SSDP on the iPhone

Question

I need to be able to send out a UDP message and also receive one in order to discover SSDP devices on the network from the iPhone.

I know that I need to send the packet to the multicast address and my HTTP request needs to look something like this:

M-SEARCH * HTTP/1.1
Host: 239.255.255.250:1900
Man: ssdp:discover
Mx: 3
ST: "urn:schemas-upnp-org:device:InternetGatewayDevice:1"

From reading the docs it appears that I can do all this with CFNetwork and despite reading (and re-reading the docs) I am struggling to get started. Can anyone recommend and tutorials or code snippets to get me over the initial learning hump?

I've got the CFNetwork programming guide:

http://developer.apple.com/mac/library/documentation/Networking/Conceptual/CFNetwork/CFNetwork.pdf

and Beej's Guide to Network programming Using Internet Sockets:

http://beej.us/guide/bgnet/

Thanks

Dave

P.S.

I am unable to use any of the 3rd party libraries and frameworks in this instance.

Answer 1

I have used AsyncUdpSocket successfully to run SSDP Discovery and find controllers. Here are my code snippets:

Initialize and setup the socket:

//  AsyncUdpSocket *ssdpSock = [[AsyncUdpSocket alloc] initWithDelegate:self];
    AsyncUdpSocket *ssdpSock = [[AsyncUdpSocket alloc] initIPv4];
    [ssdpSock setDelegate:self];

Note the first line commented out. I found on the AsyncUdpSocket forums some issues with duplicates. I don't think I was facing them but I did it anyhow.

I added error checking, and it was useful because during my debugging I wasn't closing sockets and I started getting socket setup failures:

NSError *socketError = nil;

    if (![ssdpSock bindToPort:1900 error:&socketError]) {
        NSLog(@"Failed binding socket: %@", [socketError localizedDescription]);
        return statusController;
    }

    if(![ssdpSock joinMulticastGroup:@"239.255.255.250" error:&socketError]){
        NSLog(@"Failed joining multicast group: %@", [socketError localizedDescription]);
        return statusController;
    }

    if (![ssdpSock enableBroadcast:TRUE error:&socketError]){
        NSLog(@"Failed enabling broadcast: %@", [socketError localizedDescription]);
        return statusController;
    }

    [ssdpSock sendData:[self.discoverControllerString dataUsingEncoding:NSUTF8StringEncoding]
                toHost:@"239.255.255.250"
                  port:1900
           withTimeout:2
                   tag:1];

Notice the changes I have made to the time out. And then finally did the receive setup, and closed the socket. Note the socket close. Since I am in my own class when I am running this - the code above did not work for me.

[ssdpSock receiveWithTimeout: 2 tag:1];
    [NSTimer scheduledTimerWithTimeInterval: 5 target: self 
                                   selector:@selector(completeSearch:) userInfo: self repeats: NO]; 





    [ssdpSock closeAfterSendingAndReceiving];

The most important change probably was returning "NO" if I did not find my controller. The first receive was incidentally the discovery message itself coming back. And when I read through the AsyncUdpSocket.h file carefully - returning "NO" when it is not a packet you are looking for helped.

Also note that I am using ARC in my code but I compiled the AsyncUdpSocket without ARC support.

-(void) completeSearch: (NSTimer *)t 
{

    NSLog(@"%s",__FUNCTION__);

    //[ssdpSock close];
    //ssdpSock = nil;

}


- (BOOL)onUdpSocket:(AsyncUdpSocket *)sock 
     didReceiveData:(NSData *)data 
            withTag:(long)tag 
           fromHost:(NSString *)host 
               port:(UInt16)port
{
    NSLog(@"%s %ld %@ %d",__FUNCTION__,tag,host,port);
    NSString *aStr = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];

    NSLog(@"%@",aStr);



    NSString *compareString = [aStr stringByPaddingToLength:[self.responseString length] withString:@"." startingAtIndex:0];
    //NSLog(@"%@", compareString);
    //NSLog(@"%@", self.responseString);

    if ([compareString isEqualToString:self.responseString])
    {
        NSLog(@"String Compare, Controller Found!");
        [self.controllerList addObject:aStr];
        //NSData *controllerIP = [aStr dataUsingEncoding:NSUTF8StringEncoding];
        [[NSNotificationCenter defaultCenter] postNotificationName:@"DiscoveredController" object:nil];


        return YES;
    }

    return NO;

}

Answer 2

I have the following code for SSDP search in my app:

-(void)discoverDevices {
ssdpSock = [[AsyncUdpSocket alloc] initWithDelegate:self];
[ssdpSock enableBroadcast:TRUE error:nil];
NSString *str = @"M-SEARCH * HTTP/1.1\r\nHOST: 239.255.255.250:1900\r\nMan: \"ssdp:discover\"\r\nST: mydev\r\n\r\n";    
[ssdpSock bindToPort:0 error:nil];
[ssdpSock joinMulticastGroup:@"239.255.255.250" error:nil];
[ssdpSock sendData:[str dataUsingEncoding:NSUTF8StringEncoding] 
         toHost: @"239.255.255.250" port: 1900 withTimeout:-1 tag:1];
[ssdpSock receiveWithTimeout: -1 tag:1];
[NSTimer scheduledTimerWithTimeInterval: 5 target: self 
           selector:@selector(completeSearch:) userInfo: self repeats: NO]; }


-(void) completeSearch: (NSTimer *)t {
NSLog(@"%s",__FUNCTION__);
[ssdpSock close];
ssdpSock = nil;}

- (BOOL)onUdpSocket:(AsyncUdpSocket *)sock didReceiveData:(NSData *)data withTag:(long)tag fromHost:(NSString *)host port:(UInt16)port{
NSLog(@"%s %d %@ %d",__FUNCTION__,tag,host,port);
NSString *aStr = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
NSLog(@"%@",aStr);}

It uses the AsyncUdpSocket from CocoaAsyncSocket.

Answer 3

OK, finally done it. Found a class in the public domain (thanks Chris) called AsyncUdpSocket that lets you create a UDP socket which you can then turn on broadcasting and join the multicast address.

There is a nice sendData method, complete with adding to a run loop to prevent blocking.

Hope that helps.

Dave