Passing server_config to APIHandler inside add_routes

[nat-n]

I'm using add_routes and would like to set pass a RunnableConfig as server_config to the chain that depends on the contents of the request object (such as request headers).

The only way I see to do this today is by using APIHandler directly, but it would be nice to still benefit from add_routes. One solution would be to make add_routes accept an additional optional parameter like:

server_config_mapper: Optional[Callable[[Request], RunnableConfig]] = None

Which is then used in each relevant route handler like so:

        async def invoke(request: Request) -> Response:
            server_config = (
                server_config_mapper(request) if server_config_mapper else None
            )

            return await api_handler.invoke(request, server_config=server_config)

I've implemented this with a local fork of the server.py module and would be happy to contribute a PR if the maintainers agree that it's a good solution?

Another approach would be to decompose add_routes into smaller reusable units, so a user can create their own APIHandler object (potentially with custom extensions such as decorating in invoke method to derive server_config from the request) and recompose the behavior that want around it. This would be more powerful but require a larger refactor to expand the API surface area.

Is there another way to approach this that I've missed?

For more context, my use case is that I want to add metadata to LangSmith traces that depends on the request headers, but one could easily image wanting to set other RunnableConfig attributes in the same way to control chain behavior.

[eyurtsev]

Did you take a look at the per request modifier param in add routes? It allows modifying the config based on the request

[nat-n]

Thanks for the reply @eyurtsev. I totally just didn't see that there... and it seems to do exactly what I need. Nice!

[eyurtsev]

And thank you for writing Poe the poet!

[eyurtsev]

Closing as there's currently a way to do this