How to develop a simple file download function using MySQL and Go language

How to use MySQL and Go language to develop a simple file download function

Overview:
The file download function is one of the common requirements of many web applications. This article will introduce how to use MySQL and Go language to develop a simple and reliable file download function. We will use MySQL to store file-related metadata, such as file name, path, and size, and the Go language will be used to handle file download requests and provide download services.

Steps:

1. Database design
   First, we need to design a database to store the metadata of the file. We can create a table named "files" with the following fields:
2. id: the unique identifier of the file, you can use a self-increasing integer or UUID as the primary key.
3. name: File name, stored in VARCHAR or TEXT type.
4. path: File storage path, stored in VARCHAR or TEXT type.
5. size: File size, stored using integer type.

You can use the following SQL statement to create a table:
CREATE TABLE files (
id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(255),
path VARCHAR(255 ),
size INT
);

2. File upload
   In a web application, users can upload files to the server through the upload file form. Here we use the net/http library of Go language to handle file upload requests. The following is a sample code to handle a file upload request:

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")
}

3. File Download
   Now, we can implement the file download function. The user downloads the file by sending a GET request. We need to find the relevant information of the file based on the file's id and send the file content to the user.

The following is a sample code to handle a file download request:

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)
}

4. Start the Web server
   Finally, we need to write a simple main function to start the Web server and Listen for file upload and download requests.

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))
}

To sum up, we use MySQL to store file metadata, and use Go language to process file upload and download requests, implementing a simple file download function. The above code examples provide a basic framework that you can modify and extend appropriately according to actual needs. I hope this article will help you develop a file download function!

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