./server <port> <backlog>

simple_server.c

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


#define max_mssg_len 1024


int server_fd;

void INTR_handler(int sig)
{
	close(server_fd);
	puts("\n-----Server closed-----");
	exit(0);
}

int main(int argc,char *argv[])
{
	int myport,backlog;
	if(argc !=3 )
	{
		puts("USAGE: <portno> <backlog>");
		exit(EXIT_FALIURE);
	}
	
	if(argv[1]=="" || argv[1] ==NULL)
	{
		puts("ERROR: Enter a valid port number");
		exit(EXIT_FAILURE);

	}
	
	myport = atoi(argv[1]);
	if( argv[2] == "" || argv[2] == NULL)
	{
		puts("ERROR: Enter a valid backlog value");
		exit(EXIT_FAILURE);
	}
	
	backlog = atoi(argv[2]);
	
    struct sockaddr_in server_addr,client_addr;
    int client_fd,server_status,bind_status,listen_status,accept_status;
    socklen_t client_addr_size;
    char buff[max_mssg_len];
    int n=0;

    memset(&server_addr,0,sizeof(server_addr));
    memset(&client_addr,0,sizeof(client_addr));

    /*

        struct sockaddr_in {
            short int sin_family; // Address family, AF_INET
            unsigned short int sin_port; // Port number
            struct in_addr sin_addr; // Internet address
            unsigned char sin_zero[8]; // Same size as struct sockaddr
        };



        struct in_addr {
            uint32_t s_addr; // that's a 32-bit int (4 bytes)
        };

       */

    server_addr.sin_family = AF_INET; // IPv4
    server_addr.sin_port = htons(myport); // big-endian short
    server_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK); // big-endian long // my own IPv4 address


    server_fd = socket(AF_INET,SOCK_STREAM,0);


    if ( -1 == server_fd)
    {
	perror("ERROR");
        exit(0);
    }

    bind_status = bind(server_fd,(struct sockaddr *) &server_addr,sizeof(server_addr));

    if ( -1 == bind_status)
    {
	    perror("ERROR");
    
        exit(0);
    }

    listen_status = listen(server_fd,backlog); 
 

    if( -1 == listen_status )
    {
		perror("ERROR");
        exit(0);
    }

    printf("-----------sever is UP and LISTENING on port: %d -----------\n",myport);
    

    char greetings[] = "~~~~~~~~SERVER: hi client, you are now connected~~~~~~~~\n";
    int bytes_sent;
    char addr[30]="";

    while(1)
    {
	signal(SIGINT,INTR_handler);

        puts("--------Waiting for a connection--------\n");
        client_fd = accept(server_fd,(struct sockaddr *) &client_addr, &client_addr_size);

        bytes_sent = send(client_fd,&greetings,sizeof(greetings),0);

        inet_ntop(client_addr.sin_family,&client_addr.sin_addr.s_addr,addr,sizeof(addr));
        
        printf("new client: %s :%d\n",addr,ntohs(client_addr.sin_port));
        
        bzero(buff,max_mssg_len);
        puts("----------Client says---------\n");

        while(1)
        {
            recv(client_fd,&buff,sizeof(buff),0);

            if(strncmp(buff,"!q",2)==0)
            {
                close(client_fd);
                printf("-------connection terminated by the client-------\n");
                break;;
            }

            fflush(stdout);
            printf("%s",buff);   
     }
     
    }
    return 0;
}