fix: lock files across different users

Fixes #66.

lib/locksystem.go

@@ -0,0 +1,35 @@
+package lib
+
+import (
+	"path/filepath"
+	"time"
+
+	"golang.org/x/net/webdav"
+)
+
+var _ webdav.LockSystem = &lockSystem{}
+
+// LockSystem wraps a [webdav.LockSystem] with a root directory, allowing
+// to reuse the same [webdav.LockSystem] for multiple users with different base
+// directories, meaning we can correctly lock the files across different users.
+type lockSystem struct {
+	webdav.LockSystem
+	directory string
+}
+
+func (l *lockSystem) Confirm(now time.Time, name0, name1 string, conditions ...webdav.Condition) (release func(), err error) {
+	if name0 != "" {
+		name0 = filepath.Join(l.directory, name0)
+	}
+
+	if name1 != "" {
+		name1 = filepath.Join(l.directory, name1)
+	}
+
+	return l.LockSystem.Confirm(now, name0, name1, conditions...)
+}
+
+func (l *lockSystem) Create(now time.Time, details webdav.LockDetails) (token string, err error) {
+	details.Root = filepath.Join(l.directory, details.Root)
+	return l.LockSystem.Create(now, details)
+}