seafile: fix corrupted uploads after a retried upload error

When an upload failed with a 500 error the upload was retried with a
new upload link but the same input stream. The stream had already been
consumed by the first attempt so the retry uploaded an empty file.

This fixes it by returning a RetryError instead so the caller retries
the upload with a fresh stream, which will fetch a new upload link.

backend/seafile/object.go

@@ -88,28 +88,22 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (io.ReadClo
 // But for unknown-sized objects (indicated by src.Size() == -1), Upload should either
 // return an error or update the object properly (rather than e.g. calling panic).
 func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) error {
-	// The upload sometimes return a temporary 500 error
-	// We cannot use the pacer to retry uploading the file as the upload link is single use only
-	for retry := 0; retry <= 3; retry++ {
-		uploadLink, err := o.fs.getUploadLink(ctx, o.libraryID)
-		if err != nil {
-			return err
-		}
-
-		uploaded, err := o.fs.upload(ctx, in, uploadLink, o.pathInLibrary)
-		if err == ErrorInternalDuringUpload {
-			// This is a temporary error, try again with a new upload link
-			continue
-		}
-		if err != nil {
-			return err
-		}
-		// Set the properties from the upload back to the object
-		o.size = uploaded.Size
-
-		return nil
+	uploadLink, err := o.fs.getUploadLink(ctx, o.libraryID)
+	if err != nil {
+		return err
 	}
-	return ErrorInternalDuringUpload
+
+	// The upload can't be retried here as the input stream can't be re-read and
+	// the upload link is single use, so upload returns a retry
+	// error for the caller to retry with a fresh stream.
+	uploaded, err := o.fs.upload(ctx, in, uploadLink, o.pathInLibrary)
+	if err != nil {
+		return err
+	}
+	// Set the properties from the upload back to the object
+	o.size = uploaded.Size
+
+	return nil
 }
 
 // Remove this object

backend/seafile/webapi.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/rclone/rclone/backend/seafile/api"
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/fserrors"
 	"github.com/rclone/rclone/lib/readers"
 	"github.com/rclone/rclone/lib/rest"
 )
@@ -721,8 +722,8 @@ func (f *Fs) upload(ctx context.Context, in io.Reader, uploadLink, filePath stri
 				return nil, fs.ErrorPermissionDenied
 			}
 			if resp.StatusCode == 500 {
-				// This is a temporary error - we will get a new upload link before retrying
-				return nil, ErrorInternalDuringUpload
+				// This is a temporary error - the caller will get a new upload link when it retries
+				return nil, fserrors.RetryError(ErrorInternalDuringUpload)
 			}
 		}
 		return nil, fmt.Errorf("failed to upload file: %w", err)