由于IIS站点权限等问题，总是没找到处理办法，所以改用外挂的winform的方式来下载共享文件（也可以改为使用windows服务的方式）。
前提需要先在资源管理器中登录到共享文件夹，确保系统能访问。

1. 服务端代码 (.NET后端)

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Web;public class FileDownloadService
{private const int WinFormPort = 11000;public void DownloadFile(string filePath){try{// 1. 连接到WinForm客户端using (TcpClient client = new TcpClient("127.0.0.1", WinFormPort))using (NetworkStream netStream = client.GetStream()){// 2. 发送文件路径byte[] pathData = Encoding.UTF8.GetBytes(filePath);netStream.Write(pathData, 0, pathData.Length);// 3. 设置响应头Response.Clear();Response.ContentType = "application/octet-stream";Response.AddHeader("Content-Disposition", $"attachment; filename={HttpUtility.UrlEncode(Path.GetFileName(filePath))}");// 4. 流式传输到客户端浏览器byte[] buffer = new byte[1024 * 1024]; // 1MB缓冲区int bytesRead;while ((bytesRead = netStream.Read(buffer, 0, buffer.Length)) > 0){Response.OutputStream.Write(buffer, 0, bytesRead);Response.Flush();}}}catch (Exception ex){Response.Write($"下载错误: {ex.Message}");}finally{Response.End();}}
}

2. WinForm客户端代码

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Windows.Forms;public class FileTransferService : IDisposable
{private TcpListener _listener;private const int Port = 11000;private bool _isRunning;public void Start(){_isRunning = true;_listener = new TcpListener(IPAddress.Loopback, Port);_listener.Start(10); // 允许10个等待连接BeginAcceptClient();}private void BeginAcceptClient(){if (_isRunning){_listener.BeginAcceptTcpClient(ClientHandler, null);}}private void ClientHandler(IAsyncResult ar){TcpClient client = null;try{client = _listener.EndAcceptTcpClient(ar);ThreadPool.QueueUserWorkItem(ProcessClient, client);}catch (Exception ex){client?.Dispose();MessageBox.Show($"接受连接错误: {ex.Message}");}finally{BeginAcceptClient(); // 继续监听新连接}}private void ProcessClient(object state){using (TcpClient client = (TcpClient)state){try{client.SendTimeout = 30000; // 30秒发送超时client.ReceiveTimeout = 30000; // 30秒接收超时using (NetworkStream netStream = client.GetStream()){// 1. 接收文件路径byte[] buffer = new byte[1024];int received = netStream.Read(buffer, 0, buffer.Length);string filePath = Encoding.UTF8.GetString(buffer, 0, received);// 2. 检查文件是否存在if (!File.Exists(filePath)){byte[] error = Encoding.UTF8.GetBytes("FILE_NOT_FOUND");netStream.Write(error, 0, error.Length);return;}// 3. 分块读取文件并传输using (FileStream fs = File.OpenRead(filePath)){byte[] fileBuffer = new byte[1024 * 1024]; // 1MB缓冲区int bytesRead;while ((bytesRead = fs.Read(fileBuffer, 0, fileBuffer.Length)) > 0){netStream.Write(fileBuffer, 0, bytesRead);}}}}catch (Exception ex){try{byte[] error = Encoding.UTF8.GetBytes($"ERROR:{ex.Message}");client.GetStream().Write(error, 0, error.Length);}catch { /* 忽略二次错误 */ }}}}public void Stop(){_isRunning = false;_listener?.Stop();}public void Dispose(){Stop();_listener?.Dispose();}
}

3. WinForm界面

public partial class MainForm : Form
{private FileTransferService _fileService;public MainForm(){InitializeComponent();_fileService = new FileTransferService();_fileService.Start();}protected override void OnFormClosing(FormClosingEventArgs e){_fileService.Dispose();base.OnFormClosing(e);}private void btnStart_Click(object sender, EventArgs e){_fileService.Start();lblStatus.Text = "服务已启动 (端口:11000)";}private void btnStop_Click(object sender, EventArgs e){_fileService.Stop();lblStatus.Text = "服务已停止";}
}

Windows查看端口是否被占用

netstat -ano | findstr "端口号"