chat-core

Core traits, types, and engine for chat-rs — the foundation every provider crate builds on. Exposes the Chat engine, ChatBuilder, the CompletionProvider / StreamProvider / EmbeddingsProvider traits, the Transport trait (with built-in HTTP/SSE and WebSocket impls), and the core message/tool/response types.

You usually don't depend on this crate directly — instead, depend on a provider crate (e.g. chat-openai, chat-gemini, chat-completions) which brings chat-core in transitively. Bring chat-core in explicitly when you want the engine types in your code without pulling the umbrella chat-rs crate.

Install

[dependencies]
chat-core = "0.3.0"

What's in here

• builder::ChatBuilder — the type-state builder that wires a provider into a Chat engine
• chat::Chat — the engine; orchestrates the call loop, tool calls, retries, HITL, structured output
• traits — CompletionProvider, StreamProvider, EmbeddingsProvider, ChatProvider
• transport — Transport trait + three built-in impls (feature-gated): ReqwestTransport (HTTP/SSE, default), AsyncWsTransport (tokio-tungstenite), WsTransport (tungstenite)
• types — Messages, Content, Parts, Tool, ChatOptions, ChatResponse, StreamEvent, Metadata, etc.
• error — ChatError, ChatFailure

What's new in 0.3

• StreamEvent::Structured(Value) — providers can yield complete structured objects mid-stream (each event is a whole serde_json::Value, not a fragment). The engine accumulates them into ChatResponse.content.parts as PartEnum::Structured so non-streaming consumers see them too. Drop-in for robotics consumers that produce a stream of typed action steps.
• InputStreamed<I> type-state — Chat<CP, InputStreamed<I>>::stream(&mut messages, input: I) interleaves the model's output stream with a caller-supplied Stream<Item = PartEnum> input source. Audio bytes ride as PartEnum::File, text as PartEnum::Text, tool results as PartEnum::Tool. Each input event triggers a case-by-case merge into Messages and re-opens the provider stream with the updated state — same interrupt-and-restart pattern HITL already uses, just automated. Builder transition: ChatBuilder::with_input_stream::<I>(). Bounds: I: Stream<Item = PartEnum> + Send + Unpin + 'static.

Both are additive — existing Chat<CP, Unstructured>::stream callers see no behavior change.

Feature Flags

Writing a Custom Provider

Implement CompletionProvider (and optionally StreamProvider, EmbeddingsProvider) on your client struct. Use the Transport abstraction so users can swap reqwest for their own HTTP/WS client. See providers/AGENTS.md for the conventions every existing provider follows.