Checking an entire struct has been received via GKMatchDelegate didReceiveData - ios

Question

I'm working on a Multiplayer Swift (XCode 7.3 / iOS 9.2) game using GameKit.
I'm using a custom struct as the information sent via GameKit. Copy of the struct is below. frustrationNetworkMessage is a String enum & Card is a seperate class (can post code if needed)
struct frustrationNetworkMessage {
var messageType : FrustrationNetworkMessageType
var cards : [Card]
var actingPlayer : String
init(messageType : FrustrationNetworkMessageType, cards : [Card], actingPlayer : String) {
self.messageType = messageType
self.cards = cards
self.actingPlayer = actingPlayer
}
My issue is in the 'match(match: GKMatch, didReceiveData data: NSData, fromRemotePlayer player: GKPlayer)' method. I've worked out this is being called once some data is received:
private var receivedData : NSMutableData
func decode<T>(data: NSData) -> T {
let pointer = UnsafeMutablePointer<T>.alloc(sizeof(T.Type))
data.getBytes(pointer, length: sizeof(T))
return pointer.move()
}
func match(match: GKMatch, didReceiveData data: NSData, fromRemotePlayer player: GKPlayer) {
print("Match / did receive data: size of data - \(sizeofValue(data))")
receivedData.appendData(data)
if let receivedNetworkMessage : frustrationNetworkMessage = decode(receivedData) {
print("Match / did receive data: \(receivedNetworkMessage.messageDetails())")
When I run the above code it crashes at the final print statement with EXC_BAD_ACCESS (which I understand is it complaining it's trying to access part of the struct that has not been received).
As an example:
Message summary at sent -> sendNetworkMessage: Message type: startNewGame with actingPlayer: G:118279601 & card count: 1 - message size: 40
Message length first time match didReceiveData is called -> Match / did receive data: size of data - 8
How can I check I've gotten the entire struct before acting on it? I had thought of updating the struct to include a length field (in theory I should always receive that in one go - so could use it to check the packet length).

Answer 1

You can use a background process like this to check your data structure continuously?
newQueue = NSOperationQueue()
let operation2 = NSBlockOperation(block: {
})
operation2.completionBlock = {
print("Operation 2 completed")
}
let operation1 = NSBlockOperation(block: {
})
operation1.completionBlock = {
self.newQueue.addOperation(operation2)
}
operation1.qualityOfService = .UserInitiated
newQueue.addOperation(operation1)
}
Initialise the variables and then check their length; this will save/stop it crashing.

Answer 2

I've found an answer for the minute (issue has now moved elsewhere in the code)
struct frustrationNetworkMessage {
var messageType : FrustrationNetworkMessageType
var card : Card
var actingPlayer : String
init(messageType : FrustrationNetworkMessageType, card : Card, actingPlayer : String) {
self.messageType = messageType
self.card = card
self.actingPlayer = actingPlayer
}
init(data : NSData) {
let messageTypeLength = sizeofValue(FrustrationNetworkMessageType)
let cardLength = sizeofValue(Card)
let messageTypeRange = NSMakeRange(0, messageTypeLength)
let cardLengthRange = NSMakeRange(messageTypeLength, messageTypeLength + cardLength)
let actingPlayerRange = NSMakeRange(messageTypeLength + cardLength, data.length)
self.messageType = .didDiscardCard
self.card = Card.emptyCard()
data.getBytes(&self.messageType, range: messageTypeRange)
data.getBytes(&self.card, range: cardLengthRange)
let actingPlayerData = data.subdataWithRange(actingPlayerRange)
self.actingPlayer = NSString(data: actingPlayerData, encoding: NSUTF8StringEncoding) as! String
}
func archive()->NSData {
var localMessageType = messageType.rawValue
var localCard = card
let returnValue = NSMutableData(bytes: &localMessageType, length: sizeofValue(self.messageType.rawValue))
returnValue.appendData(NSData(bytes: &localCard, length: sizeofValue(self.card)))
returnValue.appendData(actingPlayer.dataUsingEncoding(NSUTF8StringEncoding)!)
return returnValue
}
What I've found through trial an error (and a lot of follow-up reading):
match didReceiveData only seems to get called when it has received an entire packet (so don't need to handle receiving partial data)
Where possible avoid encoding class data types as NSData (through digging I found I was only encoding a local address, works fine if passing locally - not so much over the network). Close to all of my data types as either basic ones (all enums are now of type UInt8) or structs.