feat: upgrade langchain (#430)

Co-authored-by: jyong <718720800@qq.com>

api/core/data_loader/loader/pdf.py

@@ -0,0 +1,55 @@
+import logging
+from typing import List, Optional
+
+from langchain.document_loaders import PyPDFium2Loader
+from langchain.document_loaders.base import BaseLoader
+from langchain.schema import Document
+
+from extensions.ext_storage import storage
+from models.model import UploadFile
+
+logger = logging.getLogger(__name__)
+
+
+class PdfLoader(BaseLoader):
+    """Load pdf files.
+
+
+    Args:
+        file_path: Path to the file to load.
+    """
+
+    def __init__(
+        self,
+        file_path: str,
+        upload_file: Optional[UploadFile] = None
+    ):
+        """Initialize with file path."""
+        self._file_path = file_path
+        self._upload_file = upload_file
+
+    def load(self) -> List[Document]:
+        plaintext_file_key = ''
+        plaintext_file_exists = False
+        if self._upload_file:
+            if self._upload_file.hash:
+                plaintext_file_key = 'upload_files/' + self._upload_file.tenant_id + '/' \
+                                     + self._upload_file.hash + '.0625.plaintext'
+                try:
+                    text = storage.load(plaintext_file_key).decode('utf-8')
+                    plaintext_file_exists = True
+                    return [Document(page_content=text)]
+                except FileNotFoundError:
+                    pass
+        documents = PyPDFium2Loader(file_path=self._file_path).load()
+        text_list = []
+        for document in documents:
+            text_list.append(document.page_content)
+        text = "\n\n".join(text_list)
+
+        # save plaintext file for caching
+        if not plaintext_file_exists and plaintext_file_key:
+            storage.save(plaintext_file_key, text.encode('utf-8'))
+
+        return documents
+