feat: implement file download functionality in document handler

Author: liuruibin

apps/knowledge/serializers/document.py

@@ -46,6 +46,7 @@
     TaskType, File, FileSourceType
 from knowledge.serializers.common import ProblemParagraphManage, BatchSerializer, \
     get_embedding_model_id_by_knowledge_id, MetaSerializer, write_image, zip_dir
+from knowledge.serializers.file import FileSerializer
 from knowledge.serializers.paragraph import ParagraphSerializers, ParagraphInstanceSerializer, \
     delete_problems_and_mappings
 from knowledge.task.embedding import embedding_by_document, delete_embedding_by_document_list, \
@@ -548,7 +549,8 @@ def export_zip(self, with_valid=True):
             return response
 
         def download_source_file(self):
-            pass
+            self.is_valid(raise_exception=True)
+            return FileSerializer.Operate(id=self.data.get('knowledge_id')).get(with_valid=True)
 
         def one(self, with_valid=False):
             if with_valid: