server.c

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>
#include <sys/types.h>
#include <signal.h>

#define MAX_CLIENTS 100
#define BUFFER_SZ 2048

static _Atomic unsigned int cli_count = 0;
static int uid = 10;

/* struct of user */
typedef struct
{
	struct sockaddr_in address;
	int sockfd;
	int uid;
	char name[32];
} client_t;

client_t *clients[MAX_CLIENTS];

pthread_mutex_t clients_mutex = PTHREAD_MUTEX_INITIALIZER;

void str_overwrite_stdout()
{
    printf("\r%s", "> ");
    fflush(stdout);
}

void str_trim_lf (char* arr, int length)
{
  int i;
  for (i = 0; i < length; i++)
  {
    if (arr[i] == '\n')
    {
      arr[i] = '\0';
      break;
    }
  }
}

void print_client_addr(struct sockaddr_in addr)
{
    printf("%d.%d.%d.%d",
        addr.sin_addr.s_addr & 0xff,
        (addr.sin_addr.s_addr & 0xff00) >> 8,
        (addr.sin_addr.s_addr & 0xff0000) >> 16,
        (addr.sin_addr.s_addr & 0xff000000) >> 24);
}

// Adding the users into queue
void queue_add(client_t *cl)
{
	pthread_mutex_lock(&clients_mutex);

	for(int i=0; i < MAX_CLIENTS; ++i)
    {
		if(!clients[i])
        {
			clients[i] = cl;
			break;
		}
	}

	pthread_mutex_unlock(&clients_mutex);
}

// Removing users from queue
void queue_remove(int uid)
{
	pthread_mutex_lock(&clients_mutex);

	for(int i=0; i < MAX_CLIENTS; ++i)
    {
		if(clients[i])
        {
			if(clients[i]->uid == uid)
            {
				clients[i] = NULL;
				break;
			}
		}
	}

	pthread_mutex_unlock(&clients_mutex);
}
// Sends message to all users excluding sender
void send_message(char *s, int uid)
{
	pthread_mutex_lock(&clients_mutex);

	for(int i=0; i<MAX_CLIENTS; ++i)
    {
		if(clients[i])
        {
			if(clients[i]->uid != uid)
            {
				if(write(clients[i]->sockfd, s, strlen(s)) < 0)
                {
                    perror("ERROR: Sending message is failed");
					break;
				}
			}
		}
	}

	pthread_mutex_unlock(&clients_mutex);
}

// It handles the communication with users
void *handle_client(void *arg)
{
	char buff_out[BUFFER_SZ];
	char name[32];
	int leave_flag = 0;

	cli_count++;
	client_t *cli = (client_t *)arg;

	// name
	if(recv(cli->sockfd, name, 32, 0) <= 0 || strlen(name) <  2 || strlen(name) >= 32-1)
    {
		printf("You didn't write any name.\n");
		leave_flag = 1;
	}
    
    else
    {
		strcpy(cli->name, name);
		sprintf(buff_out, "%s joined to the conversation.\n", cli->name);
		printf("%s", buff_out);
		send_message(buff_out, cli->uid);
	}

	bzero(buff_out, BUFFER_SZ);

	while(1)
    {
		if (leave_flag)
        {
			break;
		}

		int receive = recv(cli->sockfd, buff_out, BUFFER_SZ, 0);
        
		if (receive > 0)
        {
			if(strlen(buff_out) > 0)
            {
				send_message(buff_out, cli->uid);

				str_trim_lf(buff_out, strlen(buff_out));
				//printf("%s -> %s\n", buff_out, cli->name);
			}
		}
        
        else if (receive == 0 || strcmp(buff_out, "exit") == 0)
        {
			sprintf(buff_out, "%s left the conversation. \n", cli->name);
			printf("%s", buff_out);
			send_message(buff_out, cli->uid);
			leave_flag = 1;
		}
        
        else
        {
			printf("ERROR: -1\n");
			leave_flag = 1;
		}

		bzero(buff_out, BUFFER_SZ);
	}

  // Removing user from queue and leaves the thread
	close(cli->sockfd);
    queue_remove(cli->uid);
    free(cli);
    cli_count--;
    pthread_detach(pthread_self());

	return NULL;
}

int main(int argc, char **argv)
{
	if(argc != 2)
    {
		printf(" %s <port> in use \n", argv[0]);
		return EXIT_FAILURE;
	}

	char *ip = "127.0.0.1";
	int port = atoi(argv[1]);
	int option = 1;
	int listenfd = 0, connfd = 0;
    struct sockaddr_in serv_addr;
    struct sockaddr_in cli_addr;
    pthread_t tid;

  // Socket settings
  listenfd = socket(AF_INET, SOCK_STREAM, 0);
  serv_addr.sin_family = AF_INET;
  serv_addr.sin_addr.s_addr = inet_addr(ip);
  serv_addr.sin_port = htons(port);

  // ignore the pipe signals
	signal(SIGPIPE, SIG_IGN);

    if(setsockopt(listenfd, SOL_SOCKET,(SO_REUSEPORT | SO_REUSEADDR),(char*)&option,sizeof(option)) < 0)
    {
		perror("ERROR: setsockopt failed");
        return EXIT_FAILURE;
	}

	//Connecting sockets
  if(bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0)
  {
      perror("ERROR: Socket connection has failed. \n");
      return EXIT_FAILURE;
  }

  // Socket listening
  if (listen(listenfd, 10) < 0)
  {
      perror("ERROR: Socket listening failed. \n");
      return EXIT_FAILURE;
  }

	printf("=== SAY HELLO TO THE CHAT APP IN BASH ===\n");

	while(1)
    {
		socklen_t clilen = sizeof(cli_addr);
		connfd = accept(listenfd, (struct sockaddr*)&cli_addr, &clilen);

        //Check for if the max users exceeded
		if((cli_count + 1) == MAX_CLIENTS)
        {
			printf("User number had reached the max number. Rejected: ");
			print_client_addr(cli_addr);
			printf(":%d\n", cli_addr.sin_port);
			close(connfd);
			continue;
		}

		// user settings
		client_t *cli = (client_t *)malloc(sizeof(client_t));
		cli->address = cli_addr;
		cli->sockfd = connfd;
		cli->uid = uid++;

        // Adding user into queue and forking thread	
		queue_add(cli);
		pthread_create(&tid, NULL, &handle_client, (void*)cli);

		//Decreases the CPU usage
		sleep(1);
	}

	return EXIT_SUCCESS;
}