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.

"Hello World" in Ring:

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

(def upcase-app (wrap-upcase app))

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

To see some working examples, first pull in Ring's dependencies using Leiningen:

$ lein deps

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

$ java -cp "lib/*" clojure.main 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.

To see a more sophisticated Ring app, run:

$ java -cp "lib/*" clojure.main 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.

• Ring namespace and function docs

• ring.middleware.file: Serve static files out of a public directory.
• ring.middleware.resource: Serve static classpath resources.
• ring.middleware.static: Serve static files with specified prefixes out of a public directory.
• ring.middleware.file-info: Augment response headers with info about File responses.
• ring.middleware.content-type: Augment response headers with a content-type based on the file extension.
• ring.middleware.params: Parse query and form params.
• ring.middleware.multipart-params: Parse multipart params.
• ring.middleware.keyword-params: Convert string param keys to keywords.
• ring.middleware.nested-params: Convert a flat map of parameters into a nested map of parameters.
• ring.middleware.cookies: Manage browser cookies.
• ring.middleware.session: Manage user sessions. Memory and cookie session stores are available by default.
• ring.middleware.flash: Adds flash message support to sessions.
• ring.util.response: Generate Ring responses.
• ring.util.codec: Encode and decode string data.
• ring.util.mime-type: Guess the mime-type from a file extension.

• ring.handler.dump: Dumps request maps as HTML responses for debugging.
• ring.middleware.lint: Lint requests and responses to ensure compliance with the Ring spec.
• ring.middleware.reload: Automatically reload selected libs before each request.
• ring.middleware.stacktrace: Catch exceptions and displays readable stacktraces for debugging.

• ring.util.servlet: Utilities for interfacing with Java Servlets.

• ring.adapter.jetty: Adapter for the Jetty webserver.

To include one of the above libraries in your Leiningen project, for example ring-core, add the following to your :dependencies:

[ring/ring-core "0.3.11"]

To include all of them, add:

[ring "0.3.11"]

Ring is being actively developed; you can track its progress on the GitHub page page and on the Google Group.

To submit a patch, please post your corresponding GitHub branch to the Ring Google Group. This allows your changes to be seen and discussed by all Ring developers. If you are attempting something substantial, consider posting to the Google Group first with your idea.

To run the Ring unit tests, first navigate to the appropriate project and then:

$ lein deps
$ lein test

This project borrows heavily from Ruby's Rack and Python's WSGI; thanks to those communities for their work.

Copyright (c) 2009-2011 Mark McGranaghan and released under an MIT license.

Clojure logo by Tom Hickey.