lib/fs/casefs.go
Rama main · réplica de lectura del repositorio original.
// 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"
"sync"
"time"
lru "github.com/hashicorp/golang-lru/v2"
"golang.org/x/text/unicode/norm"
)
const (
// How long to consider cached dirnames valid
caseCacheTimeout = time.Second
caseCacheItemLimit = 4 << 10
)
type CaseConflictError struct {
Given, Real string
}
func (e *CaseConflictError) Error() string {
return fmt.Sprintf(`remote "%v" uses different upper or lowercase characters than local "%v"; change the casing on either side to match the other`, e.Given, e.Real)
}
func IsErrCaseConflict(err error) bool {
e := &CaseConflictError{}
return errors.As(err, &e)
}
type realCaser interface {
realCase(name string) (string, error)
dropCache()
noteAdded(name string)
noteRemoved(name string)
}
type fskey struct {
fstype FilesystemType
uri, opts string
}
// caseFilesystemRegistry caches caseFilesystems and runs a routine to drop
// their cache every now and then.
type caseFilesystemRegistry struct {
caseCaches map[fskey]*caseCache
mut sync.RWMutex
startCleaner sync.Once
}
func newFSKey(fs Filesystem) fskey {
k := fskey{
fstype: fs.Type(),
uri: fs.URI(),
}
if opts := fs.Options(); len(opts) > 0 {
k.opts = opts[0].String()
for _, o := range opts[1:] {
k.opts += "&" + o.String()
}
}
return k
}
func (r *caseFilesystemRegistry) get(fs Filesystem) Filesystem {
k := newFSKey(fs)
// Use double locking when getting a caseFs. In the common case it will
// already exist and we take the read lock fast path. If it doesn't, we
// take a write lock and try again.
r.mut.RLock()
cache, ok := r.caseCaches[k]
r.mut.RUnlock()
if !ok {
r.mut.Lock()
cache, ok = r.caseCaches[k]
if !ok {
cache = newCaseCache()
r.caseCaches[k] = cache
r.startCleaner.Do(func() {
go r.cleaner()
})
l.Debugf("Created new case cache for key %v", k)
}
r.mut.Unlock()
}
if ok {
l.Debugf("Reusing case cache for key %v", k)
}
return &caseFilesystem{
Filesystem: fs,
realCaser: &defaultRealCaser{
fs: fs,
cache: cache,
},
}
}
func (r *caseFilesystemRegistry) cleaner() {
for range time.NewTicker(time.Minute).C {
// We need to not hold this lock for a long time, as it blocks
// creating new filesystems in get(), which is needed to do things
// like add new folders. The (*caseFs).dropCache() method can take
// an arbitrarily long time to kick in because it in turn waits for
// locks held by things performing I/O. So we can't call that from
// within the loop.
r.mut.RLock()
toProcess := make([]*caseCache, 0, len(r.caseCaches))
for _, cache := range r.caseCaches {
toProcess = append(toProcess, cache)
}
r.mut.RUnlock()
for _, cache := range toProcess {
cache.Purge()
}
}
}
var globalCaseFilesystemRegistry = caseFilesystemRegistry{caseCaches: make(map[fskey]*caseCache)}
// OptionDetectCaseConflicts ensures that the 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.
type OptionDetectCaseConflicts struct{}
func (*OptionDetectCaseConflicts) apply(fs Filesystem) Filesystem {
return globalCaseFilesystemRegistry.get(fs)
}
func (*OptionDetectCaseConflicts) String() string {
return "detectCaseConflicts"
}
// 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
}
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, uid, gid string) 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 {
can, err := f.checkCase(name)
if err != nil {
return err
}
if err := f.Filesystem.Mkdir(name, perm); err != nil {
return err
}
f.noteAdded(can)
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 {
can, err := f.checkCase(name)
if err != nil {
return err
}
if err := f.Filesystem.Remove(name); err != nil {
return err
}
f.noteRemoved(can)
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 {
oldcan, err := f.checkCase(oldpath)
if err != nil {
return err
}
newcan, err := f.checkCase(newpath)
if err != nil {
// Case-only rename is ok
e := &CaseConflictError{}
if !errors.As(err, &e) || e.Real != oldpath {
return err
}
}
if err := f.Filesystem.Rename(oldpath, newpath); err != nil {
return err
}
f.noteRemoved(oldcan)
f.noteAdded(newcan)
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) {
can, err := f.checkCase(name)
if err != nil {
return nil, err
}
file, err := f.Filesystem.OpenFile(name, flags, mode)
if err != nil {
return nil, err
}
f.noteAdded(can)
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) {
can, err := f.checkCase(name)
if err != nil {
return nil, err
}
file, err := f.Filesystem.Create(name)
if err != nil {
return nil, err
}
f.noteAdded(can)
return file, nil
}
func (f *caseFilesystem) CreateSymlink(target, name string) error {
can, err := f.checkCase(name)
if err != nil {
return err
}
if err := f.Filesystem.CreateSymlink(target, name); err != nil {
return err
}
f.noteAdded(can)
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) underlying() (Filesystem, bool) {
return f.Filesystem, true
}
func (f *caseFilesystem) checkCase(name string) (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 name, 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) (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
}
// We normalize the normalization (hah!) of the strings before
// comparing, as we don't want to treat a normalization difference as a
// case conflict.
if norm.NFC.String(realName) != norm.NFC.String(name) {
return "", &CaseConflictError{name, realName}
}
return realName, nil
}
type defaultRealCaser struct {
cache *caseCache
fs Filesystem
}
type caseCache struct {
*lru.TwoQueueCache[string, *caseNode]
mut sync.Mutex
}
func newCaseCache() *caseCache {
cache, err := lru.New2Q[string, *caseNode](caseCacheItemLimit)
// New2Q only errors if given invalid parameters, which we don't.
if err != nil {
panic(err)
}
return &caseCache{
TwoQueueCache: cache,
}
}
func (r *defaultRealCaser) realCase(name string) (string, error) {
realName := "."
if name == realName {
return realName, nil
}
r.cache.mut.Lock()
defer r.cache.mut.Unlock()
for _, comp := range PathComponents(name) {
node := r.cache.getExpireAdd(realName, r.fs)
if node.err != nil {
return "", node.err
}
// Try to find a direct or case match
if _, ok := node.children[comp]; !ok {
comp, ok = node.lowerToReal[UnicodeLowercaseNormalized(comp)]
if !ok {
return "", ErrNotExist
}
}
realName = filepath.Join(realName, comp)
}
return realName, nil
}
func (r *defaultRealCaser) dropCache() {
r.cache.Purge()
}
func (r *defaultRealCaser) noteAdded(canonicalName string) {
r.cache.added(canonicalName)
}
func (r *defaultRealCaser) noteRemoved(canonicalName string) {
r.cache.removed(canonicalName)
}
// added updates the cached listing of name's parent directory to include
// name, dropping any cached listing for name itself.
func (c *caseCache) added(name string) {
c.mut.Lock()
defer c.mut.Unlock()
// Remove any stale entry for the name itself, though it should already
// have been removed by a paired noteRemoved if it existed before.
c.Remove(name)
// Get and update parent
node, ok := c.Get(filepath.Dir(name))
if !ok || node.err != nil {
return
}
base := filepath.Base(name)
node.children[base] = struct{}{}
node.lowerToReal[UnicodeLowercaseNormalized(base)] = base
}
// removed updates the cached listing of name's parent directory to no longer
// include name, dropping any cached listing for name itself.
func (c *caseCache) removed(name string) {
c.mut.Lock()
defer c.mut.Unlock()
// Remove the cache entry for the name itself, if it exists
c.Remove(name)
// Get the parent and remove it from its set of children
node, ok := c.Get(filepath.Dir(name))
if !ok || node.err != nil {
return
}
if len(node.children) != len(node.lowerToReal) {
// Some entries share a lowercase form, only possible on a
// case-sensitive filesystem. That makes precise incremental removal
// awkward (we'd need to rebuild lowerToReal in sorted order etc),
// so drop the listing and let it be re-read.
c.Remove(filepath.Dir(name))
return
}
base := filepath.Base(name)
delete(node.children, base)
delete(node.lowerToReal, UnicodeLowercaseNormalized(base))
}
// getExpireAdd gets an entry for the given key. If no entry exists, or it is
// expired a new one is created and added to the cache. The caller must hold
// c.mut.
func (c *caseCache) getExpireAdd(key string, fs Filesystem) *caseNode {
node, ok := c.Get(key)
if !ok {
node := newCaseNode(key, fs)
c.Add(key, node)
return node
}
if node.expires.Before(time.Now()) {
node = newCaseNode(key, fs)
c.Add(key, node)
}
return node
}
// The keys to children are "real", case resolved names of the path
// component this node represents (i.e. containing no path separator).
// lowerToReal is a map of lowercase path components (as in UnicodeLowercase)
// to their corresponding "real", case resolved names.
// A node is created empty and populated using once. If an error occurs the node
// is removed from cache and the error stored in err, such that anyone that
// already got the node doesn't try to access the nil maps.
type caseNode struct {
expires time.Time
lowerToReal map[string]string
children map[string]struct{}
err error
}
func newCaseNode(name string, filesystem Filesystem) *caseNode {
node := new(caseNode)
dirNames, err := filesystem.DirNames(name)
// Set expiry after calling DirNames in case this is super-slow
// (e.g. dirs with many children on android)
node.expires = time.Now().Add(caseCacheTimeout)
if err != nil {
node.err = err
return node
}
num := len(dirNames)
node.children = make(map[string]struct{}, num)
node.lowerToReal = make(map[string]string, num)
lastLower := ""
for _, n := range dirNames {
node.children[n] = struct{}{}
lower := UnicodeLowercaseNormalized(n)
if lower != lastLower {
node.lowerToReal[lower] = n
lastLower = lower
}
}
return node
}