The stop parameter in openai API doesn't work since v0.2.5

[llama-assistant]

Since version v0.2.5, it seems the stop parameter in openai api is directly set conv.stop_str, rather than from request.
https://github.com/lm-sys/FastChat/blob/v0.2.5/fastchat/serve/api.py#L134

In version v0.2.3, it works when set in the request.
https://github.com/lm-sys/FastChat/blob/v0.2.3/fastchat/serve/api.py#L125

The stop parameter is a key when it works with ReAct in langchain, seems quite important to enable.

[merrymercy]

Thanks for reporting this. Could you send a pull request to fix it?

[jstzwj]

Fixed in #818.

[llama-assistant]

@jstzwj Thanks for the fix, happy to see it in next version.

[mingfang]

In the openai_api_server, stop works for non-streaming completions, but not for streaming.

The problem is the unwanted stop sequence gets streamed out before stopping.
https://github.com/lm-sys/FastChat/blob/main/fastchat/serve/openai_api_server.py#L518

As a result, this breaks LangChain ReAct agents

[merrymercy]

@andy-yang-1 does the new PR (#1246) fix this?
@mingfang If not, could you contribute a PR to fix it?

[mingfang]

I tested the PR locally and it has the same problem.
@merrymercy do you think this problem should be fixed in
https://github.com/andy-yang-1/FastChat/blob/langchain-support/fastchat/serve/inference.py#L51
so that it doesn't emit the stop sequence?

[andy-yang-1]

@merrymercy My PR didn't fix the problem, how can we solve it?

[merrymercy]

We handle the stop string here https://github.com/andy-yang-1/FastChat/blob/fae4087bbb6f7979b61f2e0c2912d77547a5c659/fastchat/serve/inference.py#L164-L175,
I think it will correctly delete the stop sequence finally. Does it occur during the middle of the streaming?

[mingfang]

The problem happens when the previous generate token is the partial beginning of the stop sequence.
It will not match the entire stop sequence until the next few tokens.
As a result the partial stop sequence is stream the client, causing ReAct to fail.

[mingfang]

@merrymercy
This is my PR with the stop detection fix
#1392

[Chessing234]

The partial-stop suffix check is fixed in #3883 so streaming should no longer emit prefixes like Obs before the full stop string.