fix: make webdav file copy atomic

chfs-ng/internal/api/server.go

@@ -1256,21 +1256,43 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 	if err != nil {
 		return false, err
 	}
-	out, err := f.store.Create(dst)
-	if err != nil {
-		in.Close()
+	defer in.Close()
+	if err := copyFileToDestination(f.store, in, dst, dstExists); err != nil {
 		return false, err
 	}
-	_, copyErr := io.Copy(out, in)
-	in.Close()
+	return !dstExists, nil
+}
+
+func copyFileToDestination(st storage.Storage, src io.Reader, dst string, dstExists bool) error {
+	tmp := fmt.Sprintf("%s.chfs-copy-%d", dst, time.Now().UnixNano())
+	for i := 0; i < 16; i++ {
+		if _, err := st.Stat(tmp); os.IsNotExist(err) {
+			break
+		} else if err != nil {
+			return err
+		}
+		tmp = fmt.Sprintf("%s.chfs-copy-%d-%d", dst, time.Now().UnixNano(), i)
+	}
+	out, err := createExclusive(st, tmp)
+	if err != nil {
+		return err
+	}
+	_, copyErr := io.Copy(out, src)
 	closeErr := out.Close()
 	if copyErr != nil {
-		return false, copyErr
+		_ = st.Remove(tmp)
+		return copyErr
 	}
 	if closeErr != nil {
-		return false, closeErr
+		_ = st.Remove(tmp)
+		return closeErr
 	}
-	return !dstExists, nil
+	if err := st.Rename(tmp, dst); err != nil {
+		_ = st.Remove(tmp)
+		return err
+	}
+	_ = dstExists
+	return nil
 }
 
 func (f *webdavStorageFS) Move(ctx context.Context, name, dest string, opts *webdav.MoveOptions) (bool, error) {

chfs-ng/internal/api/webdav_test.go

@@ -2,6 +2,7 @@ package api
 
 import (
 	"context"
+	"errors"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
@@ -113,6 +114,64 @@ func TestWebDAVAuthFSMoveMissingSourcePrecedence(t *testing.T) {
 	}
 }
 
+func TestWebDAVStorageFSCopyPreservesExistingDestinationOnSourceReadFailure(t *testing.T) {
+	root := t.TempDir()
+	if err := os.WriteFile(filepath.Join(root, "dst.txt"), []byte("original"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	store := storage.Local{Root: root}
+	if err := os.WriteFile(filepath.Join(root, "src.txt"), []byte("replacement"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	fs := &webdavStorageFS{store: store}
+	if _, err := fs.Copy(context.Background(), "/src.txt", "/dst.txt", &webdav.CopyOptions{}); err != nil {
+		t.Fatalf("copy: %v", err)
+	}
+	got, err := os.ReadFile(filepath.Join(root, "dst.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != "replacement" {
+		t.Fatalf("destination content=%q", got)
+	}
+	matches, err := filepath.Glob(filepath.Join(root, "dst.txt.chfs-copy-*"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(matches) != 0 {
+		t.Fatalf("temporary copy files leaked: %v", matches)
+	}
+}
+
+type failingReader struct{}
+
+func (failingReader) Read([]byte) (int, error) { return 0, errors.New("source read failed") }
+
+func TestWebDAVStorageFSCopyFailureDoesNotCorruptDestination(t *testing.T) {
+	root := t.TempDir()
+	store := storage.Local{Root: root}
+	if err := os.WriteFile(filepath.Join(root, "dst.txt"), []byte("original"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := copyFileToDestination(store, failingReader{}, "dst.txt", true); err == nil {
+		t.Fatal("expected source read failure")
+	}
+	got, err := os.ReadFile(filepath.Join(root, "dst.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != "original" {
+		t.Fatalf("destination was corrupted: %q", got)
+	}
+	matches, err := filepath.Glob(filepath.Join(root, "dst.txt.chfs-copy-*"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(matches) != 0 {
+		t.Fatalf("temporary copy files leaked: %v", matches)
+	}
+}
+
 func TestWebDAVStorageFSCopyAndMove(t *testing.T) {
 	root1 := t.TempDir()
 	root2 := t.TempDir()