cWinsock Development Guide

Table of Contents

• Overview
• Quick Start
• TCP Client
• TCP Server
• UDP Communication
• API Reference
• Event Reference
• Advanced Features
• FAQ

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Overview

cWinsock is a high-level wrapper class based on Windows Socket API, providing an easy-to-use VB6 network programming interface. It supports both TCP and UDP protocols, allowing you to easily create client and server applications.

Key Features

• Multi-protocol Support: Supports TCP and UDP protocols
• Asynchronous Non-blocking: Uses asynchronous I/O model without blocking UI thread
• Multi-client Management: Server automatically manages multiple client connections
• Event-driven: Handles network events through event mechanism
• Error Handling: Comprehensive error handling mechanism

Project Structure

Winsock/
念岸岸 Form1.frm          # Main form (Server + UDP example)
念岸岸 Client.frm         # Client form
念岸岸 Module1.bas        # Module file
念岸岸 Project1.vbp       # Project file
弩岸岸 README.md          # Example description

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Quick Start

Requirements

• Visual Basic 6.0 or higher
• VBMAN.dll library (located in ..\..\vbman\dist\DLL\)

Reference Library

1. Open project Project1.vbp
2. Ensure VBMANLIB library is referenced
3. Check reference path: ..\..\vbman\dist\DLL\VBMAN.dll

Basic Code Structure

' Declare cWinsock object (with events)
Private WithEvents m_oSocket As cWinsock

' Initialize object
Set m_oSocket = New cWinsock

' Set protocol type
m_oSocket.Protocol = sckTCPProtocol  ' or sckUDPProtocol

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TCP Client

A TCP client is used to connect to a remote server and establish a reliable connection for bidirectional communication.

Creating a TCP Client

Private WithEvents m_oClient As cWinsock

Private Sub InitializeClient()
    If m_oClient Is Nothing Then
        Set m_oClient = New cWinsock
        m_oClient.Protocol = sckTCPProtocol
    End If
End Sub

Connecting to Server

Private Sub ConnectToServer(ByVal sHost As String, ByVal lPort As Long)
    On Error GoTo EH
    
    InitializeClient()
    m_oClient.Connect sHost, lPort
    
    LogMessage "Connecting to " & sHost & ":" & lPort & "..."
    Exit Sub

EH:
    LogMessage "Connection error: " & Err.Description
End Sub

Parameters:

• sHost: Server IP address or hostname (e.g., "127.0.0.1" or "example.com")
• lPort: Server port number (e.g., 8080)

Sending Data

Private Sub SendData(sData As String)
    On Error GoTo EH
    
    If Not m_oClient Is Nothing And m_oClient.State = sckConnected Then
        m_oClient.SendData sData
        LogMessage "Data sent: " & sData
    Else
        LogMessage "Not connected to server"
    End If
    Exit Sub

EH:
    LogMessage "Send error: " & Err.Description
End Sub

Disconnecting

Private Sub Disconnect()
    If Not m_oClient Is Nothing Then
        m_oClient.Close_
        LogMessage "Client disconnected"
    End If
End Sub

Complete Example

Refer to Client.frm file for a complete TCP client implementation:

Private Sub cmdClientConnect_Click()
    On Error GoTo EH
    
    If m_oClient Is Nothing Then
        Set m_oClient = New cWinsock
        m_oClient.Protocol = sckTCPProtocol
    End If
    
    m_oClient.Connect txtClientHost.Text, CLng(txtClientPort.Text)
    
    LogMessage "Connecting to " & txtClientHost.Text & ":" & txtClientPort.Text & "..."
    Exit Sub
EH:
    LogMessage "Connection error: " & Err.Description
End Sub

Private Sub cmdClientDisconnect_Click()
    If Not m_oClient Is Nothing Then
        m_oClient.Close_
        LogMessage "Client disconnected"
    End If
    cmdClientConnect.Enabled = True
    cmdClientDisconnect.Enabled = False
    cmdClientSend.Enabled = False
End Sub

Private Sub cmdClientSend_Click()
    On Error GoTo EH
    
    If Not m_oClient Is Nothing And m_oClient.State = sckConnected Then
        m_oClient.SendData txtClientData.Text
        LogMessage "Data sent: " & txtClientData.Text
    End If
    Exit Sub
EH:
    LogMessage "Send error: " & Err.Description
End Sub

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TCP Server

A TCP server listens on a specified port, accepts multiple client connections, and can communicate independently with each client.

Creating a TCP Server

Private WithEvents m_oServer As cWinsock

Private Sub InitializeServer()
    If m_oServer Is Nothing Then
        Set m_oServer = New cWinsock
    End If
    
    m_oServer.Protocol = sckTCPProtocol
End Sub

Starting to Listen

Private Sub StartListening(ByVal lPort As Long)
    On Error GoTo EH
    
    InitializeServer()
    m_oServer.Listen lPort
    
    LogMessage "Server listening on port " & lPort
    Exit Sub

EH:
    LogMessage "Listen error: " & Err.Description
End Sub

Stopping Listening

Private Sub StopListening()
    If Not m_oServer Is Nothing Then
        m_oServer.Close_
        LogMessage "Server stopped listening"
    End If
End Sub

Handling Client Connection

Private Sub m_oServer_ConnectionRequest(Client As VBMANLIB.cWinsock, DisConnect As Boolean)
    ' In stress test mode, don't log connection
    If Not m_bStressTestMode Then
        LogMessage "New client connection: " & Client.RemoteHostIP & ":" & Client.RemotePort & " (Tag: " & Client.Tag & ")"
    End If

    ' Write Tag content to listbox
    lstClients.AddItem Client.Tag & " " & Client.RemoteHostIP & ":" & Client.RemotePort
End Sub

Stress Test Mode

Stress test mode is used for performance testing. In high concurrency scenarios, it only collects statistics without displaying detailed logs:

' Stress test mode variables
Private m_bStressTestMode As Boolean
Private m_lMsgCount As Long          ' Current period message count
Private m_lBytesCount As Long         ' Current period byte count
Private m_lTotalMsgCount As Long      ' Total message count
Private m_lTotalBytesCount As Long     ' Total byte count
Private m_lCurrentClientCount As Long  ' Current client count
Private m_dLastStatsTime As Double    ' Last statistics time
Private WithEvents tmrStats As VB.Timer

' Toggle stress test mode
Private Sub chkStressTest_Click()
    m_bStressTestMode = (chkStressTest.Value = vbChecked)

    If m_bStressTestMode Then
        LogMessage "Stress test mode enabled - Statistics only, no message content displayed"
        ResetStats
    Else
        LogMessage "Stress test mode disabled - Display all message content"
    End If
End Sub

' Receive data (stress test mode)
Private Sub m_oServer_DataArrival(Client As cWinsock, ByVal bytesTotal As Long)
    Dim sData As String
    Dim sResponse As String

    On Error GoTo EH

    If m_bStressTestMode Then
        ' Stress test mode: only statistics, no content display
        Client.GetData sData, vbString, bytesTotal

        ' Accumulate statistics
        m_lMsgCount = m_lMsgCount + 1
        m_lBytesCount = m_lBytesCount + bytesTotal
        m_lTotalMsgCount = m_lTotalMsgCount + 1
        m_lTotalBytesCount = m_lTotalBytesCount + bytesTotal

        ' Echo data
        sResponse = "OK"
        Client.SendData sResponse
    Else
        ' Normal mode: display content
        Client.GetData sData
        LogMessage "Received data from client " & Client.Tag & " (" & bytesTotal & " bytes): " & sData
        sResponse = "Echo: " & sData
        Client.SendData sResponse
        LogMessage "Sent echo to client " & Client.Tag & ": " & sResponse
    End If
    Exit Sub
EH:
    LogMessage "Server receive data error: " & Err.Description
End Sub

' Statistics timer (update every second)
Private Sub tmrStats_Timer()
    Dim dCurrentTime As Double
    Dim dElapsedTime As Double
    Dim lMsgPerSec As Long
    Dim lBytesPerSec As Long
    Dim sStats As String

    If m_bStressTestMode Then
        dCurrentTime = Timer
        dElapsedTime = dCurrentTime - m_dLastStatsTime

        If dElapsedTime > 0 Then
            lMsgPerSec = CLng(m_lMsgCount / dElapsedTime)
            lBytesPerSec = CLng(m_lBytesCount / dElapsedTime)

            ' Build statistics info (one item per line)
            sStats = vbCrLf & _
                     "========================================" & vbCrLf & _
                     Format$(Now, "hh:mm:ss") & " - [Statistics]" & vbCrLf & _
                     "----------------------------------------" & vbCrLf & _
                     "Current period messages: " & m_lMsgCount & vbCrLf & _
                     "Current period bytes: " & m_lBytesCount & vbCrLf & _
                     "Message rate: " & lMsgPerSec & " msg/s" & vbCrLf & _
                     "Data rate: " & Format$(lBytesPerSec / 1024, "0.00") & " KB/s" & vbCrLf & _
                     "----------------------------------------" & vbCrLf & _
                     "Current client count: " & m_lCurrentClientCount & vbCrLf & _
                     "Total messages: " & m_lTotalMsgCount & vbCrLf & _
                     "Total bytes: " & Format$(m_lTotalBytesCount / 1024 / 1024, "0.00") & " MB" & vbCrLf & _
                     "========================================" & vbCrLf

            ' Replace textbox content directly
            txtLog.Text = sStats
            txtLog.SelStart = Len(txtLog.Text)

            ' Reset current period statistics
            m_lMsgCount = 0
            m_lBytesCount = 0
            m_dLastStatsTime = dCurrentTime
        End If
    End If
End Sub

Receiving and Sending Data

Private Sub m_oServer_DataArrival(Client As cWinsock, ByVal bytesTotal As Long)
    Dim sData As String
    Dim sResponse As String
    
    On Error GoTo EH
    
    ' Get data
    Client.GetData sData
    LogMessage "Received data from client " & Client.Tag & " (" & bytesTotal & " bytes): " & sData
    
    ' Process data and send back
    sResponse = "Echo: " & sData
    Client.SendData sResponse
    LogMessage "Sent echo to client " & Client.Tag & ": " & sResponse
    Exit Sub

EH:
    LogMessage "Server receive data error: " & Err.Description
End Sub

Handling Client Disconnect

Private Sub m_oServer_CloseEvent(Client As cWinsock)
    Dim i As Long

    ' In stress test mode, don't log disconnection
    If Not m_bStressTestMode Then
        LogMessage "Client " & Client.RemoteHostIP & ":" & Client.RemotePort & " disconnected"
    End If

    ' Use Tag to traverse listbox and remove matching item
    For i = 0 To lstClients.ListCount - 1
        If InStr(lstClients.List(i), Client.Tag) > 0 Then
            lstClients.RemoveItem i
            Exit For
        End If
    Next
End Sub

Complete Example

Refer to the server implementation in Form1.frm:

Private Sub cmdServerListen_Click()
    On Error GoTo EH
    
    If m_oServer Is Nothing Then
        Set m_oServer = New cWinsock
    End If
    
    m_oServer.Protocol = sckTCPProtocol
    m_oServer.Listen CLng(txtServerPort.Text)
    
    LogMessage "Server listening on port " & txtServerPort.Text
    cmdServerListen.Enabled = False
    cmdServerStop.Enabled = True
    Exit Sub
EH:
    LogMessage "Listen error: " & Err.Description
End Sub

Private Sub m_oServer_ConnectionRequest(Client As VBMANLIB.cWinsock, DisConnect As Boolean)
    LogMessage "New client connection: " & Client.RemoteHostIP & ":" & Client.RemotePort & " (Tag: " & Client.Tag & ")"
    lstClients.AddItem Client.Tag & " - " & Client.RemoteHostIP & ":" & Client.RemotePort
End Sub

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UDP Communication

UDP (User Datagram Protocol) is a connectionless protocol, suitable for sending small amounts of data or scenarios where reliability is not critical.

Creating a UDP Socket

Private WithEvents m_oUdp As cWinsock

Private Sub InitializeUdp()
    If m_oUdp Is Nothing Then
        Set m_oUdp = New cWinsock
        m_oUdp.Protocol = sckUDPProtocol
    End If
End Sub

Binding Local Port

Private Sub BindUdpPort(ByVal lPort As Long)
    On Error GoTo EH
    
    InitializeUdp()
    m_oUdp.Bind lPort
    
    LogMessage "UDP Socket bound to port " & lPort
    Exit Sub

EH:
    LogMessage "UDP bind error: " & Err.Description
End Sub

Sending UDP Data

Private Sub SendUdpData(sHost As String, lPort As Long, sData As String)
    On Error GoTo EH
    
    With m_oUdp
        .RemoteHost = sHost
        .RemotePort = lPort
        .SendData sData
        LogMessage "UDP sent data to " & sHost & ":" & lPort & ": " & sData
    End With
    Exit Sub

EH:
    LogMessage "UDP send error: " & Err.Description
End Sub

Receiving UDP Data

Private Sub m_oUdp_DataArrival(Client As cWinsock, ByVal bytesTotal As Long)
    Dim sData As String
    
    On Error GoTo EH
    
    Client.GetData sData
    LogMessage "UDP received data (" & bytesTotal & " bytes) from " & Client.RemoteHostIP & ":" & Client.RemotePort & ": " & sData
    Exit Sub

EH:
    LogMessage "UDP receive data error: " & Err.Description
End Sub

Complete Example

Refer to the UDP implementation in Form1.frm:

Private Sub cmdUdpBind_Click()
    If m_oUdp Is Nothing Then
        Set m_oUdp = New cWinsock
        m_oUdp.Protocol = sckUDPProtocol
    End If
    
    m_oUdp.Bind CLng(txtUdpPort.Text)
    
    LogMessage "UDP Socket bound to port " & txtUdpPort.Text
End Sub

Private Sub cmdUdpSend_Click()
    On Error GoTo EH
    
    With m_oUdp
        .RemoteHost = txtUdpHost.Text
        .RemotePort = CLng(txtUdpPort.Text)
        .SendData txtUdpData.Text
        LogMessage "UDP sent data to " & txtUdpHost.Text & ":" & txtUdpPort.Text & ": " & txtUdpData.Text
    End With
    Exit Sub
EH:
    LogMessage "UDP send error: " & Err.Description
End Sub

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API Reference

Properties

Property	Type	Description
Protocol	Integer	Protocol type: sckTCPProtocol (0) or sckUDPProtocol (1)
State	Integer	Connection state, see state constants below
RemoteHost	String	Remote host address
RemoteHostIP	String	Remote host IP address (read-only)
RemotePort	Long	Remote port number
LocalPort	Long	Local port number (read-only)
Tag	Variant	Tag for storing custom data

Methods

Connect

oSocket.Connect RemoteHost, RemotePort

Connects to the specified server.

Parameters:

• RemoteHost: Server address (IP or hostname)
• RemotePort: Server port

Listen

oSocket.Listen Port

Starts listening on the specified port (TCP server mode only).

Parameters:

• Port: Listening port number

Bind

oSocket.Bind Port

Binds to a local port (UDP mode only).

Parameters:

• Port: Port number to bind

SendData

oSocket.SendData Data

Sends data to the remote endpoint.

Parameters:

• Data: Data to send (string or byte array)

GetData

oSocket.GetData Data, [Type], [MaxLen]

Retrieves received data from buffer.

Parameters:

• Data: Variable to store received data
• Type: Optional, data type (default is string)
• MaxLen: Optional, maximum read length

Close_

oSocket.Close_

Closes connection or stops listening.

State Constants

Constant	Value	Description
sckClosed	0	Connection closed
sckOpen	1	Socket opened
sckListening	2	Listening
sckConnectionPending	3	Connection pending
sckResolvingHost	4	Resolving host
sckHostResolved	5	Host resolved
sckConnecting	6	Connecting
sckConnected	7	Connected
sckClosing	8	Closing
sckError	9	Error occurred

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Event Reference

Connect

Private Sub oSocket_Connect(Client As cWinsock)

Triggered when client successfully connects to server.

Parameters:

• Client: The cWinsock object that triggered the event

CloseEvent

Private Sub oSocket_CloseEvent(Client As cWinsock)

Triggered when connection is closed.

Parameters:

• Client: The cWinsock object that triggered the event

ConnectionRequest

Private Sub oSocket_ConnectionRequest(Client As cWinsock, DisConnect As Boolean)

Triggered when server receives a new client connection request (TCP server only).

Parameters:

• Client: The new client connection object
• DisConnect: Set to True to reject connection, False to accept connection

DataArrival

Private Sub oSocket_DataArrival(Client As cWinsock, ByVal bytesTotal As Long)

Triggered when data is received.

Parameters:

• Client: The client object receiving data
• bytesTotal: Number of bytes received

Error

Private Sub oSocket_Error(Client As cWinsock, ByVal Number As Long, Description As String, ByVal Scode As Long)

Triggered when an error occurs.

Parameters:

• Client: The client object where error occurred
• Number: Error code
• Description: Error description
• Scode: System Scode error code

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Advanced Features

Multi-client Management

The server automatically creates independent client objects for each connection. You can identify different clients using the Tag property:

Private Sub m_oServer_ConnectionRequest(Client As cWinsock, DisConnect As Boolean)
    ' Assign unique identifier
    Client.Tag = "Client_" & GetNextId()
    
    ' Store in collection for management
    colClients.Add Client, Client.Tag
    
    LogMessage "New client: " & Client.Tag
End Sub

Client Authentication

Implement simple authentication in the ConnectionRequest event:

Private Sub m_oServer_ConnectionRequest(Client As cWinsock, DisConnect As Boolean)
    ' Check IP whitelist
    If Not IsAllowedIP(Client.RemoteHostIP) Then
        DisConnect = True
        LogMessage "Connection rejected: " & Client.RemoteHostIP
        Exit Sub
    End If
    
    LogMessage "Connection accepted: " & Client.RemoteHostIP
End Sub

Data Fragmentation

Handle packet transmission for large amounts of data:

Private Sub m_oServer_DataArrival(Client As cWinsock, ByVal bytesTotal As Long)
    Static sBuffer As String
    Dim sData As String
    Dim lPos As Long
    
    Client.GetData sData
    sBuffer = sBuffer & sData
    
    ' Look for message end marker (e.g., newline)
    Do
        lPos = InStr(sBuffer, vbCrLf)
        If lPos > 0 Then
            ProcessMessage Client, Left(sBuffer, lPos - 1)
            sBuffer = Mid(sBuffer, lPos + 2)
        Else
            Exit Do
        End If
    Loop
End Sub

Auto-reconnect on Error

Implement automatic reconnection:

Private Sub m_oClient_CloseEvent(Client As cWinsock)
    LogMessage "Connection closed, attempting to reconnect..."
    
    ' Delayed reconnection
    Dim i As Integer
    For i = 1 To 3
        If TryReconnect() Then
            Exit Sub
        End If
        Sleep 2000
    Next i
    
    LogMessage "Reconnection failed"
End Sub

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FAQ

Q1: How to handle connection timeout?

A: Use a timer to monitor connection state:

Private WithEvents tmrConnect As Timer

Private Sub StartConnectTimer()
    Set tmrConnect = New Timer
    tmrConnect.Interval = 10000  ' 10 second timeout
    tmrConnect.Enabled = True
End Sub

Private Sub tmrConnect_Timer()
    If m_oClient.State <> sckConnected Then
        m_oClient.Close_
        LogMessage "Connection timeout"
        tmrConnect.Enabled = False
    End If
End Sub

Q2: How to send binary data?

A: Use byte array:

Dim byData() As Byte
byData = StrConv("Hello", vbFromUnicode)
m_oClient.SendData byData

Q3: How to distinguish different senders in UDP mode?

A: Use RemoteHostIP and RemotePort properties:

Private Sub m_oUdp_DataArrival(Client As cWinsock, ByVal bytesTotal As Long)
    Dim sSender As String
    sSender = Client.RemoteHostIP & ":" & Client.RemotePort
    
    LogMessage "Received data from " & sSender
End Sub

Q4: How to limit client connections?

A: Use counter management:

Private lClientCount As Long

Private Sub m_oServer_ConnectionRequest(Client As cWinsock, DisConnect As Boolean)
    If lClientCount >= 100 Then
        DisConnect = True
        LogMessage "Connection rejected: maximum client count reached"
        Exit Sub
    End If
    
    lClientCount = lClientCount + 1
    LogMessage "Client count: " & lClientCount
End Sub

Private Sub m_oServer_CloseEvent(Client As cWinsock)
    lClientCount = lClientCount - 1
End Sub

Q5: How to debug network communication issues?

A: Use logging to record all key events:

Private Sub LogMessage(sMessage As String)
    txtLog.Text = txtLog.Text & Format$(Now, "hh:mm:ss") & " - " & sMessage & vbCrLf
    txtLog.SelStart = Len(txtLog.Text)
    Debug.Print sMessage  ' Output to immediate window
End Sub

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Best Practices

1. Always check connection state: Check State = sckConnected before sending data
2. Error handling: Include error handling for all network operations
3. Resource cleanup: Call Close_ when form unloads to release resources
4. Logging: Record key events for easier debugging
5. Timeout handling: Set reasonable connection and operation timeouts
6. Data validation: Validate format and length when receiving data

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Related Resources

• Project directory: Winsock/
• Example code: Client.frm, Form1.frm
• Dependency library: VBMAN.dll

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Changelog

• v1.0 - Initial version, includes TCP client, TCP server, and UDP examples