Behaviour for transforming Finch.Request structs just before a streaming request is sent.

This is the config-level counterpart to the per-request on_finch_request option. Because config files cannot hold anonymous functions, the adapter must be a module that implements this behaviour.

It is particularly useful for environment-specific concerns that should apply globally — for example injecting trace headers in a test environment — without touching individual call sites.

Precedence

Both mechanisms can be combined. The config-level adapter is applied first, then the per-request on_finch_request callback (if given). Each step receives the output of the previous one.

Configuration

# config/test.exs
config :req_llm, finch_request_adapter: MyApp.TestFinchAdapter

Example

defmodule MyApp.TestFinchAdapter do
  @behaviour ReqLLM.FinchRequestAdapter

  @impl true
  def call(%Finch.Request{} = request) do
    %{request | headers: request.headers ++ [{"x-test-env", "true"}]}
  end
end