VB.NET - 来自 TCP 客户端的数据不按顺序排列

Question

我已经从事这个项目大约一年了。这是一个基本的客户端/服务器聊天程序。经过长时间的改进，我决定测试一下我的服务器的强度。

在客户端上，我尽可能快地向服务器发出了 200 条聊天消息（“FLOOD# 1”...“FLOOD# 200”）。结果：服务器立即崩溃。经过一些轻微的篡改后，我让服务器在放弃之前处理了 200 条消息中的 135 条。它不再崩溃，但发生了不同的事情。来自客户端的数据是按顺序接收的，但是当我将该消息传递给函数（myForm.OnLineReceived）时，数据完全乱序。如果我在 OnLineRecieved 函数的调用之间添加轻微的延迟，则消息的顺序是完美的。

来自客户端的每条消息首先都会被加密，然后以 base64 进行编码。末尾附加一个“-”，以便服务器可以轻松找到每个数据“包”的结尾。

我相信你们会很容易发现并向我指出这是一些愚蠢的错误。感谢您的浏览；）

服务器代码：

Imports System.Net.Sockets
Imports System.Text

' The UserConnection class encapsulates the functionality of a TcpClient connection
' with streaming for a single user.
Public Class UserConnection

Private client As TcpClient
Private readBuffer(READ_BUFFER_SIZE) As Byte

Public UID As String = ""
Public isAdmin As Boolean
Public IpAddress As String
Public username As String = ""
Public Country As String = ""
Public ServerID As String = ""
Public Status As String = ""
Public UserComp As String = ""
Public OS As String = ""

Public SessionKey As String = ""
Public UsePublicKeyEncryption As Boolean = True

Public Version As Decimal = 0.0

Const READ_BUFFER_SIZE As Integer = 500

Private _commands As New System.Text.StringBuilder
Private command_count As Integer = 1

' Overload the New operator to set up a read thread.
Public Sub New(ByVal client As TcpClient) 'this runs every time a new client is added
    Me.client = client
    IpAddress = Me.client.Client.RemoteEndPoint.ToString.Substring(0, Me.client.Client.RemoteEndPoint.ToString.LastIndexOf(":")) 'ip address of client
    ' This starts the asynchronous read thread.  The data will be saved into
    ' readBuffer.
    Call Worker()
End Sub

Public Sub ForceKill()
    On Error Resume Next
    client.GetStream.Close()
    client.Close()
    client = Nothing
End Sub

Private Sub Worker()
    Try
        SyncLock client
            Dim tmp_byte(client.ReceiveBufferSize) As Byte
            Me.client.GetStream.BeginRead(tmp_byte, 0, client.ReceiveBufferSize, AddressOf RecieveDataAndSplit, Nothing)
            readBuffer = tmp_byte
        End SyncLock

    Catch
        Call myForm.OnLineReceived(Me, "D") 'this also calls ForceKill()
    End Try
End Sub


Public Event LineReceived(ByVal sender As UserConnection, ByVal Data As String)

' This subroutine uses a StreamWriter to send a message to the user.
Public Sub SendData(ByVal Data As String)
    ' Synclock ensure that no other threads try to use the stream at the same time.
    SyncLock client
        Dim writer As New IO.StreamWriter(client.GetStream)
        writer.Write(ToBase64(AES_Encrypt(Data, SessionKey)) & "-")
        ' Make sure all data is sent now.
        writer.Flush()
    End SyncLock
End Sub



Public Sub RecieveDataAndSplit(ByVal ar As IAsyncResult) 'this is the FIRST function that incoming data is ran through
    Dim BytesRead As Integer
    Dim Content As String

    Try
        ' Ensure that no other threads try to use the stream at the same time.
        SyncLock client
            ' Finish asynchronous read into readBuffer and get number of bytes read.
            BytesRead = client.GetStream.EndRead(ar)
        End SyncLock
    Catch e As Exception
        Call myForm.OnLineReceived(Me, "D") 'couldn't read the stream from the client. Kill our connection with them :P
        Exit Sub
    End Try



    Try
        Content = Encoding.ASCII.GetString(readBuffer, 0, BytesRead)
    Catch ex As Exception
        Call Worker()
        Exit Sub
    End Try


    Dim commands() As String
    Try
        commands = LineTrim(Content).Split("-")
    Catch
    End Try


    Dim i As Integer = 0

    For i = 0 To commands.Length - 1

        If commands(i) <> "" Then

            Dim decrypted_content As String = AES_Decrypt(FromBase64(commands(i)), SessionKey)
            If decrypted_content <> "" Then

                'If decrypted_content = "D" Or Nothing Then
                '    client.GetStream.Close()
                '    client.Close()
                '    Call myForm.OnLineReceived(Me, decrypted_content)
                'Else

                Call myForm.OnLineReceived(Me, decrypted_content)
                Call Worker() 'reads the stream again
                'End If
            End If
        End If
    Next

End Sub
End Class

---

客户端代码：

Public Sub SendData(ByVal data As String)
    Try
        If data = "D" Then 'telling server that we're closing
            ForceDisconnect(False)
        Else 'any other message
            Dim sendBytes As [Byte]()

            sendBytes = Encoding.ASCII.GetBytes(ToBase64(AES_Encrypt(data, SessionKey)) & "-")

            Dim networkStream As NetworkStream = tcp_client.GetStream()
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            networkStream.Flush()
        End If
    Catch ex As Exception
        connection_state_toggle(False)

        Label1.ForeColor = Color.Black
        Label1.Text = "Idle"
    End Try



End Sub

Answer 1

典型的 TCP/IP 网络错误。您假设发送的数据是消息或数据包，但它实际上是流。假设您的客户端发送消息1-消息2-消息3-消息4。在服务器端的读取回调中，您可能会得到：

message1-m

或

message1-message2-

或

message1-message2-message3-message4

或 只是

m

想想当您收到这样的消息碎片时，您的解析代码（命令的分割）会发生什么。好的 TCP/IP 代码应该能够在每次读取时接收单个字节的数据。如果不能，那么您一定会遇到问题。

典型的方法是不断添加到缓冲区并每次检查缓冲区是否有已完成的消息，然后仅弹出该消息，将任何部分消息留在缓冲区中以供稍后填写。检查 DOS 攻击/问题，例如在缓冲区太大时丢弃缓冲区（基于您的协议），也应该在某个时候添加。

Answer 2

            Dim thrd As New System.Threading.Thread(AddressOf RecieveDataAndSplit)
            thrd.Start(bytesFrom)
            thrd.Join()

您正在创建新线程来处理数据，无法保证这些线程如何获取 CPU 时间的顺序，因此它们被乱序添加。

---

    SyncLock client.GetStream
        Dim tmp_byte(client.ReceiveBufferSize) As Byte
        Me.client.GetStream.BeginRead(tmp_byte, 0, client.ReceiveBufferSize, AddressOf RecieveDataAndSplit, Nothing)
        readBuffer = tmp_byte
    End SyncLock

我现在没有任何东西可以调试，但我想知道 GetStream 是否可能在每次调用它时返回不同的对象引用，从而使 Synclock 对您尝试执行的操作无效。我会尝试仅在客户端上进行同步。

Answer 3

好的，感谢每个人的输入（主要是 tcarvin 制作部分命令的“缓冲区”的想法），我已经成功地让一些漂亮的代码运行起来了！

希望这能帮助其他人避免我自己经历的痛苦日子。

这是 100% 工作的代码：

Imports System.Net.Sockets
Imports System.Text

' The UserConnection class encapsulates the functionality of a TcpClient connection
' with streaming for a single user.
Public Class UserConnection

Private client As TcpClient

Private income_message_buffer As New System.Text.StringBuilder 'all new messages are added onto the end of this. messages are pulled from the beginning in a timely manner

Public Sub Run(ByVal client As TcpClient)
    Me.client = client
    Call MessageParser()
End Sub

Public Sub ForceKill()
    On Error Resume Next
    client.GetStream.Close()
    client.Close()
    client = Nothing
End Sub

Private Sub MessageParser()
    Do

        If client.Connected = True Then
            If client.GetStream.DataAvailable = True Then
                Dim tmp_byte(client.ReceiveBufferSize) As Byte
                Dim BytesRead As Integer
                Dim content As String

                SyncLock client
                    BytesRead = Me.client.GetStream.Read(tmp_byte, 0, client.ReceiveBufferSize)
                End SyncLock

                Try
                    content = Encoding.ASCII.GetString(tmp_byte, 0, BytesRead)
                    income_message_buffer.Append(LineTrim(content))
                Catch ex As Exception

                End Try


            End If
        End If


        Dim EndOfFirstMessage As Integer = income_message_buffer.ToString.IndexOf("-") 'gets the first occurace of "-" in the buffer
        If EndOfFirstMessage >= 0 Then
            Dim message As String = income_message_buffer.ToString.Substring(0, EndOfFirstMessage) 'gets everything before the "-"
            income_message_buffer.Remove(0, EndOfFirstMessage + 1) 'removes the first message AND the "-"
            Call ParseMessage(message)
        End If



    Loop
End Sub

Public Event LineReceived(ByVal sender As UserConnection, ByVal Data As String)

' This subroutine uses a StreamWriter to send a message to the user.
Public Sub SendData(ByVal Data As String)
    ' Synclock ensure that no other threads try to use the stream at the same time.
    SyncLock client
        Dim writer As New IO.StreamWriter(client.GetStream)
        writer.Write(ToBase64(AES_Encrypt(Data, SessionKey)) & "-")
        ' Make sure all data is sent now.
        writer.Flush()
    End SyncLock
End Sub



Public Sub ParseMessage(ByVal message As String) 'this is the FIRST function that incoming data is ran through

    Dim decrypted_content As String = AES_Decrypt(FromBase64(message), SessionKey)

    If decrypted_content <> "" Then
        Call myForm.OnLineReceived(Me, decrypted_content)
    End If


End Sub
End Class