C++ Sockets - Server doesn't accept multiple clients (linux)

Question

I have working server and client code. The server and client can connect and chat with each other correctly. But when I open another client terminal, the client is says Awaiting confirmation from the server and nothing else. Although server and client #1 can still chat.

I searched on multi-threading but the examples or code snippets they show is advanced. Maybe a little explanation or an example will help a lot!

The code below is working. I have a working server but it only accepts one connection. How do I make the server to allow multiple connection? So that I can make the program look like a group chat.

client.cpp (when client #2 connects, the code freezes at line 40)

#include <iostream>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdlib.h>
#include <unistd.h>

using namespace std;

int main()
{
    char a;
    int client;
    int portNum = 1500;
    int bufsize = 1024;
    char* buffer = new char[bufsize];
    bool isExit = false;
    char* ip = "127.0.0.1";

    struct sockaddr_in direc;

    if ((client = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        cout << "\nError creating socket..." << endl;
        exit(0);
    }

    cout << "\nSocket created successfully..." << endl;
    direc.sin_family = AF_INET;
    direc.sin_port = htons(portNum);
    inet_pton(AF_INET, ip, &direc.sin_addr);

    if (connect(client,(struct sockaddr *)&direc, sizeof(direc)) == 0)
        cout << "Connection to the server " << inet_ntoa(direc.sin_addr) << endl;

    cout << "Awaiting confirmation from the server..." << endl; //line 40
    recv(client, buffer, bufsize, 0);

    cout << "\n=> Enter # to terminate the connection\n" << endl;

    do {
        cout << "Client: ";
        do {
            cin >> buffer;
            send(client, buffer, bufsize, 0);
            if (*buffer == '#') {
                send(client, buffer, bufsize, 0);
                *buffer = '*';
                isExit = true;
            }
        } while (*buffer != 42);

        cout << "Server: ";
        do {
            recv(client, buffer, bufsize, 0);
            cout << buffer << " ";
            if (*buffer == '#') {
                *buffer = '*';
                isExit = true;
            }

        } while (*buffer != 42);
        cout << endl;

    } while (!isExit);
    cout << "=> Connection terminated.\nGoodbye";

    close(client);
    return 0;
}

server.cpp

#include <iostream>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <unistd.h>

using namespace std;

int main()
{
    int client, server;
    int bufsize = 1024;
    int portNum = 1500;
    bool isExit = false;
    char* buffer = new char[bufsize];

    struct sockaddr_in direc;
    socklen_t tamano;
    pid_t pid;

    if ((client = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        cout << "\nError establishing socket..." << endl;
        exit(1);
    }

    cout << "\nSocket server has been created..." << endl;

    direc.sin_family = AF_INET;
    direc.sin_addr.s_addr = htons(INADDR_ANY);
    direc.sin_port = htons(portNum);

    if ((bind(client, (struct sockaddr*)&direc,sizeof(direc))) < 0) {
        cout << "\nError binding connection..." << endl;
        return -1;
    }

    tamano = sizeof(direc);
    cout << "Looking for clients..." << endl;
    listen(client, 1);

    while ((server = accept(client,(struct sockaddr *)&direc,&tamano)) > 0) {
        strcpy(buffer, "Server connected...\n");
        send(server, buffer, bufsize, 0);
        cout << "Connected with the client, you are good to go..." << endl;
        cout << "Enter # to end the connection\n" << endl;

        cout << "Client: ";
        do {
            recv(server, buffer, bufsize, 0);
            cout << buffer << " ";
            if (*buffer == '#') {
                *buffer = '*';
                isExit = true;
            }
        } while (*buffer != '*');

        do {
            cout << "\nServer: ";
            do {
                cin >> buffer;
                send(server, buffer, bufsize, 0);
                if (*buffer == '#') {
                    send(server, buffer, bufsize, 0);
                    *buffer = '*';
                    isExit = true;
                }
            } while (*buffer != '*');

            cout << "Client: ";
            do {
                recv(server, buffer, bufsize, 0);
                cout << buffer << " ";
                if (*buffer == '#') {
                    *buffer == '*';
                    isExit = true;
                }
            } while (*buffer != '*');
        } while (!isExit);

        cout << "\n=> Connection terminated... " << inet_ntoa(direc.sin_addr);
        close(server);
        cout << "\nGoodbye..." << endl;
        isExit = false;
    }

    close(client);
    return 0;
}

How do I make the server accept multiple connection?

Thanks!

Answer 1

You will need to use select or poll and a state machine pattern to do what you want to do. This means that you will need to process the data as it comes in from whichever client is sending it. Take a look here for a working example.

Answer 2

In order to properly support multiple connections you should fire up a new thread for each incoming connection. Each new connection is identified by its own unique socket descriptor returned by accept(). A simple example:

while ((accepted = accept(client,(struct sockaddr *)&direc,&tamano)) > 0) {
    /*Create the thread and pass the socket descriptor*/
    if( pthread_create(new_thread, &thread_attributes, &handle_tcp_connection, (void *)accepted) != 0){
      perror("create thread");
      exit(EXIT_FAILURE);
    }
}