err
}
// If it's the same type, nothing to do.
if tt == existingTargetType {
return nil
}
// If the actual type is unknown, but the new type is file, nothing to do
if existingTargetType == LinkTargetUnknown && tt != LinkTargetDirectory {
return nil
}
return osutil.InWritableDir(func(path string) error {
// It should be a symlink as well hence no need to change permissions on
// the file.
os.Remove(path)
return fs.CreateSymlink(path, target, tt)
}, path)
}
type reparseData struct {
reparseTag uint32
reparseDataLength uint16
reserved uint16
substitueNameOffset uint16
substitueNameLength uint16
printNameOffset uint16
printNameLength uint16
flags uint32
// substituteName - 264 widechars max = 528 bytes
// printName - 260 widechars max = 520 bytes
// = 1048 bytes total
buffer [1048 / 2]uint16
}
func (r *reparseData) printName() string {
// offset and length are in bytes but we're indexing a []uint16
offset := r.printNameOffset / 2
length := r.printNameLength / 2
return string(utf16.Decode(r.buffer[offset : offset+length]))
}
func (r *reparseData) substituteName() string {
// offset and length are in bytes but we're indexing a []uint16
offset := r.substitueNameOffset / 2
length := r.substitueNameLength / 2
return string(utf16.Decode(r.buffer[offset : offset+length]))
}

81
lib/fs/basicfs_walk.go Normal file
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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This part copied directly from golang.org/src/path/filepath/path.go (Go
// 1.6) and lightly modified to be methods on BasicFilesystem.
// In our Walk() all paths given to a WalkFunc() are relative to the
// filesystem root.
package fs
import "path/filepath"
// WalkFunc is the type of the function called for each file or directory
// visited by Walk. The path argument contains the argument to Walk as a
// prefix; that is, if Walk is called with "dir", which is a directory
// containing the file "a", the walk function will be called with argument
// "dir/a". The info argument is the FileInfo for the named path.
//
// If there was a problem walking to the file or directory named by path, the
// incoming error will describe the problem and the function can decide how
// to handle that error (and Walk will not descend into that directory). If
// an error is returned, processing stops. The sole exception is when the function
// returns the special value SkipDir. If the function returns SkipDir when invoked
// on a directory, Walk skips the directory's contents entirely.
// If the function returns SkipDir when invoked on a non-directory file,
// Walk skips the remaining files in the containing directory.
type WalkFunc func(path string, info FileInfo, err error) error
// walk recursively descends path, calling walkFn.
func (f *BasicFilesystem) walk(path string, info FileInfo, walkFn WalkFunc) error {
err := walkFn(path, info, nil)
if err != nil {
if info.IsDir() && err == SkipDir {
return nil
}
return err
}
if !info.IsDir() {
return nil
}
names, err := f.DirNames(path)
if err != nil {
return walkFn(path, info, err)
}
for _, name := range names {
filename := filepath.Join(path, name)
fileInfo, err := f.Lstat(filename)
if err != nil {
if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
return err
}
} else {
err = f.walk(filename, fileInfo, walkFn)
if err != nil {
if !fileInfo.IsDir() || err != SkipDir {
return err
}
}
}
}
return nil
}
// Walk walks the file tree rooted at root, calling walkFn for each file or
// directory in the tree, including root. All errors that arise visiting files
// and directories are filtered by walkFn. The files are walked in lexical
// order, which makes the output deterministic but means that for very
// large directories Walk can be inefficient.
// Walk does not follow symbolic links.
func (f *BasicFilesystem) Walk(root string, walkFn WalkFunc) error {
info, err := f.Lstat(root)
if err != nil {
return walkFn(root, nil, err)
}
return f.walk(root, info, walkFn)
}

77
lib/fs/filesystem.go Normal file
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// 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...