Max clients in net/http

README.md

Max Clients in net/http

Based on this https://pauladamsmith.com/blog/2016/04/max-clients-go-net-http.html.

Running it

Install boom:

go get github.com/rakyll/boom

On first shell:

go run max-clients.go

On second shell:

boom -n 10 -c 2 http://127.0.0.1:8080

Try increase number of requests and concurrency level to get timeout response.

max-clients.go

package main

import (
	"log"
	"net/http"
	"time"
)

func maxClientsHandler(maxClients int, timeout time.Duration, h http.Handler) http.Handler {
	var reqCounter int
	sema := make(chan struct{}, maxClients)

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		reqCounter++
		reqId := reqCounter
		start := time.Now()
		for {
			select {
			case sema <- struct{}{}:
				defer func() { <-sema }()
				log.Printf("Request %d processed\n", reqId)
				h.ServeHTTP(w, r)
				log.Printf("Request %d finished in %s\n", reqId, time.Now().Sub(start).String())
				return
			case <-time.After(timeout):
				log.Printf("Timeout for request %d\n", reqId)
				http.Error(w, "Timeout", http.StatusRequestTimeout)
				return
			}
		}
	})
}

func final(w http.ResponseWriter, r *http.Request) {
	time.Sleep(time.Second * 2)
	w.Write([]byte("OK"))
}

func main() {
	finalHandler := http.HandlerFunc(final)
	http.Handle("/", maxClientsHandler(3, time.Second*3, finalHandler))
	http.ListenAndServe(":8080", nil)
}