<h1 align="center">RustStream</h1>
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<i>An async messaging framework for Rust: broker-agnostic traits, a router runtime, codecs, AsyncAPI generation, Prometheus and OpenTelemetry observability, and a conformance harness for broker authors.</i>
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<b><a href="https://powersemmi.github.io/ruststream/">Documentation</a></b>
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---
RustStream connects your service to a message broker through a small set of generic traits, then
gives you a router, middleware, codecs, and tooling on top. The core depends on no broker, so each
broker is an independent crate held to one contract; broker-specific configuration never leaks into
the framework.
The core is 100% safe Rust: every crate carries `#![forbid(unsafe_code)]` and CI rejects any `unsafe`
block, so the guarantee cannot regress.
## Features
- **Broker-agnostic core.** Just traits and types, zero broker dependencies. Brokers are separate
crates, and the contract is checked by a conformance harness.
- **Fully async on tokio.** No blocking APIs in the public surface.
- **Subscribers are `Stream`s, not callbacks.** Back-pressure comes for free.
- **Misuse does not compile.** Ack consumes `self` (no double-ack); the broker lifecycle is a
ladder of consuming transitions (`connect(self)` yields the connected form, `shutdown(self)`
a terminal witness), so out-of-order lifecycle calls are compile errors; transactions settle
by consuming their scope.
- **Publishers pair at startup.** Reply wiring and the `Out(..)` handler parameter attach a
publish policy where the handler is included; the runtime pairs it against the connected
broker, so a handler never sees a "not connected" publisher.
- **Pluggable codecs:** JSON, MessagePack, and CBOR behind cargo features - or none at all:
`raw` subscribers and `publish_raw` replies move payload bytes untouched.
- **Zero-boilerplate binaries.** `#[ruststream::app]` generates `main`; the `ruststream` CLI
scaffolds projects, runs them, and generates the AsyncAPI document.
- **AsyncAPI 3.0 and Prometheus metrics,** served from your own HTTP stack.
- **OpenTelemetry** behind the `otel` feature: OTLP export for traces and metrics, per-handler
dispatch metrics following the messaging semantic conventions, and W3C trace-context
propagation across the consume-transform-produce chain.
- **A cloneable health probe** off the running app, so a sibling healthz route keeps reporting
the terminal state after the messaging side stops.
- **Colored console logging** behind the `logging` feature; the generated CLI installs it on `run`,
with verbosity driven by `RUST_LOG`.
- **Capability traits** for optional features (batch subscribe, borrowed and owned transactions,
request-reply, partitioning, repositioning a live subscription in a replayable log); a broker
implements only what it supports.
## Install
```toml
[dependencies]
ruststream = { version = "0.6", features = ["macros", "memory", "json"] }
serde = { version = "1", features = ["derive"] }
schemars = "1"
```
The CLI ships with the crate behind the `cli` feature:
```bash
cargo install ruststream --features cli
```
## Write a service
```rust
use ruststream::memory::MemoryBroker;
use ruststream::runtime::{AppInfo, HandlerResult, RustStream};
use ruststream::subscriber;
use schemars::JsonSchema;
use serde::Deserialize;
#[derive(Debug, Deserialize, JsonSchema)]
struct Order {
id: u64,
}
#[subscriber("orders")]
async fn handle(order: &Order) -> HandlerResult {
println!("got order {}", order.id);
HandlerResult::Ack
}
#[ruststream::app]
fn app() -> RustStream {
RustStream::new(AppInfo::new("orders", "0.1.0"))
.with_broker(MemoryBroker::new(), |b| b.include(handle))
}
```
`#[ruststream::app]` generates `main`, so there is no runtime boilerplate.
## Injecting dependencies
Declare app state, derive `FromRef`, and take a dependency as a `State<T>` handler argument instead of
reaching through `ctx.state()`. The state is built once in `on_startup`; `#[derive(FromRef)]` makes
each field injectable, so no extractor is written by hand.
```rust
use ruststream::runtime::State;
use ruststream::FromRef;
#[derive(FromRef)]
struct AppState {
create_order: CreateOrder,
}
#[subscriber("orders")]
async fn handle(order: &Order, State(create_order): State<CreateOrder>) -> HandlerResult {
create_order.execute(order);
HandlerResult::Ack
}
```
Full compiling example: `examples/from_context.rs`.
## Run it
```bash
ruststream run # start the service (or: cargo run -- run)
ruststream asyncapi gen # print the AsyncAPI document
```
Scaffold a fresh project with `cargo generate --git https://github.com/powersemmi/ruststream
templates/memory --name my-service` (each broker crate ships its own template). See the
[quick start](https://powersemmi.github.io/ruststream/latest/getting-started/quickstart/).
## Testing the service
Unit-test a built service against the in-memory broker, with no external service. `MemoryBroker` is a
real broker here, not a test double: the `TestApp` harness drives it through the same dispatch path
the production runtime uses, so you assert on handler behaviour, middleware, and decoding exactly as
in production.
```rust
use ruststream::testing::TestApp;
let tb = TestApp::start(service()).await?;
// Inject an order; the harness drives the handler to completion before returning.
tb.broker::<MemoryBroker>()
.publish("orders", &Order { id: 42 })
.await?;
// The handler ran once, decoded the order, and acked.
tb.broker::<MemoryBroker>()
.subscriber("orders")
.assert_called_once()
.with(&Order { id: 42 })
.settled(HandlerResult::Ack);
// It published the matching receipt downstream.
tb.broker::<MemoryBroker>()
.published::<Receipt>("receipts")
.assert_called_once()
.with(&Receipt { order_id: 42 });
```
Full compiling example: `examples/testing.rs`. See the
[testing guide](https://powersemmi.github.io/ruststream/latest/guides/testing/).
## Project documentation
Build the AsyncAPI spec and the interactive viewer HTML programmatically from a built service, then
serve them from your own HTTP stack. The CLI `ruststream asyncapi gen` (see `Run it` above) prints the
same document to stdout; this is the in-process path.
```rust
use ruststream::asyncapi::{build_spec, render_viewer_html, ViewerOptions};
let spec = build_spec(&service()).to_json()?;
let viewer = render_viewer_html("/asyncapi.json", &ViewerOptions::default());
// serve `viewer` at `/` and `spec` at `/asyncapi.json` from your own HTTP stack
```
Full compiling example: `examples/asyncapi_http.rs`.
- Guide and tutorials: <https://powersemmi.github.io/ruststream/latest>
- API reference: <https://docs.rs/ruststream>
- Writing a broker: <https://powersemmi.github.io/ruststream/latest/broker-authors/>
## Ecosystem
- [`ruststream-nats`](https://github.com/powersemmi/ruststream-nats): the NATS broker (Core NATS and
JetStream).
- [`ruststream-fred`](https://github.com/powersemmi/ruststream-fred): the Redis broker (Redis Streams
with consumer groups; standalone, cluster, and sentinel topologies) via the `fred` client.
- [`ruststream-lapin`](https://github.com/powersemmi/ruststream-lapin): the RabbitMQ broker (AMQP
0.9.1: topology descriptors, native dead-letter and delayed retry, keyed worker lanes, publisher
confirms and server-side transactions) via the `lapin` client.
- [`ruststream-rdkafka`](https://github.com/powersemmi/ruststream-rdkafka): the Apache Kafka broker
(consumer groups, tracked and transactional commits, retry and dead-letter topics, partition-scoped
transactions and exactly-once pipelines, a service template) via the `rdkafka` client.
Concrete brokers live in their own crates and pull `ruststream` from crates.io.
## Minimum supported Rust version
The MSRV is **1.85** (edition 2024, native `async fn in trait`). CI builds the crate on every
stable toolchain from 1.85 up to current stable, so any floor in that range works.
The policy:
- The published `rust-version` stays at the floor. Raising it is a breaking change (a minor
version bump pre-1.0) and is reviewed against the broker crates' client requirements at each
minor release.
- Broker crates (`ruststream-nats`, ...) may require a newer toolchain than the core when their
underlying clients do; cargo allows a dependent crate to have a stricter floor than its
dependency. Check the broker crate's own `rust-version` for its floor.
## Contributing
```bash
just check # fmt, clippy, and feature checks
just test # the test suite
```
## License
Licensed under the [Apache-2.0](./LICENSE) license.
<sub>Inspired by [FastStream](https://github.com/ag2ai/faststream).</sub>