Multiclient Server Implementation in C - c

Question

I am trying to implement multi client server using C. I have write code for server and client is a software that will continuously send some packet to server. Server will read the packet and process it. I am trying for 5 connection at a time to server. But there is some problem with server code that I have written due to which I can not connect 5 client to server. Exact Problem is that when client is trying to connect with server it gets connection for but when I close client software and try to start again it is not getting connection. Following is my code for server side. can anybody help me regarding this problem.
#include <ctype.h>
#include <sys/time.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/utsname.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>
#include <sys/file.h>
int sock; /* The socket file descriptor for our "listening"socket */
int connectlist[15]; /* Array of connected sockets so we know who we are talking to */
fd_set socks; /* Socket file descriptors we want to wake up for, using select() */
int highsock = 1; /* Highest #'d file descriptor, needed for select() */
struct sockaddr_in client_address[5];
unsigned int clientLength = sizeof(client_address) ;
#define PORTNO (int)49153
int port; /* The port number after conversion from ascport */
struct sockaddr_in server_address; /* bind info structure */
int reuse_addr = 1;
struct timeval timeout; /* Timeout for select */
int readsocks; /* Number of sockets ready for reading */
int err = 0 ;
#define BACKLOG (int)10
void deal_with_data(int listnum /* Current item in connectlist for for loops */)
{
//Here I am trying to read packet from client s/w and process it
}
void setnonblocking(int sock)
{
int opts;
opts = fcntl(sock,F_GETFL);
if (opts < 0)
{
printf("fcntl(F_GETFL)_error");
exit(0);
}
opts = (opts | O_NONBLOCK);
if (fcntl(sock,F_SETFL,opts) < 0)
{
printf("fcntl(F_SETFL)_error");
exit(0);
}
return;
}
void build_select_list()
{
int listnum; /* Current item in connectlist for for loops */
FD_ZERO(&socks);
FD_SET(sock,&socks);
for (listnum = 0; listnum < 5; listnum++)
{
if (connectlist[listnum] != 0)
{
FD_SET(connectlist[listnum],&socks);
if (connectlist[listnum] > highsock)
highsock = connectlist[listnum];
}
}
}
void handle_new_connection() {
int listnum; /* Current item in connectlist for for loops */
int connection; /* Socket file descriptor for incoming connections */
connection = accept(sock, (struct sockaddr *)&client_address[highsock], &clientLength);
if (connection < 0)
{
printf("accept_error");
exit(0);
}
setnonblocking(connection);
for (listnum = 0; (listnum < 5) && (connection != -1); listnum ++)
if (connectlist[listnum] == 0)
{
printf("\nConnection accepted: FD=%d; Slot=%d\n",
connection,listnum);
printf("Connection accepted from %s\n",inet_ntoa(client_address[highsock].sin_addr));
connectlist[listnum] = connection;
connection = -1;
}
if (connection != -1)
{
printf("\nNo room left for new client.\n");
write(connection,"Sorry, this server is too busy.Try again later!\r\n",80);
close(connection);
}
printf("return from handle_new_connection\n");
}
void read_socks(void)
{
int listnum; /* Current item in connectlist for for loops */
if (FD_ISSET(sock,&socks))
handle_new_connection();
for (listnum = 0; listnum < 5; listnum++)
{
if (FD_ISSET(connectlist[listnum],&socks))
{
//printf("read_socks2\n");
deal_with_data(listnum);
}
}
}
int main (/*int argc, char *argv[]*/)
{
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock < 0)
{
printf("socket_error");
exit(EXIT_FAILURE);
}
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &reuse_addr,sizeof(reuse_addr));
setnonblocking(sock);
memset((char *) &server_address, 0, sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(port);
if (bind(sock, (struct sockaddr *) &server_address,sizeof(server_address)) < 0 )
{
printf("bind_error");
close(sock);
exit(EXIT_FAILURE);
}
if((err = listen(sock,10)) == -1)
{
printf("listen_error");
}
highsock = sock;
memset((char *) &connectlist, 0, sizeof(connectlist));
while (1)
{ /* Main server loop - forever */
build_select_list();
timeout.tv_sec = 2;
timeout.tv_usec = 0;
readsocks = select(highsock+2, &socks, (fd_set *) 0,(fd_set *) 0, &timeout);
if (readsocks < 0)
{
printf("select_error");
exit(EXIT_FAILURE);
}
if (readsocks == 0)
{
printf(".");
fflush(stdout);
}
else
{
read_socks();
}
} /* while(1) */
} /* main */

Answer 1

Your problem is that your main loop doesn't exit when the socket has been closed by the client. This means that it cannot accept new connections. I would use fork() to do the processing of the data from the socket, and the main() function to accept connections and fork() the process. Also, you need to have some code which will kill the fork()ed (i.e. to check if the client has disconnected in the fork()ed process) process (since it won't close by itself and it takes up memory).
EDIT:
Ok, I can't find a call to recv() in your program. According the the recv(3) man page it will return 0 if the client disconnect "gracefully" and return -1 and set errno to ECONNRESET if the client forcefully disconnected. In order to use fork, I would (in the main() function) wrap your while loop in this:
int childpid = fork();
if(childpid == -1) {
printf("Could not fork process");
exit(EXIT_FAILURE);
}
else if(childpid == 0) { /* in child process*/
while(/* check if the socket has been closed */) {
/* While loop stuff */
}
/* free up memory */
exit(EXIT_SUCCESS);
}
And your main function should be in a loop, waiting for new connections.
N.B. I have not tested any of this code, so it might not work. But if you read the man pages for fork(3) and recv(3) it should work.

Answer 2

Aren't you better off using something off the shelf like Apache and customize it as necessary?