Using Select for Multiple Socket Connections C - c

Question

I am trying to build a server and client for a chat server using sockets. I know that I am supposed to use select() to get input from multiple sockets, but I am not sure how to do it and still read from them properly. As my code sits, it reads perfectly fine from one client, but when two are open it ignores everything that the second client does, until the first is closed.
I am wondering how to properly implement select to make sure that I can take input from multiple sockets. Thanks in advance.
#include "../../include/my.h"
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
void interrupt();
void interrupt()
{
my_str("Server exiting.\n");
exit(0);
}
int str_to_num(char* str)
{
int i = 0;
int numDigits = 0;
int ret = 0;
while (str[numDigits] != '\0')
{
numDigits++;
}
while (i < numDigits)
{
int digit = str[i];
if (digit < 48 && digit > 57)
return -1;
digit -= 48;
ret += digit * my_pow(10, numDigits - i - 1);
i++;
}
return ret;
}
char* add_null_term(char* str)
{
int i = 0;
while (str[i] != '\0')
i++;
str[i] = '\0';
return str;
}
int main(int argc, char **argv)
{
int sockfd, newsockfd, portnum;
int len;
char buffer[256];
/*char *username = (char*)malloc(256*sizeof(char));*/
socklen_t clilen;
struct sockaddr_in serv_addr, cli_addr;
/*check args*/
if (argc < 2)
{
my_str("Usage: ./server <port_number>\n");
exit(0);
}
portnum = str_to_num(argv[1]);
if (portnum < 1024)
{
perror("Ports below 1024 are reserved for root access.\n");
exit(0);
}
if (portnum < 1 || portnum > 65535)
{
my_str("Port must be between 1 and 65535\n");
exit(0);
}
signal(SIGINT, interrupt);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
bzero((char*)&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(portnum);
serv_addr.sin_addr.s_addr = INADDR_ANY;
if (bind(sockfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr))<0)
{
perror("bind");
exit(0);
}
listen(sockfd, 5);
clilen = sizeof(cli_addr);
while(1)
{
if ((newsockfd=accept(sockfd, (struct sockaddr*)&cli_addr, &clilen)) < 0)
{
perror("accept");
exit(0);
}
usleep(2000);
my_str("Server received: ");
while ((len = read(newsockfd, &buffer, 256)) > 0)
{
buffer[my_strlen(buffer)] = '\0';
if (my_strcmp(buffer, "/") == 0)
{
my_str("Error: command ");
my_str(buffer);
my_str("not found.\n");
bzero((char*)&buffer, sizeof(buffer));
}
/*if (count == 0)
{
my_strcpy(username, buffer);
my_str("setting nickname to: ");
my_str(username);
bzero((char*)&buffer, sizeof(buffer));
my_str(buffer);
count++;
my_str("\n");
}*/
/*else if (my_strncmp(buffer, "/me", 3) == 0)
{
my_str(username);
my_str(" ");
my_str(&buffer[4]);
bzero((char*)&buffer, sizeof(buffer));
my_str("\n");
}
else if (my_strncmp(buffer, "/nick", 5) == 0)
{
my_str("Changing nickname of ");
my_str(username);
my_strcpy(username, &buffer[6]);
my_str(" to ");
my_str(username);
bzero((char*)&buffer, sizeof(buffer));
my_str("\n");
}*/
/*else
{*/
/*my_str(username);
my_str(": ");*/
my_str(buffer);
bzero((char*)&buffer, sizeof(buffer));
my_str(buffer);
my_str("\n");
/*}*/
}
my_str("\nServer: Message end. Waiting for next connection.\n");
}
return 0;
}

Answer 1

If your question is HOW to use select() in a server...
Here is a snippet off the top of my head of one technique
to get you started... bear in mind all error checking is not
present, and it is not optimized to function in a round robin
basis...
listen(sockfd, SOMAXCONN)
fd_set my_set;
fd_set wk_set;
FD_ZERO(&my_set); /* initialize fd_set */
FD_SET(sock_fd, &my_set) /* put listener into fd_set */
max_fd = sockfd;
while( TRUE )
{
memcpy(&wk_set, &my_set, sizeof(my_set));
rc = select(max_fd + 1, &wk_set, NULL, NULL, NULL )
if ( rc == -1 )
{
if ( errno == EINTR )
continue;
printf("select failed: errno = %d\n", errno);
exit(1);
}
for(i = 0; i < max_fd; i++) /* check everything in wk_set */
{
if ( FD_ISSET(i, &wk_set)
{
if ( i == sockfd ) /* is it the listener socket?? */
{
wk_sock=accept(sockfd, (struct sockaddr*)&cli_addr, &clilen);
if ( wk_sock == -1 )
{
printf("accept failed: errno=%d\n", errno);
exit(1);
}
FD_SET(wk_sock, &my_set); /* put into fd_set */
if ( wk_sock > max_sock )
max_sock = wk_sock;
}else{
/* ready to read from this socket */
recv_len = recv(i, .... )
if ( recv_len == 0 ) /* client disconnected */
{
close(i);
FD_CLR(i, &my_set);
if (i == max_fd )
{
for(x=0;x<max_fd;x++) /* find new max_fd */
{
if ( FD_ISSET(x, &my_set )
max_fd = x;
}
}
} else {
handle message from client
}
}
}
}
}