hammer.go

package main

import (
	"fmt"
	"net/http"
	"os"
	"sync"
	"time"
)

// Based on ulimit to prevent "too many open files"
const NumberOfTokens = 2000
const HttpTimeout = time.Second * 10

func main() {
	url := os.Args[1]
	ch := make(chan string)
	var wg sync.WaitGroup

	poolCh := make(chan bool, NumberOfTokens)
	for i := 0; i < NumberOfTokens; i++ {
		poolCh <- true
	}

	defer close(ch)
	defer close(poolCh)

	wg.Add(1) // One extra to block

	go func() {
		i := 0
		for {
			i += 1
			wg.Add(1)
			go callUrl(i, url, ch, &wg, poolCh)
		}
	}()

	go func() {
		for message := range ch {
			fmt.Println(message)
		}
	}()

	wg.Wait()
}

func callUrl(i int, url string, ch chan string, wg *sync.WaitGroup, sem chan bool) {
	defer wg.Done()

	// Wait until we get a token
	<-sem
	defer func() {
		// Put token back to pool
		sem <- true
	}()

	transport := &http.Transport{
		Proxy: http.ProxyFromEnvironment,
		ResponseHeaderTimeout: HttpTimeout,
	}
	client := &http.Client{Transport: transport}

	resp, err := client.Get(url)
	if err != nil {
		ch <- fmt.Sprintf("%d: Error: %s", i, err.Error())
		return
	}
	ch <- fmt.Sprintf("%d: Success: %s", i, resp.Status)
}