Duplicate first chunk in playground streaming chat

[yangxikun]

Bug Description

The first chunk content is 今天，will send two events add_message and token with same content 今天.

Reproduction

This bug can be reproduced when the llm response first message chunk content is not empty

Expected behavior

Expected output: 今天是2024年12月19日，星期四，农历是二零二四年十一月十九。

Who can help?

@anovazzi1

Operating System

mac

Langflow Version

v1.1.1

Python Version

3.12

Screenshot

No response

Flow File

No response

[dosubot]

To fix the bug in the _process_chunk method that causes the first chunk to be duplicated, you need to ensure that the complete_message is only updated with the chunk content after the initial message has been sent. The duplication occurs because the complete_message is updated with the chunk content before the initial message is sent in the first chunk. Here's the corrected code:

async def _process_chunk(
    self, chunk: str, complete_message: str, message_id: str, message: Message, *, first_chunk: bool = False
) -> str:
    if self._event_manager:
        if first_chunk:
            # Send the initial message only on the first chunk
            msg_copy = message.model_copy()
            msg_copy.text = complete_message + chunk
            await self._send_message_event(msg_copy, id_=message_id)
        await asyncio.to_thread(
            self._event_manager.on_token,
            data={
                "chunk": chunk,
                "id": str(message_id),
            },
        )
    complete_message += chunk
    return complete_message

In this corrected version, the complete_message is updated with the chunk after the initial message is sent, preventing the duplication of the first chunk ^[1].

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