Ensō

/!\ WIP

Fast, low-allocation, zero-dependency* HTTP/1.1 + HTTP/2 + HTTP/3 Ring server adapter for Clojure.

Java core optimized for Ring, not a wrapper. Built on/for virtual threads. Plain sync handler.

• Fast. ~5M rps pipelined depth 64 (HTTP/1.1); ~894k rps HTTP/2 over TLS; ~53k rps HTTP/3 (edges Netty by ~2%, ~19× Jetty).
  • Low allocation. ~0.001 sample/req at 1 MB TLAB interval — near-zero GC pressure on hot paths.
• Zero third-party Java dependencies. Java core + thin Clojure adapter. Clojure runtime is the only requirement (for http1+2). Release jars bundle a JNI shim per platform with libquiche statically linked in — no system libquiche install needed. HTTP/3 remains opt-in.
• Virtual threads, sync API. One vthread per connection, blocking I/O. Handler is a plain Ring function — no async arity, no callbacks.
• HTTP/1.1 complete.
• HTTP/2. ALPN over TLS (:http2 true). h2spec pass.
• HTTP/3. Cloudflare libquiche over UDP via JNI shim. Pure-Java QPACK + H3 framing on top of quiche's transport primitives. Alt-Svc auto-advertised from h1/h2 responses when h3 enabled. Faster than Netty h3 in bench — see doc/performance.md.
• WebSocket. Ring 1.5+ listener shape.
• SSE / long-poll. Streaming writer
• Correct. Rejects request smuggling, header injection, slowloris. CVE-2023-44487 rapid-reset mitigation. Body-size caps enforced.

Requirements

• JDK 21+ (HTTP/3 requires 22+).
• Clojure 1.12+.
• HTTP/3: add a matching classifier — see below.

deps.edn

;; core only, no h3
{:deps {com.s-exp/enso {:mvn/version "..."}}}

;; core + per-platform http3 shim
{:deps {com.s-exp/enso              {:mvn/version "..."}
        com.s-exp/enso$darwin-arm64 {:mvn/version "..."}}}

Classifiers: darwin-arm64, linux-{amd64,arm64}, linux-musl-{amd64,arm64}. Full detail in doc/http3.md.

Quick start

(require '[s-exp.enso :as enso])

(def server
  (enso/run-server
    (fn [req] {:status 200 :body "hello"})
    {:port 8080}))

(enso/stop server)

Documentation

• doc/options.md — full configuration reference (network, timeouts, keep-alive, TCP, TLS, HTTP/2, HTTP/3, limits).
• doc/handlers.md — response body types, WebSocket, SSE, error handling, correctness notes.
• doc/http3.md — HTTP/3 setup, release-jar distribution, dev build against system libquiche.
• doc/performance.md — bench numbers vs http-kit / Jetty / Aleph / Netty; allocation profile; reproduction steps.
• doc/build.md — build tasks, jar flavors, release CI.

Prior art

The HTTP/2 write architecture — dedicated writer vthread, bounded frame queue, fair lock around HPACK, SSLEngine over SocketChannel — is inspired by Helidon Níma (Apache 2.0). Ensō re-implements the pattern from scratch, no code copied.

License

Copyright © 2026 Max Penet.

Ensō is distributed under the Mozilla Public License 2.0. Practical summary: https://www.mozilla.org/en-US/MPL/2.0/FAQ/.