Chatroom in C / Socket programming in Linux

Question

I have a simple server and client C code to do a chatroom for multiclients using threads (pthread library). The problem I've been having is that I can't think a way of making the server write every message that a client sends over the socket into all other clients. I've read other similar posts in here and it was helpless. Please help me I need to do this for school. I'll send both codes right away.

Server.c:

#include<stdio.h>
#include<string.h>    //strlen
#include<stdlib.h>    //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h>    //write

#include<pthread.h> //for threading , link with lpthread

void *connection_handler(void *);


int main(int argc , char *argv[])
{
    int socket_desc , new_socket , c , *new_sock;
    struct sockaddr_in server , client;
    char *message;

    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }

    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons( 8888 );

    //Bind
    if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
        puts("bind failed");
        return 1;
    }
    puts("bind done");

    //Listen
    listen(socket_desc , 3);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while( (new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)) )
    {
        puts("Connection accepted");

        pthread_t sniffer_thread;
        new_sock = malloc(1);
        *new_sock = new_socket;

        if( pthread_create( &sniffer_thread , NULL ,  connection_handler , (void*) new_sock) < 0)
        {
            perror("could not create thread");
            return 1;
        }

        //Now join the thread , so that we dont terminate before the thread
        //pthread_join( sniffer_thread , NULL);
        puts("Handler assigned");
    }

    if (new_socket<0)
    {
        perror("accept failed");
        return 1;
    }

    return 0;
}

/*
 * This will handle connection for each client
 * */
void *connection_handler(void *socket_desc)
{
    //Get the socket descriptor
    int sock = *(int*)socket_desc;
    int read_size;
    char *message , client_message[2000];


    //Receive a message from client
    while( (read_size = recv(sock , client_message , 2000 , 0)) > 0 )
    {
        //Send the message back to client
        write(sock , client_message , strlen(client_message));
    }

    if(read_size == 0)
    {
        puts("Client disconnected");
        fflush(stdout);
    }
    else if(read_size == -1)
    {
        perror("recv failed");
    }

    //Free the socket pointer
    free(socket_desc);

    return 0;
}

Client.c

#include<stdio.h> //printf
#include<string.h>    //strlen
#include<sys/socket.h>    //socket
#include<arpa/inet.h> //inet_addr

int main(int argc , char *argv[])
{
    int sock;
    struct sockaddr_in server;
    char message[1000] , server_reply[2000];

    //Create socket
    sock = socket(AF_INET , SOCK_STREAM , 0);
    if (sock == -1)
    {
        printf("Could not create socket");
    }
    puts("Socket created");

    server.sin_addr.s_addr = inet_addr("127.0.0.1");
    server.sin_family = AF_INET;
    server.sin_port = htons( 8888 );

    //Connect to remote server
    if (connect(sock , (struct sockaddr *)&server , sizeof(server)) < 0)
    {
        perror("connect failed. Error");
        return 1;
    }

    puts("Connected\n");
    puts("Bienvenido al Chatroom, puedes empezar a escribir en la sala!");

    //keep communicating with server
    while(1)
    {

        printf("Enter message: ");
    fgets(message, sizeof(message),stdin);
        //scanf("%s" , message);

        //Send some data
        if( send(sock , message , strlen(message) , 0) < 0)
        {
            puts("Send failed");
            return 1;
        }

        //Receive a reply from the server
        if( recv(sock , server_reply , 2000 , 0) < 0)
        {
            puts("recv failed");
            break;
        }

    printf("Server Reply: %s\n", server_reply);
    server_reply[0]='\0'; 
    }

    close(sock);
    return 0;
}

These programs are very simple, the client sends what the user writes in console and the server send the same message back. I just need the server to send the same message to every thread (client) connected (not only the one who sent the original message).

I know this is long for anyone to care, but if you can, I'll be glad to get some help :)

Answer 1

You need a global table of all clients, protected by a mutex. When a new client connects, add them to the global table of clients. When a client disconnects, remove them from the global table.

When a client sends a message, acquire the lock on the global table and traverse it. Send the message to all clients (other than the one that sent the message, if you don't want to echo a message back to its source).

This is a gross oversimplification of how real servers do it. But it should be enough to get you started.