exclRenameIfExists: Restore Stat from and and minor tweaks

diff --git a/storage/file-piece.go b/storage/file-piece.go
index 1f7491af2c342da2e420130b0b715f9afb88d44b..30746320de11016dd0e8aeddecb1c3229bca1f18 100644 (file)
--- a/storage/file-piece.go
+++ b/storage/file-piece.go
@@ -198,7 +198,17 @@ func (me *filePieceImpl) promotePartFile(f file) (err error) {
 }
 
 // Rename from if exists, and if so, to must not exist.
-func (me *filePieceImpl) exclRenameIfExists(from, to string) (err error) {
+func (me *filePieceImpl) exclRenameIfExists(from, to string) error {
+       if true {
+               // Might be cheaper to check source exists than to create destination regardless.
+               _, err := os.Stat(from)
+               if errors.Is(err, fs.ErrNotExist) {
+                       return nil
+               }
+               if err != nil {
+                       return err
+               }
+       }
        // We don't want anyone reading or writing to this until the rename completes.
        f, err := os.OpenFile(to, os.O_CREATE|os.O_EXCL, 0)
        if errors.Is(err, fs.ErrExist) {
@@ -207,21 +217,26 @@ func (me *filePieceImpl) exclRenameIfExists(from, to string) (err error) {
                        return nil
                }
                if err != nil {
-                       return
+                       return err
                }
                return errors.New("source and destination files both exist")
        }
        if err != nil {
-               return
+               return fmt.Errorf("exclusively creating destination file: %w", err)
        }
        f.Close()
        err = os.Rename(from, to)
        if err != nil {
-               os.Remove(to)
-               return
+               if errors.Is(err, fs.ErrNotExist) {
+                       // Someone else has moved it already.
+                       return nil
+               }
+               // If we can't rename it, remove the blocking destination file we made. Maybe the remove
+               // error should be logged separately since it's not actionable.
+               return errors.Join(err, os.Remove(to))
        }
        me.logger().Debug("renamed file", "from", from, "to", to)
-       return
+       return nil
 }
 
 func (me *filePieceImpl) onFileNotComplete(f file) (err error) {