1. 功能介绍（使用方法）

MultithreadedDownloader.exe为使用golang实现的多线程下载器，实现对大文件的多线程下载，加快下载速度。文件接收4个可选参数，分别如下：

url
文件下载路径，默认值：“https://dldir1.qq.com/qqfile/qq/PCQQ9.6.2/QQ9.6.2.28756.exe”

folder
文件存储路径（默认为当前路径），默认值：“.”

filename
文件存储名称，默认值：“GoDownFile”

thread
最大同时下载协程数量，默认值：6

可直接通过运行程序，或在cmd中指定相应参数后运行，例如：
.\MultithreadedDownloader -url https://down.sandai.net/thunder11/XunLeiWebSetup11.3.12.1932dl.exe -folder . -filename XunLei -thread 8
运行输出：

Try to parse the object file...
File total size -> 5.18M
Parse the target file successfully, start downloading the target file...
Download progress -> 33.33%
Download progress -> 66.67%
Download progress -> 100.00%
Download file successeed!
Combine file successed, rename successed, new file name is -> ./XunLei.exe
Spend time:%v 682.2625ms
PS H:\soft\go_projects\ReChat\swpu.rby\filedown>

2. 完整代码（带少量注释）

完整代码如下，下载需要的依赖后可直接运行，目前注释较少，后期完善…

package mainimport ("bytes""encoding/hex""errors""flag""fmt""io/ioutil""net/http""os""strconv""strings""sync""time"
)var fileTypeMap sync.Mapfunc init() { //用于判断文件名的后缀fileTypeMap.Store("ffd8ffe000104a464946", "jpg")  //JPEG (jpg)fileTypeMap.Store("89504e470d0a1a0a0000", "png")  //PNG (png)fileTypeMap.Store("47494638396126026f01", "gif")  //GIF (gif)fileTypeMap.Store("49492a00227105008037", "tif")  //TIFF (tif)fileTypeMap.Store("424d228c010000000000", "bmp")  //16色位图(bmp)fileTypeMap.Store("424d8240090000000000", "bmp")  //24位位图(bmp)fileTypeMap.Store("424d8e1b030000000000", "bmp")  //256色位图(bmp)fileTypeMap.Store("41433130313500000000", "dwg")  //CAD (dwg)fileTypeMap.Store("3c21444f435459504520", "html") //HTML (html)   3c68746d6c3e0  3c68746d6c3e0fileTypeMap.Store("3c68746d6c3e0", "html")        //HTML (html)   3c68746d6c3e0  3c68746d6c3e0fileTypeMap.Store("3c21646f637479706520", "htm")  //HTM (htm)fileTypeMap.Store("48544d4c207b0d0a0942", "css")  //cssfileTypeMap.Store("696b2e71623d696b2e71", "js")   //jsfileTypeMap.Store("7b5c727466315c616e73", "rtf")  //Rich Text Format (rtf)fileTypeMap.Store("38425053000100000000", "psd")  //Photoshop (psd)fileTypeMap.Store("46726f6d3a203d3f6762", "eml")  //Email [Outlook Express 6] (eml)fileTypeMap.Store("d0cf11e0a1b11ae10000", "doc")  //MS Excel 注意：word、msi 和 excel的文件头一样fileTypeMap.Store("d0cf11e0a1b11ae10000", "vsd")  //Visio 绘图fileTypeMap.Store("5374616E64617264204A", "mdb")  //MS Access (mdb)fileTypeMap.Store("252150532D41646F6265", "ps")fileTypeMap.Store("255044462d312e350d0a", "pdf")  //Adobe Acrobat (pdf)fileTypeMap.Store("2e524d46000000120001", "rmvb") //rmvb/rm相同fileTypeMap.Store("464c5601050000000900", "flv")  //flv与f4v相同fileTypeMap.Store("00000020667479706d70", "mp4")fileTypeMap.Store("49443303000000002176", "mp3")fileTypeMap.Store("000001ba210001000180", "mpg") //fileTypeMap.Store("3026b2758e66cf11a6d9", "wmv") //wmv与asf相同fileTypeMap.Store("52494646e27807005741", "wav") //Wave (wav)fileTypeMap.Store("52494646d07d60074156", "avi")fileTypeMap.Store("4d546864000000060001", "mid") //MIDI (mid)fileTypeMap.Store("504b0304140000000800", "zip")fileTypeMap.Store("526172211a0700cf9073", "rar")fileTypeMap.Store("235468697320636f6e66", "ini")fileTypeMap.Store("504b03040a0000000000", "jar")fileTypeMap.Store("4d5a9000030000000400", "exe")        //可执行文件fileTypeMap.Store("3c25402070616765206c", "jsp")        //jsp文件fileTypeMap.Store("4d616e69666573742d56", "mf")         //MF文件fileTypeMap.Store("3c3f786d6c2076657273", "xml")        //xml文件fileTypeMap.Store("494e5345525420494e54", "sql")        //xml文件fileTypeMap.Store("7061636b616765207765", "java")       //java文件fileTypeMap.Store("406563686f206f66660d", "bat")        //bat文件fileTypeMap.Store("1f8b0800000000000000", "gz")         //gz文件fileTypeMap.Store("6c6f67346a2e726f6f74", "properties") //bat文件fileTypeMap.Store("cafebabe0000002e0041", "class")      //bat文件fileTypeMap.Store("49545346030000006000", "chm")        //bat文件fileTypeMap.Store("04000000010000001300", "mxp")        //bat文件fileTypeMap.Store("504b0304140006000800", "docx")       //docx文件fileTypeMap.Store("d0cf11e0a1b11ae10000", "wps")        //WPS文字wps、表格et、演示dps都是一样的fileTypeMap.Store("6431303a637265617465", "torrent")fileTypeMap.Store("6D6F6F76", "mov")         //Quicktime (mov)fileTypeMap.Store("FF575043", "wpd")         //WordPerfect (wpd)fileTypeMap.Store("CFAD12FEC5FD746F", "dbx") //Outlook Express (dbx)fileTypeMap.Store("2142444E", "pst")         //Outlook (pst)fileTypeMap.Store("AC9EBD8F", "qdf")         //Quicken (qdf)fileTypeMap.Store("E3828596", "pwl")         //Windows Password (pwl)fileTypeMap.Store("2E7261FD", "ram")         //Real Audio (ram)
}// 获取前面结果字节的二进制
func bytesToHexString(src []byte) string {res := bytes.Buffer{}if src == nil || len(src) <= 0 {return ""}temp := make([]byte, 0)for _, v := range src {sub := v & 0xFFhv := hex.EncodeToString(append(temp, sub))if len(hv) < 2 {res.WriteString(strconv.FormatInt(int64(0), 10))}res.WriteString(hv)}return res.String()
}// 用文件前面几个字节来判断
// fSrc: 文件字节流（就用前面几个字节）
func GetFileType(fSrc []byte) string {var fileType stringfileCode := bytesToHexString(fSrc)fileTypeMap.Range(func(key, value interface{}) bool {k := key.(string)v := value.(string)if strings.HasPrefix(fileCode, strings.ToLower(k)) ||strings.HasPrefix(k, strings.ToLower(fileCode)) {fileType = vreturn false}return true})return fileType
}func SafeMkdir(folder string) {if _, err := os.Stat(folder); os.IsNotExist(err) {os.MkdirAll(folder, os.ModePerm)}
}func GetBytesFile(filename string, bufferSize int) []byte {file, err := os.Open(filename)if err != nil {fmt.Println(err)return nil}defer file.Close()buffer := make([]byte, bufferSize)_, err = file.Read(buffer)if err != nil {fmt.Println(err)return nil}return buffer
}type DownloadTask struct {customFunc func(params interface{}) // 执行方法paramsInfo interface{}              // 执行方法参数
}type DownloadThreadController struct {TaskQueue              chan DownloadTask       // 用于接收下载任务TaskCount              chan int                // 用于记载当前任务数量Exit                   chan int                // 用于记载当前任务数量ThreadCount            int                     // 最大协程数WaitGroup              sync.WaitGroup          // 等待协程完成RangeStrs              map[int]string          // 所有需要下载的文件名FileUrl                string                  // 下载链接DownloadResultInfoChan chan DownloadFileParams // 下载任务响应通道DownloadFolder         string                  // 下载文件保存文件夹DownloadFileName       string                  // 下载文件保存文件名Filenames              []string                // 子文件名，有序
}type DownloadFileParams struct {UrlStr       stringRangeStr     stringRangeIndex   intTempFilename stringSuccessed    bool
}func (controller *DownloadThreadController) Put(task DownloadTask) {// 用于开启单个协程任务，下载文件的部分内容defer func() {err := recover() //内置函数，可以捕捉到函数异常if err != nil {fmt.Println("Chnnel closed", err)}}()controller.WaitGroup.Add(1)  // 每插入一个任务，就需要计数controller.TaskCount <- 1    // 含缓冲区的通道，用于控制下载器的协程最大数量controller.TaskQueue <- task // 插入下载任务//go task.customFunc(task.paramsInfo)
}func (controller *DownloadThreadController) DownloadFile(paramsInfo interface{}) {// 下载任务，接收对应的参数，负责从网页中下载对应部分的文件资源defer func() {controller.WaitGroup.Done() // 下载任务完成，协程结束}()switch paramsInfo.(type) {case DownloadFileParams:params := paramsInfo.(DownloadFileParams)params.Successed = falsedefer func() {err := recover() //内置函数，可以捕捉到函数异常if err != nil {// 如果任意环节出错，表明下载流程未成功完成，标记下载失败fmt.Println("Failed to download file：", err)params.Successed = false}}()//fmt.Println("Start to down load " + params.UrlStr + ", Content-type: " + params.RangeStr + " , save to file: " + params.TempFilename)urlStr := params.UrlStrrangeStr := params.RangeStrtempFilename := params.TempFilenameos.Remove(tempFilename) // 删除已有的文件, 避免下载的数据被污染// 发起文件下载请求req, _ := http.NewRequest("GET", urlStr, nil)req.Header.Add("Range", rangeStr)      // 测试下载部分内容res, err := http.DefaultClient.Do(req) // 发出下载请求，等待回应if err != nil {fmt.Println("Failed to connet " + urlStr)params.Successed = false // 无法连接, 标记下载失败} else if res.StatusCode != 206 {params.Successed = false} else { // 能正常发起请求// 打开文件，写入文件fileObj, err := os.OpenFile(tempFilename, os.O_RDONLY|os.O_CREATE|os.O_APPEND, 0666)if err != nil {fmt.Println("Failed to open file " + tempFilename)params.Successed = false // 无法打开文件, 标记下载失败} else {defer fileObj.Close()                 // 关闭文件流body, err := ioutil.ReadAll(res.Body) // 读取响应体的所有内容if err != nil {fmt.Println("Failed to read response body.")params.Successed = false} else {defer res.Body.Close()  // 关闭连接流fileObj.Write(body)     // 写入字节数据到文件params.Successed = true // 成功执行到最后一步，则表示下载成功}}}controller.DownloadResultInfoChan <- params // 将下载结果传入}
}func (controller *DownloadThreadController) Run() {// 只需要将待下载的请求发送一次即可，成功了会直接剔除，不成功则由接收方重试for rangeIndex, rangeStr := range controller.RangeStrs {params := DownloadFileParams{UrlStr: controller.FileUrl, RangeStr: rangeStr, TempFilename: controller.DownloadFolder + "/" + rangeStr, RangeIndex: rangeIndex, Successed: true} // 下载参数初始化task := DownloadTask{controller.DownloadFile, params}controller.Put(task) // 若通道满了会阻塞，等待空闲时再下载}
}func (controller DownloadThreadController) GetSuffix(contentType string) string {suffix := ""contentTypes := map[string]string{"image/gif":                    "gif","image/jpeg":                   "jpg","application/x-img":            "img","image/png":                    "png","application/json":             "json","application/pdf":              "pdf","application/msword":           "word","application/octet-stream":     "rar","application/x-zip-compressed": "zip","application/x-msdownload":     "exe","video/mpeg4":                  "mp4","video/avi":                    "avi","audio/mp3":                    "mp3","text/css":                     "css","application/x-javascript":     "js","application/vnd.android.package-archive": "apk",}for key, value := range contentTypes {if strings.Contains(contentType, key) {suffix = valuebreak}}return suffix
}func (controller *DownloadThreadController) ResultProccess(trunkSize int) string {// 负责处理各个协程下载资源的结果， 若成功则从下载列表中剔除，否则重新将该任务Put到任务列表中；超过5秒便会停止MAX_RETRY_TIME := 100nowRetryTime := 0result_msg := ""for {select {case resultInfo := <-controller.DownloadResultInfoChan:<-controller.TaskCount    // 取出一个计数器，表示一个协程已经完成if resultInfo.Successed { // 成功下载该文件，清除文件名列表中的信息delete(controller.RangeStrs, resultInfo.RangeIndex) // 删除任务队列中的该任务（rangeStr队列）fmt.Println("Download progress -> " + strconv.FormatFloat((1.0-float64(len(controller.RangeStrs))/float64(trunkSize))*100, 'f', 2, 64) + "%")if len(controller.RangeStrs) == 0 {result_msg = "SUCCESSED"break}} else {nowRetryTime += 1if nowRetryTime > MAX_RETRY_TIME { // 超过最大的重试次数退出下载result_msg = "MAX_RETRY"break}task := DownloadTask{customFunc: controller.DownloadFile, paramsInfo: resultInfo} // 重新加载该任务go controller.Put(task)}case task := <-controller.TaskQueue:function := task.customFuncgo function(task.paramsInfo)case <-time.After(5 * time.Second):result_msg = "TIMEOUT"break}if result_msg == "MAX_RETRY" {fmt.Println("The network is unstable, exceeding the maximum number of redownloads.")break} else if result_msg == "SUCCESSED" {fmt.Println("Download file successeed!")break} else if result_msg == "TIMEOUT" {fmt.Println("Download timeout!")break}}close(controller.TaskCount)close(controller.TaskQueue)close(controller.DownloadResultInfoChan)return result_msg
}func (controller *DownloadThreadController) Download(oneThreadDownloadSize int) bool {fmt.Println("Try to parse the object file...")length, rangeMaps, tempFilenames, contentType, err := TestDownload(controller.FileUrl, oneThreadDownloadSize)fmt.Println("File total size -> " + strconv.FormatFloat(float64(length)/(1024.0*1024.0), 'f', 2, 64) + "M")if err != nil {fmt.Println("The file does not support multi-threaded download.")return false}fmt.Println("Parse the target file successfully, start downloading the target file...")controller.Init() // 初始化通道、分片等配置//oneThreadDownloadSize := 1024 * 1024 * 2 // 1024字节 = 1024bite = 1kb -> 2MoneThreadDownloadSize = 1024 * 1024 * 4 // 1024字节 = 1024bite = 1kb -> 4Mfilenames := []string{}for _, value := range tempFilenames {filenames = append(filenames, controller.DownloadFolder+"/"+value)}fileSuffix := controller.GetSuffix(contentType)filename := controller.DownloadFileName // 获取文件下载名controller.Filenames = filenames        //下载文件的切片列表controller.RangeStrs = rangeMaps        // 下载文件的Range范围go controller.Run()                     // 开始下载文件proccessResult := controller.ResultProccess(len(rangeMaps))downloadResult := false // 定义下载结果标记if proccessResult == "SUCCESSED" {absoluteFilename := controller.DownloadFolder + "/" + filename + "." + fileSuffixdownloadResult = controller.CombineFiles(filename + "." + fileSuffix)if downloadResult {newSuffix := GetFileType(GetBytesFile(absoluteFilename, 10))err = os.Rename(absoluteFilename, controller.DownloadFolder+"/"+filename+"."+newSuffix)if err != nil {downloadResult = falsefmt.Println("Combine file successed, Rename file failed " + absoluteFilename)} else {fmt.Println("Combine file successed, rename successed, new file name is -> " + controller.DownloadFolder + "/" + filename + "." + newSuffix)}} else {fmt.Println("Failed to downlaod file.")}} else {fmt.Println("Failed to download file. Reason -> " + proccessResult)downloadResult = false}return downloadResult
}func (controller *DownloadThreadController) CombineFiles(filename string) bool {os.Remove(controller.DownloadFolder + "/" + filename)goalFile, err := os.OpenFile(controller.DownloadFolder+"/"+filename, os.O_CREATE|os.O_WRONLY|os.O_APPEND, os.ModePerm)if err != nil {fmt.Println("Failed to open file ")return false}// 正确的话应按照初始计算的文件名顺序合并，并且无缺失for _, value := range controller.Filenames {retryTime := 3tempFileBytes := []byte{}for retryTime > 0 {tempFileBytes = ReadFile(value)time.Sleep(100) // 休眠100毫秒，看看是不是文件加载错误if tempFileBytes != nil {break}retryTime = retryTime - 1}goalFile.Write(tempFileBytes)os.Remove(value)}goalFile.Close()return true
}func ReadFile(filename string) []byte {tempFile, err := os.OpenFile(filename, os.O_RDONLY, os.ModePerm)if err != nil {fmt.Println("Failed to open file " + filename)return nil}tempFileBytes, err := ioutil.ReadAll(tempFile)if err != nil {fmt.Println("Failed to read file data " + filename)return nil}tempFile.Close()return tempFileBytes
}func TestDownload(urlStr string, perThreadSize int) (int, map[int]string, []string, string, error) {// 尝试连接目标资源，目标资源是否可以使用多线程下载length := 0rangeMaps := make(map[int]string)req, _ := http.NewRequest("GET", urlStr, nil)req.Header.Add("Range", "bytes=0-1") // 测试下载部分内容res, err := http.DefaultClient.Do(req)contentType := ""rangeIndex := 1filenames := []string{}if err != nil {rangeMaps[rangeIndex] = urlStrreturn length, rangeMaps, filenames, contentType, errors.New("Failed to connet " + urlStr)}if res.StatusCode != 206 {rangeMaps[rangeIndex] = urlStrreturn length, rangeMaps, filenames, contentType, errors.New("Http status is not equal to 206!")}// 206表示响应成功，仅仅返回部分内容contentLength := res.Header.Get("Content-Range")contentType = res.Header.Get("Content-Type")total_length, err := strconv.Atoi(strings.Split(contentLength, "/")[1])if err != nil {return length, rangeMaps, filenames, contentType, errors.New("Can't calculate the content-length form server " + urlStr)}now_length := 0 // 记录byte偏移量for {if now_length >= total_length {break}var tempRangeStr string // 记录临时文件名if now_length+perThreadSize >= total_length {tempRangeStr = "bytes=" + strconv.Itoa(now_length) + "-" + strconv.Itoa(total_length-1)now_length = total_length} else {tempRangeStr = "bytes=" + strconv.Itoa(now_length) + "-" + strconv.Itoa(now_length+perThreadSize-1)now_length = now_length + perThreadSize}rangeMaps[rangeIndex] = tempRangeStrfilenames = append(filenames, tempRangeStr)rangeIndex = rangeIndex + 1}return total_length, rangeMaps, filenames, contentType, nil
}func (controller *DownloadThreadController) Init() {taskQueue := make(chan DownloadTask, controller.ThreadCount)taskCount := make(chan int, controller.ThreadCount+1)exit := make(chan int)downloadResultInfoChan := make(chan DownloadFileParams)controller.TaskQueue = taskQueuecontroller.TaskCount = taskCountcontroller.Exit = exitcontroller.DownloadResultInfoChan = downloadResultInfoChancontroller.WaitGroup = sync.WaitGroup{}controller.RangeStrs = make(map[int]string)SafeMkdir(controller.DownloadFolder)
}func main() {now := time.Now()url := flag.String("url", "https://dldir1.qq.com/qqfile/qq/PCQQ9.6.2/QQ9.6.2.28756.exe", "The http file's download url")downloadFolder := flag.String("folder", ".", "The downloaded file save path")downloadFilename := flag.String("filename", "GoDownFile", "The downloaded file save name")threadCount := flag.Int("thread", 6, "Tht number of child threads to download file")flag.Parse()oneThreadDownloadSize := 1024 * 1024 * 2 // 一个线程下载文件的大小controller := DownloadThreadController{ThreadCount: *threadCount, FileUrl: *url, DownloadFolder: *downloadFolder, DownloadFileName: *downloadFilename}controller.Download(oneThreadDownloadSize)fmt.Println("Spend time:%v", time.Since(now))
}

3. 可执行文件（exe）

通执行 `go build  -o MultithreadedDownloader.exe .\main.go` 将该程序编译为可执行文件，如果是想直接使用则可以直接[下载该文件](https://download.csdn.net/download/qq_43826939/85988540)，无需积分可直接下载。

4. 下载器实现思想（待续）

该多线程下载器基于http协议，服务端需支持下载文件指定内容，即在请求头中加入req.Header.Add("Range", "bytes=0-1")后，返回的相应头中若包含Content-Range，则视为支持文件部分内容下载；否则只能一次性下载，具体协议内容请参考http1.1范围请求；若文件支持多线程下载，则事先根据文件大小进行文件拆分，事先为每块文件分配文件名等信息，随后将每块文件的下载任务加入通道（类似消息队列）中，ResultProccess()方法会根据通道中的任务来开启下载协程，并处理下载结果（失败重试，大于一定重试次数退出；成功则从map中剔除该任务，由于操作map只有主线程，因此无需使用sync.Map）；最后根据该方法的返回值来判断下载完成情况；若完成下载，则合并所有临时下载的文件块，最后根据文件内容的开头来判断文件类型，对文件后缀名进行更改。