How to create multiple tcp connections between server and client - c

Question

I am new in Unix/Linux networking programming, so I have written server-client program in below.In this code there is one socket between client and server, client requests to server, then server responses from 1 to 100 numbers to client. So my question is how can we do this process with 3 socket( tcp connection) without using thread? ( e.g. First socket runs then second runs then third runs then first again. ) Do you have any suggestion?
Client.c
int main()
{
int sock;
struct sockaddr_in sa;
int ret;
char buf[1024];
int x;
sock = socket (AF_INET, SOCK_STREAM, 0);
bzero (&sa, sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_port = htons(SERVER_PORT);
inet_pton (AF_INET, SERVER_IP, &sa.sin_addr);
ret = connect (sock,
(const struct sockaddr *) &sa,sizeof (sa));
if (ret != 0) {
printf ("connect failed\n");
exit (0);
}
x = 0;
while (x != -1) {
read (sock, buf , sizeof(int));
x = ntohl(*((int *)buf));
if (x != -1)
printf ("int rcvd = %d\n", x);
}
close (sock);
exit (0);
}
Server.c
int main()
{
int list_sock;
int conn_sock;
struct sockaddr_in sa, ca;
socklen_t ca_len;
char buf[1024];
int i;
char ipaddrstr[IPSTRLEN];
list_sock = socket (AF_INET, SOCK_STREAM, 0);
bzero (&sa, sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = htonl(INADDR_ANY);
sa.sin_port = htons(SERVER_PORT);
bind (list_sock,(struct sockaddr *) &sa,sizeof(sa));
listen (list_sock, 5);
while (1){
bzero (&ca, sizeof(ca));
ca_len = sizeof(ca); // important to initialize
conn_sock = accept (list_sock,(struct sockaddr *) &ca,&ca_len);
printf ("connection from: ip=%s port=%d \n",inet_ntop(AF_INET, &(ca.sin_addr),
ipaddrstr, IPSTRLEN),ntohs(ca.sin_port));
for (i=0; i<100; ++i){
*((int *)buf) = htonl(i+20);
// we using converting to network byte order
write (conn_sock, buf, sizeof(int));
}
* ((int *)buf) = htonl(-1);
write (conn_sock, buf, sizeof(int));
close (conn_sock);
printf ("server closed connection to client\n");
}
}

Answer 1

I think it best to look at the excellent resource Beej's Guide to Netwokr Programming which goes into detail about this. He also has some good examples which you can use as a starting point and he covers all the major platforms including windows.
Basically you do:
socket()
bind()
listen()
accept()
accept() returns a socket connected to a unique client. Then you'd use select, poll or epoll to determine when data is available on those sockets. I suggest you can look at the man pages for these API's and Beej's guide. It's where I first learned network programming.
Looking at your code, your inner loop is wrong. When you accept a connection, you need to add it to a list or something. Currently, you overwrite it and loose it. You should use (e)poll or select to tell you which has data. You can write to any of them at any time. Again, look at the examples in Beej's guide, they are most helpful.

Answer 2

Maybe it's not exactly what you want,but I think you could try epoll,There is a simple example
typedef struct event_loop
{
int max_event;
int epfd;
}event_loop;
event_loop* create_event_loop()
{
event_loop *ep = malloc(sizeof(event_loop));
ep->max_event = 512;
ep->epfd = epoll_create(512);
return ep;
}
int add_event(event_loop *ep, int fd)
{
epoll_event ee;
ee.data.fd = fd;
ee.event = EPOLLIN | EPOLLPRI;
epoll_ctl(ep->epfd, EPOLL_CTL_ADD, fd, &ee);
}
void event_main(event_loop *ep, int listenfd)
{
epoll_event events[512];
int nfds, i, newfd;
while(1)
{
if(nfds = epoll_wait(ep->epfd, events, 512, -1) == -1)
exit(1);
for(i = 0; i < nfds; i++)
{
if(events[nfds].data.fd == listenfd)
{
newfd = accept(listenfd, NULL, NULL);
add_event(ep, newfd);
}
else
{
//do what you want
}
}
}
}
epoll is a high-efficiency solution,just man epoll get more information