XDRIVE transport: Retry "local" Get on Windows sharing violations (#7316)

https://github.com/XTLS/Xray-core/pull/7316#issuecomment-6575472342

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

transport/internet/xdrive/local.go

@@ -72,7 +72,7 @@ func (s *localStorage) Get(ctx context.Context, name string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	data, err := os.ReadFile(full)
+	data, err := readFile(ctx, full)
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil, errNotFound

transport/internet/xdrive/local_other.go

@@ -0,0 +1,12 @@
+//go:build !windows
+
+package xdrive
+
+import (
+	"context"
+	"os"
+)
+
+func readFile(_ context.Context, name string) ([]byte, error) {
+	return os.ReadFile(name)
+}

transport/internet/xdrive/local_windows.go

@@ -0,0 +1,30 @@
+package xdrive
+
+import (
+	"context"
+	"errors"
+	"os"
+	"time"
+
+	"golang.org/x/sys/windows"
+)
+
+// readFile retries os.ReadFile for up to 2 seconds on sharing violations:
+// os.Rename (MoveFileEx) in Put holds the file with DELETE access, which
+// os.ReadFile does not share, until a moment after its new name appears in List
+func readFile(ctx context.Context, name string) ([]byte, error) {
+	deadline := time.Now().Add(2 * time.Second)
+	delay := time.Millisecond
+	for {
+		data, err := os.ReadFile(name)
+		if !errors.Is(err, windows.ERROR_SHARING_VIOLATION) || time.Now().Add(delay).After(deadline) {
+			return data, err
+		}
+		select {
+		case <-ctx.Done():
+			return nil, err
+		case <-time.After(delay):
+		}
+		delay = min(2*delay, 100*time.Millisecond)
+	}
+}

transport/internet/xdrive/local_windows_test.go

@@ -0,0 +1,57 @@
+package xdrive
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"testing"
+	"time"
+
+	"golang.org/x/sys/windows"
+)
+
+func TestLocalSharingViolation(t *testing.T) {
+	storage, err := newLocalStorage(t.TempDir())
+	if err != nil {
+		t.Fatalf("newLocalStorage: %v", err)
+	}
+	const name = "streams/session/c2s/000000000.seg"
+	if err := storage.Put(context.Background(), name, []byte("segment")); err != nil {
+		t.Fatalf("Put: %v", err)
+	}
+	full, err := storage.resolve(name)
+	if err != nil {
+		t.Fatalf("resolve: %v", err)
+	}
+	path, err := windows.UTF16PtrFromString(full)
+	if err != nil {
+		t.Fatalf("UTF16PtrFromString: %v", err)
+	}
+
+	// os.Rename holds the file like this until a moment after its new name
+	// appears
+	handle, err := windows.CreateFile(path, windows.DELETE,
+		windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
+		nil, windows.OPEN_EXISTING, 0, 0)
+	if err != nil {
+		t.Fatalf("CreateFile: %v", err)
+	}
+	var once sync.Once
+	release := func() { once.Do(func() { windows.CloseHandle(handle) }) }
+	defer release()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancel()
+	if _, err := storage.Get(ctx, name); !errors.Is(err, windows.ERROR_SHARING_VIOLATION) {
+		t.Fatalf("Get returned %v while the file is held, want a sharing violation", err)
+	}
+
+	time.AfterFunc(100*time.Millisecond, release)
+	data, err := storage.Get(context.Background(), name)
+	if err != nil {
+		t.Fatalf("Get: %v", err)
+	}
+	if string(data) != "segment" {
+		t.Fatalf("Get returned %q, want %q", data, "segment")
+	}
+}