c# - SMTP 中继器记录器

Question

我正在尝试做一个中继器（作为代理）来记录 SMTP 客户端和服务器之间的数据交换。我认为这很简单：倾听客户；

• 监听客户端IP连接；
• 随叫随到，连接服务器；
• 发回服务器消息；
• 将客户端消息发送给服务器，并将服务器反馈返回给客户端；

但是，正如我所看到的，一些服务器作为 MS 交换发送多个反馈女巫正在打破握手。像：

• 250 尺寸 41943040
• 250-流水线
• 250-DSN
• 250 增强状态代码
• 250-STARTTLS
• 250-AUTH 登录
• 250-8BITMIME
• 250-BINARYMIME

• 第250章

  这是课程

  导入 System.Text 导入 System.Net 导入 System.Net.Sockets 导入 System.Threading

  公共类 SmtpProxy

  Private client As TcpClient
  Private cltstream As NetworkStream
  Private cltreader As System.IO.StreamReader
  Private cltwriter As System.IO.StreamWriter
  
  Private smtpserver As New TcpClient
  Private srvstream As NetworkStream
  Private srvreader As System.IO.StreamReader
  Private srvwriter As System.IO.StreamWriter
  
  
  Private Shared mHostSrv As String
  Public Shared Property HostSrv() As String
      Get
          Return mHostSrv
      End Get
      Set(ByVal value As String)
          mHostSrv = value
      End Set
  End Property
  
  Private Shared mServerPort As Integer = 25
  Public Shared Property ServerPort() As Integer
      Get
          Return mServerPort
      End Get
      Set(ByVal value As Integer
      )
          mServerPort = value
      End Set
  End Property
  
  Private Shared mUserNm As String
  Public Shared Property UserNm() As String
      Get
          Return mUserNm
      End Get
      Set(ByVal value As String)
          mUserNm = value
      End Set
  End Property
  
  Private Shared mPassword As String
  Public Shared Property Password() As String
      Get
          Return mPassword
      End Get
      Set(ByVal value As String)
          mPassword = value
      End Set
  End Property
  
  
  Public Sub New(ByVal client As TcpClient)
      Me.client = client
      cltstream = client.GetStream()
      cltreader = New System.IO.StreamReader(cltstream)
      cltwriter = New System.IO.StreamWriter(cltstream)
      cltwriter.NewLine = vbCr & vbLf
      cltwriter.AutoFlush = True
  
  End Sub
  
  
  Public Shared Sub Start() 'ByVal args As String())
      Dim listener As New TcpListener(IPAddress.Loopback, 2525)
      listener.Start()
      While True
          Dim handler As New SmtpProxy(listener.AcceptTcpClient())
          Dim thread As Thread = New System.Threading.Thread(New ThreadStart(AddressOf handler.Run))
          thread.Start()
      End While
  End Sub
  
  
  Public Sub Run()
  
      If mHostSrv Like "*.*.*.*" Then
          Dim IpS As IPAddress = Nothing
          IpS = IPAddress.Parse(mHostSrv)
          smtpserver.Connect(IpS, mServerPort)
      Else
          smtpserver.Connect(mHostSrv, mServerPort)
      End If
  
      srvstream = smtpserver.GetStream
      srvreader = New System.IO.StreamReader(srvstream)
      srvwriter = New System.IO.StreamWriter(srvstream)
      srvwriter.NewLine = vbCrLf
      srvwriter.AutoFlush = True
  
  
      Dim srvline As String = srvreader.ReadLine
      cltwriter.WriteLine(srvline)
      Debug.Print("Server sent: {0}", srvline & vbCrLf)
  
      Try
  
          Dim line As String = cltreader.ReadLine
          While line IsNot Nothing
              Debug.Print("Read line {0}", line)
              srvwriter.WriteLine(line)
              Application.DoEvents()
              srvline = srvreader.ReadLine()
              Debug.Print("Server sent: {0}", srvline)
              cltwriter.WriteLine(srvline.Replace("-", " "))
              Application.DoEvents()
              line = cltreader.ReadLine()
          End While
      Catch ex As Exception
          client.Close()
          smtpserver.Close()
      End Try
  
  End Sub
  

  结束类

我尝试一次读取多个服务器行，但与此同时，如果我发送整个返回的服务器行，客户端将返回并出错...

Private Function ReadSrvLines() As String

    Dim strRet As String = ""
    Do
        If strRet Like "220*" OrElse srvreader.EndOfStream Then Exit Do
        Dim strTmp As String = srvreader.ReadLine
        If strTmp Is Nothing Then Exit Do
        strRet &= strTmp.Replace("-", " ") & vbCrLf
        cltwriter.WriteLine(strTmp.Replace("-", " "))
        Debug.Print("Server sent: {0}", strTmp.Replace("-", " ") & vbCrLf)
    Loop

    Return strRet
End Function

那么有人有什么解决方案可以提出吗？

谢谢大家！！

坦率

Answer 1

You will need to perform simultaneous asynchronous reading/writing between client and server to make this work properly. SMTP responses can contain any number of lines and client or server can return a message without the need for a command (to say bye for example). Parsing the data is also unnecessary to achieve a basic log.

Edit: If it helps, if the 3 digit message number if followed by a (minus) rather than a (space) it means that there is another line to follow.