Windows Socket Programming tutorial : Part-1 (Implementing Winsock Server) [ All Languages » VB »  Socket] Total Hit ( 44759) Rate this article:     Poor     Excellent   Submit Your Question/Comment about this article Rating Click here to download the attached file

In this article we will explore power of winsock api. We will implement very simple Asynchronous client and server using API without using Winsock Active-X control. Before we go into more detail let me clear why one more article on the earth for winsock API ... Why This Article ??? You might have question that Microsoft Winsock Active-X control is great for client/server application then why should I care to learn API based Socket programming ? Here are the reasons If you want application without any dependancy OCX file (Winsock ocx) If you want to handle several connections without putting huge memory overhead. Coz when you use winsock ocx you have to use Control array to handle multiple connection and its extra overhead to maintain Array of Winsock Control. If you want more flexibility. Steps to implement Winsock Server Initialize WSA (Winsock Service). Create a socket. Bind the socket. Listen on the socket. Accept a connection. Send and receive data. Disconnect. Steps to implement Winsock Client Initialize WSA (Winsock Service). Create a socket. Connect to the server. Send and receive data. Disconnect. In this article we will implement Winsock server. To learn about how to implement Winsock Client Please check Windows Socket (Winsock) Programming tutorial : Part-2 Now we will go through each step to construct winsock server [1] Initialize WSA (Winsock Service) The Very first step to implement winsock client/server is initialize winsock service. We will use StartWinsock and EndWinsock function to start and stop winsock service. Implementing StartWinsock and EndWinsock routines Click here to copy the following block Public Function StartWinsock(Optional sDescription) As Boolean   Dim StartupData As WSADataType   If Not WSAStartedUp Then 'WSAStartedUp is a flag     If Not WSAStartup(&H101, StartupData) Then       WSAStartedUp = True       sDescription = StartupData.szDescription     Else       WSAStartedUp = False     End If   End If   StartWinsock = WSAStartedUp End Function Public Sub EndWinsock()   Dim Ret&   If WSAIsBlocking() Then     Ret = WSACancelBlockingCall()   End If   Ret = WSACleanup()   WSAStartedUp = False End Sub code Explaination To start winsock service you must call the WSAStartup function. For each call of WSAStartup function you need to call WSACleanup in order to unload the library and clear resources allocated by the system. Click here to copy the following block Declare Function WSAStartup Lib "ws2_32.dll" _   (ByVal wVersionRequired As Long, lpWSAData As WSAData) As Long Declare Function WSACleanup Lib "ws2_32.dll" () As Long Click here to copy the following block '//Some other function to check blocking while WSA shutdown Declare Function WSACancelBlockingCall Lib "wsock32.dll" () As Long Declare Function WSAIsBlocking Lib "wsock32.dll" () As Long The wVersionRequired parameter defines highest version of Windows Sockets support that the caller can use. The high-order byte specifies the minor version (revision) number; the low-order byte specifies the major version number. Below are 2 examples of usage of the function in Visual Basic for 2 versions of the Winsock service: Click here to copy the following block RetVal = WSAStartup(&H101, udtWinsockData) 'To initialize version 1.1 RetVal = WSAStartup(&H202, udtWinsockData) 'To initialize version 2.2 The second parameter is the WSADATA data structure that is to receive details of the Windows Sockets implementation. Click here to copy the following block Type WSADataType   wVersion As Integer   'Winsock version caller going to use   wHighVersion As Integer 'Highest supported version   szDescription As String * WSA_DescriptionSize 'Description of winsock implementation   szSystemStatus As String * WSA_SysStatusSize 'status or configuration information   iMaxSockets As Integer 'Maximum number of sockets   iMaxUdpDg As Integer  'Maximum UDP datagram size   lpVendorInfo As Long  'Vendor-specific information End Type [2] Create a socket Once you initialize the Winsock service the next step is create a socket which will be used to listen on a specified port. To create a new socket we canuse following VB function Click here to copy the following block Public Function NewSocket(ByVal AdrFamily As Long, ByVal SckType As Long, ByVal SckProtocol As Long, HWndForMsg As Long) As Long '******************************************************************************** 'Purpose  :Creates a new socket 'Returns  :The socket handle if successful, otherwise INVALID_SOCKET 'Arguments :AddressFamily, SocketType and SocketProtocol '********************************************************************************   On Error GoTo errHandler   Dim hSocket As Long  'value returned by the socket API function   Dim lngEvents As Long   'Call the socket Winsock API function in order create a new socket   hSocket = socket(AdrFamily, SckType, SckProtocol)   NewSocket = hSocket  'Assign returned value ( -1 => INVALID_SOCKET)   If hSocket <> INVALID_SOCKET Then     'The lngEvents variable contains a bitmask of events we are     'going to catch with the window callback function.     lngEvents = FD_CONNECT Or FD_READ Or FD_WRITE Or FD_CLOSE Or FD_ACCEPT     'Force the Winsock service to send the network event notifications     'to the window which handle is p_lngWindowHandle.     lngRetValue = WSAAsyncSelect(hSocket, HWndForMsg, WINSOCKMSG, lngEvents)   End If   Exit Function errHandler:   NewSocket = INVALID_SOCKET End Function code Explaination To create a new socket you can use socket api. Click here to copy the following block Declare Function socket Lib "wsock32.dll" (ByVal AddressFamily As Long _   , ByVal SocketType As Long _   , ByVal Protocol As Long) As Long socket function expect 3 parameters : AddressFamily, SocketType and Protocol. If call is successful then it returns socket handle which you can use for subsecuent socket api calls. If function fails to create new socket then it returns -1 (SOCKET_ERROR). You can get socket error using WSAGetLastError Click here to copy the following block Declare Function WSAGetLastError Lib "wsock32.dll" () As Long Now we will discuss each input parameter for socket api. AddressFamily: First parameter for socket function is Addressfamily which can be one of the following options. Here we have created enum for easy use. In our example we will use AF_INET address family with TCP protocol and STREAM socket which are most common options with windows socket. Click here to copy the following block Public Enum AddressFamily   AF_UNSPEC = 0   '/* unspecified */ '/* ' * Although AF_UNSPEC is defined for backwards compatibility , using ' * AF_UNSPEC for the "af" parameter when creating a socket is STRONGLY ' * DISCOURAGED.  The interpretation of the "protocol" parameter ' * depends on the actual address family chosen. As environments grow ' * to include more and more address families that use overlapping ' * protocol values there is more and more chance of choosing an ' * undesired address family when AF_UNSPEC is used. ' */   AF_UNIX = 1    '/* local to host (pipes, portals) */   AF_INET = 2    '/* internetwork: UDP, TCP, etc. */   AF_IMPLINK = 3  '/* arpanet imp addresses */   AF_PUP = 4    '/* pup protocols: e.g. BSP */   AF_CHAOS = 5   '/* mit CHAOS protocols */   AF_NS = 6     '/* XEROX NS protocols */   AF_IPX = AF_NS  '/* IPX protocols: IPX, SPX, etc. */   AF_ISO = 7    '/* ISO protocols */   AF_OSI = AF_ISO  '/* OSI is ISO */   AF_ECMA = 8    '/* european computer manufacturers */   AF_DATAKIT = 9  '/* datakit protocols */   AF_CCITT = 10   '/* CCITT protocols, X.25 etc */   AF_SNA = 11    '/* IBM SNA */   AF_DECnet = 12  '/* DECnet */   AF_DLI = 13    '/* Direct data link interface */   AF_LAT = 14    '/* LAT */   AF_HYLINK = 15  '/* NSC Hyperchannel */   AF_APPLETALK = 16 '/* AppleTalk */   AF_NETBIOS = 17  '/* NetBios-style addresses */   AF_VOICEVIEW = 18 '/* VoiceView */   AF_FIREFOX = 19  '/* Protocols from Firefox */   AF_UNKNOWN1 = 20 '/* Somebody is using this! */   AF_BAN = 21    '/* Banyan */   AF_ATM = 22    '/* Native ATM Services */   AF_INET6 = 23   '/* Internetwork Version 6 */   AF_CLUSTER = 24  '/* Microsoft Wolfpack */   AF_12844 = 25   '/* IEEE 1284.4 WG AF */   AF_MAX = 26 End Enum SocketType: Second parameter for socket function is SocketType. Socket type can be one of the following options. Click here to copy the following block Public Enum SocketType   SOCK_STREAM = 1  ' /* stream socket */   SOCK_DGRAM = 2  ' /* datagram socket */   SOCK_RAW = 3   ' /* raw-protocol interface */   SOCK_RDM = 4   ' /* reliably-delivered message */   SOCK_SEQPACKET = 5 ' /* sequenced packet stream */ End Enum Protocol: Third parameter for socket function is Protocol. Protocol can be one of the following options. Click here to copy the following block Public Enum SocketProtocol   IPPROTO_IP = 0      '/* dummy for IP */   IPPROTO_ICMP = 1     '/* control message protocol */   IPPROTO_IGMP = 2     '/* internet group management protocol */   IPPROTO_GGP = 3      '/* gateway^2 (deprecated) */   IPPROTO_TCP = 6      '/* tcp */   IPPROTO_PUP = 12     '/* pup */   IPPROTO_UDP = 17     '/* user datagram protocol */   IPPROTO_IDP = 22     '/* xns idp */   IPPROTO_ND = 77      '/* UNOFFICIAL net disk proto */   IPPROTO_RAW = 255     '/* raw IP packet */   IPPROTO_MAX = 256 End Enum There are two type of sockets programming mode available in windows. 1. Blocking socket 2. Non-Blocking socket # Blocking socket # For Blocking socket you have to check the status of any socket event or any error. To do that you can use select function. The select function determines the status of one or more sockets, waiting if necessary, to perform synchronous I/O. Click here to copy the following block Declare Function vbselect Lib "ws2_32.dll" Alias "select" (ByVal nfds As Long _     , ByRef readfds As Any _     , ByRef writefds As Any _     , ByRef exceptfds As Any _     , ByRef timeout As Long) As Long 'Structures used for select function Public Type timeval   tv_sec As Long  'seconds   tv_usec As Long  'and microseconds End Type Public Type fd_set   fd_count As Long  '// how many are SET?   fd_array(1 To FD_SETSIZE) As Long  '// an array of SOCKETs End Type Parameters: nfds [in] Ignored. The nfds parameter is included only for compatibility with Berkeley sockets. readfds [in, out] Optional pointer to a set of sockets to be checked for readability. writefds [in, out] Optional pointer to a set of sockets to be checked for writability. exceptfds [in, out] Optional pointer to a set of sockets to be checked for errors. timeout [in] Maximum time for select to wait, provided in the form of a TIMEVAL structure. Set the timeout parameter to null for blocking operations. Return Value: The select function returns the total number of socket handles that are ready and contained in the fd_set structures, zero if the time limit expired, or SOCKET_ERROR if an error occurred. If the return value is SOCKET_ERROR, WSAGetLastError can be used to retrieve a specific error code. Example: You can execute select in timer event or may be in while loop but while loop can block your thread. Click here to copy the following block '// Here we assume that our newly created sockets is hSocket '// If you are dealing with multiple connections then You can store socket '// handles in Array or collections Private Sub Timer1_Timer()   Dim cntSocks As Long, lngRetValue As Long   Dim udtRead_fds  As fd_set   Dim udtWrite_fds  As fd_set   Dim udtError_fds  As fd_set   '////////////////////////////////////////////////////////////   'for multiple sockets :   'Assume that socket handles are stored in hSocketsArr() array   '////////////////////////////////////////////////////////////   'cntSocks = UBound(hSocketsArr)+1   'For i = 0 To UBound(hSocketsArr)   '  udtRead_fds.fd_array(i) = hSocketArr(i)   '  udtWrite_fds.fd_array(i) = hSocketArr(i)   '  udtError_fds.fd_array(i) = hSocketArr(i)   'Next   '////////////////////////////////////////////////////////////   'for single socket :   'Assume that socket handle is stored in hSocket variable   '////////////////////////////////////////////////////////////   udtRead_fds.fd_array(0) = hSocket   udtWrite_fds.fd_array(0) = hSocket   udtError_fds.fd_array(0) = hSocket   'Call the select function   lngRetValue = vbselect(0&, udtRead_fds, udtWrite_fds, udtError_fds, 0&)   If lngRetValue = SOCKET_ERROR Then     'some error handling stuff   ElseIf lngRetValue > 0 Then     'If returned value grater than 0 that means that     'the select function has found some sockets that     'can be writable, readable or in error state     'Check for writable sockets     If udtWrite_fds.fd_count > 0 Then       For i = 0 To udtWrite_fds.fd_count - 1         lngSocket = udtWrite_fds.fd_array(i)  '//get socket Handle         '<TODO>: Write to this socket using lngSocket socket handle         'use send api function to send the data       Next     End If     'Check for readable sockets     If udtRead_fds.fd_count > 0 Then       For i = 0 To udtRead_fds.fd_count - 1         lngSocket = udtRead_fds.fd_array(i)  '//get socket Handle         '<TODO>: Read from this socket using lngSocket socket handle         'use recv api function to read data       Next     End If     'Check for sockets in error state     If udtError_fds.fd_count > 0 Then       For i = 0 To udtError_fds.fd_count - 1         lngSocket = udtError_fds.fd_array(i)  '//get socket Handle         '<TODO>: Read from this socket using lngSocket socket handle         'use getsockopt api function with SO_ERROR option to retrive error       Next     End If   End If End Sub # Non Blocking socket # In Non-Blocking socket windows sends you various socket events. On successful socket creation you can Register socket for asynchrous events using WSAAsyncSelect api which takes two parameters (1) socket handle (2) Event mask (socket events which you want to receive from windows). Click here to copy the following block Declare Function WSAAsyncSelect Lib "ws2_32.dll" (ByVal s As Long _   , ByVal hwnd As Long _   , ByVal wMsg As Long _   , ByVal lEvent As Long) As Long Parameters: s [in] Descriptor that identifies the socket for which event notification is required. hwnd [in] Handle that identifies the window that will receive a message when a network event occurs. wMsg [in] Message to be received when a network event occurs. (For socket messages you have to provide WINSOCKMSG) lEvent [in] Bitmask that specifies a combination of network events in which the application is interested. You can create lEvent (Event Mask) parameter using OR logical operator e.g. Click here to copy the following block lEvent = FD_READ Or FD_WRITE Or FD_CONNECT Here is a summary of some events and conditions for each asynchronous notification message. FD_READ: When WSAAsyncSelect is called, if there is data currently available to receive. When data arrives, if FD_READ is not already posted. After recv or recvfrom is called (with or without MSG_PEEK), if data is still available to receive. FD_WRITE: When WSAAsyncSelect called, if a send or sendto is possible. After connect or accept called, when connection established. After send or sendto fail with WSAEWOULDBLOCK, when send or sendto are likely to succeed. After bind on a connectionless socket. FD_WRITE may or may not occur at this time (implementation-dependent). In any case, a connectionless socket is always writeable immediately after a bind operation. FD_ACCEPT: When WSAAsyncSelect called, if there is currently a connection request available to accept. When a connection request arrives, if FD_ACCEPT not already posted. After accept called, if there is another connection request available to accept. FD_CONNECT: When WSAAsyncSelect called, if there is currently a connection established. After connect called, when connection is established (even when connect succeeds immediately, as is typical with a datagram socket). After calling WSAJoinLeaf, when join operation completes. After connect, WSAConnect, or WSAJoinLeaf was called with a nonblocking, connection-oriented socket. The initial operation returned with a specific error of WSAEWOULDBLOCK, but the network operation went ahead. Whether the operation eventually succeeds or not, when the outcome has been determined, FD_CONNECT happens. The client should check the error code to determine whether the outcome was successful or failed. FD_CLOSE: Only valid on connection-oriented sockets (for example, SOCK_STREAM) When WSAAsyncSelect called, if socket connection has been closed. After remote system initiated graceful close, when no data currently available to receive (note: if data has been received and is waiting to be read when the remote system initiates a graceful close, the FD_CLOSE is not delivered until all pending data has been read). After local system initiates graceful close with shutdown and remote system has responded with "End of Data" notification (for example, TCP FIN), when no data currently available to receive. When remote system terminates connection (for example, sent TCP RST), and lParam will contain WSAECONNRESET error value. In order to receive Windows Messages with VB6 we will use a technique called Subclassing.To implement subclassing you have to Hook a window with Windows for additional Windows Messages which you want to receive. and when you dont want any further messages you can UnHook that When you Hook a form or any other window then windows will start sending you messages and you can process messages which you are interested in. Before we implement Hook and UnHook lets go through some declarations for subclassing. Click here to copy the following block Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long _     , ByVal nIndex As Long _     , ByVal dwNewLong As Long) As Long Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long _     , ByVal hwnd As Long _     , ByVal Msg As Long _     , ByVal wParam As Long _     , ByVal lParam As Long) As Long Public Const GWL_WNDPROC = (-4) Public Const WINSOCKMSG = 1025 Public PrevProc As Long For parameters check MSDN documentation. Here are the steps to HOOK and UNHOOK the window. To Hook/Unhook a window Click here to copy the following block Public Sub HookForm(F As Form)   PrevProc = SetWindowLong(F.hwnd, GWL_WNDPROC, AddressOf WindowProc) End Sub Public Sub UnHookForm(F As Form)   If PrevProc <> 0 Then     SetWindowLong F.hwnd, GWL_WNDPROC, PrevProc     PrevProc = 0   End If End Sub To Hook a window you have to pass a handle of the window (in our case its a VB form) and you sepecify mwssagetype (in our case WINSOCK Messages) and very last one is pointer to Windows Procedure which has to be in a certain signature which windows expect(i.e number of parameter and type of parameters). Here is the implementation of Windows Procedure. Click here to copy the following block 'Windows Message handler (Put this procedure in a module) Public Function WindowProc(ByVal hwnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long   If uMsg = WINSOCKMSG Then     '//If winsock message is received then process     ProcessMessage wParam, lParam   Else     WindowProc = CallWindowProc(PrevProc, hwnd, uMsg, wParam, lParam)   End If End Function 'our Winsock-message handler Public Sub ProcessMessage(ByVal lFromSocket As Long, ByVal lParam As Long)   Select Case lParam   Case FD_CONNECT  'we are connected   Case FD_WRITE  'we can write to our connection   Case FD_READ  'we have data waiting to be processed   Case FD_CLOSE  'the connection with server is closed   End Select End Sub [3] Bind the socket Before you start listining on a port you have to bind your server socket with a Port and a local IP address. In this tutorial we will use the following VB function to bind a socket. Click here to copy the following block Public Function SocketBind(ByVal lngSocket As Long, _   ByVal lngLocalPort As Long, _   Optional ByVal strLocalHost As String = "127.0.0.1") As Long '******************************************************************************** 'Purpose  :Binds the socket to the local address 'Return  :If no error occurs, returns zero. Otherwise, it returns SOCKET_ERROR. 'Arguments :lngSocket  - the socket to bind '      strLocalHost - name or IP address of the local host to bind to '      lngLocalPort - the port number to bind to '********************************************************************************   On Error GoTo errHandler   Dim udtSocketAddress As SOCKADDR   Dim lngReturnValue As Long   Dim lngAddress   As Long   SocketBind = SOCKET_ERROR   With udtSocketAddress     .sin_family = AF_INET     '////////////////////////////////////////////////////////     '[1] The strRemoteHost may contain the host name     '  or IP address - GetAddressLong returns a valid     '  value anyway     '////////////////////////////////////////////////////////     '.sin_addr = inet_addr(strLocalHost) 'Will accept only IP     .sin_addr = GetAddressLong(strLocalHost)     '////////////////////////////////////////////////////////     '[2] convert the port number to the network byte ordering     '////////////////////////////////////////////////////////     .sin_port = htons(lngLocalPort)     If .sin_port = INVALID_SOCKET Then       SocketBind = INVALID_SOCKET       Exit Function     End If   End With   '//Set option to reuse the port if its already in use   Dim optvalue As Boolean   optvalue = True   If setsockopt(lngSocket, SOL_SOCKET, SO_REUSEADDR, optvalue, Len(optval)) Then     ShowLog "Error setting SO_REUSEADDR option : " & WSAGetLastError()   End If   SocketBind = bind(lngSocket, udtSocketAddress, LenB(udtSocketAddress))   Exit Function errHandler:   SocketBind = SOCKET_ERROR End Function code Explaination To bind s socket Binds the socket to a local address we can use bind api. Bind takes 3 arguments. Click here to copy the following block Declare Function bind Lib "ws2_32.dll" ( _   ByVal s As Long, _   ByRef addr As SOCKADDR, _   ByVal namelen As Long) As Long Parameters: s [in] Descriptor identifying an unbound socket. addr [in] Address to assign to the socket from the sockaddr structure. Click here to copy the following block Type SOCKADDR   sin_family As Integer 'Address family   sin_port As Integer  'Port   sin_addr As Long    'IP address   sin_zero As String * 8 End Type namelen [in] Length of the value in the name parameter, in bytes. Returns Values : If no error occurs, bind returns zero. Otherwise, it returns SOCKET_ERROR, and a specific error code can be retrieved by calling WSAGetLastError. Convert Host or IP to long SOCKADDR structure requires sin_addr which is Long. To retrive Long number from IP or Host name we can use following helper function. Click here to copy the following block Function GetHostByNameAlias(ByVal hostname$) As Long   On Error Resume Next   Dim phe&   Dim heDestHost As HostEnt   Dim addrList&   Dim retIP&   'If no error occurs, inet_addr returns an unsigned long Value   'containing a suitable binary representation of the Internet   'address given. If the string in the cp parameter does not   'contain a legitimate Internet address,   'for example if a portion of an "a.b.c.d" address exceeds 255,   'then inet_addr returns the value INADDR_NONE.   retIP = inet_addr(hostname)   If retIP = INADDR_NONE Then     phe = gethostbyname(hostname)     If phe <> 0 Then       MemCopy heDestHost, ByVal phe, hostent_size       MemCopy addrList, ByVal heDestHost.h_addr_list, 4       MemCopy retIP, ByVal addrList, heDestHost.h_length     Else       retIP = INADDR_NONE     End If   End If   GetHostByNameAlias = retIP   If Err Then GetHostByNameAlias = INADDR_NONE End Function [4] Listen on the socket After successful socket bind you can call listen function so server can accept incoming connection requests. We will use following VB function to start listen. Click here to copy the following block Function StartListen(hSocket As Long, Port As Long) As Long '******************************************************************************** 'Purpose  :Turns a socket into a listening state. 'Return  :If no error occurs, returns zero. Otherwise, it returns SOCKET_ERROR. 'Arguments :lngSocketHandle - the socket to turn into a listening state. '********************************************************************************   Dim lngRetValue As Long   If SocketBind(hSocket, Port) = SOCKET_ERROR Then StartListen = SOCKET_ERROR   lngRetValue = listen(hSocket, SOMAXCONN)   '   StartListen = lngRetValue End Function code Explaination Listen function takes 2 parameters. Click here to copy the following block Declare Function listen Lib "ws2_32.dll" ( _     ByVal s As Long, _     ByVal backlog As Long) As Long 'Other functions used Declare Function gethostbyname _     Lib "ws2_32.dll" (ByVal host_name As String) As Long Declare Function inet_addr _     Lib "ws2_32.dll" (ByVal cp As String) As Long Declare Function htons _     Lib "ws2_32.dll" (ByVal hostshort As Integer) As Integer Parameters: s [in] Descriptor identifying a bound, unconnected socket. backlog [in] Maximum length of the queue of pending connections. If set to SOMAXCONN, the underlying service provider responsible for socket s will set the backlog to a maximum reasonable value. There is no standard provision to obtain the actual backlog value. We can use following declaration Click here to copy the following block 'Maximum queue length specifiable by listen. Public Const SOMAXCONN = &H7FFFFFFF Return Values : If no error occurs, listen returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError. [5] Accept a connection Once socket goes into listining mode you can start accepting new connection requests from client. To accept connection request you can use following VB function to make your interface more clean. You can call SocketAccept function when you receive FD_ACCEPT event which means that client is waiting for connection. Once server accept incoming request for new connection client will receive FD_CONNECT event. Click here to copy the following block Public Function SocketAccept(ByVal lngSocketHandle As Long) As Long '******************************************************************************** 'Purpose  :Accepts a connection request, and creates a new socket. 'Return  :If no error occurs, returns the new socket's handle. '      Otherwise, it returns INVALID_SOCKET. 'Arguments :lngSocketHandle - the listening socket. '********************************************************************************   Dim lngRetValue    As Long   Dim udtSocketAddress  As SOCKADDR   Dim lngBufferSize   As Long   '   'Calculate the buffer size   lngBufferSize = LenB(udtSocketAddress)   'Call the accept Winsock API function in order to create a new socket   lngRetValue = accept(lngSocketHandle, udtSocketAddress, lngBufferSize)   SocketAccept = lngRetValue   'You can use collection to store handles of sockets (colConnections is a collection)   If lngRetValue <> INVALID_SOCKET Then colConnections.Add lngRetValue End Function code Explaination accept function takes 3 parameters. Click here to copy the following block Private Declare Function accept Lib "ws2_32.dll" ( _   ByVal s As Long, _   ByRef addr As SOCKADDR, _   ByRef addrlen As Long) As Long Parameters: s [in] Descriptor that identifies a socket that has been placed in a listening state with the listen function. The connection is actually made with the socket that is returned by accept. addr [out] Optional pointer to a buffer that receives the address of the connecting entity, as known to the communications layer. The exact format of the addr parameter is determined by the address family that was established when the socket from the sockaddr structure was created. addrlen [in, out] Optional pointer to an integer that contains the length of addr. Return Values If no error occurs, accept returns a value of type SOCKET that is a descriptor for the new socket. This returned value is a handle for the socket on which the actual connection is made. Otherwise, a value of INVALID_SOCKET is returned, and a specific error code can be retrieved by calling WSAGetLastError. [6] Send and receive data After connection is established you can start send/receive data. We will use Send following functions for this purpose. Click here to copy the following block Dim strData As String ' Global variable to hold received data Dim ReadBuffer(1 to 1024) As Byte 'Buffer of received bytes 'Max 1k '************************************************************ 'Sending data '************************************************************ Public Function SendData(ByVal lToSocket As Long, vMessage As Variant) As Long   Dim TheMsg() As Byte, sTemp$   TheMsg = ""   Select Case VarType(vMessage)   Case 8209  'byte array     sTemp = vMessage     TheMsg = sTemp   Case 8  'string, if we recieve a string, its assumed we are linemode     sTemp = StrConv(vMessage, vbFromUnicode)   Case Else     sTemp = CStr(vMessage)     sTemp = StrConv(vMessage, vbFromUnicode)   End Select   TheMsg = sTemp   If UBound(TheMsg) > -1 Then     SendData = send(lToSocket, TheMsg(0), (UBound(TheMsg) - LBound(TheMsg) + 1), 0)   End If End Function '************************************************************ 'Reading data '************************************************************ Function RecvDataToBuffer(lFromSocket As Long) As Long   Dim X As Long   'start reading the data   Do     'Read in 1K chunk , ReadBuffer is a bytearray     X = recv(lFromSocket, ReadBuffer(1), 1024, 0)     If X > 0 Then       strData = strData & Left$(StrConv(ReadBuffer, vbUnicode), X)     End If     If X <> 1024 Or X = SOCKET_ERROR Then Exit Do   Loop   RecvDataToBuffer = X End Function code Explaination Send function takes 4 parameters Click here to copy the following block Declare Function send Lib "ws2_32.dll" ( _   ByVal s As Long, _   ByVal buf As String, _   ByVal lLen As Long, _   ByVal flags As Long) As Long Parameters: s [in] Descriptor identifying a connected socket. buf [in] Buffer containing the data to be transmitted. len [in] Length of the data in buf, in bytes. flags [in] Indicator specifying the way in which the call is made. Return Values If no error occurs, send returns the total number of bytes sent, which can be less than the number indicated by len. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError. recv function takes 4 parameters Click here to copy the following block Declare Function recv Lib "ws2_32.dll" ( _   ByVal s As Long, _   ByVal buf As String, _   ByVal lLen As Long, _   ByVal flags As Long) As Long Parameters: s [in] The descriptor that identifies a connected socket. buf [out] The buffer for incoming data. len [in] The length, in bytes, of buf. flags [in] The flag that specifies the way in which the call is made. Return Values If no error occurs, recv returns the number of bytes received. If the connection has been gracefully closed, the return value is zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError. [7] Disconnect To assure that all data is sent and received on a connected socket before it is closed, an application should use shutdown to close connection before calling closesocket. For example, to initiate a graceful disconnect: Call WSAAsyncSelect to register for FD_CLOSE notification. Call shutdown with how=SD_SEND. When FD_CLOSE received, call recv until zero returned, or SOCKET_ERROR. Call closesocket. Click here to copy the following block Declare Function shutdown Lib "ws2_32.dll" ( _   ByVal s As Long, _   ByVal how As Long) As Long Declare Function closesocket Lib "ws2_32.dll" ( _   ByVal s As Long) As Long

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