Two way communication between Client and Server using Win32 Threads

Prerequisite: Socket Programming in C/C++
It is possible to send data from the server and receive a response from the client. Similarly, the client can also send and receive data to-and-from. Here we will discuss the approach using Win32 Threads in C/C++.

Approach:

1. Use CreateThread function which creates a new thread for a process.
2. The CreateThread method must specify the starting address of the code that the new thread is to execute. Following is the prototype of CreateThread function:

   HANDLE CreateThread( 
     LPSECURITY_ATTRIBUTES lpThreadAttributes,
     DWORD dwStackSize, 
     LPTHREAD_START_ROUTINE lpStartAddress,
     LPVOID lpParameter, DWORD dwCreationFlags,
      LPDWORD lpThreadId 
   );
   

3. Then using WaitForSingleObject function that returns message in form of object received from client, to receive data from client. Following is the prototype of WaitForSingleObject function:

   DWORD WaitForSingleObject(
     HANDLE hHandle,        
     DWORD dwMilliseconds
   );
   

Creating the Server program
In the Server Program, we will be using two threads, one for Sending data to the client and another for Receiving data from the client. The process of communication stops when both Client and Server type “exit“.

Below is the implementation of the Server Program:

Server

// C++ program to create Server

#include <iostream>
#include <string.h>
#include <winsock2.h>
using namespace std;

// Function that receive data
// from client
DWORD WINAPI serverReceive(LPVOID lpParam)
{
    // Created buffer[] to
    // receive message
    char buffer[1024] = { 0 };

    // Created client socket
    SOCKET client = *(SOCKET*)lpParam;

    // Server executes continuously
    while (true) {

        // If received buffer gives
        // error then return -1
        if (recv(client, buffer, sizeof(buffer), 0)
            == SOCKET_ERROR) {
            cout << "recv function failed with error "
                 << WSAGetLastError() << endl;
            return -1;
        }

        // If Client exits
        if (strcmp(buffer, "exit") == 0) {
            cout << "Client Disconnected."
                 << endl;
            break;
        }

        // Print the message
        // given by client that
        // was stored in buffer
        cout << "Client: " << buffer << endl;

        // Clear buffer message
        memset(buffer, 0,
               sizeof(buffer));
    }
    return 1;
}

// Function that sends data to client
DWORD WINAPI serverSend(LPVOID lpParam)
{
    // Created buffer[] to
    // receive message
    char buffer[1024] = { 0 };

    // Created client socket
    SOCKET client = *(SOCKET*)lpParam;

    // Server executes continuously
    while (true) {

        // Input message server
        // wants to send to client
        gets(buffer);

        // If sending failed
        // return -1
        if (send(client,
                 buffer,
                 sizeof(buffer), 0)
            == SOCKET_ERROR) {
            cout << "send failed with error "
                 << WSAGetLastError() << endl;
            return -1;
        }

        // If server exit
        if (strcmp(buffer, "exit") == 0) {
            cout << "Thank you for using the application"
                 << endl;
            break;
        }
    }
    return 1;
}

// Driver Code
int main()
{
    // Data
    WSADATA WSAData;

    // Created socket server
    // and client
    SOCKET server, client;

    // Socket address for server
    // and client
    SOCKADDR_IN serverAddr, clientAddr;

    WSAStartup(MAKEWORD(2, 0), &WSAData);

    // Making server
    server = socket(AF_INET,
                    SOCK_STREAM, 0);

    // If invalid socket created,
    // return -1
    if (server == INVALID_SOCKET) {
        cout << "Socket creation failed with error:"
             << WSAGetLastError() << endl;
        return -1;
    }
    serverAddr.sin_addr.s_addr = INADDR_ANY;
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(5555);

    // If socket error occurred,
    // return -1
    if (bind(server,
             (SOCKADDR*)&serverAddr,
             sizeof(serverAddr))
        == SOCKET_ERROR) {
        cout << "Bind function failed with error: "
             << WSAGetLastError() << endl;
        return -1;
    }

    // Get the request from
    // server
    if (listen(server, 0)
        == SOCKET_ERROR) {
        cout << "Listen function failed with error:"
             << WSAGetLastError() << endl;
        return -1;
    }

    cout << "Listening for
            incoming connections...." << endl;

            // Create buffer[]
            char buffer[1024];

    // Initialize client address
    int clientAddrSize = sizeof(clientAddr);

    // If connection established
    if ((client = accept(server,
                         (SOCKADDR*)&clientAddr,
                         &clientAddrSize))
        != INVALID_SOCKET) {
        cout << "Client connected!" << endl;
        cout << "Now you can use our live chat application."
             << "Enter \"exit\" to disconnect" << endl;

        // Create variable of
        // type DWORD
        DWORD tid;

        // Create Thread t1
        HANDLE t1 = CreateThread(NULL,
                                 0,
                                 serverReceive,
                                 &client,
                                 0,
                                 &tid);

        // If created thread
        // is not created
        if (t1 == NULL) {
            cout << "Thread Creation Error: "
                 << WSAGetLastError() << endl;
        }

        // Create Thread t2
        HANDLE t2 = CreateThread(NULL,
                                 0,
                                 serverSend,
                                 &client,
                                 0,
                                 &tid);

        // If created thread
        // is not created
        if (t2 == NULL) {
            cout << "Thread Creation Error: "
                 << WSAGetLastError() << endl;
        }

        // Received Objects
        // from client
        WaitForSingleObject(t1,
                            INFINITE);
        WaitForSingleObject(t2,
                            INFINITE);

        // Close the socket
        closesocket(client);

        // If socket closing
        // failed.
        if (closesocket(server)
            == SOCKET_ERROR) {
            cout << "Close socket failed with error: "
                 << WSAGetLastError() << endl;
            return -1;
        }
        WSACleanup();
    }
}

Run the ServerApplication.cpp file using the command:

g++ ServerApplication.cpp -lws2_32 

Creating the Client Program
In the Client Program, we will be using two threads one for Sending data to the server and another for Receiving data from the server. The process of communication stops when both Server and Client type “exit“.

Client

// C++ program to create client

#include <iostream>
#include <string.h>
#include <winsock2.h>
using namespace std;

// Function that receive data from server
DWORD WINAPI clientReceive(LPVOID lpParam)
{
    // Created buffer[] to
    // receive message
    char buffer[1024] = { 0 };

    // Created server socket
    SOCKET server = *(SOCKET*)lpParam;

    // Client executes continuously
    while (true) {

        // If received buffer gives
        // error then return -1
        if (recv(server, buffer,
                 sizeof(buffer), 0)
            == SOCKET_ERROR) {
            cout << "recv function failed with error: "
                 << WSAGetLastError()
                 << endl;
            return -1;
        }

        // If Server exits
        if (strcmp(buffer, "exit") == 0) {
            cout << "Server disconnected."
                 << endl;
            return 1;
        }

        // Print the message
        // given by server that
        // was stored in buffer
        cout << "Server: " << buffer << endl;

        // Clear buffer message
        memset(buffer, 0, sizeof(buffer));
    }
    return 1;
}

// Function that sends data to server
DWORD WINAPI clientSend(LPVOID lpParam)
{
    // Created buffer[] to
    // receive message
    char buffer[1024] = { 0 };

    // Created server socket
    SOCKET server = *(SOCKET*)lpParam;

    // Client executes continuously
    while (true) {

        // Input message client
        // wants to send to server
        gets(buffer);

        // If sending failed
        // return -1
        if (send(server,
                 buffer,
                 sizeof(buffer), 0)
            == SOCKET_ERROR) {
            cout << "send failed with error: "
                 << WSAGetLastError() << endl;
            return -1;
        }

        // If client exit
        if (strcmp(buffer, "exit")
            == 0) {
            cout << "Thank you for using the application"
                 << endl;
            break;
        }
    }
    return 1;
}

// Driver Code
int main()
{
    // Input data
    WSADATA WSAData;

    // Created socket server
    SOCKET server;
    SOCKADDR_IN addr;

    WSAStartup(MAKEWORD(2, 0), &WSAData);

    // If invalid socket created,
    // return -1
    if ((server = socket(AF_INET,
                         SOCK_STREAM, 0))
        == INVALID_SOCKET) {
        cout << "Socket creation failed with error: "
             << WSAGetLastError() << endl;
        return -1;
    }

    addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    addr.sin_family = AF_INET;
    addr.sin_port = htons(5555);

    // If connection failed
    if (connect(server,
                (SOCKADDR*)&addr,
                sizeof(addr))
        == SOCKET_ERROR) {
        cout << "Server connection failed with error: "
             << WSAGetLastError() << endl;
        return -1;
    }

    // If connection established
    cout << "Connected to server!"
         << endl;
    cout << "Now you can use our live chat application."
         << " Enter \"exit\" to disconnect"
         << endl;
    DWORD tid;

    // Create Thread t1
    HANDLE t1 = CreateThread(NULL,
                             0,
                             clientReceive,
                             &server,
                             0, &tid);

    // If created thread
    // is not created
    if (t1 == NULL)
        cout << "Thread creation error: "
             << GetLastError();

    // Create Thread t2
    HANDLE t2 = CreateThread(NULL,
                             0,
                             clientSend,
                             &server,
                             0, &tid);

    // If created thread
    // is not created
    if (t2 == NULL)
        cout << "Thread creation error: "
             << GetLastError();

    // Received Objects
    // from client
    WaitForSingleObject(t1, INFINITE);
    WaitForSingleObject(t2, INFINITE);

    // Socket closed
    closesocket(server);
    WSACleanup();
}

Run the ClientApplication.cpp file using the command:

g++ ClientApplication.cpp -lws2_32 

Output After communication between Server and Client

The left side command prompt is the ServerApplication and the right side command prompt is the ClientApplication.