S3: fix quota update after an upload error

S3 uploads are atomic, if the upload fails we have no partial file so we
have to update the user quota only if the upload succeed

sftpd/handler.go

@@ -479,11 +479,16 @@ func (c Connection) handleSFTPUploadToExistingFile(pflags sftp.FileOpenFlags, re
 		return nil, vfs.GetSFTPError(c.fs, err)
 	}
 
+	initialSize := int64(0)
 	if pflags.Append && osFlags&os.O_TRUNC == 0 {
 		c.Log(logger.LevelDebug, logSender, "upload resume requested, file path: %#v initial size: %v", filePath, fileSize)
 		minWriteOffset = fileSize
 	} else {
-		dataprovider.UpdateUserQuota(dataProvider, c.User, 0, -fileSize, false)
+		if vfs.IsLocalOsFs(c.fs) {
+			dataprovider.UpdateUserQuota(dataProvider, c.User, 0, -fileSize, false)
+		} else {
+			initialSize = fileSize
+		}
 	}
 
 	vfs.SetPathPermissions(c.fs, filePath, c.User.GetUID(), c.User.GetGID())
@@ -506,6 +511,7 @@ func (c Connection) handleSFTPUploadToExistingFile(pflags sftp.FileOpenFlags, re
 		transferError:  nil,
 		isFinished:     false,
 		minWriteOffset: minWriteOffset,
+		initialSize:    initialSize,
 		lock:           new(sync.Mutex),
 	}
 	addTransfer(&transfer)