Hello,
I'm working with the Network framework in Swift and have encountered an issue when attempting to create multiple NWListener instances on the same port. I am specifically trying to set the allowLocalEndpointReuse property on the NWParameters used for both listeners, but it seems that even with this property set, the second listener fails to start.
Here’s a simplified version of my implementation:
import Foundation
import Network
class UDPServer {
private var listener1: NWListener?
private var listener2: NWListener?
private let port: NWEndpoint.Port
init(port: UInt16) {
self.port = NWEndpoint.Port(rawValue: port) ?? NWEndpoint.Port(45000)
startListeners()
}
private func startListeners() {
let udpOptions = NWProtocolUDP.Options()
let params = NWParameters(udp: udpOptions)
params.allowLocalEndpointReuse = true
// Create first listener
do {
listener1 = try NWListener(using: params, on: port)
listener1?.start(queue: .global())
} catch {
print("Failed to create Listener 1: \(error)")
}
// Create second listener
do {
listener2 = try NWListener(using: params, on: port)
listener2?.start(queue: .global())
} catch {
print("Failed to create Listener 2: \(error)")
}
}
}
// Usage example
let udpServer = UDPServer(port: 45000)
RunLoop.main.run()
Observations:
I expect both listeners to operate without issues since I set allowLocalEndpointReuse to true.
However, when I attempt to start the second listener on the same port, it fails with an error.
output
nw_path_evaluator_evaluate NECP_CLIENT_ACTION_ADD error [48: Address already in use]
nw_path_create_evaluator_for_listener nw_path_evaluator_evaluate failed
nw_listener_start_on_queue [L2] nw_path_create_evaluator_for_listener failed
Listener 1 ready on port 45000
Listener 2 failed: POSIXErrorCode(rawValue: 48): Address already in use
Listener 2 cancelled
Questions:
Is there a limitation in the Network framework regarding multiple listeners on the same port even with allowLocalEndpointReuse?
Should I be using separate NWParameters for each listener, or is it acceptable to reuse them?
Even when trying to initialize NWParameters with NWProtocolUDP.Options, it doesn't seem to change anything. What steps should I take to modify these properties effectively?
If I wanted to set the noDelay option for TCP, how would I do that? Even when initializing NWParameters with init(.tls: , .tcp:), it doesn't seem to have any effect.
Any insights or recommendations would be greatly appreciated!
Thank you!
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