syncthing/lib/fs/casefs.go

435 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"
)
const (
// How long to consider cached dirnames valid
caseCacheTimeout = time.Second
)
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
}
// caseFilesystemRegistry caches caseFilesystems and runs a routine to drop
// their cache every now and then.
type caseFilesystemRegistry struct {
fss map[fskey]*caseFilesystem
mut sync.RWMutex
startCleaner sync.Once
}
func (r *caseFilesystemRegistry) get(fs Filesystem) Filesystem {
k := fskey{fs.Type(), fs.URI()}
// 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()
caseFs, ok := r.fss[k]
r.mut.RUnlock()
if !ok {
r.mut.Lock()
caseFs, ok = r.fss[k]
if !ok {
caseFs = &caseFilesystem{
Filesystem: fs,
realCaser: newDefaultRealCaser(fs),
}
r.fss[k] = caseFs
r.startCleaner.Do(func() {
go r.cleaner()
})
}
r.mut.Unlock()
}
return caseFs
}
func (r *caseFilesystemRegistry) cleaner() {
for range time.NewTicker(time.Minute).C {
r.mut.RLock()
for _, caseFs := range r.fss {
caseFs.dropCache()
}
r.mut.RUnlock()
}
}
var globalCaseFilesystemRegistry = caseFilesystemRegistry{fss: make(map[fskey]*caseFilesystem)}
// 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 {
return wrapFilesystem(fs, globalCaseFilesystemRegistry.get)
}
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
mut sync.RWMutex
}
func newDefaultRealCaser(fs Filesystem) *defaultRealCaser {
caser := &defaultRealCaser{
fs: fs,
root: &caseNode{name: "."},
}
return caser
}
func (r *defaultRealCaser) realCase(name string) (string, error) {
out := "."
if name == out {
return out, nil
}
r.mut.Lock()
defer r.mut.Unlock()
node := r.root
for _, comp := range strings.Split(name, string(PathSeparator)) {
if node.dirNames == nil || node.expires.Before(time.Now()) {
// Haven't called DirNames yet, or the node has expired
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.expires = time.Now().Add(caseCacheTimeout)
node.child = nil
}
// If we don't already have a correct cached child, try to find it.
if node.child == nil || node.child.name != comp {
// Actually loop dirNames to search for a match.
n, err := findCaseInsensitiveMatch(comp, node.dirNames, node.dirNamesLower)
if err != nil {
return "", err
}
node.child = &caseNode{name: n}
}
node = node.child
out = filepath.Join(out, node.name)
}
return out, nil
}
func (r *defaultRealCaser) dropCache() {
r.mut.Lock()
r.root = &caseNode{name: "."}
r.mut.Unlock()
}
// 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
expires time.Time
dirNames []string
dirNamesLower []string
child *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
}