Sending HTTP requests concurrently with Go

post.go

package main

import (
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"strings"
	"time"
)

var (
	httpClient = http.Client{Timeout: time.Duration(10 * time.Second)}
	url        = flag.String("url", "https://example.com", "Destination URL")
)

type httpResponse struct {
	payload    string
	statusCode int
	err        error
}

func asyncPost(payloads []string) (err error) {
	// Send ~150 requests per second
	throttle := time.Tick(time.Second / 150)

	ch := make(chan *httpResponse)
	sentCounter := 0
	for _, payload := range payloads {
		go func(payload string) {
			log.Infof("Sending %s \n", payload)
			<-throttle
			ch <- post(payload)
		}(payload)
	}

	for {
		select {
		case r := <-ch:
			if r.err != nil || r.statusCode != 200 {
				if r.err != nil {
					log.Errorf("Error sending %s: %s", r.payload, r.err)
				} else if r.statusCode != 200 {
					log.Infoln("Non-200 response status code for %s: %s", r.payload, r.statusCode)
				}

			} else {
				log.Infof("%s sent\n", r.payload)
			}
			sentCounter++
			if sentCounter == len(payloads) {
				return
			}
		case <-time.After(50 * time.Millisecond):
			fmt.Printf(".")
		}
	}
}

func post(payload string) *httpResponse {
	reader := strings.NewReader(payload)
	req, _ := http.NewRequest("POST", *url, reader)
	resp, err := httpClient.Do(req)

	var statusCode int
	if resp != nil {
		statusCode = resp.StatusCode
		io.Copy(ioutil.Discard, resp.Body)
		resp.Body.Close()
	}

	return &httpResponse{statusCode: statusCode, payload: payload, err: err}
}

func main() {
	asyncPost([]string{"payload1", "payload2", "payload3"})
}