return last error

server/download.go

@@ -149,9 +149,10 @@ func (b *blobDownload) run(ctx context.Context, requestURL *url.URL, opts *Regis
 
 		i := i
 		g.Go(func() error {
+			var err error
 			for try := 0; try < maxRetries; try++ {
 				w := io.NewOffsetWriter(file, part.StartsAt())
-				err := b.downloadChunk(inner, requestURL, w, part, opts)
+				err = b.downloadChunk(inner, requestURL, w, part, opts)
 				switch {
 				case errors.Is(err, context.Canceled), errors.Is(err, syscall.ENOSPC):
 					// return immediately if the context is canceled or the device is out of space
@@ -164,7 +165,7 @@ func (b *blobDownload) run(ctx context.Context, requestURL *url.URL, opts *Regis
 				}
 			}
 
-			return errMaxRetriesExceeded
+			return fmt.Errorf("%w: %w", errMaxRetriesExceeded, err)
 		})
 	}
 

server/upload.go

@@ -135,9 +135,10 @@ func (b *blobUpload) Run(ctx context.Context, opts *RegistryOptions) {
 		case <-inner.Done():
 		case requestURL := <-b.nextURL:
 			g.Go(func() error {
+				var err error
 				for try := 0; try < maxRetries; try++ {
 					part.ReadSeeker = io.NewSectionReader(f, part.Offset, part.Size)
-					err := b.uploadChunk(inner, http.MethodPatch, requestURL, part, opts)
+					err = b.uploadChunk(inner, http.MethodPatch, requestURL, part, opts)
 					switch {
 					case errors.Is(err, context.Canceled):
 						return err
@@ -151,7 +152,7 @@ func (b *blobUpload) Run(ctx context.Context, opts *RegistryOptions) {
 					return nil
 				}
 
-				return errMaxRetriesExceeded
+				return fmt.Errorf("%w: %w", errMaxRetriesExceeded, err)
 			})
 		}
 	}
@@ -227,7 +228,7 @@ func (b *blobUpload) uploadChunk(ctx context.Context, method string, requestURL
 		}
 
 		for try := 0; try < maxRetries; try++ {
-			err := b.uploadChunk(ctx, http.MethodPut, redirectURL, part, nil)
+			err = b.uploadChunk(ctx, http.MethodPut, redirectURL, part, nil)
 			switch {
 			case errors.Is(err, context.Canceled):
 				return err
@@ -241,7 +242,7 @@ func (b *blobUpload) uploadChunk(ctx context.Context, method string, requestURL
 			return nil
 		}
 
-		return errMaxRetriesExceeded
+		return fmt.Errorf("%w: %w", errMaxRetriesExceeded, err)
 
 	case resp.StatusCode == http.StatusUnauthorized:
 		auth := resp.Header.Get("www-authenticate")