server.cpp

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <pthread.h>
struct client_info {
    int sockno;
    char ip[INET_ADDRSTRLEN];
};
int clients[100];
int n = 0;
int cnt=1;
long long binpow(long long a, long long b, long long m) {
    a %= m;
    long long res = 1;
    while (b > 0) {
        if (b & 1)
            res = res * a % m;
        a = a * a % m;
        b >>= 1;
    }
    return res;
}
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
void sendtoall(char *msg,int curr)
{
    int i;
    pthread_mutex_lock(&mutex);
    for(i = 0; i < n; i++) {
        if(clients[i] != curr) {
            if(send(clients[i],msg,strlen(msg),0) < 0) {
                perror("sending failure");
                continue;
            }
        }
    }
    pthread_mutex_unlock(&mutex);
}
void *recvmg(void *sock)
{
    struct client_info cl = *((struct client_info *)sock);
    char msg[500];
    int len;
    int i;
    int j;
    while((len = recv(cl.sockno,msg,500,0)) > 0) {
        msg[len] = '\0';
        sendtoall(msg,cl.sockno);
        memset(msg,'\0',sizeof(msg));
    }
    pthread_mutex_lock(&mutex);
    printf("%s disconnected\n",cl.ip);
    for(i = 0; i < n; i++) {
        if(clients[i] == cl.sockno) {
            j = i;
            while(j < n-1) {
                clients[j] = clients[j+1];
                j++;
            }
        }
    }
    n--;
    pthread_mutex_unlock(&mutex);
}
int main(int argc, char *argv[]) {
    struct sockaddr_in my_addr, their_addr;
    int my_sock;
    int their_sock;
    socklen_t their_addr_size;
    int portno;
    pthread_t sendt, recvt;
    char msg[500];
    int len;
    struct client_info cl;
    char ip[INET_ADDRSTRLEN];

    if (argc > 2) {
        printf("too many arguments");
        exit(1);
    }

    portno = atoi(argv[1]);
    my_sock = socket(AF_INET, SOCK_STREAM, 0);
    memset(my_addr.sin_zero, '\0', sizeof(my_addr.sin_zero));
    my_addr.sin_family = AF_INET;
    my_addr.sin_port = htons(portno);
    my_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    their_addr_size = sizeof(their_addr);

    if (bind(my_sock, (struct sockaddr *)&my_addr, sizeof(my_addr)) != 0) {
        perror("binding unsuccessful");
        exit(1);
    }

    if (listen(my_sock, 5) != 0) {
        perror("listening unsuccessful");
        exit(1);
    }
while (1) {
    if ((their_sock = accept(my_sock, (struct sockaddr *)&their_addr, &their_addr_size)) < 0) {
        perror("accept unsuccessful");
        exit(1);
    }

    pthread_mutex_lock(&mutex);
    inet_ntop(AF_INET, (struct sockaddr *)&their_addr, ip, INET_ADDRSTRLEN);
    printf("%s connected\n", ip);
    cl.sockno = their_sock;
    strcpy(cl.ip, ip);
    clients[n] = their_sock;
    n++;

    // Send the value of cnt to the newly connected client and switch cnt.
    char cnt_msg[10];
    snprintf(cnt_msg, sizeof(cnt_msg), "%d", cnt);
    if (send(their_sock, cnt_msg, strlen(cnt_msg), 0) < 0) {
        perror("sending failure");
        // Additional debug information
        printf("Failed to send cnt_msg to client. their_sock: %d\n", their_sock);
    }
    
    cnt = (cnt == 1) ? 2 : 1;
    
    pthread_create(&recvt, NULL, recvmg, &cl);
    pthread_mutex_unlock(&mutex);
}
    return 0;
}