NWConnection SSDP Discovery not receiving data - ios

Question

I'm trying to do an SSDP Discovery broadcast and unable to get reply data from NWConnection.receive.
Network.framework is relatively new and there is not a lot of info out there. What I'm missing here?
SSDP Discovery broadcast was sent and a UPnP device replied. (Wireshark screenshot below)
import Foundation
import Network
let connection = NWConnection(host: "239.255.255.250", port: 1_900, using: .udp)
func sendBroadcast() {
let message = """
M-SEARCH * HTTP/1.1
ST: ssdp:all
HOST: 239.255.255.250:1900
MAN: ssdp:discover
MX: 1
""".data(using: .utf8)
connection.send(content: message, completion: .contentProcessed { error in
if let error = error {
print("Send Error: \(error)")
} else {
print("Broadcast sent")
}
}
)
}
connection.stateUpdateHandler = { newState in
switch newState {
case .setup:
print("Connection: Setup")
case .preparing:
print("Connection: Preparing")
case .waiting:
print("Connection: Waiting")
case .ready:
print("Connection: Ready")
sendBroadcast()
case .failed:
print("Connection: Failed")
case .cancelled:
print("Connection: Cancelled")
}
}
connection.receive(minimumIncompleteLength: 2, maximumLength: 4_096) { data, context, isComplete, error in
/// This is never executed
///
print(data ?? "", context ?? "", isComplete, error ?? "")
}
connection.viabilityUpdateHandler = { update in
print(update)
}
connection.betterPathUpdateHandler = { path in
print(path)
}
connection.start(queue: .main)
RunLoop.main.run()

Answer 1

Turns out Network.framework does not support UDP Broadcasts yet (Feb 2019)
https://forums.developer.apple.com/message/316357#316357

Answer 2

With UDP try this method instead:
connection.receiveMessage { (data, context, isComplete, error) in
print(data ?? "", context ?? "", isComplete, error ?? "")
}
Here is a good example of it in use here
I had the opposite problem with TCP and was using connection.receiveMessage(...) and the same thing was happening -the callback was never entered. I posted a question in Apple Forums. It turns out with TCP you can only use:
connection.receive(minimumIncompleteLength: 1, maximumLength: 65535) { data, context, isComplete, error in
print(data ?? "", context ?? "", isComplete, error ?? "")
}
An Apple Developer Technical Support Specialist named eskimo answered it here:
. TCP is not a message-oriented protocol, and thus
receiveMessage(…)
doesn’t make any sense. What you want is
receive(minimumIncompleteLength:maximumLength:completion:)
That being said, with UDP try connection.receiveMessage(…)