Golang语言社区--golang 进度下载文件

package main

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

func main() {

   downloadFile("http://localhost:8089/ThunderSpeed1.0.35.366.exe", func(length, downLen int64) {
      fmt.Println(length, downLen, float32(downLen)/float32(length))
   })

}

func downloadFile(url string, fb func(length, downLen int64)) error {
   var (
      fsize   int64
      buf     = make([]byte, 32*1024)
      written int64
   )
   //创建一个http client
   client := new(http.Client)
   //get方法获取资源
   resp, err := client.Get(url)
   if err != nil {
      return err
   }
   //读取服务器返回的文件大小
   fsize, err = strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 32)
   if err != nil {
      fmt.Println(err)
   }
   //创建文件
   file, err := os.Create("test.exe")
   if err != nil {
      return err
   }
   defer file.Close()
   if resp.Body == nil {
      return errors.New("body is null")
   }
   defer resp.Body.Close()
   //下面是 io.copyBuffer() 的简化版本
   for {
      //读取bytes
      nr, er := resp.Body.Read(buf)
      if nr > 0 {
         //写入bytes
         nw, ew := file.Write(buf[0:nr])
         //数据长度大于0
         if nw > 0 {
            written += int64(nw)
         }
         //写入出错
         if ew != nil {
            err = ew
            break
         }
         //读取是数据长度不等于写入的数据长度
         if nr != nw {
            err = io.ErrShortWrite
            break
         }
      }
      if er != nil {
         if er != io.EOF {
            err = er
         }
         break
      }
      //没有错误了快使用 callback

      fb(fsize, written)
   }
   return err
}