Disable WiFi from Multi Peer Connectivity - ios

Question

I have gone over the documentation, but there isn't much information on Multipeer Connectivity related to choosing a possible medium for peers to connect.
Multipeer Connectivity automatically discovers peers based on WiFi, or Bluetooth. Is there a way to limit this to only Bluetooth?

Answer 1

As #kdogisthebest correctly states, there's no way to force Multipeer Connectivity to use a particular network technology, but as your question relates to a particular problem with WiFi, this answer details what I'm doing to work around that.
I've worked around the issue of 'phantom' peers over WiFi by sending a shortened timestamp in the discoveryInfo when creating the MCNearybyServiceAdvertiser. There are several caveats here:
1) This solution assumes both devices have the same time. I ensure this by using a modified version of ios-ntp as the app's time source.
2) It also assumes that Advertising and Browsing do not run for too long. I have a set length of 60 seconds for discovery phases, and I completely re-init the browser/advertiser on each restart.
3) MPC doesn't seem to like too many bytes in the discoveryInfo so sending an NSTimeInterval based on epoch doesn't work. I had to truncate them.
So when my app enters discovery mode, it starts browsing and advertising simultaneously. The advertising code looks like:
- (void)startAdvertising {
if (_advertising){
NSLog(#"Already advertising");
return;
}
self.acceptedPeerIDNameMap = [NSMutableDictionary dictionary];
NSInteger timeStamp = [self shortenedNetworkTimeStamp];
NSDictionary *discoveryInfo = #{kAdvertisingDiscoveryInfoTimestampKey:[NSString stringWithFormat:#"%ld",(long)timeStamp]};
NSLog(#"Starting advertiser");
self.serviceAdvertiser = [[MCNearbyServiceAdvertiser alloc] initWithPeer:_myPeerID
discoveryInfo:discoveryInfo
serviceType:kServiceType];
_serviceAdvertiser.delegate = self;
[_serviceAdvertiser startAdvertisingPeer];
self.advertising = YES;
}
The method shortenedNetworkTimestamp just takes an NSTimeInterval (either using the ntp framework or timeIntervalSinceReferenceDate and removing 1400000000 from it.
Then when the browser discovers a peer, it checks whether the advertiser's timestamp is within the known discovery duration (in my case 60 seconds):
- (void)browser:(MCNearbyServiceBrowser *)browser foundPeer:(MCPeerID *)peerID withDiscoveryInfo:(NSDictionary *)info {
DLog(#"Browser found peer ID %#",peerID.displayName);
//Only one peer should invite the other
BOOL shouldInvite = [peerID.displayName compare:_myPeerID.displayName]==NSOrderedAscending;
//Don't re-send invitations
if (_peerInfoDisplayNameMap[peerID.displayName]){
DLog(#"Already connected to peerID %#",peerID.displayName);
shouldInvite = NO;
}
else if (_invitedPeerIDNameMap[peerID.displayName]){
DLog(#"Already invited peerID %#",peerID.displayName);
shouldInvite = NO;
}
//Invite if discovery info is valid
if (shouldInvite && [self discoveryInfoIsValid:info]) {
DLog(#"Inviting");
_invitedPeerIDNameMap[peerID.displayName] = peerID;
MCSession *session = [self availableSession];
[_serviceBrowser invitePeer:peerID toSession:session withContext:nil timeout:0];
}
else {
DLog(#"Not inviting");
}
}
The discovery info validity check is pretty simple - just make sure the timestamp sent in the info is inside of the discovery time range (in my case kDiscoveryPhaseDuration is 60 seconds):
- (BOOL)discoveryInfoIsValid:(NSDictionary *)info {
BOOL isValid = YES;
NSString *infoTimeStamp = info[kAdvertisingDiscoveryInfoTimestampKey];
NSTimeInterval sentTimeStamp = (infoTimeStamp) ? [infoTimeStamp doubleValue] : -1;
NSTimeInterval currentTimeStamp = [self shortenedNetworkTimeStamp];
if (sentTimeStamp==-1 || (currentTimeStamp - sentTimeStamp) > kDiscoveryPhaseDuration){
DLog(#"Expired discovery info (current=%f, sent=%f)",currentTimeStamp,sentTimeStamp);
isValid = NO;
}
return isValid;
}
Hopefully this helps. There are many other quirks in MPC that I'm handling in my own code but I think the above covers this specific problem.

Answer 2

This isn't possible with Multipeer Connectivity. There are no methods Apple puts in place to limit the connection to Bluetooth.
One answer here: Multipeer connectivity over Bluetooth? states "There is no explicit setting for bluetooth or Wifi, It will connect devices in whatever possible way they are available."