fetchall.go

// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// See page 17.
//!+

// Fetchall fetches URLs in parallel and reports their times and sizes.
package main

import (
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"os"
	"time"
)

func main() {
	start := time.Now()

	ch := make(chan string)

	for _, url := range os.Args[1:] {
		fmt.Printf("Fetching %s...\n", url)
		go fetch(url, ch) // start a goroutine
	}

	for range os.Args[1:] {
		fmt.Println("Listening for response...")
		fmt.Println(<-ch) // receive from channel ch
	}

	fmt.Printf("%.2fs elapsed\n", time.Since(start).Seconds())
}

func fetch(url string, ch chan<- string) {
	start := time.Now()

	resp, err := http.Get(url)
	defer resp.Body.Close() // don't leak resources
	if err != nil {
		ch <- fmt.Sprint(err) // send to channel ch
		return
	}

	nbytes, err := io.Copy(ioutil.Discard, resp.Body)
	if err != nil {
		ch <- fmt.Sprintf("while reading %s: %v", url, err)
		return
	}

	secs := time.Since(start).Seconds()
	ch <- fmt.Sprintf("%.2fs  %7d  %s", secs, nbytes, url)
}

//!-

output

D:\Development\go_projects\projects\src\gopl.io>fetchall_b1.exe http://iohelix.net/games https://google.com http://gopl.io https://golang.org http://ihbuc5xciuv75f7vboyg8
6rciugvivo.com
Fetching http://iohelix.net/games...
Fetching https://google.com...
Fetching http://gopl.io...
Fetching https://golang.org...
Fetching http://ihbuc5xciuv75f7vboyg86rciugvivo.com...
Listening for response...
Get http://ihbuc5xciuv75f7vboyg86rciugvivo.com: dial tcp: lookup ihbuc5xciuv75f7vboyg86rciugvivo.com: no such host
Listening for response...
0.18s     2662  http://iohelix.net/games
Listening for response...
0.22s     4154  http://gopl.io
Listening for response...
0.37s     7902  https://golang.org
Listening for response...
0.45s    12947  https://google.com
0.45s elapsed