added missing file

callback.py

@@ -0,0 +1,18 @@
+# adapted from https://github.com/hwchase17/langchain/issues/2428#issuecomment-1512280045
+from queue import Queue
+from typing import Any
+
+from langchain.callbacks.base import BaseCallbackHandler
+
+
+class QueueCallback(BaseCallbackHandler):
+    """Callback handler for streaming LLM responses to a queue."""
+
+    def __init__(self, queue: Queue):
+        self.queue = queue
+
+    def on_llm_new_token(self, token: str, **kwargs: Any) -> None:
+        self.queue.put(token)
+
+    def on_llm_end(self, *args, **kwargs: Any) -> None:
+        return self.queue.empty()