perf: 大幅优化静态文件下载性能

- 使用 http.ServeFile 替代手动实现，利用 sendfile 零拷贝
- gzip 中间件跳过 /uploads/ 路径，避免额外开销
- 支持 Range 请求和断点续传（由标准库自动处理）
- 移除不必要的手动 MIME 类型映射

Co-Authored-By: Claude <noreply@anthropic.com>

backend/cmd/main.go

@@ -4,14 +4,12 @@ import (
 	"compress/gzip"
 	"embed"
 	"fmt"
-	"io"
 	"io/fs"
 	"log"
 	"net/http"
 	"net/url"
 	"os"
 	"path/filepath"
-	"strconv"
 	"strings"
 	"verification-platform-backend/internal/config"
 	"verification-platform-backend/internal/database"
@@ -388,6 +386,12 @@ func isCompressibleContentType(contentType string) bool {
 
 func gzipMiddleware() gin.HandlerFunc {
 	return func(c *gin.Context) {
+		// 静态文件下载路径跳过 gzip 处理，避免影响下载性能
+		if strings.HasPrefix(c.Request.URL.Path, "/uploads/") {
+			c.Next()
+			return
+		}
+
 		if !strings.Contains(c.GetHeader("Accept-Encoding"), "gzip") {
 			c.Next()
 			return
@@ -443,11 +447,7 @@ func (w *gzipResponseWriter) WriteString(s string) (int, error) {
 	return w.ResponseWriter.WriteString(s)
 }
 
-// 32KB 缓冲区用于文件传输
-// 1MB 缓冲区用于高速文件传输，适合 G 口带宽和大文件
-const fileBufferSize = 1024 * 1024
-
-// handleOptimizedStaticFile 优化的静态文件处理，支持 Range 请求和断点续传
+// handleOptimizedStaticFile 优化的静态文件处理，使用 http.ServeFile 实现最高性能
 func handleOptimizedStaticFile(c *gin.Context) {
 	// 获取请求的文件路径
 	filepathParam := c.Param("filepath")
@@ -467,170 +467,13 @@ func handleOptimizedStaticFile(c *gin.Context) {
 		return
 	}
 
-	// 打开文件
-	file, err := os.Open(cleanPath)
-	if err != nil {
-		if os.IsNotExist(err) {
-			c.Status(http.StatusNotFound)
-		} else {
-			c.Status(http.StatusInternalServerError)
-		}
-		return
-	}
-	defer file.Close()
-
-	// 获取文件信息
-	fileInfo, err := file.Stat()
-	if err != nil {
-		c.Status(http.StatusInternalServerError)
-		return
-	}
-
-	// 如果是目录，返回 404
-	if fileInfo.IsDir() {
-		c.Status(http.StatusNotFound)
-		return
-	}
-
-	// 获取文件大小
-	fileSize := fileInfo.Size()
-
-	// 设置响应头
-	c.Header("Accept-Ranges", "bytes")
+	// 设置缓存头
 	c.Header("Cache-Control", "public, max-age=31536000, immutable")
 
-	// 获取 MIME 类型
-	ext := strings.ToLower(filepath.Ext(cleanPath))
-	if mimeType, ok := mimeTypes[ext]; ok {
-		c.Header("Content-Type", mimeType)
-	} else {
-		c.Header("Content-Type", "application/octet-stream")
-	}
-
-	// 处理 Range 请求（断点续传）
-	rangeHeader := c.GetHeader("Range")
-	if rangeHeader != "" {
-		// 解析 Range 头
-		// 格式: bytes=start-end 或 bytes=start-
-		rangeParts := strings.TrimPrefix(rangeHeader, "bytes=")
-		if rangeParts != rangeHeader {
-			// 解析范围
-			var start, end int64
-			if strings.Contains(rangeParts, "-") {
-				parts := strings.Split(rangeParts, "-")
-				if len(parts) == 2 {
-					if parts[0] != "" {
-						start, _ = strconv.ParseInt(parts[0], 10, 64)
-					}
-					if parts[1] != "" {
-						end, _ = strconv.ParseInt(parts[1], 10, 64)
-					} else {
-						end = fileSize - 1
-					}
-				}
-			}
-
-			// 验证范围
-			if start >= fileSize || start < 0 || end < start || end >= fileSize {
-				c.Header("Content-Range", fmt.Sprintf("bytes */%d", fileSize))
-				c.Status(http.StatusRequestedRangeNotSatisfiable)
-				return
-			}
-
-			// 设置部分内容响应
-			c.Header("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, fileSize))
-			c.Header("Content-Length", strconv.FormatInt(end-start+1, 10))
-			c.Status(http.StatusPartialContent)
-
-			// 定位到起始位置
-			file.Seek(start, io.SeekStart)
-
-			// 使用缓冲区传输
-			buf := make([]byte, fileBufferSize)
-			remaining := end - start + 1
-			for remaining > 0 {
-				toRead := int64(fileBufferSize)
-				if remaining < toRead {
-					toRead = remaining
-				}
-				n, err := file.Read(buf[:toRead])
-				if err != nil && err != io.EOF {
-					break
-				}
-				if n == 0 {
-					break
-				}
-				c.Writer.Write(buf[:n])
-				remaining -= int64(n)
-			}
-			return
-		}
-	}
-
-	// 普通请求，发送整个文件
-	c.Header("Content-Length", strconv.FormatInt(fileSize, 10))
-	c.Status(http.StatusOK)
-
-	// 使用缓冲区高效传输
-	buf := make([]byte, fileBufferSize)
-	_, err = io.CopyBuffer(c.Writer, file, buf)
-	if err != nil {
-		log.Printf("Error sending file %s: %v", cleanPath, err)
-	}
-}
-
-// mimeTypes 常见 MIME 类型映射
-var mimeTypes = map[string]string{
-	".zip":    "application/zip",
-	".exe":    "application/vnd.microsoft.windows.executable",
-	".dll":    "application/vnd.microsoft.windows.dll",
-	".apk":    "application/vnd.android.package-archive",
-	".ipa":    "application/vnd.apple.ipa",
-	".dmg":    "application/vnd.apple.dmg",
-	".pdf":    "application/pdf",
-	".doc":    "application/msword",
-	".docx":   "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
-	".xls":    "application/vnd.ms-excel",
-	".xlsx":   "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
-	".ppt":    "application/vnd.ms-powerpoint",
-	".pptx":   "application/vnd.openxmlformats-officedocument.presentationml.presentation",
-	".mp4":    "video/mp4",
-	".mp3":    "audio/mpeg",
-	".wav":    "audio/wav",
-	".ogg":    "audio/ogg",
-	".flac":   "audio/flac",
-	".avi":    "video/x-msvideo",
-	".mkv":    "video/x-matroska",
-	".mov":    "video/quicktime",
-	".wmv":    "video/x-ms-wmv",
-	".jpg":    "image/jpeg",
-	".jpeg":   "image/jpeg",
-	".png":    "image/png",
-	".gif":    "image/gif",
-	".bmp":    "image/bmp",
-	".webp":   "image/webp",
-	".svg":    "image/svg+xml",
-	".ico":    "image/x-icon",
-	".html":   "text/html; charset=utf-8",
-	".htm":    "text/html; charset=utf-8",
-	".css":    "text/css; charset=utf-8",
-	".js":     "application/javascript; charset=utf-8",
-	".mjs":    "application/javascript; charset=utf-8",
-	".json":   "application/json; charset=utf-8",
-	".xml":    "application/xml; charset=utf-8",
-	".txt":    "text/plain; charset=utf-8",
-	".md":     "text/markdown; charset=utf-8",
-	".log":    "text/plain; charset=utf-8",
-	".csv":    "text/csv; charset=utf-8",
-	".tar":    "application/x-tar",
-	".gz":     "application/gzip",
-	".tgz":    "application/gzip",
-	".rar":    "application/vnd.rar",
-	".7z":     "application/x-7z-compressed",
-	".iso":    "application/x-iso9660-image",
-	".woff":   "font/woff",
-	".woff2":  "font/woff2",
-	".ttf":    "font/ttf",
-	".eot":    "application/vnd.ms-fontobject",
-	".otf":    "font/otf",
+	// 使用 http.ServeFile，它已经：
+	// 1. 支持 Range 请求（断点续传）
+	// 2. 使用 sendfile 系统调用（零拷贝）
+	// 3. 自动处理 MIME 类型
+	// 4. 高效处理大文件
+	http.ServeFile(c.Writer, c.Request, cleanPath)
 }