Track and show downloading file summary ( in percentage ) - Go lang

I'm doing a process that downloads a file via a url parameter passed. download is being done properly but what i cant do is to print a summary of the percentage of download done. ( every second )

ive built one simulated kind of this summary but its not download anything, its just to show how i want it.

i tried to bring io.copy inside my source so i could change it ant print while the copy is being done, but it fails.

can someone help me?
thanks

 package main
import (
"fmt"
"io"
"net/http"
"os"
"strings"
//	"time"
)
func downloadFromUrl(url string) {
tokens := strings.Split(url, "/")
fileName := tokens[len(tokens)-1]
fmt.Println("Downloading", url, "to", fileName)
//create file
output, err := os.Create(fileName)
if err != nil {
fmt.Println("Error while creating", fileName, "-", err)
return
}
fmt.Println("Creating", fileName)
defer output.Close()
//get url
response, err := http.Get(url)
if err != nil {
fmt.Println("Error while downloading", url, "-", err)
return
}			
defer response.Body.Close()
//copy and bytes		
n, err := io.Copy(output, response.Body)
if err != nil {
fmt.Println("Error while downloading", url, "-", err)
return
}
//track progress
for i := 1; float64(i) < float64(n); i++ {
fmt.Println("",float64(i),float64(n))
percent := float64(i) / (float64(n) / float64(100))
percentTot := fmt.Sprintf(" %#.02f%% ", percent)
fmt.Println(percentTot,"downloaded\n")
//time.Sleep(3000 * time.Millisecond)
}	
}
func main() {
//read args	
args := os.Args
//loop args
for i := 1; i < len(args); i++ {
url := args[i]
//call download			
downloadFromUrl(url)		
}
}
**Output:**
go run main.go http://download.geonames.org/export/dump/AD.zip
Downloading http://download.geonames.org/export/dump/AD.zip to AD.zip
Creating AD.zip
1 64639
0.00%  downloaded
2 64639
0.00%  downloaded
3 64639
0.00%  downloaded
4 64639
0.01%  downloaded
5 64639
0.01%  downloaded

I have done that in my senvgo project with a io.Reader wrapper

// PassThru wraps an existing io.Reader.
//
// It simply forwards the Read() call, while displaying
// the results from individual calls to it.
type PassThru struct {
io.Reader
total    int64 // Total # of bytes transferred
length   int64 // Expected length
progress float64
}

You define a Read() method on that wrapper (to make it an io.Reader)

// Read 'overrides' the underlying io.Reader's Read method.
// This is the one that will be called by io.Copy(). We simply
// use it to keep track of byte counts and then forward the call.
func (pt *PassThru) Read(p []byte) (int, error) {
n, err := pt.Reader.Read(p)
if n > 0 {
pt.total += int64(n)
percentage := float64(pt.total) / float64(pt.length) * float64(100)
i := int(percentage / float64(10))
is := fmt.Sprintf("%v", i)
if percentage-pt.progress > 2 {
fmt.Fprintf(os.Stderr, is)
pt.progress = percentage
}
}
return n, err
}

And you use that io.Reader to read the Response (result of your http request):

client := &http.Client{
CheckRedirect: redirectPolicyFunc,
}
response, err := client.Get("http://example.com/something/large.zip")
defer response.Body.Close()
readerpt := &PassThru{Reader: response.Body, length: response.ContentLength}
body, err := ioutil.ReadAll(readerpt)

The ReadAll() call triggers the actual download, and the PassThru.Read() will print the % downloaded against the expected length (response.ContentLength)

Inspirations:

• this <kbd>play.golang.org</kbd> for the Copy() function

• "How to print the bytes while the file is being downloaded ?"