Go语言中高效使用mgo将上传文件直接存储到MongoDB GridFS

func uploadfilePageHandler(w http.ResponseWriter, req *http.Request) {
  // 1. 捕获multipart表单文件信息
  file, handler, err := req.FormFile("filename")
  if err != nil {
    fmt.Printf("Error getting form file: %v\n", err)
    http.Error(w, "Error getting form file", http.StatusInternalServerError)
    return
  }
  defer file.Close() // 确保文件句柄关闭

  // 2. 将文件完全读入内存
  data, err := ioutil.ReadAll(file) // 问题所在：将整个文件读入内存
  if err != nil {
    fmt.Printf("Error reading file into memory: %v\n", err)
    http.Error(w, "Error reading file", http.StatusInternalServerError)
    return
  }

  // 3. 连接MongoDB并创建GridFS文件
  my_db := mongo_session.DB("your_database_name") // 假设mongo_session已初始化
  unique_filename := handler.Filename // 或生成一个唯一文件名
  my_file, err := my_db.GridFS("fs").Create(unique_filename)
  if err != nil {
    fmt.Printf("Error creating GridFS file: %v\n", err)
    http.Error(w, "Error creating GridFS file", http.StatusInternalServerError)
    return
  }
  defer my_file.Close() // 确保GridFS文件关闭

  // 4. 将内存中的数据写入GridFS
  n, err := my_file.Write(data)
  if err != nil {
    fmt.Printf("Error writing data to GridFS: %v\n", err)
    http.Error(w, "Error writing file", http.StatusInternalServerError)
    return
  }

  fmt.Printf("%d bytes written to the Mongodb instance\n", n)
  // ... 其他业务逻辑 ...
}

package main

import (
    "fmt"
    "io"
    "net/http"
    "path/filepath"
    "time"

    "github.com/globalsign/mgo" // 使用最新的mgo版本
    "github.com/globalsign/mgo/bson"
)

// 全局MongoDB会话，实际应用中应进行适当的初始化和管理
var mongoSession *mgo.Session

func init() {
    // 示例：初始化MongoDB连接
    // 实际应用中，连接字符串和错误处理应更健壮
    var err error
    mongoSession, err = mgo.Dial("mongodb://localhost:27017")
    if err != nil {
        panic(fmt.Sprintf("Failed to connect to MongoDB: %v", err))
    }
    mongoSession.SetMode(mgo.Monotonic, true) // 设置会话模式
    fmt.Println("MongoDB connected successfully.")
}

func uploadFileHandler(w http.ResponseWriter, req *http.Request) {
    if req.Method != http.MethodPost {
        http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
        return
    }

    // 1. 获取文件句柄
    file, handler, err := req.FormFile("filename") // "filename"是HTML表单中input type="file"的name属性
    if err != nil {
        fmt.Printf("Error retrieving file from form: %v\n", err)
        http.Error(w, "Failed to retrieve file", http.StatusBadRequest)
        return
    }
    defer file.Close() // 确保上传文件的输入流关闭

    // 2. 获取MongoDB会话和数据库
    session := mongoSession.Copy() // 为每个请求复制会话，保证线程安全
    defer session.Close()         // 确保会话关闭

    db := session.DB("your_database_name") // 替换为您的数据库名

    // 3. 为GridFS文件生成唯一名称或使用原始文件名
    // 建议使用UUID或其他方式生成唯一文件名，以避免冲突
    // 这里为了简化，使用原始文件名，但实际生产环境应更严谨
    originalFilename := handler.Filename
    // 假设我们想给文件添加一些元数据，例如原始文件名和上传时间
    fileId := bson.NewObjectId() // 为GridFS文件生成一个ObjectId作为主键
    gridFileName := fmt.Sprintf("%s_%s%s", fileId.Hex(), time.Now().Format("20060102150405"), filepath.Ext(originalFilename))


    // 4. 创建GridFS文件写入器
    gridFile, err := db.GridFS("fs").Create(gridFileName)
    if err != nil {
        fmt.Printf("Error creating GridFS file: %v\n", err)
        http.Error(w, "Failed to create GridFS file", http.StatusInternalServerError)
        return
    }
    defer gridFile.Close() // 确保GridFS文件关闭

    // 5. 使用 io.Copy 将上传文件内容直接流式传输到GridFS
    bytesWritten, err := io.Copy(gridFile, file)
    if err != nil {
        fmt.Printf("Error copying file to GridFS: %v\n", err)
        http.Error(w, "Failed to store file", http.StatusInternalServerError)
        return
    }

    // 6. （可选）添加额外元数据到GridFS文件
    // mgo的GridFS.Create默认会设置filename、uploadDate、length等字段
    // 您可以通过gridFile.SetMeta或直接在GridFS集合中更新来添加更多自定义元数据
    // 例如，记录原始文件名和MIME类型
    gridFile.SetMeta(bson.M{
        "originalFilename": originalFilename,
        "contentType":      handler.Header.Get("Content-Type"),
        "uploadedBy":       "user_id_example", // 假设有用户ID
    })

    fmt.Printf("Successfully uploaded file '%s' (%s) to GridFS as '%s'. Bytes written: %d\n",
        originalFilename, handler.Header.Get("Content-Type"), gridFileName, bytesWritten)

    w.WriteHeader(http.StatusOK)
    fmt.Fprintf(w, "File '%s' uploaded successfully with ID: %s", originalFilename, fileId.Hex())
}

func main() {
    http.HandleFunc("/upload", uploadFileHandler)
    fmt.Println("Server listening on :8080")
    err := http.ListenAndServe(":8080", nil)
    if err != nil {
        panic(fmt.Sprintf("Server failed to start: %v", err))
    }
}