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A simple, high-performance event-driven HTTP client+server for Clojure

CHANGELOG | API | current Break Version:

[http-kit "2.6.0"]  ; Published by contributors, see CHANGELOG for details (stable)
[http-kit "2.1.19"] ; Legacy, published by @shenfeng

Project status

http-kit's author (@shenfeng) unfortunately hasn't had much time to maintain http-kit recently. To help out I'll be doing basic issue triage, accepting minor/obvious PRs, etc.

A big thank you to the current contributors for keeping the project going! Additional contributors welcome: please ping me if you'd be interested in lending a hand.

See the (unmaintained, outdated) project website for original documentation, examples, benchmarks, etc.

- @ptaoussanis


  • Ring compliant: HTTP Kit is an (almost) drop-in replacement for the standard Ring Jetty adapter. So you can use it with all your current libraries (e.g. Compojure) and middleware.

  • High performance: Using an event-driven architecture like Nginx, HTTP-kit is very, very fast. It comfortably handles tens of thousands of requests/sec on even midrange hardware. Here is another test about how it stacks up with others.

  • High concurrency: It's not only fast, but efficient! Each connection costs nothing but a few kB of memory. RAM usage grows O(n) with connections.

  • Clean, simple, small: Written from the ground-up to be lean, the entire client/server is available as a single ~90kB JAR with zero dependencies and ~3k lines of (mostly Java) code.

  • Sync or async: Synchronous is simple. Asynchronous is fast & flexible. With HTTP Kit you get the best of both with a simple API that lets you mix & match to best fit your use case.

  • WebSockets and Comet: With great out-the-box support for both WebSockets and efficient handling of long-held HTTP requests, realtime web applications are a breeze to write.

Enabling client SNI support (DISABLED BY DEFAULT)

To retain backwards-compatibility with JVMs < 8, http-kit client's SNI support is DISABLED by default.

Common cause of: Received fatal alert: handshake_failure

This default may be changed in a future breaking release. In the meantime, manually enabling support is easy:

  (:require [org.httpkit.sni-client :as sni-client]) ; Needs Java >= 8, http-kit >= 2.4.0-alpha6

  ;; Change default client for your whole application:
  (alter-var-root #'org.httpkit.client/*default-client* (fn [_] sni-client/default-client))

  ;; or temporarily change default client for a particular thread context:
  (binding [org.httpkit.client/*default-client* sni-client/default-client]

See org.httpkit.client/*default-client* docstring for more details.

Hack locally

Hacker friendly: zero dependencies, written from the ground-up with only ~3.5k lines of code (including java), clean and tidy.

# Modify as you want, unit tests back you up:
lein test

# May be useful (more info), see `server_test.clj`:

# Some numbers on how fast can http-kit's client can run:
lein test :benchmark

Contact & Contribution

Please use the GitHub issues page for feature suggestions, bug reports, or general discussions. Current contributors are listed here. The project website is also on GitHub.

Native Image

http-kit server and client are compatible with GraalVM's native-image compiler.

To ensure the image can build, provide the following options to the native-image compiler:


In your reflection-config.json

{"name": "java.lang.reflect.AccessibleObject",
 "methods" : [{"name":"canAccess"}]}

Class initialization

As of version 2.5.2 add the following flags:



Copyright © 2012-2022 @shenfeng and contributors. Distributed under the Apache License Version 2.0.

Can you improve this documentation? These fine people already did:
feng, Peter Taoussanis, Ben Sless, iacopo, Philip Aston, Dmitri Sotnikov, Samy Dindane, Alexander Oloo & Francesco Pischedda
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