Sending udp packets in iOS 6 - iphone

Question

I am struggling to get anything to send from the iphone, I followed This Guide At first I started off with cfSocketRef as I thought you used them for UDP and and TCP by changing protocol but I had no luck.
So here is the code for the BSD sockets. Nothing seems to be sending. I have a java socket server waiting on localhost:port.
Any ideas? or maybe a guide/sample xcode project that works.
#import "ViewController.h"
#include <CFNetwork/CFNetwork.h> //temp //dont leave here put it in a header
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#interface ViewController ()
#end
#implementation ViewController
static void socketCallback(CFSocketRef cfSocket, CFSocketCallBackType
type, CFDataRef address, const void *data, void *userInfo)
{
NSLog(#"socketCallback called");
}
//
- (void)viewDidLoad
{
[super viewDidLoad];
int sock = 0; /// ?
unsigned int echolen;
NSLog(#"starting udp testing");
cfSocketRef = CFSocketCreate(/*CFAllocatorRef allocator*/ NULL,
/*SInt32 protocolFamily*/ PF_INET,
/*SInt32 socketType*/ SOCK_DGRAM,
/*SInt32 protocol*/ IPPROTO_UDP,
/*CFOptionFlags callBackTypes*/ kCFSocketAcceptCallBack | kCFSocketDataCallBack,
/*CFSocketCallBack callout*/ (CFSocketCallBack)socketCallback,
/*const CFSocketContext *context*/ NULL);
struct sockaddr_in destination;
memset(&destination, 0, sizeof(struct sockaddr_in));
destination.sin_len = sizeof(struct sockaddr_in);
destination.sin_family = AF_INET;
NSString *ip = #"localhost";
destination.sin_addr.s_addr = inet_addr([ip UTF8String]);
destination.sin_port = htons(33033); //port
NSString *msg = #"message sent from iPhone";
/* server port */
setsockopt(sock,
IPPROTO_IP,
IP_MULTICAST_IF,
&destination,
sizeof(destination));
const char *cmsg = [msg UTF8String];
echolen = strlen(cmsg);
if (sendto(sock,
cmsg,
echolen,
0,
(struct sockaddr *) &destination,
sizeof(destination)) != echolen)
{
NSLog(#"did send");
}
else
{
NSLog(#"did not send");
}
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end

Answer 1

First problem: You forgot to create the socket:
if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
NSLog(#"Failed to create socket, error=%s", strerror(errno));
}
This part does not work:
NSString *ip = #"localhost";
destination.sin_addr.s_addr = inet_addr([ip UTF8String]);
inet_addr converts strings representing IPv4 addresses in the dot notation, such as "127.0.0.1".
To convert a host name such as "localhost" to an IP address, you have to use gethostbyname, or getaddrinfo (the latter works with IPv4 and IPv6).
There is another error when you check the return value of sendto: sendto returns the number of bytes sent in the success case, and (-1) in error case. So it should look like:
if (sendto(sock, ...) == -1) {
NSLog(#"did not send, error=%s",strerror(errno));
} else {
NSLog(#"did send");
}
Checking the value of errno would have revealed your problem quickly. If you forget to create the socket, the error message is
did not send, error=Socket operation on non-socket
Remarks:
cfSocketRef is completely unused in your function.
Why do you set the IP_MULTICAST_IF socket option? As far as I know, that is not needed for unicast messages, only for multicast messages.