UDP broadcast using CFSocket on IOS

Question

Have been doing some google search and some reading on this subject but cannot seem to get it right no matter how much time i spent searching.

What i want to do is to receive broadcast message of devices that are connected on my network by advertising my interest in their services that they supply. Using wireshark i can see the broadcast/notification messages from the network devices that i want to connect to sent over my network but not my broadcast search for interest of their services. But with network utility i can see that the socket is created but don't know which state it is in, whether listen or connected.

Yes i know that there are libraries that i can use to do this, but i wanted to build something of my own from the ground up and get a better understand of how it works.

MySocket.h

#import <Foundation/Foundation.h>
#import <CoreFoundation/CoreFoundation.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#if TARGET_OS_IPHONE
#import <CFNetwork/CFNetwork.h>
#endif

 @interface MySocket : NSObject
 {
    NSString* _message;
    CFSocketRef cfSocket;
    CFRunLoopSourceRef cfSource;

 }

 - (void)listen;
 @end

MySocket.m

#import "MySocket.h"

#define MAX_UDP_DATAGRAM_SIZE 65507

@implementation MySocket


static void socketCallback(CFSocketRef cfSocket, CFSocketCallBackType
                           type, CFDataRef address, const void *data, void *userInfo)
{
    NSLog(@"socketCAllBAck was called");
}    

- (void)listen
{
    //Enable broadcast to network hosts        
    int yes = 1;
    int setSockResult = 0;
    _message = [[NSMutableString alloc ] initWithString: @"M-SEARCH *HTTP/1.1\r\nHOST:239.255.255.250:1900\r\nMAN:\"ssdp:discover\"\r\nST:ssdp:all\r\nMX:1\r\n\r\n"];

    CFSocketContext socketContext = {0, self, NULL, NULL, NULL};

    /* Create the server socket as a UDP IPv4 socket and set a callback */
    /* for calls to the socket's lower-level accept() function */
    cfSocket = CFSocketCreate(NULL, PF_INET, SOCK_DGRAM, IPPROTO_UDP,
                              kCFSocketAcceptCallBack | kCFSocketDataCallBack , (CFSocketCallBack)socketCallback, &socketContext);
    if (cfSocket == NULL)
        NSLog(@"UDP socket could not be created\n");

    /* Re-use local addresses, if they're still in TIME_WAIT */
   setSockResult = setsockopt(CFSocketGetNative(cfSocket), SOL_SOCKET, SO_BROADCAST, (void *)&yes, sizeof(yes));

    if(setSockResult < 0)
        NSLog(@"Could not setsockopt for broabcast");

    /* Set the port and address we want to listen on */
    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_len = sizeof(addr);
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr("239.255.255.250");
    //inet_pton(AF_INET, "239.255.255.250", &(addr.sin_addr));

    addr.sin_port = htons(1900);
    //addr.sin_addr.s_addr = htonl(INADDR_ANY);

    NSData *address = [ NSData dataWithBytes: &addr length: sizeof(addr) ];
    if (address != nil && CFSocketSetAddress(cfSocket, (CFDataRef) address) != kCFSocketSuccess) {
        NSLog(@"CFSocketSetAddress() failed\n");
        CFRelease(cfSocket);
    }      

    CFDataRef data = CFDataCreate(NULL, (const UInt8*)[_message UTF8String], [_message lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);

    setSockResult = CFSocketSendData(cfSocket, (CFDataRef)address, data, 0.0);
    if(kCFSocketSuccess != setSockResult) NSLog(@"Unable to send data, %i", setSockResult);
    else NSLog(@"Sending data");

    cfSource = CFSocketCreateRunLoopSource(kCFAllocatorDefault, cfSocket, 0); 

    if(cfSource == NULL)
        NSLog(@"CFRunLoopSourceRef is null");

    CFRunLoopAddSource(CFRunLoopGetCurrent(), cfSource, kCFRunLoopDefaultMode);

    NSLog(@"Socket listening on port 1900");

        CFRelease(cfSource);
    CFRelease(cfSocket);
    [address release];
    data = nil;
    CFRunLoopRun();
}

- (void)dealloc
{
    CFRunLoopRemoveSource(CFRunLoopGetCurrent(), cfSource, kCFRunLoopDefaultMode);
    CFRelease(cfSource);
    CFRelease(cfSocket);
    [_message release];
    [super dealloc];
}

@end

Edit: Everything runs well until the call to send data.

Is there something small but critical in order for this to work that i'm missing? Or i'm missing the big picture?

Any help or guide is appreciated. Thanks in advance and have a nice weekend

Answer 1

remove SetAdress and all will be work fine. i've tested this now;

Answer 2

如何使用地址初始化

CFDataRef address=CFDataCreate(kCFAllocatorDefault,(UInt8 *)&addr,sizeof(addr));