community[minor]: Add ability to specify file encoding and json encod…

…ing for FileChatMessageHistory (#24258)

Description:
Add UTF-8 encoding support

Issue:
Inability to properly handle characters from certain languages (e.g.,
Korean)

Fix:
Implement UTF-8 encoding in FileChatMessageHistory

---------

Co-authored-by: Eugene Yurtsev <eugene@langchain.dev>
Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/community/langchain_community/chat_message_histories/file.py

@@ -1,6 +1,6 @@
 import json
 from pathlib import Path
-from typing import List
+from typing import List, Optional
 
 from langchain_core.chat_history import (
     BaseChatMessageHistory,
@@ -11,30 +11,46 @@
 class FileChatMessageHistory(BaseChatMessageHistory):
     """Chat message history that stores history in a local file."""
 
-    def __init__(self, file_path: str) -> None:
+    def __init__(
+        self,
+        file_path: str,
+        *,
+        encoding: Optional[str] = None,
+        ensure_ascii: bool = True,
+    ) -> None:
         """Initialize the file path for the chat history.
-
         Args:
             file_path: The path to the local file to store the chat history.
+            encoding: The encoding to use for file operations. Defaults to None.
+            ensure_ascii: If True, escape non-ASCII in JSON. Defaults to True.
         """
         self.file_path = Path(file_path)
+        self.encoding = encoding
+        self.ensure_ascii = ensure_ascii
+
         if not self.file_path.exists():
             self.file_path.touch()
-            self.file_path.write_text(json.dumps([]))
+            self.file_path.write_text(
+                json.dumps([], ensure_ascii=self.ensure_ascii), encoding=self.encoding
+            )
 
     @property
     def messages(self) -> List[BaseMessage]:  # type: ignore
         """Retrieve the messages from the local file"""
-        items = json.loads(self.file_path.read_text())
+        items = json.loads(self.file_path.read_text(encoding=self.encoding))
         messages = messages_from_dict(items)
         return messages
 
     def add_message(self, message: BaseMessage) -> None:
         """Append the message to the record in the local file"""
         messages = messages_to_dict(self.messages)
         messages.append(messages_to_dict([message])[0])
-        self.file_path.write_text(json.dumps(messages))
+        self.file_path.write_text(
+            json.dumps(messages, ensure_ascii=self.ensure_ascii), encoding=self.encoding
+        )
 
     def clear(self) -> None:
         """Clear session memory from the local file"""
-        self.file_path.write_text(json.dumps([]))
+        self.file_path.write_text(
+            json.dumps([], ensure_ascii=self.ensure_ascii), encoding=self.encoding
+        )