Why isn't my C socket server recieving data - c

Question

I've set up a very simple C socket server, there are two files.
main.c:
#include "socket_server.h"
#include "main.h"
int main (int argc, char* argv[])
{
start_socket_server(SOCKET_SERVER_PORT);
while (1)
{
update_clients();
}
return 0;
}
socket_server.c:
#include "socket_server.h"
int listen_fd, fdmax, newfd, nbytes, i, j, k;
char buf[256];
fd_set master;
fd_set read_fds;
struct timeval tv;
void start_socket_server(int port)
{
struct sockaddr_in servaddr;
FD_ZERO(&master);
FD_ZERO(&read_fds);
bzero( &servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htons(INADDR_ANY);
servaddr.sin_port = htons(port);
tv.tv_sec = 0;
tv.tv_usec = 100;
listen_fd = socket(AF_INET, SOCK_STREAM, 0);
bind(listen_fd, (struct sockaddr *) &servaddr, sizeof(servaddr));
listen(listen_fd, 10);
FD_SET(listen_fd, &master);
fdmax = listen_fd;
}
void update_clients()
{
read_fds = master;
select(fdmax+1, &read_fds, NULL, NULL, &tv);
for(i = 0; i<= fdmax; i++)
{
if (FD_ISSET(i, &read_fds))
{
if (i == listen_fd) //new connection
{
newfd = accept(listen_fd, (struct sockaddr *) NULL, NULL);
if (newfd != -1)
{
fprintf(stderr, "New connection!");
FD_SET(newfd, &master);
if (newfd > fdmax) {
fdmax = newfd;
}
}
} else {
nbytes = recv(i, buf, sizeof buf, 0);
if(nbytes <= 0)
{
fprintf(stderr, "Dead");
close(i);
FD_CLR(i, &master);
} else {
for(j = 0; j <= fdmax; j++)
{
if(FD_ISSET(j, &master))
{
if(j != listen_fd && j != i)
{
fprintf(stderr, "%s", buf);
}
}
}
}
}
}
}
}
Then I have a simple flash file to connect to it with the following actionscript:
var socket = new XMLSocket;
socket.connect("12.34.56.78", 8080);
socket.onConnect = function(status) {
if(status) {
trace("connected");
socket.writeUTF("Hello!");
socket.flush();
} else {
trace("couldn't connect");
}
};
If I run the server, then my actionscript, I would expect the following:
Server sits and waits
Flash file starts
Server says "New connection!" and flash file says "connected"
Server says "Hello!".
Only 1-3 happen. "Hello!" is never output to my terminal. In fact as best I can tell this block:
nbytes = recv(i, buf, sizeof buf, 0);
if(nbytes <= 0)
{
fprintf(stderr, "Dead");
close(i);
FD_CLR(i, &master);
} else {
for(j = 0; j <= fdmax; j++)
{
if(FD_ISSET(j, &master))
{
if(j != listen_fd && j != i)
{
fprintf(stderr, "%s", buf);
}
}
}
}
Is never executed at all (except for when I close my flash file and the server prints "Dead".
What's going on? Why can't I see the data sent from flash? I've managed to send data TO flash, but I haven't been able to receive any FROM it. Also this is being run from within flash, so there is no need to worry about policy files at this stage.

Answer 1

You need to set all your sockets to be non-blocking. For example,
void start_socket_server(int port)
{
struct sockaddr_in servaddr;
int val;
FD_ZERO(&master);
FD_ZERO(&read_fds);
bzero( &servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htons(INADDR_ANY);
servaddr.sin_port = htons(port);
tv.tv_sec = 0;
tv.tv_usec = 100;
listen_fd = socket(AF_INET, SOCK_STREAM, 0);
if (-1 == ioctl(listen_fd, FIONBIO, (val = 1, &val)))
{
perror("ioctl failed!\n");
goto ERROR; /* TODO: or however else you want to deal with errors */
}
bind(listen_fd, (struct sockaddr *) &servaddr, sizeof(servaddr));
listen(listen_fd, 10);
FD_SET(listen_fd, &master);
fdmax = listen_fd;
}
...
if (i == listen_fd) //new connection
{
newfd = accept(listen_fd, (struct sockaddr *) NULL, NULL);
if (newfd != -1)
{
int val;
fprintf(stderr, "New connection!");
if (-1 == ioctl(newfd, FIONBIO, (val = 1, &val)))
{
perror("ioctl failed!\n");
goto ERROR; /* TODO: or however else you want to deal with errors */
}
FD_SET(newfd, &master);
if (newfd > fdmax) {
fdmax = newfd;
}
}
} else {
nbytes = recv(i, buf, sizeof buf, 0);
if(nbytes <= 0)
{
fprintf(stderr, "Dead");
close(i);
FD_CLR(i, &master);
} else {
fprintf(stdout, "Received %d bytes: '%s'\n", nbytes, buf);
}
}
You should also do this on your main listening socket too after you create it initially so that you can't get stuck in a call to accept() somehow.
Also, the way you are outputting read-in data doesn't make much sense. As initially posted, the code would only print out if it had multiple client connections established. Then, when data was read in, it would print it N - 1 times, where N was the number of current client connections.