Robust, ergonomic CoAP server in Rust

An asynchronous CoAP server with a modern and ergonomic API for larger scale applications, inspired by warp and actix. CoAP offers an excellent alternative to HTTP for resource constrained environments like IoT devices.

• Ergonomic: Fluent app-builder API makes it easy to compose rich applications, including those that use more advanced CoAP features.
• Concurrent: High concurrency is supported by using a separate spawned task for each request, allowing long running requests to not interfere with shorter running ones at scale.
• Feature-rich: Conveniently supports a wide range of CoAP server features including Observe, and Block-wise Transfer.
• Flexible: Supports pluggable transport backends with goals of supporting alternative async runtimes like embassy.

Example

use coap_server::app::{CoapError, Request, Response};
use coap_server::{app, CoapServer, FatalServerError, UdpTransport};

#[tokio::main]
async fn main() -> Result<(), FatalServerError> {
    let server = CoapServer::bind(UdpTransport::new("0.0.0.0:5683")).await?;
    server.serve(
        app::new().resource(
            app::resource("/hello").get(handle_get_hello))
    ).await
}

async fn handle_get_hello(request: Request<SocketAddr>) -> Result<Response, CoapError> {
    let whom = request
        .unmatched_path
        .first()
        .cloned()
        .unwrap_or_else(|| "world".to_string());

    let mut response = request.new_response();
    response.message.payload = format!("Hello, {whom}").into_bytes();
    Ok(response)
}

To experiment, I recommend using the excellent coap-client command-line tool, as with:

$ coap-client -m get coap://localhost/hello
Hello, world

See examples for more.

Features

This project aims to be a robust and complete CoAP server, and in particular a more convenient alternative to MQTT for Rust-based projects:

• Correct and convenient Observe support (RFC 7641)
• Block-wise transfer support (RFC 7959)
• Resource discovery and filtering via /.well-known/core (RFC 6690)
• Multicast UDP
• Fully concurrent request handling (no head-of-line blocking or scaling surprises!)
• Ping/Pong keep-alive messages

Desired but not implemented:

• Non-piggybacked responses
• Secure transports (OSCORE and DTLS)

Related Projects

• martindisch/coap-lite: used by this project as the low-level basis for CoAP protocol support
• Covertness/coap-rs: original server I used but outgrew when I needed more robust features like generic Observe support and /.well-known/core filtering.
• ryankurte/rust-coap-client: inspired the creation of this crate based on the excellent generalization of client backends
• google/rust-async-coap