syncthing/lib/fs/casefs.go
Simon Frei 932d8c69de lib/fs: Properly handle case insensitive systems (fixes #1787, fixes #2739, fixes #5708)
With this change we emulate a case sensitive filesystem on top of
insensitive filesystems. This means we correctly pick up case-only renames
and throw a case conflict error when there would be multiple files differing
only in case.

This safety check has a small performance hit (about 20% more filesystem
operations when scanning for changes). The new advanced folder option
`caseSensitiveFS` can be used to disable the safety checks, retaining the
previous behavior on systems known to be fully case sensitive.

Co-authored-by: Jakob Borg <jakob@kastelo.net>
2020-07-28 11:15:11 +02:00

449 lines
10 KiB
Go

// Copyright (C) 2020 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 (
"context"
"errors"
"fmt"
"path/filepath"
"strings"
"sync"
"time"
)
// Both values were chosen by magic.
const (
caseCacheTimeout = time.Second
// When the number of names (all lengths of []string from DirNames)
// exceeds this, we drop the cache.
caseMaxCachedNames = 1 << 20
)
type ErrCaseConflict struct {
given, real string
}
func (e *ErrCaseConflict) Error() string {
return fmt.Sprintf(`given name "%v" differs from name in filesystem "%v"`, e.given, e.real)
}
func IsErrCaseConflict(err error) bool {
e := &ErrCaseConflict{}
return errors.As(err, &e)
}
type realCaser interface {
realCase(name string) (string, error)
dropCache()
}
type fskey struct {
fstype FilesystemType
uri string
}
var (
caseFilesystems = make(map[fskey]Filesystem)
caseFilesystemsMut sync.Mutex
)
// caseFilesystem is a BasicFilesystem with additional checks to make a
// potentially case insensitive underlying FS behave like it's case-sensitive.
type caseFilesystem struct {
Filesystem
realCaser
}
// NewCaseFilesystem ensures that the given, potentially case-insensitive filesystem
// behaves like a case-sensitive filesystem. Meaning that it takes into account
// the real casing of a path and returns ErrCaseConflict if the given path differs
// from the real path. It is safe to use with any filesystem, i.e. also a
// case-sensitive one. However it will add some overhead and thus shouldn't be
// used if the filesystem is known to already behave case-sensitively.
func NewCaseFilesystem(fs Filesystem) Filesystem {
caseFilesystemsMut.Lock()
defer caseFilesystemsMut.Unlock()
k := fskey{fs.Type(), fs.URI()}
if caseFs, ok := caseFilesystems[k]; ok {
return caseFs
}
caseFs := &caseFilesystem{
Filesystem: fs,
}
switch k.fstype {
case FilesystemTypeBasic:
caseFs.realCaser = newBasicRealCaser(fs)
default:
caseFs.realCaser = newDefaultRealCaser(fs)
}
caseFilesystems[k] = caseFs
return caseFs
}
func (f *caseFilesystem) Chmod(name string, mode FileMode) error {
if err := f.checkCase(name); err != nil {
return err
}
return f.Filesystem.Chmod(name, mode)
}
func (f *caseFilesystem) Lchown(name string, uid, gid int) error {
if err := f.checkCase(name); err != nil {
return err
}
return f.Filesystem.Lchown(name, uid, gid)
}
func (f *caseFilesystem) Chtimes(name string, atime time.Time, mtime time.Time) error {
if err := f.checkCase(name); err != nil {
return err
}
return f.Filesystem.Chtimes(name, atime, mtime)
}
func (f *caseFilesystem) Mkdir(name string, perm FileMode) error {
if err := f.checkCase(name); err != nil {
return err
}
if err := f.Filesystem.Mkdir(name, perm); err != nil {
return err
}
f.dropCache()
return nil
}
func (f *caseFilesystem) MkdirAll(path string, perm FileMode) error {
if err := f.checkCase(path); err != nil {
return err
}
if err := f.Filesystem.MkdirAll(path, perm); err != nil {
return err
}
f.dropCache()
return nil
}
func (f *caseFilesystem) Lstat(name string) (FileInfo, error) {
var err error
if name, err = Canonicalize(name); err != nil {
return nil, err
}
stat, err := f.Filesystem.Lstat(name)
if err != nil {
return nil, err
}
if err = f.checkCaseExisting(name); err != nil {
return nil, err
}
return stat, nil
}
func (f *caseFilesystem) Remove(name string) error {
if err := f.checkCase(name); err != nil {
return err
}
if err := f.Filesystem.Remove(name); err != nil {
return err
}
f.dropCache()
return nil
}
func (f *caseFilesystem) RemoveAll(name string) error {
if err := f.checkCase(name); err != nil {
return err
}
if err := f.Filesystem.RemoveAll(name); err != nil {
return err
}
f.dropCache()
return nil
}
func (f *caseFilesystem) Rename(oldpath, newpath string) error {
if err := f.checkCase(oldpath); err != nil {
return err
}
if err := f.Filesystem.Rename(oldpath, newpath); err != nil {
return err
}
f.dropCache()
return nil
}
func (f *caseFilesystem) Stat(name string) (FileInfo, error) {
var err error
if name, err = Canonicalize(name); err != nil {
return nil, err
}
stat, err := f.Filesystem.Stat(name)
if err != nil {
return nil, err
}
if err = f.checkCaseExisting(name); err != nil {
return nil, err
}
return stat, nil
}
func (f *caseFilesystem) DirNames(name string) ([]string, error) {
if err := f.checkCase(name); err != nil {
return nil, err
}
return f.Filesystem.DirNames(name)
}
func (f *caseFilesystem) Open(name string) (File, error) {
if err := f.checkCase(name); err != nil {
return nil, err
}
return f.Filesystem.Open(name)
}
func (f *caseFilesystem) OpenFile(name string, flags int, mode FileMode) (File, error) {
if err := f.checkCase(name); err != nil {
return nil, err
}
file, err := f.Filesystem.OpenFile(name, flags, mode)
if err != nil {
return nil, err
}
f.dropCache()
return file, nil
}
func (f *caseFilesystem) ReadSymlink(name string) (string, error) {
if err := f.checkCase(name); err != nil {
return "", err
}
return f.Filesystem.ReadSymlink(name)
}
func (f *caseFilesystem) Create(name string) (File, error) {
if err := f.checkCase(name); err != nil {
return nil, err
}
file, err := f.Filesystem.Create(name)
if err != nil {
return nil, err
}
f.dropCache()
return file, nil
}
func (f *caseFilesystem) CreateSymlink(target, name string) error {
if err := f.checkCase(name); err != nil {
return err
}
if err := f.Filesystem.CreateSymlink(target, name); err != nil {
return err
}
f.dropCache()
return nil
}
func (f *caseFilesystem) Walk(root string, walkFn WalkFunc) error {
// Walking the filesystem is likely (in Syncthing's case certainly) done
// to pick up external changes, for which caching is undesirable.
f.dropCache()
if err := f.checkCase(root); err != nil {
return err
}
return f.Filesystem.Walk(root, walkFn)
}
func (f *caseFilesystem) Watch(path string, ignore Matcher, ctx context.Context, ignorePerms bool) (<-chan Event, <-chan error, error) {
if err := f.checkCase(path); err != nil {
return nil, nil, err
}
return f.Filesystem.Watch(path, ignore, ctx, ignorePerms)
}
func (f *caseFilesystem) Hide(name string) error {
if err := f.checkCase(name); err != nil {
return err
}
return f.Filesystem.Hide(name)
}
func (f *caseFilesystem) Unhide(name string) error {
if err := f.checkCase(name); err != nil {
return err
}
return f.Filesystem.Unhide(name)
}
func (f *caseFilesystem) checkCase(name string) error {
var err error
if name, err = Canonicalize(name); err != nil {
return err
}
// Stat is necessary for case sensitive FS, as it's then not a conflict
// if name is e.g. "foo" and on dir there is "Foo".
if _, err := f.Filesystem.Lstat(name); err != nil {
if IsNotExist(err) {
return nil
}
return err
}
return f.checkCaseExisting(name)
}
// checkCaseExisting must only be called after successfully canonicalizing and
// stating the file.
func (f *caseFilesystem) checkCaseExisting(name string) error {
realName, err := f.realCase(name)
if IsNotExist(err) {
// It did exist just before -> cache is outdated, try again
f.dropCache()
realName, err = f.realCase(name)
}
if err != nil {
return err
}
if realName != name {
return &ErrCaseConflict{name, realName}
}
return nil
}
type defaultRealCaser struct {
fs Filesystem
root *caseNode
count int
timer *time.Timer
timerStop chan struct{}
mut sync.RWMutex
}
func newDefaultRealCaser(fs Filesystem) *defaultRealCaser {
caser := &defaultRealCaser{
fs: fs,
root: &caseNode{name: "."},
timer: time.NewTimer(0),
}
<-caser.timer.C
return caser
}
func (r *defaultRealCaser) realCase(name string) (string, error) {
out := "."
if name == out {
return out, nil
}
r.mut.Lock()
defer func() {
if r.count > caseMaxCachedNames {
select {
case r.timerStop <- struct{}{}:
default:
}
r.dropCacheLocked()
}
r.mut.Unlock()
}()
node := r.root
for _, comp := range strings.Split(name, string(PathSeparator)) {
if node.dirNames == nil {
// Haven't called DirNames yet
var err error
node.dirNames, err = r.fs.DirNames(out)
if err != nil {
return "", err
}
node.dirNamesLower = make([]string, len(node.dirNames))
for i, n := range node.dirNames {
node.dirNamesLower[i] = UnicodeLowercase(n)
}
node.children = make(map[string]*caseNode)
node.results = make(map[string]*caseNode)
r.count += len(node.dirNames)
} else if child, ok := node.results[comp]; ok {
// Check if this exact name has been queried before to shortcut
node = child
out = filepath.Join(out, child.name)
continue
}
// Actually loop dirNames to search for a match
n, err := findCaseInsensitiveMatch(comp, node.dirNames, node.dirNamesLower)
if err != nil {
return "", err
}
child, ok := node.children[n]
if !ok {
child = &caseNode{name: n}
}
node.results[comp] = child
node.children[n] = child
node = child
out = filepath.Join(out, n)
}
return out, nil
}
func (r *defaultRealCaser) startCaseResetTimerLocked() {
r.timerStop = make(chan struct{})
r.timer.Reset(caseCacheTimeout)
go func() {
select {
case <-r.timer.C:
r.dropCache()
case <-r.timerStop:
if !r.timer.Stop() {
<-r.timer.C
}
r.mut.Lock()
r.timerStop = nil
r.mut.Unlock()
}
}()
}
func (r *defaultRealCaser) dropCache() {
r.mut.Lock()
r.dropCacheLocked()
r.mut.Unlock()
}
func (r *defaultRealCaser) dropCacheLocked() {
r.root = &caseNode{name: "."}
r.count = 0
}
// Both name and the key to children are "Real", case resolved names of the path
// component this node represents (i.e. containing no path separator).
// The key to results is also a path component, but as given to RealCase, not
// case resolved.
type caseNode struct {
name string
dirNames []string
dirNamesLower []string
children map[string]*caseNode
results map[string]*caseNode
}
func findCaseInsensitiveMatch(name string, names, namesLower []string) (string, error) {
lower := UnicodeLowercase(name)
candidate := ""
for i, n := range names {
if n == name {
return n, nil
}
if candidate == "" && namesLower[i] == lower {
candidate = n
}
}
if candidate == "" {
return "", ErrNotExist
}
return candidate, nil
}