Hexeract

Hexeract: the batteries-included messaging framework for Rust.

In-process mediator (CQRS), external message bus (RabbitMQ) and a transactional outbox/inbox, unified in a single coherent SDK with compile-time guarantees.

Hexeract is a server-side messaging framework written in Rust. It unifies in-process mediator handlers, external message bus transports, and a transactional outbox/inbox in a single coherent SDK. The framework relies on Rust's type system and procedural macros to provide compile-time guarantees in place of runtime reflection.

Hexeract is sponsored by Nubster.

What do you need?

Status

🛡️ v0.5.0: reliability hardening shipped. This release closes the delivery-reliability gaps in the outbox and the RabbitMQ bus: durable poison-message handling with opt-in dead-lettering, dispatch outside the database transaction, bounded exponential backoff with jitter, publisher confirms, bounded consumer buffers and a deadline/cancellation-safe shutdown. The legacy hexeract-outbox-postgres crate has been removed in 0.5.0; use hexeract-outbox-sql with the postgres feature instead. Mediator, middlewares, the #[handler] macro and Bus RabbitMQ stay stable from v0.3.0.

See the CHANGELOG for the detailed history.

Quick start

Outbox (PostgreSQL)

Add the umbrella crate with the outbox-sql-postgres feature to your Cargo.toml (outbox-sql-mysql and outbox-sql-sqlite ship the same surface):

[dependencies]
hexeract = { version = "0.5", features = ["outbox-sql-postgres"] }

Power users who prefer a strict SemVer per crate can keep depending on hexeract-outbox, hexeract-outbox-sql, hexeract-bus, hexeract-bus-rabbitmq etc. directly.

Declare a domain event, a handler and wire a worker:

use std::time::Duration;
use hexeract::core::HandlerContext;
use hexeract::outbox::{Event, Handler, OutboxError, OutboxPublisher};
use hexeract::outbox_sql::{PgOutboxPublisher, PgOutboxWorkerBuilder};
use serde::{Deserialize, Serialize};
use tokio_util::sync::CancellationToken;
use uuid::Uuid;

#[derive(Debug, Serialize, Deserialize)]
struct UserRegistered { user_id: Uuid }

impl Event for UserRegistered {
    const EVENT_TYPE: &'static str = "users.registered";
}

struct AuditWriter;
impl Handler<UserRegistered> for AuditWriter {
    type Error = OutboxError;
    async fn handle(&self, event: UserRegistered, _ctx: &HandlerContext) -> Result<(), Self::Error> {
        // ... write to audit storage ...
        Ok(())
    }
}

# async fn run(pool: sqlx::PgPool) -> Result<(), Box<dyn std::error::Error>> {
let publisher = PgOutboxPublisher::new(pool.clone(), "audit_outbox")?;

let worker = PgOutboxWorkerBuilder::new(pool.clone())
    .table_name("audit_outbox")
    .register_handler::<UserRegistered, _>(AuditWriter)
    .poll_interval(Duration::from_millis(50))
    .build()?;

let cancel = CancellationToken::new();
let join = tokio::spawn(worker.run(cancel.clone()));

// inside a business use case:
let mut tx = pool.begin().await?;
let event_id = publisher.publish_in_tx(&mut tx, &UserRegistered { user_id: Uuid::new_v4() }).await?;
tx.commit().await?;
println!("published event {event_id}");

cancel.cancel();
join.await??;
# Ok(()) }

See docs/tutorial/getting-started.md for the full integration walkthrough.

Bus (RabbitMQ)

Add the umbrella crate with the bus-rabbitmq feature to your Cargo.toml:

[dependencies]
hexeract = { version = "0.5", features = ["bus-rabbitmq"] }

Declare a domain message, a handler and wire a publisher plus a worker:

use hexeract::bus::{Handler, Message, Transport};
use hexeract::bus_rabbitmq::{RabbitMqConnection, RabbitMqTransport, RabbitMqWorkerBuilder};
use hexeract::core::HandlerContext;
use serde::{Deserialize, Serialize};
use tokio_util::sync::CancellationToken;
use uuid::Uuid;

#[derive(Debug, Serialize, Deserialize)]
struct OrderPlaced { order_id: Uuid }

impl Message for OrderPlaced {
    const MESSAGE_TYPE: &'static str = "orders.placed";
}

struct Projector;
impl Handler<OrderPlaced> for Projector {
    type Error = hexeract::bus::BusError;
    async fn handle(&self, msg: OrderPlaced, _ctx: &HandlerContext) -> Result<(), Self::Error> {
        // ... project to read model, forward to downstream system, ...
        let _ = msg.order_id;
        Ok(())
    }
}

# async fn run(uri: &str) -> Result<(), Box<dyn std::error::Error>> {
let transport = RabbitMqTransport::new(uri).await?;
let consumer_conn = RabbitMqConnection::connect(uri).await?;

let worker = RabbitMqWorkerBuilder::new(consumer_conn)
    .queue("orders.received")
    .register_handler::<OrderPlaced, _>(Projector)
    .build()?;

let cancel = CancellationToken::new();
let join = tokio::spawn(worker.run(cancel.clone()));

let message_id = transport
    .publish("orders.received", &OrderPlaced { order_id: Uuid::new_v4() })
    .await?;
println!("published message {message_id}");

cancel.cancel();
join.await??;
# Ok(()) }

In production, declare your topology once at service startup (or out of band through the CLI). The topology::ensure_topology helper and the CLI live for dev convenience; do not call them on the hot path.

The hexeract bus CLI provisions and inspects a broker without writing ad-hoc lapin scripts:

export HEXERACT_BUS_URL=amqp://guest:guest@localhost:5672

# 1. Apply a typed topology described in TOML.
hexeract bus declare --topology crates/hexeract-cli/examples/topology.toml

# 2. Peek the first messages of a queue (non-destructive, requeues each delivery).
hexeract bus peek --queue orders.received --count 5

# 3. Drop every message in a queue (gated by an explicit safety flag).
hexeract bus purge --queue orders.received --yes-i-know

See the runnable crates/hexeract-examples/examples/03_bus_pubsub.rs for an end-to-end pub/sub against a real RabbitMQ container, and crates/hexeract-cli/examples/topology.toml for the topology file format consumed by hexeract bus declare.

Mediator (in-process)

Add the umbrella crate with the mediator feature to your Cargo.toml:

[dependencies]
hexeract = { version = "0.5", features = ["mediator"] }

Register a command handler and dispatch through the mediator:

use hexeract::core::{Command, CommandHandler, HandlerContext, HexeractError};
use hexeract::mediator::MediatorBuilder;

struct Greet { name: String }

impl Command for Greet {
    type Output = String;
}

struct GreetHandler;

impl CommandHandler<Greet> for GreetHandler {
    type Error = HexeractError;
    async fn handle(&self, cmd: Greet, _ctx: &HandlerContext) -> Result<String, Self::Error> {
        Ok(format!("hello {}", cmd.name))
    }
}

# async fn run() -> Result<(), Box<dyn std::error::Error>> {
let mediator = MediatorBuilder::new()
    .register_command_handler::<Greet, _>(GreetHandler)
    .build()?;

let greeting = mediator.send(Greet { name: "world".into() }).await?;
assert_eq!(greeting, "hello world");
# Ok(()) }

Queries (Mediator::query) and notifications (Mediator::publish) follow the same pattern. Notifications fan out to every handler registered for the type in registration order; failures are aggregated so siblings keep running. Wire your own [Middleware] implementations through MediatorBuilder::with_middleware to add tracing, timeouts or any cross-cutting behavior around every dispatch.

Why Hexeract

Building event-driven services in Rust today means manually wiring a broker client, an outbox table, and an in-process dispatch layer together. Hexeract closes that gap with a single SDK that covers the full shipped surface while keeping each feature independently usable:

• Mediator, dispatch commands to handlers in-process, type-safe and reflection-free.
• Bus, publish and consume over a message broker through a unified transport abstraction.
• Outbox, save business state and outgoing messages atomically in a single database transaction.

The bet behind Hexeract is that Rust's compile-time guarantees turn the outbox pattern from a vigilance discipline into something the type system enforces.

Roadmap

Available today: Mediator, Bus, Outbox/Inbox, and delivery reliability (dead-letter handling, publisher confirms, idempotency).

Planned: Sagas, Scheduler, Request/Reply. See ROADMAP.md.

What Hexeract is not

To stay focused, the following are explicitly out of scope:

• Not a service mesh. No automatic mTLS or network policies between services. Use Linkerd or Istio.
• Not a broker. Hexeract is a client; you keep your existing RabbitMQ, NATS or Kafka.
• Not a standalone workflow engine. Sagas live inside your services, not in a dedicated cluster. Use Temporal or Airflow when you need that shape.
• Not an event streaming engine. No real-time stream processing. Use Kafka Streams or Apache Flink.

Audience

• Rust backend teams building microservices who want a cohesive messaging toolkit instead of stacking incompatible crates.
• Developers migrating to Rust looking for a cohesive messaging SDK.
• Polyglot teams with part of their stack moving to Rust and the need to stay interoperable on a shared bus alongside their Node, Python or Go services.

Contributing

Contributions are welcome. Please read CONTRIBUTING.md first for the workflow and conventions, and CODE_OF_CONDUCT.md for the community guidelines. For vulnerability reports, see SECURITY.md. For open-ended questions and design conversations, use GitHub Discussions.

Stability and versioning are documented in docs/SEMVER_POLICY.md and docs/MSRV_POLICY.md.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT License (LICENSE-MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual-licensed as above, without any additional terms or conditions.

See CONTRIBUTING.md for details, including the Contributor License Agreement (CLA).

Copyright © Nubster.