Download files off of GoPro concurrently

download_concurrent.go

package main

import (
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"sync"
	"time"

	"github.com/vbauerster/mpb/v8"
	"github.com/vbauerster/mpb/v8/decor"
)

const (
	FILE_1 = "http://172.23.120.51:8080/videos/DCIM/100GOPRO/GX010375.MP4"
	FILE_2 = "http://172.23.120.51:8080/videos/DCIM/100GOPRO/GOPR0377.JPG"
	FILE_3 = "http://172.23.120.51:8080/videos/DCIM/100GOPRO/G0010378.JPG"
)

var (
	FILES = []string{FILE_1, FILE_2, FILE_3}
)

func head(path string) (int, error) {

	client := &http.Client{}
	req, err := http.NewRequest("HEAD", path, nil)
	if err != nil {
		return 0, err
	}
	resp, err := client.Do(req)
	if err != nil {
		return 0, err
	}
	length, err := strconv.Atoi(resp.Header.Get("Content-Length"))
	if err != nil {
		return 0, err
	}
	return length, nil
}

func downloadFile(filePath string, bar *mpb.Bar) error {
	resp, err := http.Get(filePath)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	name := filepath.Base(filePath)

	file, err := os.Create(name)
	if err != nil {
		return err
	}
	defer file.Close()
	proxyReader := bar.ProxyReader(resp.Body)
	defer proxyReader.Close()

	_, err = io.Copy(file, proxyReader)
	if err != nil {
		return err
	}
	return nil
}

func main() {
	var wg sync.WaitGroup
	p := mpb.New(mpb.WithWaitGroup(&wg),
		mpb.WithWidth(60),
		mpb.WithRefreshRate(180*time.Millisecond))
	nfiles := len(FILES)

	for i := 0; i < nfiles; i++ {
		head, err := head(FILES[i])
		if err != nil {
			panic(err)
		}
		bar := p.AddBar(int64(head),
			mpb.PrependDecorators(
				decor.CountersKiloByte("% .2f / % .2f"),
			),
			mpb.AppendDecorators(
				decor.OnComplete(
					decor.EwmaETA(decor.ET_STYLE_GO, 60, decor.WCSyncWidth), "✔️",
				),
			),
		)

		wg.Add(1)
		go func(current int) {
			defer wg.Done()
			err := downloadFile(FILES[current], bar)
			if err != nil {
				log.Fatal(err.Error())
			}
		}(i)
	}
	p.Wait()
}