如何用 Golang 实现文件下载限速_Golang 并发下载与速率控制实践

package main
<p>import (
"golang.org/x/time/rate"
"io"
"net/http"
"os"
)</p><p>func downloadWithRateLimit(url, filename string, limit rate.Limit) error {
resp, err := http.Get(url)
if err != nil {
return err
}
defer resp.Body.Close()</p><pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">file, err := os.Create(filename)
if err != nil {
    return err
}
defer file.Close()

limiter := rate.NewLimiter(limit, int(limit)*2) // 每秒 limit 字节，突发为两倍
buf := make([]byte, 32*1024)

for {
    n, err := resp.Body.Read(buf)
    if n > 0 {
        // 等待所需令牌释放，实现限速
        limiter.WaitN(context.Background(), n)
        _, writeErr := file.Write(buf[:n])
        if writeErr != nil {
            return writeErr
        }
    }
    if err == io.EOF {
        break
    }
    if err != nil {
        return err
    }
}
return nil

type Part struct {
    Start, End int64
    Index      int
}
<p>func concurrentDownload(url, filename string, parts int, totalLimit rate.Limit) error {
resp, <em> := http.Head(url)
size, </em> := strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 64)</p><pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">partSize := (size + int64(parts) - 1) / int64(parts)
var wg sync.WaitGroup
errors := make(chan error, parts)

limiter := rate.NewLimiter(totalLimit, int(totalLimit)*2)

for i := 0; i < parts; i++ {
    start := int64(i) * partSize
    end := start + partSize
    if end > size {
        end = size
    }

    wg.Add(1)
    go func(partIdx int, start, end int64) {
        defer wg.Done()
        err := downloadRange(url, filename+".part"+strconv.Itoa(partIdx), start, end, limiter)
        if err != nil {
            errors <- err
        }
    }(i, start, end)
}

go func() {
    wg.Wait()
    close(errors)
}()

for err := range errors {
    if err != nil {
        return err
    }
}

return mergeParts(filename, parts)

func mergeParts(finalFile string, partCount int) error {
    outFile, _ := os.Create(finalFile)
    defer outFile.Close()
<pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">for i := 0; i < partCount; i++ {
    partName := finalFile + ".part" + strconv.Itoa(i)
    part, _ := os.Open(partName)
    io.Copy(outFile, part)
    part.Close()
    os.Remove(partName) // 删除临时片段
}
return nil