multis.c

#include <stdio.h>
#include <string.h>   
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>  
#include <arpa/inet.h>   
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/time.h> 
#include <time.h>
#include <stdint.h>
#include <sys/resource.h>
#define MAX 20 //for max amount of client to connected  
#define TRUE   1
#define FALSE  0
 
int main(int argc , char *argv[])
{
    int opt = TRUE;
    int master_sock , new_sock , client_sock[MAX] , max_client = MAX , act, cl ,addrlen , valread , sd;
    int max_sd;
fd_set sock_desc;
    struct sockaddr_in servaddr;
    
char buffer1[2000];  //data buffer1 
 
//now set the socket descriptors


    //here initialise all client_sock[] to 0 
    for (cl = 0; cl < max_client; cl++) 
    {
        client_sock[cl] = 0;
    }
      
    //create a master socket
    if( (master_sock = socket(AF_INET , SOCK_STREAM , 0)) == 0) 
    {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
  
    //set master socket to allow multiple connections 
    if( setsockopt(master_sock, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(opt)) < 0 )
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
  
    //type of socket created
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = INADDR_ANY;
    servaddr.sin_port = htons( atoi(argv[1]) );      

    //bind the socket to localhost port specified

    if (bind(master_sock, (struct sockaddr *)&servaddr, sizeof(servaddr))<0) 
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    printf("here Listener on port %s \n", argv[1]);
     
    //try to specify maximum of 3 pending connections for the master socket
    if (listen(master_sock, 3) < 0)
    {
        perror("listen");
        exit(EXIT_FAILURE);
    }
      
    //accept the incoming connection
    addrlen = sizeof(servaddr);
    puts("Now Waiting for connections ...");
     
    while(TRUE) 
    {
        //clear the socket set
        FD_ZERO(&sock_desc);
  
        //add master socket to set
        FD_SET(master_sock, &sock_desc);
        max_sd = master_sock;
         
        //add child sockets to set
        for ( cl = 0 ; cl < max_client ; cl++) 
        {
            //socket descriptor
            sd = client_sock[cl];
             
            //if valid socket descriptor then add to read list
            if(sd > 0)
                FD_SET( sd , &sock_desc);
             
            //highest file descriptor number, need it for the select function
            if(sd > max_sd)
                max_sd = sd;
        }
  
        //wait for an act on one of the sockets , timeout is NULL , so wait indefinitely
        act = select( max_sd + 1 , &sock_desc , NULL , NULL , NULL);
    
        if ((act < 0) && (errno!=EINTR)) 
        {
            printf("select error here \n");
        }
          
        // an incoming connection
        if (FD_ISSET(master_sock, &sock_desc)) 
        {
            if ((new_sock = accept(master_sock, (struct sockaddr *)&servaddr, (socklen_t*)&addrlen))<0)
            {
                perror("accept");
                exit(EXIT_FAILURE);
            }
          
            //inform user of socket number - used in send and receive commands
            printf("New connection , socket fd is : %d , ip is : %s , Port : %d \n" , new_sock , inet_ntoa(servaddr.sin_addr) , ntohs(servaddr.sin_port));
        
            
              
            //add new socket to array of sockets
            for (cl = 0; cl < max_client; cl++) 
            {
                //if position is empty
                if( client_sock[cl] == 0 )
                {
                    client_sock[cl] = new_sock;
                    printf("Adding the list of sockets here: %d\n" ,cl);
                     
                    break;
                }
            }
        }
          
        //else its some IO operation on some other socket
        for (cl = 0; cl < max_client; cl++) 
        {
            sd = client_sock[cl];
              
            if (FD_ISSET( sd , &sock_desc)) 
            {
                //Check if it was for closing , and also read the incoming message
                if ((valread = read( sd , buffer1, 1024)) == 0)
                {
                    //Somebody disconnected , get his details and print               getpeername(sd , (struct sockaddr*)&servaddr , (socklen_t*)&addrlen);
                    printf("Host disconnected here sorry ip %s , port %d \n" , inet_ntoa(servaddr.sin_addr) , ntohs(servaddr.sin_port));
                      
                    //Close the socket and mark as 0 in list for reuse
                    close( sd );
                    client_sock[cl] = 0;
                }
                  
                //Echo back the message that came in
                else
                {
              //set the string terminating NULL byte on the end of the data read
                  buffer1[valread] = '\0';
                    //puts(buffer1); host name recived checked.
                    //printf("%s", );
                  
                   
		 send(sd , buffer1 , strlen(buffer1) , 0 );

               }
            }
        }
    }
      
    return 0;
}