Golang实现文件上传下载功能详解

package main
import (
"io"
"log"
"net/http"
"os"
)
func uploadHandler(w http.ResponseWriter, r *http.Request) {
if r.Method != "POST" {
http.Error(w, "只允许POST方法", http.StatusMethodNotAllowed)
return
}
// 解析上传的文件（限制内存中最多10MB）
err := r.ParseMultipartForm(10 << 20)
if err != nil {
    http.Error(w, "解析表单失败", http.StatusBadRequest)
    return
}

file, handler, err := r.FormFile("file")
if err != nil {
    http.Error(w, "获取文件失败", http.StatusBadRequest)
    return
}
defer file.Close()

// 创建本地文件用于保存
dst, err := os.Create("./uploads/" + handler.Filename)
if err != nil {
    http.Error(w, "创建本地文件失败", http.StatusInternalServerError)
    return
}
defer dst.Close()

// 将上传的文件内容复制到本地
_, err = io.Copy(dst, file)
if err != nil {
    http.Error(w, "保存文件失败", http.StatusInternalServerError)
    return
}

w.WriteHeader(http.StatusOK)
w.Write([]byte("文件上传成功: " + handler.Filename))
}
func main() {
// 确保上传目录存在
os.MkdirAll("./uploads", os.ModePerm)
http.HandleFunc("/upload", uploadHandler)
http.Handle("/", http.FileServer(http.Dir("./static/"))) // 提供静态页面

log.Println("服务器启动，监听 :8080")
log.Fatal(http.ListenAndServe(":8080", nil))
}

func downloadHandler(w http.ResponseWriter, r *http.Request) {
    filename := r.URL.Query().Get("file")
    if filename == "" {
        http.Error(w, "缺少文件名参数", http.StatusBadRequest)
        return
    }
filepath := "./uploads/" + filename

// 检查文件是否存在
_, err := os.Stat(filepath)
if os.IsNotExist(err) {
    http.Error(w, "文件不存在", http.StatusNotFound)
    return
}

// 设置响应头，触发下载
w.Header().Set("Content-Disposition", "attachment; filename="+filename)
w.Header().Set("Content-Type", "application/octet-stream")

// 读取并发送文件内容
http.ServeFile(w, r, filepath)
}

<!-- 存放在 ./static/index.html -->
<form action="/upload" method="post" enctype="multipart/form-data">
    <input type="file" name="file" required>
    <button type="submit">上传文件</button>
</form>
<a href="/download?file=test.txt">下载示例文件</a>