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，连接到服务器；
• 发回服务器消息；
• 向服务器发送客户端消息，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-SIZE 41943040
• 250-流水线
• 250-DSN
• 250-增强状态代码
• 250-STARTTLS
• 250-AUTH 登录
• 250-8BITMIME
• 250-BINARYMIME

• 250 分块

  这是课程

  导入 System.Text 进口系统.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，客户端会返回并出错...

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

那么有没有人可以提出解决方案？

谢谢大家！！

弗兰克

Answer 1

您需要在客户端和服务器之间同时执行异步读/写，以使其正常工作。 SMTP 响应可以包含任意数量的行，客户端或服务器无需命令即可返回消息（例如说再见）。实现基本日志也不需要解析数据。

编辑：如果有帮助，如果 3 位消息编号后跟一个（减号）而不是一个（空格），则意味着还有另一行要遵循。