如何利用MySQL和Go语言开发一个简单的文件下载功能

func uploadHandler(w http.ResponseWriter, r *http.Request) {
  file, handler, err := r.FormFile("file")
  if err != nil {
    // 处理错误
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
  }
  defer file.Close()

  // 保存文件到服务器
  path := "/path/to/save/files/" + handler.Filename
  f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE, 0666)
  if err != nil {
    // 处理错误
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
  }
  defer f.Close()
  io.Copy(f, file)

  // 将文件元数据插入数据库
  size := handler.Size
  name := handler.Filename
  insertSQL := "INSERT INTO files (name, path, size) VALUES (?, ?, ?)"
  _, err = db.Exec(insertSQL, name, path, size)
  if err != nil {
    // 处理错误
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
  }

  fmt.Fprintf(w, "文件上传成功")
}

func downloadHandler(w http.ResponseWriter, r *http.Request) {
  id := r.URL.Query().Get("id")
  // 根据文件id查询文件元数据
  querySQL := "SELECT name, path, size FROM files WHERE id = ?"
  var name, path string
  var size int64
  err := db.QueryRow(querySQL, id).Scan(&name, &path, &size)
  if err != nil {
    // 处理错误
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
  }

  // 打开文件
  file, err := os.Open(path)
  if err != nil {
    // 处理错误
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
  }
  defer file.Close()

  // 设置响应头
  w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%s", name))
  w.Header().Set("Content-Type", "application/octet-stream")
  w.Header().Set("Content-Length", fmt.Sprintf("%d", size))

  // 发送文件数据给用户
  io.Copy(w, file)
}

func main() {
  // 连接MySQL数据库
  db, err := sql.Open("mysql", "user:password@tcp(localhost:3306)/database")
  if err != nil {
    log.Fatal(err)
  }
  defer db.Close()

  // 注册路由处理函数
  http.HandleFunc("/upload", uploadHandler)
  http.HandleFunc("/download", downloadHandler)

  // 启动HTTP服务器
  log.Fatal(http.ListenAndServe(":8080", nil))
}