how to register listener to `NWConnectionGroup` for QUIC

I am trying to make http3 client with Network.framework on Apple platforms.

Codes that implement NWConnectionGroup.start with NWListener don't always work with warning below. I assume NWConnectionGroup.newConnectionHandler or NWListener.newConnectionHandler will be called to start connection from the server if it works.

nw_protocol_instance_add_new_flow [C1.1.1:2] No listener registered, cannot accept new flow
quic_stream_add_new_flow [C1.1.1:2] [-fde1594b83caa9b7] failed to create new stream for received stream id 3

so I tried:

• create the NWListener -> not work
• check whether NWConnectionGroup has a member to register or not NWListener -> not work (it doesn't have).
• use NWConnection instead of NWConnectionGroup -> not work

Is my understanding correct?

How should I do to set or associate listener with NWConnection/Group for newConnectionHandler is called and to delete wanings?

What is the best practice in the case?

Sample codes are below.

Thanks in advance.

// http3 needs unidirectional stream by the server and client. 

// listener
private let _listener: NWListener

let option: NWProtocolQUIC.Options = .init(alpn:["h3"])
let param: NWParameters = .init(quic: option)

_listener = try! .init(using: param)

_listener.stateUpdateHandler = { state in
    print("listener state: \(state)")
}
_listener.newConnectionHandler = { newConnection in
    print("new connection added")
}
_listener.serviceRegistrationUpdateHandler = { registrationState in
    print("connection registrationstate")
}

// create connection
private let _group: NWConnectionGroup

let options: NWProtocolQUIC.Options = .init(alpn: ["h3"])
options.direction = .unidirectional
options.isDatagram = false
options.maxDatagramFrameSize = 65535

sec_protocol_options_set_verify_block(options.securityProtocolOptions, {(_: sec_protocol_metadata_t, _: sec_trust_t, completion: @escaping sec_protocol_verify_complete_t) in
    print("cert completion.")
    completion(true)
}, .global())

let params: NWParameters = .init(quic: options)

let group: NWMultiplexGroup = .init(
    to: .hostPort(host: NWEndpoint.Host("google.com"),
                  port: NWEndpoint.Port(String(443))!))

_group = .init(with: group, using: params)

_group.setReceiveHandler {message,content,isComplete in
    print("receive: \(message)")
}
_group.newConnectionHandler = {newConnection in
    print("newConnectionHandler: \(newConnection.state)")
}
_group.stateUpdateHandler = { state in
    print("state: \(state)")
}
_group.start(queue: .global())

_listener.start(queue: .global())

if let conn = _group.extract() {
    let data: Data = .init()
    let _ = _group.reinsert(connection: conn)
    conn.send(content: data, completion: .idempotent)
}