storage/filesystem: add R/W locking

This commit adds read/write locking for individual files, so that
concurrent requests (e.g. to read and write the same file) cannot
interfere with one another.

The locking is not very fine-grained at the moment, and can probably be
improved upon. But it does ensure consistency.

storage/filesystem.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+	"sync"
 
 	"github.com/rs/zerolog/log"
 
@@ -20,9 +21,13 @@ import (
 
 type filesystemBackend struct {
 	webdav.UserPrincipalBackend
+
 	path          string
 	caldavPrefix  string
 	carddavPrefix string
+
+	// maps file path to *sync.RWMutex
+	locks sync.Map
 }
 
 var (
@@ -47,6 +52,36 @@ func NewFilesystem(fsPath, caldavPrefix, carddavPrefix string, userPrincipalBack
 	return backend, backend, nil
 }
 
+func (b *filesystemBackend) RLock(filename string) {
+	lock_, _ := b.locks.LoadOrStore(filename, &sync.RWMutex{})
+	lock := lock_.(*sync.RWMutex)
+	lock.RLock()
+}
+
+func (b *filesystemBackend) RUnlock(filename string) {
+	lock_, ok := b.locks.Load(filename)
+	if !ok {
+		panic("attempt to unlock non-existing lock")
+	}
+	lock := lock_.(*sync.RWMutex)
+	lock.RUnlock()
+}
+
+func (b *filesystemBackend) Lock(filename string) {
+	lock_, _ := b.locks.LoadOrStore(filename, &sync.RWMutex{})
+	lock := lock_.(*sync.RWMutex)
+	lock.Lock()
+}
+
+func (b *filesystemBackend) Unlock(filename string) {
+	lock_, ok := b.locks.Load(filename)
+	if !ok {
+		panic("attempt to unlock non-existing lock")
+	}
+	lock := lock_.(*sync.RWMutex)
+	lock.Unlock()
+}
+
 func ensureLocalDir(path string) error {
 	if _, err := os.Stat(path); os.IsNotExist(err) {
 		err = os.MkdirAll(path, 0755)

storage/filesystem_caldav.go

@@ -85,6 +85,9 @@ func (b *filesystemBackend) loadAllCalendarObjects(ctx context.Context, urlPath
 			return nil
 		}
 
+		b.RLock(filename)
+		defer b.RUnlock(filename)
+
 		cal, err := calendarFromFile(filename, propFilter)
 		if err != nil {
 			fmt.Printf("load calendar error for %s: %v\n", filename, err)
@@ -138,7 +141,12 @@ func (b *filesystemBackend) createDefaultCalendar(ctx context.Context) (*caldav.
 	if err != nil {
 		return nil, fmt.Errorf("error creating default calendar: %s", err.Error())
 	}
-	err = os.WriteFile(path.Join(localPath, calendarFileName), blob, 0644)
+
+	filename := path.Join(localPath, calendarFileName)
+	b.Lock(filename)
+	defer b.Unlock(filename)
+
+	err = os.WriteFile(filename, blob, 0644)
 	if err != nil {
 		return nil, fmt.Errorf("error writing default calendar: %s", err.Error())
 	}
@@ -167,6 +175,10 @@ func (b *filesystemBackend) ListCalendars(ctx context.Context) ([]caldav.Calenda
 		}
 
 		calPath := path.Join(filename, calendarFileName)
+
+		b.RLock(calPath)
+		defer b.RUnlock(calPath)
+
 		data, err := os.ReadFile(calPath)
 		if err != nil {
 			if os.IsNotExist(err) {
@@ -209,6 +221,9 @@ func (b *filesystemBackend) GetCalendar(ctx context.Context, urlPath string) (*c
 
 	log.Debug().Str("path", localPath).Msg("loading calendar")
 
+	b.RLock(localPath)
+	defer b.RUnlock(localPath)
+
 	data, err := os.ReadFile(localPath)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -237,6 +252,9 @@ func (b *filesystemBackend) GetCalendarObject(ctx context.Context, objPath strin
 		return nil, err
 	}
 
+	b.RLock(localPath)
+	defer b.RUnlock(localPath)
+
 	info, err := os.Stat(localPath)
 	if err != nil {
 		if errors.Is(err, fs.ErrNotExist) {
@@ -320,6 +338,9 @@ func (b *filesystemBackend) PutCalendarObject(ctx context.Context, objPath strin
 		return nil, err
 	}
 
+	b.Lock(localPath)
+	defer b.Unlock(localPath)
+
 	flags := os.O_RDWR | os.O_CREATE | os.O_TRUNC
 	// TODO handle IfNoneMatch == ETag
 	if opts.IfNoneMatch.IsWildcard() {
@@ -384,6 +405,10 @@ func (b *filesystemBackend) DeleteCalendarObject(ctx context.Context, path strin
 	if err != nil {
 		return err
 	}
+
+	b.Lock(localPath)
+	defer b.Unlock(localPath)
+
 	err = os.Remove(localPath)
 	if err != nil {
 		return err

storage/filesystem_carddav.go

@@ -69,6 +69,7 @@ func vcardPropFilter(card vcard.Card, props []string) vcard.Card {
 }
 
 func vcardFromFile(path string, propFilter []string) (vcard.Card, error) {
+
 	f, err := os.Open(path)
 	if err != nil {
 		return nil, err
@@ -103,6 +104,10 @@ func (b *filesystemBackend) loadAllAddressObjects(ctx context.Context, urlPath s
 			return nil
 		}
 
+		// TODO use single file read for data & etag
+		b.RLock(filename)
+		defer b.RUnlock(filename)
+
 		card, err := vcardFromFile(filename, propFilter)
 		if err != nil {
 			return err
@@ -141,7 +146,12 @@ func (b *filesystemBackend) writeAddressBook(ctx context.Context, ab *carddav.Ad
 	if err != nil {
 		return err
 	}
-	return os.WriteFile(path.Join(localPath, addressBookFileName), blob, 0644)
+
+	filename := path.Join(localPath, addressBookFileName)
+	b.Lock(filename)
+	defer b.Unlock(filename)
+
+	err = os.WriteFile(filename, blob, 0644)
 	if err != nil {
 		return fmt.Errorf("error writing address book: %s", err.Error())
 	}
@@ -208,6 +218,9 @@ func (b *filesystemBackend) ListAddressBooks(ctx context.Context) ([]carddav.Add
 		}
 
 		abPath := path.Join(filename, addressBookFileName)
+		b.RLock(abPath)
+		defer b.RUnlock(abPath)
+
 		data, err := os.ReadFile(abPath)
 		if err != nil {
 			if os.IsNotExist(err) {
@@ -250,6 +263,9 @@ func (b *filesystemBackend) GetAddressBook(ctx context.Context, urlPath string)
 
 	log.Debug().Str("path", localPath).Msg("loading addressbook")
 
+	b.RLock(localPath)
+	defer b.RUnlock(localPath)
+
 	data, err := os.ReadFile(localPath)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -303,6 +319,9 @@ func (b *filesystemBackend) GetAddressObject(ctx context.Context, objPath string
 		return nil, err
 	}
 
+	b.RLock(localPath)
+	defer b.RUnlock(localPath)
+
 	info, err := os.Stat(localPath)
 	if err != nil {
 		if errors.Is(err, fs.ErrNotExist) {
@@ -381,6 +400,9 @@ func (b *filesystemBackend) PutAddressObject(ctx context.Context, objPath string
 		return nil, err
 	}
 
+	b.Lock(localPath)
+	defer b.Unlock(localPath)
+
 	flags := os.O_RDWR | os.O_CREATE | os.O_TRUNC
 	// TODO handle IfNoneMatch == ETag
 	if opts.IfNoneMatch.IsWildcard() {
@@ -444,6 +466,10 @@ func (b *filesystemBackend) DeleteAddressObject(ctx context.Context, path string
 	if err != nil {
 		return err
 	}
+
+	b.Lock(localPath)
+	defer b.Unlock(localPath)
+
 	err = os.Remove(localPath)
 	if err != nil {
 		return err