Ring is a Clojure web applications library inspired by Python's WSGI and Ruby's Rack. By abstracting the details of HTTP into a simple, unified API, Ring allows web applications to be constructed of modular components that can be shared among a variety of applications, web servers, and web frameworks.

The SPEC file at the root of this distribution for provides a complete description of the Ring interface.

Examples

A Ring handler:

(use 'ring.adapter.jetty)

(defn app [req]
  {:status  200
   :headers {"Content-Type" "text/html"}
   :body    "Hello World from Ring"})

(run-jetty app {:port 8080})

Adding simple middleware:

(defn with-upcase [app]
  (fn [req]
    (let [orig-resp (app req)]
      (assoc orig-resp :body (.toUpperCase (:body orig-resp))))))

(def upcase-app (with-upcase app))

(run-jetty upcase-app {:port 8080})

Quick Start

First, pull in Ring's dependencies using Leiningen:

$ lein deps

To see a live "Hello World" Ring app, run:

$ clj src/ring/example/hello_world.clj

Now visit http://localhost:8080/ in your browser; the Ring app will respond to your request with a simple HTML page indicating the time of day.

Note that your clj script needs to add the src directory and the jars in lib to your classpath.

To see a more sophisticated Ring app, run:

$ clj src/ring/example/wrapping.clj

• If you request http://localhost:8080/ in your browser the ring.handler.dump handler will respond with an HTML page representing the request map that it received (see the SPEC for details on the request map).
• If you request http://localhost:8080/clojure.png, the ring.middleware.file middleware will detect that there is a clojure.png file in the app's public directory and return that image as a response.
• If you request http://localhost:8080/error, the app will produce an error that will be caught by the ring.middleware.stacktrace middleware, which will in turn return a readable stacktrace as the HTML response.

Included Libs

• ring.adapter.jetty: Adapter for the Jetty webserver.
• ring.adapter.httpcore: Adapter for the Apache HttpCore webserver.
• ring.middleware.file: Middleware that serves static files out of a public directory.
• ring.middleware.file-info: Middleware that augments response headers with info about File responses.
• ring.middleware.lint: Linter for the Ring interface, ensures compliance with the Ring spec.
• ring.middleware.reload: Middleware to automatically reload selected libs before each requests, minimizing server restarts.
• ring.middleware.stacktrace: Middleware that catches exceptions and displays readable stacktraces for debugging.
• ring.middleware.static: Middleware that serves static files with specified prefixes out of a public directory.
• ring.handler.dump: Handler that dumps request maps as HTML responses for debugging.
• ring.util.servlet: Utilities for interfacing with Java Servlets.
• ring.example.*: Various example Ring apps.

Development

Ring is being actively developed; you can track its progress and contribute at the project's GitHub page.

To run all the Ring unit tests:

$ clj test/ring/run.clj

Thanks

This project borrows heavily from Ruby's Rack and Python's WSGI, and I thank the communities developing and supporting those projects.

License

Copyright (c) 2009 Mark McGranaghan and released under an MIT license.

Clojure logo by Tom Hickey.