ØMQ (ZeroMQ) for tokio

Run asynchronous ØMQ sockets with Rust's tokio framework.

Rust is a systems programming language that runs blazingly fast, prevents segfaults, and guarantees thread safety.

ZeroMQ (also known as ØMQ, 0MQ, or zmq) looks like an embeddable networking library but acts like a concurrency framework. It gives you sockets that carry atomic messages across various transports like in-process, inter-process, TCP, and multicast. You can connect sockets N-to-N with patterns like fan-out, pub-sub, task distribution, and request-reply. It's fast enough to be the fabric for clustered products. Its asynchronous I/O model gives you scalable multicore applications, built as asynchronous message-processing tasks. It has a score of language APIs and runs on most operating systems. ZeroMQ is from iMatix and is LGPLv3 open source.

mio. Lightweight non-blocking IO.

futures. Zero-cost futures and streams in Rust.

Tokio. A platform for writing fast networking code with Rust.

This crate uses rust-zmq's bindings.

Status

• zmq-futures documentation
• zmq-mio documentation
• zmq-tokio documentation

This is the barely budding seed of providing access to ZeroMQ via the tokio async I/O abstraction.

This project is in its very infancy. Do not expect to be able to build something useful on top of this (yet). The API will certainly change wildly before approaching some kind of stability.

The underlying library API is still not complete.

Justification

ZeroMQ is a fully-documented library that is meant to act as an intelligent transport layer for messaging patterns. It's portable across OS platforms, as well as across programming languages.

Rust's bindings for the ZeroMQ library, rust-zmq, wrap the C library into a very ergonomic implementation of most of the API.

ZeroMQ's model is asynchronous by nature, however, it is handled automatically unless the DONTWAIT flag is specified when sending/receiving. This flag configures the socket to non-blocking mode, for which the user API states that there is a need for IO error handling, specifically for the case of std::io::ErrorKind::WouldBlock.

So, to properly use ZMQ sockets asynchronously, it is necessary to have some higher-level code that can enforce correct handling of non-blocking messaging. In Rust, this is what tokio can do, with certain adaptations to the underlying ZMQ socket.

These adaptions are carried out by mio, which helps build the bridge that connects the synchronous with the asynchronous, by adding non-blocking compatibility in the form of std::io::Error, as well as a polling mechanism that is meant to be cross-platform, and which is implemented via the mio::Evented trait. Since rust-zmq provides a RawFd reference to the ZMQ socket, and since mio provides the wrapper type EventedFd, making a ZMQ socket mio-compatible, is basically a matter of using the DONTWAIT flag on the socket, making sure that our functions and methods return Result<_, io::Error>, and wrap it into a new type that uses EventedFd to automatically make everything work for polling.

Finally, futures in Rust, which aim to provide a robust implementation of handling asynchronous computations, ergonomic composition and usage, and zero-cost abstractions over what would otherwise be written by hand, are way that data is handled and processed in tokio.

It can be argued that integrating ZeroMQ into the tokio ecosystem is a perfect match.

It can be used to extend existing ZeroMQ infrastructure, as well as to create new network components that are guaranteed to be safe, fast, and concurrent. The Rust way.

Goals

• The main goal, is to bring in ZeroMQ's messaging patterns, via their sockets, into the tokio ecosystem.
• To bridge the existing asynchronous support provided by ZeroMQ, via rust-zmq, with tokio's `polling mechanism.
• To create Future, Stream, and Sink types that blend in with the existing zmq::Socket API.
• To provide full technical documentation.
• To provide end-user documentation.
• To provide end-user examples.

Usage

For a typical crate, you need at least futures, tokio\_core and zmq\_tokio.

Add this to your Cargo.toml:

[dependencies]
futures = "0.1"
tokio_core = "0.1"
zmq_tokio = { git = "https://github.com/saibatizoku/zmq-tokio.git" }

Then, on your crates main module, for example src/main.rs:

extern crate futures;
extern crate tokio_core;
extern crate zmq_tokio;

use futures::Future;
use tokio_core::reactor::Core;
use zmq_tokio::{Context, Socket, PUB};


fn main() {
    // Start the ZMQ context and the tokio reactor.
    let context = Context::new();
    let mut reactor = Core::new().unwrap();

    // Create a publisher socket, connected to a given address.
    let socket = context.socket(PUB, &reactor.handle()).unwrap();
    let _ = socket.connect("inproc://test").unwrap();

    // Create a future that will send a simple message to subscribers.
    let send_msg = socket.send(b"HELLO");

    // Execute the future on the reactor.
    let _ = core.run(run_pub).unwrap();
}

Examples

Please consult the examples directory.