Accelerate networking with HTTP/3 and QUIC

// Create a connection using QUIC
let connection = NWConnection(host: "example.com", port: 443, using: .quic(alpn: ["myproto"]))

// Set the state update handler to be notified when the connection is ready
connection.stateUpdateHandler = { newState in
    switch newState {
    case .ready:
        print("Connected using QUIC!")
    default:
        break
    }
}

// Start the connection with callback queue
connection.start(queue: queue)

// Establish a tunnel with NWMultiplexGroup

// Create a group
let descriptor = NWMultiplexGroup(to: .hostPort(host: "example.com", port: 443))
let group = NWConnectionGroup(with: descriptor, using: .quic(alpn: ["myproto"]))

// Set the state update handler to be notified when the group is ready
group.stateUpdateHandler = { newState in
    switch newState {
    case .ready:
        print("Connected using QUIC!")
    default:
        break
    }
}

// Start the group with callback queue
group.start(queue: queue)

// Manage streams with NWConnectionGroup

// Create a new outgoing stream
let connection = NWConnection(from: group)

// Receive new incoming streams initiated by the remote endpoint
group.newConnectionHandler = { newConnection in

    // Set state update handler on incoming stream
    newConnection.stateUpdateHandler = { newState in
        // Handle stream states
    }

    // Start the incoming stream
    newConnection.start(queue: queue)

}

// Receive incoming QUIC tunnels from NWListener

// Set the new connection group handler
listener.newConnectionGroupHandler = { group in

    group.stateUpdateHandler = { newState in
        // Handle tunnel states
    }

    group.newConnectionHandler = { stream in
        // Set up and start new incoming streams
    }

    group.start(queue: queue)

}

// Access QUIC metadata to learn about and modify streams

// Find the stream ID of a particular QUIC stream
if let metadata = connection.metadata(definition: NWProtocolQUIC.definition)
                             as? NWProtocolQUIC.Metadata {
    print("QUIC Stream ID is \(metadata.streamIdentifier)")

    // Some time later...

    // Set the application error, if appropriate, before cancelling the stream
    metadata.applicationError = 0x100
    connection.cancel()

}