Client Server Communication

• Download server source - 80.5 Kb
• Download client source - 28.5 Kb
• Download demo EXEs - 26.8 Kb

Introduction

This article gives information on client server communication using sockets. Thanks to Ernest Laurentin for writing such an excellent class called SocketComm which provides methods which are useful in developing client-server applications.

Overview

Figure I-1 shows one of the programming frameworks. The left block represents the client application. The rest represents the server application. If the client application wants to send/receive data to/from a server, the client needs to create a socket (client socket) and use this socket to communicate with the server. At the server side, there are two kinds of sockets. One is the listening socket, which is responsible to take care of requests from new clients. The other is the service socket whose job is to taking care of all the communication between existing clients and the server. Once a new user requests to join the service, the listening socket will create a new service socket for this new user. The functionality of the service socket is like that of a representative of each client. In other words, if there are N users in this system, there will be N service sockets in the server side.

Overview of Server Application

The server will set up the service first. It will keep waiting any request from a new user. If a new request is granted, the server will create a new service socket to serve this new user.

Code for Listening Request

DWORD WINAPI CallServerThread(LPVOID lpPtr)
{
   AFX_MANAGE_STATE(AfxGetStaticModuleState())
   CSampleServerDlg* pThis = reinterpret_cast( lpPtr );
   _ASSERTE( pThis != NULL );
   SOCKET Soc;
   while(TRUE)
   {
    TCHAR szBuf[MAX_PATH] = {0};
    Soc = (SOCKET)pThis->m_hComm;
    fd_set fdRead = { 0 };
    Soc = accept(Soc,0,0);
    DWORD dWW = GetLastError();
    if(Soc != INVALID_SOCKET)
    {
      CString strTotClients = "";
      pThis->m_hNewSocHandle = (HANDLE) Soc;
      pThis->UpdateUserInfo();
    }     Sleep(500);
   }
   return 0;
}

Code for Service Socket

DWORD WINAPI ListeningThread(LPVOID lpPtr)
{
   AFX_MANAGE_STATE(AfxGetStaticModuleState())
   TCHAR szBuf[MAX_PATH] = {0};
   CListeningClass *pThis = reinterpret_cast(lpPtr);
   SOCKET Soc ;
   Soc = (SOCKET)pThis->m_hComm;
   if(Soc != INVALID_SOCKET)
   {
     while(TRUE)
     {
     int nRet = recv(Soc,szBuf,sizeof(szBuf),0);
     if(nRet != SOCKET_ERROR )
     {
     if(!::IsWindowVisible(pThis->m_hWnd))
     pThis->ShowWindow(SW_SHOW);
          CString strText = szBuf;
     pThis->m_Recv.SetWindowText(strText);
     }
     Sleep(100);
     }
   }
   return 0;
}

Code for Terminating Thread at the End

void CListeningClass::TerminateThread()
{
   DWORD dwExitCode = 0;
   while(TRUE)
   {
   ::TerminateThread(m_handle,dwExitCode);
    if(::GetExitCodeThread(m_handle,&dwExitCode))
    {
    if (dwExitCode !=STILL_ACTIVE)
    { 
    break;
    }
    else
     Sleep(10);
    }
  }
}

How the Demo Works

1. Invoke the server application and click on “Start Server”. Now, the application starts listening to clients.
2. Invoke the client application, specify the IP address, and click on “Connect”.