Go 语言显示下载文件进度/分段读取 io.TeeReader()

package main

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

// WriteCounter counts the number of bytes written to it. It implements to the io.Writer
// interface and we can pass this into io.TeeReader() which will report progress on each
// write cycle.
type WriteCounter struct {
   Total uint64
}

func (wc *WriteCounter) Write(p []byte) (int, error) {
   n := len(p)
   wc.Total += uint64(n)
   wc.PrintProgress()
   return n, nil
}

func (wc WriteCounter) PrintProgress() {
   // Clear the line by using a character return to go back to the start and remove
   // the remaining characters by filling it with spaces
   fmt.Printf("\r%s", strings.Repeat(" ", 35))

   // Return again and print current status of download
   // We use the humanize package to print the bytes in a meaningful way (e.g. 10 MB)
   fmt.Printf("\rDownloading... %d B complete", wc.Total)
}

func main() {
   fmt.Println("Download Started")

   fileUrl := "https://dl.google.com/go/go1.11.1.src.tar.gz"
   err := DownloadFile("go1.11.1.src.tar.gz", fileUrl)
   if err != nil {
      panic(err)
   }

   fmt.Println("Download Finished")
}

// DownloadFile will download a url to a local file. It's efficient because it will
// write as it downloads and not load the whole file into memory. We pass an io.TeeReader
// into Copy() to report progress on the download.
func DownloadFile(filepath string, url string) error {

   // Create the file, but give it a tmp file extension, this means we won't overwrite a
   // file until it's downloaded, but we'll remove the tmp extension once downloaded.
   out, err := os.Create(filepath + ".tmp")
   if err != nil {
      return err
   }
   //defer out.Close() 看评论

   // Get the data
   resp, err := http.Get(url)
   if err != nil {
      return err
   }
   defer resp.Body.Close()

   // Create our progress reporter and pass it to be used alongside our writer
   counter := &WriteCounter{}
   _, err = io.Copy(out, io.TeeReader(resp.Body, counter))
   if err != nil {
      return err
   }

   out.Close() // 看评论
   // The progress use the same line so print a new line once it's finished downloading
   fmt.Print("\n")
   err = os.Rename(filepath+".tmp", filepath)
   if err != nil {
      return err
   }

   return nil
}

运行结果：

转载自：https://www.twle.cn/t/385