c# 使用特定帐号密码访问Windows网路共享

透过程式存取Windows网路分享的档案也算常见需求，但存取身分是个问题。之前我惯用的技巧是用有权限的AD网域帐号执行排程存取网路分享，但这招要搬进网站或遇到不同网路分享用不同帐号便会破功。最近遇上类似议题，直觉要得回头靠WinAPI Impersonation解决，之前曾写过通用元件，担心11年前Windows Vista/7时代的作品有点过时，就爬文找找更好的做法。

之前的变身做法是改变Thread的执行身分，然而针对网路分享还有另一个WinAPI - WNetAddConnection2，可做到对多个网路分享使用不同登入身分。在stackoverflow找到有人分享把它包成搭配using使用的Context物件，符合我惯用的风格，二话不说，按赞并写文分享。

为方便使用，我再做了一层包装，写了一个NetworkCopier，将查目录或复制档案动作简化成Copy(srcNetPath, targetPath, domain, userId, passwd)、DirFiles(srcNetPath, domain, userId, passwd)，并支援预设帐密可省略输入domain, userId, passwd；另外还有GetConnetionContext(path, domain, userId, passwd) 可取回NetworkConnection 物件方便用同一连线身分进行多项操作，若来源与目的属不同网路分享则可套叠多重身分，写成：

using (var ctxA = NetworkCopier.GetConnetionContext("\\SvrA\Share", MyAD", "userX", "***")
{
 using (var ctxB = NetworkCopier.GetConnetionContext("\\SvrB\Share", MyAD", "userY", "***") 
 {
  File.Copy(@"\\SvrA\Share\SubFolder\test.txt", @"\\SvrB\Share\test.txt");
  File.Copy(@"\\SvrA\Share\hello.txt", @"\\SvrB\Share\Temp\hello.txt");
 }
}

建立NetworkConnection时，需要引入共享路径而不是完整路径，例如要访问\\SvrA\Share\SubFolder\test.txt，建立NetworkConnection的参数为\\SvrA\Share\，为省去人工截取的麻烦，我写了一段正则表达式更顺手。

完整程式如下，需要的朋友请自取使用：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Linq;
using System.Net;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;
using System.Web;

namespace MyApp.Models
{
 public class NetworkCopier
 {
  static string defaultDomain = null;
  static string defaultUserId = null;
  static string defaultPasswd = null;
  static NetworkCopier()
  {
   try
   {
    //TODO: 由設定檔、Registry 或 DB 取得帳號設定，密碼記得要加密保存
    var p = ReadCredentialInfo().Split('\t');
    defaultDomain = p[0];
    defaultUserId = p[1];
    defaultPasswd = p[2];
   }
   catch { }
  }
  static string NotNull(string s)
  {
   if (string.IsNullOrEmpty(s)) 
    throw new ApplicationException("未設定預設登入身分");
   return s;
  }
  static string DefaultDomain => NotNull(defaultDomain);
  static string DefaultUserId => NotNull(defaultUserId);
  static string DefaultPassword => NotNull(defaultPasswd);
  static string GetSharePath(string path)
  {
   var m = Regex.Match(path, @"^\\\\[^\\]+\\[^\\]+");
   if (m.Success) return m.Value;
   return path;
  }
  public static void Copy(string srcPath, string dstPath, string domain = null, string userId = null, string passwd = null)
  {
   using (new NetworkConnection(GetSharePath(srcPath), 
    new NetworkCredential(userId ?? DefaultUserId, passwd ?? DefaultPassword, domain ?? DefaultDomain)))
   {
    File.Copy(srcPath, dstPath);
   }
  }
  public static string[] DirFiles(string path, string pattern, string domain = null, string userId = null, string passwd = null)
  {
   using (new NetworkConnection(GetSharePath(path), 
    new NetworkCredential(userId ?? DefaultUserId, passwd ?? DefaultPassword, domain ?? DefaultDomain)))
   {
    return Directory.GetFiles(path, pattern);
   }
  }
  
  public static GetConnectionContext(string path, string domain = null, string userId = null, string passwd = null) 
  {
   return new NetworkConnection(GetSharePath(path), 
    new NetworkCredential(userId ?? DefaultUserId, passwd ?? DefaultPassword, domain ?? DefaultDomain));
  }
  
 }
 //引用來源: https://stackoverflow.com/a/1197430/288936
 public class NetworkConnection : IDisposable
 {
  string _networkName;
  public NetworkConnection(string networkName, NetworkCredential credentials)
  {
   _networkName = networkName;
   var netResource = new NetResource()
   {
    Scope = ResourceScope.GlobalNetwork,
    ResourceType = ResourceType.Disk,
    DisplayType = ResourceDisplaytype.Share,
    RemoteName = networkName
   };
   var userName = string.IsNullOrEmpty(credentials.Domain)
    ? credentials.UserName
    : string.Format(@"{0}\{1}", credentials.Domain, credentials.UserName);
   var result = WNetAddConnection2(
    netResource,
    credentials.Password,
    userName,
    0);
   if (result != 0)
   {
    throw new Win32Exception(result);
   }
  }
  ~NetworkConnection()
  {
   Dispose(false);
  }
  public void Dispose()
  {
   Dispose(true);
   GC.SuppressFinalize(this);
  }
  protected virtual void Dispose(bool disposing)
  {
   WNetCancelConnection2(_networkName, 0, true);
  }
  [DllImport("mpr.dll")]
  private static extern int WNetAddConnection2(NetResource netResource, string password, string username, int flags);
  [DllImport("mpr.dll")]
  private static extern int WNetCancelConnection2(string name, int flags, bool force);
 }
 [StructLayout(LayoutKind.Sequential)]
 public class NetResource
 {
  public ResourceScope Scope;
  public ResourceType ResourceType;
  public ResourceDisplaytype DisplayType;
  public int Usage;
  public string LocalName;
  public string RemoteName;
  public string Comment;
  public string Provider;
 }
 public enum ResourceScope : int
 {
  Connected = 1,
  GlobalNetwork,
  Remembered,
  Recent,
  Context
 };
 public enum ResourceType : int
 {
  Any = 0,
  Disk = 1,
  Print = 2,
  Reserved = 8,
 }
 public enum ResourceDisplaytype : int
 {
  Generic = 0x0,
  Domain = 0x01,
  Server = 0x02,
  Share = 0x03,
  File = 0x04,
  Group = 0x05,
  Network = 0x06,
  Root = 0x07,
  Shareadmin = 0x08,
  Directory = 0x09,
  Tree = 0x0a,
  Ndscontainer = 0x0b
 }
}

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