Monocoque

A Rust-native ZeroMQ-compatible messaging runtime built on io_uring

Monocoque is a ZeroMQ-compatible messaging library written in Rust. It implements ZMTP 3.1 from scratch on top of io_uring (via compio), so it interoperates with any existing libzmq peer while staying entirely within Rust's memory model.

The name comes from Formula 1 engineering, where the monocoque chassis achieves structural strength through form rather than bolt-on reinforcement. Same idea here: performance through correct architecture, not unsafe shortcuts.

Features

• All 11 ZeroMQ socket types: REQ, REP, DEALER, ROUTER, PUB, SUB, XPUB, XSUB, PUSH, PULL, PAIR
• PLAIN and CURVE (CurveZMQ/X25519) authentication, ZAP support
• TCP and IPC (Unix domain socket) transports
• Automatic reconnection with exponential backoff on all socket types
• ZMTP 3.1 heartbeating (PING/PONG) wired into all send/recv loops
• Socket monitoring via channel-based lifecycle events
• Explicit batching API for maximum throughput
• Zero-copy message passing via Bytes refcounting

Performance

Benchmarked against rust-zmq (FFI bindings to libzmq). REQ/REP round-trip latency on loopback TCP (Intel Core i7-1355U, Linux 6.17, release build):

Throughput with the batching API reaches 2.5M+ msg/sec for small messages (2.97M at 64B, 1.23M at 1KB). IPC is about 35% faster than TCP loopback for local communication. See docs/performance.md for the full breakdown.

Quick Start

[dependencies]
monocoque-rs = { version = "0.1", features = ["zmq"] }
compio = { version = "0.13", features = ["runtime"] }

use monocoque::zmq::{DealerSocket, RouterSocket};

// Connect a DEALER
let mut dealer = DealerSocket::connect("tcp://127.0.0.1:5555").await?;
dealer.send(vec![b"Hello".into()]).await?;
let reply = dealer.recv().await?;

// Bind a ROUTER
let mut router = RouterSocket::bind("tcp://127.0.0.1:5555").await?;
let msg = router.recv().await?;  // msg[0] is the routing identity

// PUB/SUB
let mut publisher = PubSocket::bind("tcp://127.0.0.1:5556").await?;
publisher.send(vec![b"events".into(), b"payload".into()]).await?;

let mut subscriber = SubSocket::connect("tcp://127.0.0.1:5556").await?;
subscriber.subscribe(b"events").await?;
let msg = subscriber.recv().await?;

For high throughput, buffer messages and flush once:

for msg in &batch {
    dealer.send_buffered(msg.clone())?;
}
dealer.flush().await?;

Safety

unsafe code is confined to a single file: monocoque-core/src/alloc.rs, which implements the arena allocator for io_uring-safe buffer management. Everything else is 100% safe Rust.

Memory invariants:

• Buffers are never reused while referenced (tracked via Bytes refcounts)
• SlabMut -> Bytes is a one-way transition; no mutation after freeze
• PUB fanout is refcount-based (Bytes::clone()), never copies payloads

Development

cargo build --release --workspace
cargo test --workspace --features zmq
cargo bench --features zmq       # runs the benchmark suite

Interop testing against libzmq: see docs/INTEROP_TESTING.md.

Roadmap

Core features are complete. Possible future work:

• io_uring fixed buffers (IORING_OP_READ_FIXED) - removes the last kernel-boundary copy per read; ~5-15% latency improvement at an already low baseline
• Prefix trie for topic matching - only relevant with 100+ concurrent subscribers using deep topic hierarchies
• Concurrent PUB fanout - prevents one slow subscriber from delaying others in large-subscriber deployments

Long term: high-performance RPC, additional transports (QUIC, shared memory), custom protocol framework.

License

MIT - see LICENSE.

Built with: compio, bytes, flume, smallvec