celeris

Ultra-low latency Go HTTP engine with a protocol-aware dual-architecture (io_uring & epoll) designed for high-throughput infrastructure and zero-allocation microservices. It provides a familiar route-group and middleware API similar to Gin and Echo, so teams can adopt it without learning a new programming model.

Highlights

• io_uring and epoll at parity — both engines deliver equivalent throughput
• Zero hot-path allocations on the H1 / H2 fast paths (pool-based contexts, pre-encoded HPACK responses)
• Continuously validated — a probatorium 48-cell adversarial matrix runs nightly + a deeper weekend soak; see the badges above

Features

• Tiered io_uring — auto-selects the best io_uring feature set (multishot accept/recv, provided buffers, SQ poll, fixed files) for your kernel
• Edge-triggered epoll — per-core event loops with CPU pinning
• Adaptive meta-engine — dynamically switches between io_uring and epoll based on runtime telemetry
• SIMD HTTP parser — SSE2 (amd64) and NEON (arm64) with generic SWAR fallback
• HTTP/2 cleartext (h2c) — full stream multiplexing, flow control, HPACK, inline handler execution, zero-alloc HEADERS fast path
• Auto-detect — protocol negotiation from the first bytes on the wire
• Error-returning handlers — HandlerFunc returns error; structured HTTPError for status codes
• Pre-routing middleware — Server.Pre() runs middleware before route matching (method override, URL rewrite)
• Serialization — JSON and XML response methods; Bind auto-detects request format from Content-Type
• net/http compatibility — wrap existing http.Handler via celeris.Adapt()
• Streaming responses — Detach() + StreamWriter for SSE and chunked responses on native engines
• Connection hijacking — Hijack() for WebSocket and custom protocol upgrades (H1 only)
• Engine-integrated WebSocket — UpgradeWebSocket() hands the conn directly to the worker loop with backpressure, deflate, and a Hub for fan-out broadcast
• Response buffering — BufferResponse/FlushResponse for transform middleware (compress, ETag, cache)
• File serving — File() from OS, FileFromFS() from embed.FS / fs.FS
• Content negotiation — Negotiate, Respond, AcceptsEncodings, AcceptsLanguages
• Configurable body limits — MaxRequestBodySize enforced on H1 and H2 (the net/http bridge has a fixed 100 MB cap)
• 100-continue control — OnExpectContinue callback for upload validation before body transfer
• Accept control — PauseAccept()/ResumeAccept() for graceful load shedding
• Zero-downtime restart — InheritListener + StartWithListener for socket inheritance
• Built-in metrics — atomic counters, CPU utilization sampling, on-by-default Server.Collector().Snapshot() (opt out via Config.DisableMetrics)
• Per-handler async dispatch — Route.Async() / Route.Sync() choose inline-on-worker vs. per-conn dispatch goroutine per route; H2 chooses per-stream

TLS: the io_uring/epoll engines speak cleartext only (HTTP/1.1 + h2c). Terminate TLS upstream (Caddy/Nginx/Envoy) or use the std engine if you need in-process HTTPS.

Quick Start

go get github.com/goceleris/celeris@latest

Requires Go 1.26.3+. Linux for io_uring/epoll engines; any OS for the std engine.

Hello World

package main

import (
	"log"

	"github.com/goceleris/celeris"
)

func main() {
	s := celeris.New(celeris.Config{Addr: ":8080"})
	s.GET("/hello", func(c *celeris.Context) error {
		return c.String(200, "Hello, World!")
	})
	log.Fatal(s.Start())
}

Routing

s := celeris.New(celeris.Config{Addr: ":8080"})

// Static routes
s.GET("/health", healthHandler)

// Named parameters
s.GET("/users/:id", func(c *celeris.Context) error {
	id := c.Param("id")
	return c.JSON(200, map[string]string{"id": id})
})

// Catch-all wildcards
s.GET("/files/*path", staticFileHandler)

// Route groups with middleware
api := s.Group("/api")
api.Use(authMiddleware)
api.GET("/items", listItems)
api.POST("/items", createItem)

// Named routes + reverse URL generation
s.GET("/users/:id", showUser).Name("user")
url, _ := s.URL("user", "42") // "/users/42"

// Pre-routing middleware (runs before route matching)
s.Pre(methodOverride, urlRewrite)

Middleware

All middleware is in-tree under middleware/:

Package	Description
adapters	Bidirectional stdlib ↔ celeris middleware/handler conversion
basicauth	HTTP Basic authentication with hashed password support
bodylimit	Request body size enforcement
cache	HTTP response cache with singleflight + Cache-Control honoring
circuitbreaker	Circuit breaker (3-state, sliding window error rate, 503 + Retry-After)
compress	Response compression (zstd, brotli, gzip, deflate; separate go.mod)
cors	Cross-Origin Resource Sharing (zero-alloc)
csrf	CSRF protection (double-submit cookie + origin validation)
debug	Debug/introspection endpoints (loopback-only by default)
etag	Automatic ETag generation and conditional 304 responses
healthcheck	Kubernetes-style liveness/readiness/startup probes
idempotency	Idempotency-Key replay protection (state machine: in-flight 409 + cached replay)
jwt	JWT authentication (HMAC/RSA/ECDSA/EdDSA, JWKS auto-refresh)
keyauth	API key authentication with constant-time comparison
logger	Structured request logging (slog, zero-alloc FastHandler)
methodoverride	HTTP method override via header or form field
metrics	Prometheus metrics (separate go.mod)
otel	OpenTelemetry tracing + metrics (separate go.mod)
overload	5-stage CPU + queue-depth + tail-latency-EMA overload control (503 + Retry-After)
pprof	Go profiling endpoints (loopback-only by default)
protobuf	Protobuf serialization with content negotiation (separate go.mod)
proxy	Trusted proxy header extraction (X-Forwarded-For, X-Real-IP)
ratelimit	Sharded token bucket / sliding window rate limiter (Redis store adapter)
recovery	Panic recovery with broken pipe detection
redirect	URL redirect/rewrite (HTTPS, www, trailing slash)
requestid	Request ID generation (buffered UUID v4)
rewrite	Regex-based URL rewriting with capture group support
secure	Security headers (HSTS, CSP, COOP/CORP/COEP, OWASP defaults)
session	Cookie-based sessions on the unified store.KV (memory / Redis / Postgres / memcached adapters)
singleflight	Request coalescing (collapse identical in-flight requests)
sse	Server-Sent Events: heartbeat, Last-Event-ID resumption with pluggable replay store (in-memory ring buffer or KV-backed for cross-restart durability), per-client MaxQueueDepth + OnSlowClient policy (Drop/Close/Block), and a Broker for fan-out to N subscribers with per-subscriber bounded queues + OnSlowSubscriber policy (Drop/Remove/Close)
static	Static file serving with directory browse, ETag/Last-Modified caching
store	Unified in-memory KV (LRU); shared by session / csrf / ratelimit / cache / idempotency / jwt JWKS. Redis / Postgres / memcached adapters live under session/redisstore, session/postgresstore, session/memcachedstore, plus ratelimit/redisstore / ratelimit/memcachedstore
swagger	OpenAPI spec + Swagger UI / Scalar / ReDoc (CDN-loaded)
timeout	Request timeout with cooperative and preemptive modes
websocket	RFC 6455 WebSocket: permessage-deflate, engine-integrated backpressure, plus a Hub for fan-out broadcast to N connections (via cached PreparedMessage for O(1) per-message wire-encoding cost) with OnSlowConn policy (Drop/Remove/Close) and per-Conn filter via BroadcastFilter

import (
	"github.com/goceleris/celeris/middleware/cors"
	"github.com/goceleris/celeris/middleware/logger"
	"github.com/goceleris/celeris/middleware/recovery"
)

s := celeris.New(celeris.Config{Addr: ":8080"})
s.Use(recovery.New())
s.Use(logger.New())
s.Use(cors.New())

For middleware with external dependencies, use separate imports:

import "github.com/goceleris/celeris/middleware/metrics" // requires prometheus
import "github.com/goceleris/celeris/middleware/otel"    // requires opentelemetry

Error Handling

HandlerFunc has the signature func(*Context) error. Returning a non-nil error propagates it up through the middleware chain. If no middleware handles the error, the router's safety net converts it to an HTTP response:

• *HTTPError — responds with Code and Message from the error.
• Any other error — responds with 500 Internal Server Error.

// Return a structured HTTP error
s.GET("/item/:id", func(c *celeris.Context) error {
	item, err := store.Find(c.Param("id"))
	if err != nil {
		return celeris.NewHTTPError(404, "item not found").WithError(err)
	}
	return c.JSON(200, item)
})

// Use Status() + StatusJSON() for fluent responses
s.POST("/items", func(c *celeris.Context) error {
	var item Item
	if err := c.Bind(&item); err != nil {
		return celeris.NewHTTPError(400, "invalid body").WithError(err)
	}
	created := store.Create(item)
	return c.Status(201).StatusJSON(created)
})

Configuration

s := celeris.New(celeris.Config{
	Addr:               ":8080",
	Protocol:           celeris.Auto,       // HTTP1, H2C, or Auto
	Engine:             celeris.Adaptive,    // IOUring, Epoll, Adaptive, or Std
	Workers:            8,
	ReadTimeout:        30 * time.Second,
	WriteTimeout:       30 * time.Second,
	IdleTimeout:        120 * time.Second,
	ShutdownTimeout:    10 * time.Second,    // max wait for in-flight requests (default 30s)
	MaxRequestBodySize: 50 << 20,            // 50 MB (default 100 MB, -1 for unlimited)
	AsyncHandlers:      false,               // server-level default (per-route .Async() overrides)
	Logger:             slog.Default(),
})

Async Handlers (per-route)

Celeris runs every handler inline on the I/O worker by default — lowest latency, zero handoff. For handlers that block on I/O (database, RPC, file system) you can opt per-route into the per-connection dispatch goroutine, so the worker stays free to drive other connections:

// CPU-only / cache-only — runs inline (default).
s.GET("/healthz", healthHandler)

// Blocking I/O — async, runs on per-conn goroutine.
s.GET("/db", dbHandler).Async()

// Or flip the default at the group level:
api := s.Group("/api").Async()
api.GET("/products", productHandler)        // async (inherited)
api.GET("/cached", cachedHandler).Sync()    // opt back to sync

Precedence is route > group > server default (Config.AsyncHandlers). Works identically across iouring, epoll, and adaptive (both sub-engines honor the per-route flag and async promotions survive sub-engine swaps): the conn is promoted once via the ErrAsyncDispatch sentinel (sticky — subsequent requests skip the inline check entirely); H2 routes the choice per stream between inline-on-event-loop and the shared H2 worker pool (runtime.GOMAXPROCS*4 goroutines). The Async/Sync distinction is a no-op on the std engine (net/http already does goroutine-per-request).

Observe how often the inline → goroutine handoff fires via Server.EngineInfo().Metrics.AsyncRoutes (static count of .Async() routes) and .AsyncPromotedConns (cumulative promotions).

net/http Compatibility

Wrap existing net/http handlers and middleware:

// Wrap http.Handler
s.GET("/legacy", celeris.Adapt(legacyHandler))

// Wrap http.HandlerFunc
s.GET("/func", celeris.AdaptFunc(func(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("from stdlib"))
}))

The bridge buffers the adapted handler's response in memory, capped at a compile-time 100 MB limit (independent of Config.MaxRequestBodySize). Responses exceeding this limit return an error.

Engine Selection

Engine	Platform	Use Case
IOUring	Linux 5.10+	Lowest latency, highest throughput
Epoll	Linux	Broad kernel support, proven stability
Adaptive	Linux	Auto-switch based on telemetry
Std	Any OS	Development, compatibility, non-Linux deploys

Use Adaptive (the default on Linux) unless you have a specific reason to pin an engine. On non-Linux platforms, only Std is available.

Graceful Shutdown

Use StartWithContext for production deployments. When the context is canceled, the server drains in-flight requests up to ShutdownTimeout (default 30s).

ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()

s := celeris.New(celeris.Config{
	Addr:            ":8080",
	ShutdownTimeout: 15 * time.Second,
})
s.GET("/hello", helloHandler)

if err := s.StartWithContext(ctx); err != nil {
	log.Fatal(err)
}

Observability

The core provides a lightweight metrics collector accessible via Server.Collector():

snap := server.Collector().Snapshot()
fmt.Println(snap.RequestsTotal, snap.ErrorsTotal, snap.ActiveConns, snap.CPUUtilization)

For Prometheus exposition and debug endpoints, use the middleware/metrics and middleware/debug packages. For OpenTelemetry, use middleware/otel.

Feature Matrix

Feature	io_uring	epoll	std
HTTP/1.1	yes	yes	yes
H2C	yes	yes	yes
Auto-detect	yes	yes	yes
CPU pinning	yes	yes	no
Provided buffers	yes (5.19+)	no	no
Multishot accept	yes (5.19+)	no	no
Multishot recv	opt-in (5.19+, CELERIS_IOURING_MULTISHOT_RECV=1)	no	no
Zero-alloc HEADERS	yes	yes	no
Inline H2 handlers	yes	yes	no
Detach / StreamWriter	yes	yes	yes
Connection hijack	yes	yes	yes

Benchmarks

Cross-framework performance benchmarks live in test/perfmatrix/ — a (scenario × server × protocol) matrix driven by goceleris/loadgen. Run the full sweep with mage matrixBench or the dev-loop subset with mage matrixBenchQuick. Driver-isolation benchmarks remain in test/drivercmp/ and WebSocket comparisons in test/benchcmp_ws/. Reproducible release-gate numbers are published by probatorium's publish-results workflow.

Note: In-tree middleware benchmarks (e.g., middleware/compress/bench_test.go) use celeristest which provides pool-based contexts with no HTTP overhead. These numbers measure pure middleware logic and should not be compared directly with httptest-based competitor benchmarks. Use test/perfmatrix/ for fair cross-framework comparisons.

Continuous Validation

Correctness is validated by goceleris/probatorium — an adversarial cluster matrix run on real hardware:

• PR tier (matrix-pr-tier) — fast gate that every celeris PR must pass before merge.
• Nightly (matrix-nightly-tier) — 48 cells × every engine × every protocol × refapp; ~7h, every night.
• Weekend soak (matrix-weekend-tier) — deeper run with the same matrix at higher request counts; multi-hour endurance.

Bug oracles include slowloris hang detection, malformed-request acceptance, WebSocket torture-frame acceptance, h2c churn-crash detection, and tier-3 property seeds. Badge status above.

Project Structure

adaptive/       Adaptive meta-engine (Linux)
celeristest/    Test helpers (NewContext, NewContextT, ResponseRecorder, With* options)
cmd/            Celeris CLI binary (validation / diagnostics entrypoint)
driver/         First-party event-loop database drivers (postgres, redis, memcached)
engine/         Engine interface + implementations (iouring, epoll, std)
internal/       Shared internals (conn, cpumon, ctxkit, negotiate, platform, sockopts)
middleware/     In-tree middleware ecosystem (36 packages)
observe/        Collector, CPUMonitor, Snapshot
probe/          System capability detection (kernel version, io_uring feature probe)
protocol/       Protocol parsers (h1, h2, detect)
resource/       Configuration, presets, defaults
test/           Conformance, spec compliance, integration, benchmarks (perfmatrix, drivercmp, benchcmp_ws, …)
validation/     Runtime invariant assertions + validation hooks (debug builds)

Requirements

• Go 1.26.3+
• Linux for io_uring and epoll engines (kernel 5.10+ for io_uring; 5.19+ for the multishot / provided-buffers tier)
• Any OS for the std engine
• Direct runtime dependencies: golang.org/x/sys, golang.org/x/net (only)

Contributing

See CONTRIBUTING.md for development setup, testing, and pull request guidelines.

License

Apache License 2.0