Handle multiple socket connections with fd_set and select on Linux

/** Handle multiple socket connections with select and fd_set on Linux

Silver Moon ( [email protected])

*/

#include <stdio.h> #include <string.h> //strlen #include <stdlib.h> #include <errno.h> #include <unistd.h> //close #include <arpa/inet.h> //close #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <sys/time.h> //FD_SET, FD_ISSET, FD_ZERO macros

#define TRUE 1 #define FALSE 0 #define PORT 8888

int main(int argc , char *argv[]) { int opt = TRUE; int master_socket , addrlen , new_socket , client_socket[30] , max_clients = 30 , activity, i , valread , sd; int max_sd; struct sockaddr_in address;

char buffer[1025];  //data buffer of 1K
  
//set of socket descriptors
fd_set readfds;
  
//a message
char *message = "ECHO Daemon v1.0 \r\n";

//initialise all client_socket[] to 0 so not checked
for (i = 0; i < max_clients; i++) 
{
    client_socket[i] = 0;
}
  
//create a master socket
if( (master_socket = socket(AF_INET , SOCK_STREAM , 0)) == 0) 
{
    perror("socket failed");
    exit(EXIT_FAILURE);
}

//set master socket to allow multiple connections , this is just a good habit, it will work without this
if( setsockopt(master_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(opt)) < 0 )
{
    perror("setsockopt");
    exit(EXIT_FAILURE);
}

//type of socket created
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons( PORT );
  
//bind the socket to localhost port 8888
if (bind(master_socket, (struct sockaddr *)&address, sizeof(address))<0) 
{
    perror("bind failed");
    exit(EXIT_FAILURE);
}
printf("Listener on port %d \n", PORT);
 
//try to specify maximum of 3 pending connections for the master socket
if (listen(master_socket, 3) < 0)
{
    perror("listen");
    exit(EXIT_FAILURE);
}
  
//accept the incoming connection
addrlen = sizeof(address);
puts("Waiting for connections ...");
 
while(TRUE) 
{
    //clear the socket set
    FD_ZERO(&readfds);

    //add master socket to set
    FD_SET(master_socket, &readfds);
    max_sd = master_socket;
     
    //add child sockets to set
    for ( i = 0 ; i < max_clients ; i++) 
    {
        //socket descriptor
        sd = client_socket[i];
         
        //if valid socket descriptor then add to read list
        if(sd > 0)
            FD_SET( sd , &readfds);
         
        //highest file descriptor number, need it for the select function
        if(sd > max_sd)
            max_sd = sd;
    }

    //wait for an activity on one of the sockets , timeout is NULL , so wait indefinitely
    activity = select( max_sd + 1 , &readfds , NULL , NULL , NULL);

    if ((activity < 0) && (errno!=EINTR)) 
    {
        printf("select error");
    }
      
    //If something happened on the master socket , then its an incoming connection
    if (FD_ISSET(master_socket, &readfds)) 
    {
        if ((new_socket = accept(master_socket, (struct sockaddr *)&address, (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_socket , inet_ntoa(address.sin_addr) , ntohs(address.sin_port));
    
        //send new connection greeting message
        if( send(new_socket, message, strlen(message), 0) != strlen(message) ) 
        {
            perror("send");
        }
          
        puts("Welcome message sent successfully");
          
        //add new socket to array of sockets
        for (i = 0; i < max_clients; i++) 
        {
            //if position is empty
            if( client_socket[i] == 0 )
            {
                client_socket[i] = new_socket;
                printf("Adding to list of sockets as %d\n" , i);
                 
                break;
            }
        }
    }
      
    //else its some IO operation on some other socket :)
    for (i = 0; i < max_clients; i++) 
    {
        sd = client_socket[i];
          
        if (FD_ISSET( sd , &readfds)) 
        {
            //Check if it was for closing , and also read the incoming message
            if ((valread = read( sd , buffer, 1024)) == 0)
            {
                //Somebody disconnected , get his details and print
                getpeername(sd , (struct sockaddr*)&address , (socklen_t*)&addrlen);
                printf("Host disconnected , ip %s , port %d \n" , inet_ntoa(address.sin_addr) , ntohs(address.sin_port));
                  
                //Close the socket and mark as 0 in list for reuse
                close( sd );
                client_socket[i] = 0;
            }
              
            //Echo back the message that came in
            else
            {
                //set the string terminating NULL byte on the end of the data read
                buffer[valread] = '\0';
                send(sd , buffer , strlen(buffer) , 0 );
            }
        }
    }
}
  
return 0;

}