Simple command line progress bar in Go

progbar.go

package main

import (
	"flag"
	"fmt"
	"io"
	"log"
	"net/http"
	"net/url"
	"os"
	"path"
	"time"
)

const (
	maxbars  int           = 100
	interval time.Duration = 500 * time.Millisecond
)

var src string

type Progbar struct {
	total int
}

func (p *Progbar) PrintProg(portion int) {
	bars := p.calcBars(portion)
	spaces := maxbars - bars - 1
	percent := 100 * (float32(portion) / float32(p.total))

	fmt.Print("\r[")

	for i := 0; i < maxbars; i++ {
		fmt.Print("=")
	}

	fmt.Print(">")

	for i := 0; i <= spaces; i++ {
		fmt.Print(" ")
	}

	fmt.Printf(" ] %3.2f%% (%d/%d)", percent, portion, p.total)
}

func (p *Progbar) PrintComplete() {
	p.PrintProg(p.total)
	fmt.Print("\n")
}

func (p *Progbar) calcBars(portion int) int {
	if portion == 0 {
		return portion
	}

	return int(float32(maxbars) / (float32(p.total) / float32(portion)))
}

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func init() {
	flag.Parse()
	src = flag.Args()[0]
}

func main() {
	fmt.Printf("Downloading %s\n", src)

	res, err := http.Get(src)
	check(err)
	defer res.Body.Close()

	u, err := url.Parse(src)
	check(err)

	out, err := os.Create(path.Base(u.Path))
	defer out.Close()

	size := res.ContentLength
	bar := &Progbar{total: int(size)}
	written := make(chan int, 500)

	go func() {
		copied := 0
		c := 0
		tick := time.Tick(interval)

		for {
			select {
			case c = <-written:
				copied += c
			case <-tick:
				bar.PrintProg(copied)
			}
		}
	}()

	buf := make([]byte, 32*1024)
	for {
		rc, re := res.Body.Read(buf)
		if rc > 0 {
			wc, we := out.Write(buf[0:rc])
			check(we)

			if wc != rc {
				log.Fatal("Read and Write count mismatch")
			}

			if wc > 0 {
				written <- wc
			}
		}
		if re == io.EOF {
			break
		}
		check(re)
	}
	bar.PrintComplete()
	fmt.Println("Download complete")
}