Problems with GKSession and sendDataToAllPeers:withDataMode:error: - ios

Question

Alright, this involves a lot of network coding from this part of a multiplayer tutorial.
Basically, I'm trying to implement a multiplayer game using GameKit as per the tutorial linked above. I put in all of the necessary network coding and more or less understand it, however I've hit a snag somewhere along the line of method calls. Basically, the setup that I have is that one device acts as the host and the rest act as the clients. I have two separate UIViewcontrollers for the host and clients respectively where the connection is established.
Now the thing is, the connection gets established, but it's only the host that recognizes the connection, not the client. The problem is here:
- (void)sendPacketToAllClients:(Packet *)packet
{
[_players enumerateKeysAndObjectsUsingBlock:^(id key, Player *obj, BOOL *stop)
{
obj.receivedResponse = [_session.peerID isEqualToString:obj.peerID];
}];
GKSendDataMode dataMode = GKSendDataReliable;
NSData *data = [packet data];
NSError *error;
if (![_session sendDataToAllPeers:data withDataMode:dataMode error:&error])
{
NSLog(#"Error sending data to clients: %#", error);
}
}
This is implemented in GameMultiplayer, where the actual game will be implemented. What this method is supposed to be doing is sending data packets to each of the clients saying that the host received the connection request and is able to connect with them. After [_session sendDataToAllPeers:data withDataMode:dataMode error:&error] is called (the method in the if statement), this method is supposed to be triggered:
- (void)receiveData:(NSData *)data fromPeer:(NSString *)peerID inSession:(GKSession *)session context:(void *)context
{
#ifdef DEBUG
NSLog(#"Game: receive data from peer: %#, data: %#, length: %d", peerID, data, [data length]);
#endif
Packet *packet = [Packet packetWithData:data];
if (packet == nil)
{
NSLog(#"Invalid packet: %#", data);
return;
}
Player *player = [self playerWithPeerID:peerID];
if (player != nil)
{
player.receivedResponse = YES; // this is the new bit
}
if (self.isServer)
[self serverReceivedPacket:packet fromPlayer:player];
else
[self clientReceivedPacket:packet];
}
This method is in the next part of the tutorial I linked above (which is here) and is supposed to receive the packets that the host sends to all clients and implement the next methods in this networking chain. However, the method never gets called. No debug breakpoints are triggered and I get nothing in the console.
I understand if I need to provide more source material, but there is a lot of network coding already implemented, so I want to keep it down to what people need to see. Also, [_session setDataReceiveHandler:self withContext:nil] and _session.delegate = self are written in another method that is called in GameMultiplayer, so that's not the problem. Does anyone know what I need to fix?
EDIT: As requested, here's where GKSession is initialized:
#property (nonatomic, strong, readonly) GKSession *session; //This is done in the header file
#synthesize session = _session; //This is done in the main file
- (void)startAcceptingConnectionsForSessionID:(NSString *)sessionID
{
if (_serverState == ServerStateIdle)
{
_serverState = ServerStateAcceptingConnections;
_connectedClients = [NSMutableArray arrayWithCapacity:self.maxClients];
_session = [[GKSession alloc] initWithSessionID:sessionID displayName:nil sessionMode:GKSessionModeServer];
_session.delegate = self;
_session.available = YES;
}
}
The session is initialized in MatchmakingServer, which is used in the host view controller. The session is then passed on to the main view controller of the app, which then initializes GameMultiplayer and sends the GKSession to it. Here's where the host view controller sends it to the main view controller:
- (IBAction)startAction:(id)sender
{
if (_matchmakingServer != nil && [_matchmakingServer connectedClientCount] > 0)
{
NSString *name = [self.nameTextField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
if ([name length] == 0)
name = _matchmakingServer.session.displayName;
[_matchmakingServer stopAcceptingConnections];
[self.delegate hostViewController:self startGameWithSession:_matchmakingServer.session playerName:name clients:_matchmakingServer.connectedClients];
}
}
and then the main view controller handles that method call here:
- (void)hostViewController:(MatchmakerHost *)controller startGameWithSession:(GKSession *)session playerName:(NSString *)name clients:(NSArray *)clients
{
[self dismissViewControllerAnimated:NO completion:^
{
[self startGameWithBlock:^(GameMultiplayer *aGame)
{
[aGame startServerGameWithSession:session playerName:name clients:clients];
}];
}];
}
and finally, this is where that method call is implemented in GameMultiplayer:
- (void)startServerGameWithSession:(GKSession *)session playerName:(NSString *)name clients:(NSArray *)clients
{
_clients = clients;
const char* className = class_getName([[_clients objectAtIndex:0] class]);
NSLog(#"yourObject is a: %s", className);
self.isServer = YES;
_session = session;
_session.available = NO;
_session.delegate = self;
[_session setDataReceiveHandler:self withContext:nil];
_state = GameStateWaitingForSignIn;
[self.delegate gameWaitingForClientsReady:self];
// Create the Player object for the server.
Player *player = [[Player alloc] init];
player.name = name;
player.peerID = _session.peerID;
player.position = PlayerPositionBottom;
[_players setObject:player forKey:player.peerID];
// Add a Player object for each client.
int index = 0;
for (NSString *peerID in clients)
{
Player *player = [[Player alloc] init];
player.peerID = peerID;
[_players setObject:player forKey:player.peerID];
if (index == 0)
player.position = ([clients count] == 1) ? PlayerPositionTop : PlayerPositionLeft;
else if (index == 1)
player.position = PlayerPositionTop;
else
player.position = PlayerPositionRight;
index++;
}
NSLog(#"Players:");
Packet *packet = [Packet packetWithType:PacketTypeSignInRequest];
[self sendPacketToAllClients:packet];
// for (int i = 0; i < [_players count]; i++) {
// NSLog([NSString stringWithFormat:#"%#", [clients objectAtIndex:i]]);
// }
}

Answer 1

I think you are calling send to fast. When server realize about connection it will send confirmation to client to really establish connection - so client knows about it succeed.
If you are sending packets before that happens - it will be lost.
Just do this:
[self performSelector:#selector(sendPacketToAllClients) withObject:nil afterDelay:1.0];
instead of:
[self sendPacketToAllClients];
I had the same problem that connection is established in different moment with small delay on client. The best is to send first packet from client that he is ready to receive packets from server - and than proceed normally from there.
Also try debugging:
- (void)session:(GKSession *)session peer:(NSString *)peerID didChangeState:(GKPeerConnectionState)state
On both devices (server and client).

Answer 2

I have also had my troubles with GKSession. I was interested to learn (on this site) today that GKSession is being deprecated in favor of using the Multipeer Connectivity Framework. With luck, Wenderlich et al. will do a tutorial using the new technology. :)
The system has some similarities to GKSession, so is not too hard to wrap your head around.
Apple's doc link.