iOS UDP broadcast vs. PHP UDP broadcast - networking

Question

I'm trying to send data via UDP to the network. I've got some PHP code running on my local machine which works:
#!/usr/bin/php -q
<?php
$socket = stream_socket_client('udp://225.0.0.0:50000');
for($i=0;$i<strlen($argv[1]);$i++) $b.="\0\0\0".$argv[1][$i];
fwrite($socket,$b,strlen($argv[1])*4);
fclose($socket);
?>
Gives me the output in tcpdump:
18:53:24.504447 IP 10.0.1.2.52919 > 225.0.0.0.50000: UDP, length 36
I'm trying to get to the same result on a remote iOS with the following code:
- (void)broadcast:(NSString *)dx {
NSData* data=[dx dataUsingEncoding:NSUTF8StringEncoding];
NSLog(#"Broadcasting data: %#", dx);
int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
struct sockaddr_in addr4client;
memset(&addr4client, 0, sizeof(addr4client));
addr4client.sin_len = sizeof(addr4client);
addr4client.sin_family = AF_INET;
addr4client.sin_port = htons(PORT);
addr4client.sin_addr.s_addr = htonl(INADDR_BROADCAST);
int yes = 1;
if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, (void *)&yes, sizeof(yes)) == -1) {
NSLog([NSString stringWithFormat:#"Failure to set broadcast! : %d", errno]);
}
char *toSend = (char *)[data bytes];
if (sendto(fd, toSend, [data length], 0, (struct sockaddr *)&addr4client, sizeof(addr4client)) == -1) {
NSLog([NSString stringWithFormat:#"Failure to send! : %d", errno]);
}
close(fd);
}
Which gives me the following output in tcpdump:
19:01:22.776192 IP 10.0.1.4.60643 > broadcasthost.50000: UDP, length 9
Looks basically OK, but doesn't arrive in Quartz Composer for some reason, I guess there should be the IP address or something instead of 'broadcasthost'.
Any idea?

Answer 1

The problem was not in the implementation of the broadcaster, but the format of the string. To work with Quartz Composer, every character needs to be preceded by a backslash-zero combination: "\0\0\0", so "abc" has to be formatted and sent as "\0\0\0a\0\0\0b\0\0\0c".
See also Celso Martinho's blog article: Leopard’s Quartz Composer and Network events.

Answer 2

I suggest using AsyncSocket ( google it, its on googlecode ), very well tested objective-c code that runs on iOS.
That way you can send data really easy using a NSData object. AsyncSocket manages the hard part for you.
If that isn't an option for you you should use CFSocket. What you are doing is implementing code that has been written for you already, CFSocket.