如何在下载文件时打印字节？-golang

Question

我想知道是否可以计算和打印下载文件时下载的字节数。out, err := os.Create("file.txt")    defer out.Close()    if err != nil {        fmt.Println(fmt.Sprint(err) )        panic(err)    }    resp, err := http.Get("http://example.com/zip")    defer resp.Body.Close()    if err != nil {        fmt.Println(fmt.Sprint(err) )        panic(err)    }    n, er := io.Copy(out, resp.Body)    if er != nil {        fmt.Println(fmt.Sprint(err) )    }    fmt.Println(n, "bytes ")

Answer 1

stdlib 现在提供类似 jimt 的内容PassThru：io.TeeReader。它有助于简化一些事情：

// WriteCounter counts the number of bytes written to it.

type WriteCounter struct {

    Total int64 // Total # of bytes transferred

}

// Write implements the io.Writer interface.  

// 

// Always completes and never returns an error.

func (wc *WriteCounter) Write(p []byte) (int, error) {

    n := len(p)

    wc.Total += int64(n)

    fmt.Printf("Read %d bytes for a total of %d\n", n, wc.Total)

    return n, nil

}

func main() {

    // ...    

    // Wrap it with our custom io.Reader.

    src = io.TeeReader(src, &WriteCounter{})

    // ...

}