VLLMOpenAI compatible class

[Samoed]

Checked

• I searched existing ideas and did not find a similar one
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• I've clearly described the feature request and motivation for it

Feature request

Hi! I want to add VLLM OpenAI compatible client with additional parameters.

Motivation

Now all additional vLLM generation params should be passed through extra_body without validation. This class will explicitly specify supported params and add validations.

Proposal (If applicable)

I've implemented solution in #23692. The problem with this proposal is that @efriis suggested moving this class to the community package. However, this class would require OpenAI and ChatOpenAI as parent classes. I'm not sure how to do this without adding additional requirements to langchain_community.

[efriis]

From my understanding, you are able to use ChatOpenAI as-is with a custom base url. Let me know if that's incorrect! You're welcome to add documentation for how to do this to the vllm section of the documentation.

If you'd prefer to have a custom vllm implementation in community, you're welcome to do that as well. However, as you've found, you can't have this subclass the implementation in langchain-openai.

[Samoed]

Currently, I can use ChatOpenAI for Vllm and pass Vllm-specific parameters to extra_body, but it would be better to set parameters directly without using extra_body.

[efriis]

Sounds good, and we'd welcome a contribution to the langchain-community implementations for vllm!

[Samoed]

I'm interested in contributing to the Langchain. However, I don't see a clear solution to the problem I mentioned previously. It seems odd for langchain_community to have langchain_openai as a dependency, and maintaining two separate implementations of the OpenAI API client is not an ideal solution. I'd like to contribute, but I'm unsure how to proceed.