How to print the bytes while the file is being downloaded ? -golang

Question

I\'m wondering if it\'s possible to count and print the number of bytes downloaded while the file is being downloaded.

out, err := os.Create(\"file.txt\")
    d         


        

Answer 1

Other answers have explained about PassThru. Just provide a full example with callback function base on Dave Jack's answer.

package main

import (
    "fmt"
    "io"
    "net/http"
    "os"
    "strconv"
)

// writeCounter counts the number of bytes written to it.
type writeCounter struct {
    total      int64 // total size
    downloaded int64 // downloaded # of bytes transferred
    onProgress func(downloaded int64, total int64)
}

// Write implements the io.Writer interface.
//
// Always completes and never returns an error.
func (wc *writeCounter) Write(p []byte) (n int, e error) {
    n = len(p)
    wc.downloaded += int64(n)
    wc.onProgress(wc.downloaded, wc.total)
    return
}

func newWriter(size int64, onProgress func(downloaded, total int64)) io.Writer {
    return &writeCounter{total: size, onProgress: onProgress}
}

func main() {
    client := http.DefaultClient
    url := "http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/ForBiggerFun.mp4"
    saveTo := "/Users/tin/Desktop/ForBiggerFun.mp4"

    download(client, url, saveTo, func(downloaded, total int64) {
        fmt.Printf("Downloaded %d bytes for a total of %d\n", downloaded, total)
    })
}

func download(client *http.Client, url, filePath string, onProgress func(downloaded, total int64)) (err error) {
    // Create file writer
    file, err := os.Create(filePath)
    if err != nil {
        return
    }
    defer file.Close()

    // Determinate the file size
    resp, err := client.Head(url)
    if err != nil {
        return
    }
    contentLength := resp.Header.Get("content-length")
    length, err := strconv.Atoi(contentLength)
    if err != nil {
        return
    }

    // Make request
    resp, err = client.Get(url)
    if err != nil {
        return
    }
    defer resp.Body.Close()

    // pipe stream
    body := io.TeeReader(resp.Body, newWriter(int64(length), onProgress))
    _, err = io.Copy(file, body)
    return err
}