h5开发工程师是做什么的seo和sem的区别是什么

前言

你好，我是醉墨居士，最近在开发文件传输相关的项目，然后顺手写了一个多协程文件下载器，代码非常精简，核心代码只有100行左右，适合分享给大家学习使用

流程图

主函数

func main() {fileURL := flag.String("u", "", "downloade url of the file")flag.Parse()if *fileURL == "" {log.Println("Please input a download url")flag.Usage()return}fileDir, err := os.Getwd()if err != nil {log.Println(err)return}// 下载文件保存路径filePath := filepath.Join(fileDir, filepath.Base(*fileURL))err = downloadFile(*fileURL, filePath)if err != nil {log.Println(err)return}log.Println("download file success:", filePath)
}

下载文件

// 下载文件
func downloadFile(fileURL string, filePath string) error {log.Println("downloading file:", fileURL, "to", filePath)taskCh := make(chan [2]int64, runtime.NumCPU())wg := new(sync.WaitGroup)// 创建执行下载任务的 workererr := initWorker(fileURL, filePath, taskCh, wg)if err != nil {return fmt.Errorf("init worker failed: %v", err)}// 分发下载任务err = dispatchTask(fileURL, taskCh)if err != nil {return fmt.Errorf("dispacth task failed: %v", err)}// 等待所有下载任务完成wg.Wait()return nil
}

初始化分片下载worker

// 初始化 下载 worker
func initWorker(url string, filePath string, taskCh chan [2]int64, wg *sync.WaitGroup) error {for i := 0; i < runtime.NumCPU(); i++ {// 打开文件句柄file, err := os.OpenFile(filePath, os.O_CREATE|os.O_RDWR, 0644)if err != nil {return err}wg.Add(1)go func(file *os.File, taskCh chan [2]int64) {defer wg.Done()defer file.Close()// 循环从 taskCh 中获取下载任务并下载for part := range taskCh {log.Printf("downloading part, start offset: %d, end offset: %d", part[0], part[1])// 重试下载，最大重试次数为 10 次，每次下载失败后等待 1 秒err := retryWithWaitTime(10, func() error {return downloadPart(url, file, part[0], part[1])}, time.Second)if err != nil {log.Printf("download part %d failed: %v", part, err)}}}(file, taskCh)}return nil
}

分发下载任务

// 分发下载任务
func dispatchTask(url string, taskCh chan [2]int64) error {defer close(taskCh)fileSize, err := getFileSize(url)if err != nil {return err}// 分片大小 1MBconst chunkSize = 1024 * 1024parts := fileSize / chunkSizelog.Println("file size:", fileSize, "parts:", parts, "chunk size:", chunkSize)for i := int64(0); i < parts; i++ {// 计算分片的起始和结束位置startOffset := i * chunkSizeendOffset := startOffset + chunkSize - 1// 发送下载任务taskCh <- [2]int64{startOffset, endOffset}}// 发送最后一个分片的下载任务if fileSize % chunkSize != 0 {taskCh <- [2]int64{parts * chunkSize, fileSize - 1}}return nil
}

获取下载文件的大小

// 获取文件大小
func getFileSize(url string) (int64, error) {resp, err := http.Head(url)if err != nil {return 0, err}defer resp.Body.Close()return resp.ContentLength, nil
}

下载文件分片

// 下载文件分片
func downloadPart(url string, file *os.File, startPos, endPos int64) error {req, err := http.NewRequest("GET", url, nil)if err != nil {return err}// 设置文件分片区间的请求头req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", startPos, endPos))resp, err := http.DefaultTransport.RoundTrip(req)if err != nil {return err}defer resp.Body.Close()// 如果服务器返回的状态码不是 206 Partial Content，则说明下载失败if resp.StatusCode != http.StatusPartialContent {data, err := io.ReadAll(resp.Body)if err != nil {return err}log.Println("unexpected data:", string(data))return fmt.Errorf("unexpected status code: %d", resp.StatusCode)}// 文件指针移动到分片的起始位置_, err = file.Seek(startPos, 0)if err != nil {return err}// 写入分片数据到文件_, err = io.Copy(file, resp.Body)if err != nil {return err}return nil
}

错误重试

// 重试函数
func retryWithWaitTime(retryCount int, fn func() error, waitTime time.Duration) error {var err errorfor i := 0; i < retryCount; i++ {e := fn()if e != nil {errors.Join(err, e)time.Sleep(waitTime)continue}return nil}return err
}

项目演示

最后

我是醉墨居士，如果这个项目对你有所帮助，希望你能多多支持，我们下期再见