Support more file reader

Signed-off-by: Jael Gu <mengjia.gu@zilliz.com>

loader.py

@@ -4,8 +4,9 @@ from typing import List, Optional
 
 class TextLoader(PyOperator):
     '''Load data from url or file (paths or file-like objects).'''
-    def __init__(self) -> None:
+    def __init__(self, **kwargs) -> None:
         super().__init__()
+        self.unstructured_kwargs = kwargs
     
     def __call__(self, data_src) -> List[str]:
         if data_src.startswith('http'):
@@ -20,9 +21,10 @@ class TextLoader(PyOperator):
             file_path = file.name
         else:
             file_path = file
-        with open(file_path, encoding=encoding) as f:
-            text = f.read()
-        return text
+        from langchain.document_loaders import UnstructuredFileLoader
+        loader = UnstructuredFileLoader(file_path, mode='single', strategy='fast')
+        doc = loader.load()[0]
+        return doc.page_content
     
     def _from_url(self, url: str) -> str:
         from langchain.document_loaders import UnstructuredURLLoader