重构文件下载，支持多线程和分片

Signed-off-by: 勤快的小晴同学 <941403820@qq.com>

kit/file/file.go

@@ -5,26 +5,113 @@ import (
 	"mime/multipart"
 	"net/http"
 	"os"
+	"pandax/kit/biz"
+	"strconv"
+	"sync"
 )
 
-// DownloadFile 会将url下载到本地文件，它会在下载时写入，而不是将整个文件加载到内存中。
-func DownloadFile(url, filepath string) error {
-	// Get the data
-	resp, err := http.Get(url)
+const (
+	MaxConcurrency = 16 // 最大并发数
+)
+
+type DownloadTask struct {
+	URL      string
+	FilePath string
+}
+
+func DownloadFileWithConcurrency(url, filepath string) error {
+	resp, err := http.Head(url)
 	if err != nil {
 		return err
 	}
 	defer resp.Body.Close()
 
-	// Create the file
-	out, err := os.Create(filepath)
+	fileSize, err := strconv.Atoi(resp.Header.Get("Content-Length"))
 	if err != nil {
 		return err
 	}
-	defer out.Close()
-	// Write the body to file
-	_, err = io.Copy(out, resp.Body)
-	return err
+
+	file, err := os.OpenFile(filepath, os.O_RDWR|os.O_CREATE, 0666)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	// 检查本地文件大小
+	localFileSize, err := file.Seek(0, io.SeekEnd)
+	if err != nil {
+		return err
+	}
+
+	// 计算剩余未下载的文件大小
+	remainingSize := fileSize - int(localFileSize)
+
+	// 计算每个片段的大小
+	chunkSize := remainingSize / MaxConcurrency
+
+	// 创建等待组，用于等待所有goroutine完成
+	var wg sync.WaitGroup
+	wg.Add(MaxConcurrency)
+
+	// 创建并发下载任务
+	for i := 0; i < MaxConcurrency; i++ {
+		start := localFileSize + int64(i*chunkSize)
+		end := start + int64(chunkSize) - 1
+
+		// 最后一个片段的结束位置可能超过文件大小，需要修正
+		if i == MaxConcurrency-1 {
+			end = int64(fileSize) - 1
+		}
+
+		go func(index int, start, end int64) {
+			defer wg.Done()
+
+			err := downloadChunk(url, filepath, start, end)
+			if err != nil {
+				biz.NewBizErr("文件下载失败")
+				// 处理下载错误
+			}
+		}(i, start, end)
+	}
+
+	// 等待所有goroutine完成
+	wg.Wait()
+
+	return nil
+}
+
+func downloadChunk(url, filepath string, start, end int64) error {
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return err
+	}
+
+	// 设置Range头部
+	req.Header.Set("Range", "bytes="+strconv.FormatInt(start, 10)+"-"+strconv.FormatInt(end, 10))
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	file, err := os.OpenFile(filepath, os.O_RDWR, 0666)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	_, err = file.Seek(start, io.SeekStart)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.CopyN(file, resp.Body, end-start+1)
+	if err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func SaveUploadedFile(file *multipart.FileHeader, dst string) error {