arrays - 跟踪并显示下载文件摘要(百分比) - Go lang

Question

我正在执行一个通过传递的 url 参数下载文件的过程。下载正在正确完成，但我不能做的是打印已完成下载百分比的摘要。 (每秒)

我构建了一种模拟的这种摘要，但它没有下载任何东西，它只是为了展示我想要它的方式。

我试图将 io.copy 放入我的源代码中，这样我就可以在复制完成时更改它，但它失败了。

有人可以帮助我吗？谢谢

 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

Answer 1

我已经在我的 senvgo project 中做到了使用 io.Reader 包装器

// 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
}

您在该包装器上定义一个 Read() 方法(使其成为一个 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
}

然后您使用 io.Reader 阅读 Response (您的 http 请求的结果):

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)

ReadAll() 调用触发实际下载，PassThru.Read() 将根据预期长度打印下载的百分比(response.ContentLength )

---

灵感:

• 这play.golang.org对于 Copy() 函数
• "How to print the bytes while the file is being downloaded ? "