Programming language: Rust
License: MIT License
Tags: Web Programming     HTTP Server    
Latest version: v0.6.1

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Build Status Crates.io Status License

Extensible, Concurrency Focused Web Development in Rust.

Response Timer Example

Note: This example works with the current iron code in this repository (master branch). If you are using iron 0.6 from crates.io, please refer to the corresponding example in the branch 0.6-maintenance.

extern crate iron;
extern crate time;

use iron::prelude::*;
use iron::{typemap, AfterMiddleware, BeforeMiddleware};
use time::precise_time_ns;

struct ResponseTime;

impl typemap::Key for ResponseTime { type Value = u64; }

impl BeforeMiddleware for ResponseTime {
    fn before(&self, req: &mut Request) -> IronResult<()> {

impl AfterMiddleware for ResponseTime {
    fn after(&self, req: &mut Request, res: Response) -> IronResult<Response> {
        let delta = precise_time_ns() - *req.extensions.get::<ResponseTime>().unwrap();
        println!("Request took: {} ms", (delta as f64) / 1000000.0);

fn hello_world(_: &mut Request) -> IronResult<Response> {
    Ok(Response::with((iron::StatusCode::OK, "Hello World")))

fn main() {
    let mut chain = Chain::new(hello_world);


Iron is a high level web framework built in and for Rust, built on hyper. Iron is designed to take advantage of Rust's greatest features - its excellent type system and its principled approach to ownership in both single threaded and multi threaded contexts.

Iron is highly concurrent and can scale horizontally on more machines behind a load balancer or by running more threads on a more powerful machine. Iron avoids the bottlenecks encountered in highly concurrent code by avoiding shared writes and locking in the core framework.

Iron is 100% safe code:

$ rg unsafe src | wc
       0       0       0


Iron is meant to be as extensible and pluggable as possible; Iron's core is concentrated and avoids unnecessary features by leaving them to middleware, plugins, and modifiers.

Middleware, Plugins, and Modifiers are the main ways to extend Iron with new functionality. Most extensions that would be provided by middleware in other web frameworks are instead addressed by the much simpler Modifier and Plugin systems.

Modifiers allow external code to manipulate Requests and Response in an ergonomic fashion, allowing third-party extensions to get the same treatment as modifiers defined in Iron itself. Plugins allow for lazily-evaluated, automatically cached extensions to Requests and Responses, perfect for parsing, accessing, and otherwise lazily manipulating an http connection.

Middleware are only used when it is necessary to modify the control flow of a Request flow, hijack the entire handling of a Request, check an incoming Request, or to do final post-processing. This covers areas such as routing, mounting, static asset serving, final template rendering, authentication, and logging.

Iron comes with only basic modifiers for setting the status, body, and various headers, and the infrastructure for creating modifiers, plugins, and middleware. No plugins or middleware are bundled with Iron.


Iron averages 72,000+ requests per second for hello world and is mostly IO-bound, spending over 70% of its time in the kernel send-ing or recv-ing data.*

* Numbers from profiling on my OS X machine, your mileage may vary.

Core Extensions

Iron aims to fill a void in the Rust web stack - a high level framework that is extensible and makes organizing complex server code easy.

Extensions are painless to build. Some important ones are:




This allows for extremely flexible and powerful setups and allows nearly all of Iron's features to be swappable - you can even change the middleware resolution algorithm by swapping in your own Chain.

* Due to the rapidly evolving state of the Rust ecosystem, not everything builds all the time. Please be patient and file issues for breaking builds, we're doing our best.

Underlying HTTP Implementation

Iron is based on and uses hyper as its HTTP implementation, and lifts several types from it, including its header representation, status, and other core HTTP types. It is usually unnecessary to use hyper directly when using Iron, since Iron provides a facade over hyper's core facilities, but it is sometimes necessary to depend on it as well.

<!-- FIXME: expand on when it is necessary to user hyper for serving, e.g. when doing HTTPS. -->


If you're using Cargo, just add Iron to your Cargo.toml:

version = "*"


The documentation is hosted online and auto-updated with each successful release. You can also use cargo doc to build a local copy.


Check out the examples directory!

You can run an individual example using cargo run --bin example-name inside the examples directory. Note that for benchmarking you should make sure to use the --release flag, which will cause cargo to compile the entire toolchain with optimizations. Without --release you will get truly sad numbers.

Getting Help

Feel free to ask questions as github issues in this or other related repos.

The best place to get immediate help is on IRC, on any of these channels on the mozilla network:

  • #rust-webdev
  • #iron
  • #rust

One of the maintainers or contributors is usually around and can probably help. We encourage you to stop by and say hi and tell us what you're using Iron for, even if you don't have any questions. It's invaluable to hear feedback from users and always nice to hear if someone is using the framework we've worked on.


Jonathan Reem (reem) is the core maintainer and author of Iron.

Commit Distribution (as of 8e55759):

Jonathan Reem (415)
Zach Pomerantz (123)
Michael Sproul (9)
Patrick Tran (5)
Corey Richardson (4)
Bryce Fisher-Fleig (3)
Barosl Lee (2)
Christoph Burgdorf (2)
da4c30ff (2)
arathunku (1)
Cengiz Can (1)
Darayus (1)
Eduardo Bautista (1)
Mehdi Avdi (1)
Michael Sierks (1)
Nerijus Arlauskas (1)
SuprDewd (1)



*Note that all licence references and agreements mentioned in the Iron README section above are relevant to that project's source code only.