Function build_request_body 

pub fn build_request_body(
    messages: &[Message],
    tools: Option<&[ToolSchema]>,
    options: &CompletionOptions,
) -> Value

Builds the JSON body of a streaming chat-completions request.

The body names the model given by options.model() and carries messages as given. Every request streams, so stream is always true. The body also sets stream_options.include_usage. That asks the backend to send token usage in a final chunk with an empty choices list, so token counts still arrive when the reply streams as server-sent events.

When tools is Some and holds at least one schema, the body sends each schema in its tools array as an OpenAI function tool. Each entry is an object with type set to "function" and a function object that holds the tool’s name, description, and parameters. The body then also sets tool_choice to "auto". When tools is None or an empty slice, the body omits both fields and the request is a plain chat completion.

The optional settings in options extend the body only when set. temperature and max_tokens become fields of the same name. thinking becomes chat_template_kwargs.enable_thinking.

A transport that performs a Chat effect must build its request body here. It passes the effect’s messages, tools, and options, sends the result as the JSON body of its chat-completions request, and later hands the same value to read_completion_stream. One shared builder keeps every transport sending the same request for one effect.