Swift networking with Apple's NWListener and NWConnection

NetworkConnection.swift

/*
This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
*/


import Foundation
import Network

protocol NetworkConnectionDelegate: AnyObject
{
    func connectionOpened(connection: NetworkConnection)
    func connectionClosed(connection: NetworkConnection)
    func connectionError(connection: NetworkConnection, error: Error)
    func connectionReceivedData(connection: NetworkConnection, data: Data)
}

class NetworkConnection
{
    private static var nextID: Int = 0
    
    weak var delegate: NetworkConnectionDelegate?
    private let nwConnection: NWConnection
    let id: Int
    private var queue: DispatchQueue?
    
    init(nwConnection: NWConnection)
    {
        self.nwConnection = nwConnection
        self.id = NetworkConnection.nextID
        NetworkConnection.nextID += 1
    }
    
    func start(queue: DispatchQueue)
    {
        self.queue = queue
        self.nwConnection.stateUpdateHandler = self.onStateDidChange(to:)
        self.doReceive()
        self.nwConnection.start(queue: queue)
    }

    func send(data: Data)
    {
        let sizePrefix = withUnsafeBytes(of: UInt16(data.count).bigEndian) { Data($0) }
                
        log.info("Send \(data.count) bytes")
        
        self.nwConnection.batch {
            self.nwConnection.send(content: sizePrefix, completion: .contentProcessed( { error in
                if let error = error {
                    self.delegate?.connectionError(connection: self, error: error)
                    return
                }
            }))
            
            self.nwConnection.send(content: data, completion: .contentProcessed( { error in
                if let error = error {
                    self.delegate?.connectionError(connection: self, error: error)
                    return
                }
            }))
        }
    }

    private func onStateDidChange(to state: NWConnection.State)
    {
        switch state {
            case .setup:
                break
            case .waiting(let error):
                self.delegate?.connectionError(connection: self, error: error)
            case .preparing:
                break
            case .ready:
                self.delegate?.connectionOpened(connection: self)
            case .failed(let error):
                self.delegate?.connectionError(connection: self, error: error)
            case .cancelled:
                break
            default:
                break
        }
    }

    func close()
    {
        self.nwConnection.stateUpdateHandler = nil
        self.nwConnection.cancel()
        delegate?.connectionClosed(connection: self)
    }

    private func doReceive()
    {
        self.nwConnection.receive(minimumIncompleteLength: MemoryLayout<UInt16>.size, maximumLength: MemoryLayout<UInt16>.size) { (sizePrefixData, _, isComplete, error) in
            var sizePrefix: UInt16 = 0
            
            // Decode the size prefix
            if let data = sizePrefixData, !data.isEmpty
            {
                sizePrefix = data.withUnsafeBytes
                {
                    $0.bindMemory(to: UInt16.self)[0].bigEndian
                }
            }
            
            if isComplete
            {
                self.close()
            }
            else if let error = error
            {
                self.delegate?.connectionError(connection: self, error: error)
            }
            else
            {
                // If there is nothing to read
                if sizePrefix == 0
                {
                    log.error("Received size prefix of 0")
                    self.doReceive()
                    return
                }
                
                log.info("Read \(sizePrefix) bytes")
                
                // At this point we received a valid message and a valid size prefix 
                self.nwConnection.receive(minimumIncompleteLength: Int(sizePrefix), maximumLength: Int(sizePrefix)) { (data, _, isComplete, error) in
                    if let data = data, !data.isEmpty
                    {
                        self.delegate?.connectionReceivedData(connection: self, data: data)
                    }
                    if isComplete
                    {
                        self.close()
                    }
                    else if let error = error
                    {
                        self.delegate?.connectionError(connection: self, error: error)
                    }
                    else
                    {
                        self.doReceive()
                    }
                }
            }
        }
    }
}

NetworkServer.swift

/*
This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
*/


import Foundation
import Network

protocol NetworkServerDelegate: AnyObject
{
    func serverBecameReady()
    func connectionOpened(id: Int)
    func connectionReceivedData(id: Int, data: Data)
}

class NetworkServer: NetworkConnectionDelegate
{
    weak var delegate: NetworkServerDelegate?
    let listener: NWListener
    
    private var serverQueue: DispatchQueue?
    
    private var connectionsByID: [Int: NetworkConnection] = [:]
    
    init()
    {
        self.listener = try! NWListener(using: .tcp, on: 12345)
    }
    
    init(name: String?, type: String, domain: String?, txtRecord: NWTXTRecord)
    {
        self.listener = try! NWListener(using: .tcp, on: 0)
        self.listener.service = NWListener.Service(name: name, type: type, domain: domain, txtRecord: txtRecord)
    }
    
    func start(queue: DispatchQueue) throws
    {
        self.serverQueue = queue
        
        self.listener.stateUpdateHandler = self.onStateDidChange(to:)
        self.listener.newConnectionHandler = self.onNewConnectionAccepted(nwConnection:)
        self.listener.start(queue: queue)
    }

    func onStateDidChange(to newState: NWListener.State)
    {
        switch newState {
        case .setup:
            break
        case .waiting:
            break
        case .ready:
            self.delegate?.serverBecameReady()
            break
        case .failed(let error):
            print("server did fail, error: \(error)")
            self.stop()
        case .cancelled:
            break
        default:
            break
        }
    }

    private func onNewConnectionAccepted(nwConnection: NWConnection)
    {
        let connection = NetworkConnection(nwConnection: nwConnection)
        self.connectionsByID[connection.id] = connection
        connection.delegate = self
        connection.start(queue: self.serverQueue!)
        
        log.info("Server accepted connection \(connection)")
    }

    private func stop()
    {
        self.listener.stateUpdateHandler = nil
        self.listener.newConnectionHandler = nil
        self.listener.cancel()
        closeAllConnections()
    }

    private func heartbeat() {
        let timestamp = Date()
        print("server heartbeat, timestamp: \(timestamp)")
        for connection in self.connectionsByID.values {
            let data = "heartbeat, connection: \(connection.id), timestamp: \(timestamp)\r\n"
            connection.send(data: Data(data.utf8))
        }
    }
    
    func closeAllConnections()
    {
        for connection in self.connectionsByID.values{
            connection.close()
        }
        // Theoretically next call shouldn't have to remove anything as the connections
        // removed them selves by calling our connectionClosed function
        self.connectionsByID.removeAll()
    }
    
    func sendToAll(data: Data)
    {
        for conn in self.connectionsByID {
            conn.value.send(data: data)
        }
    }
    
    func sendTo(id: Int, data: Data)
    {
        self.connectionsByID[id]?.send(data: data)
    }
    
    func sendToAllExcept(id: Int, data: Data)
    {
        for conn in self.connectionsByID
        {
            if (conn.value.id != id)
            {
                conn.value.send(data: data)
            }
        }
    }
    
    var port: NWEndpoint.Port?
    {
        get {
            return self.listener.port
        }
    }
    
    // MARK: NetworkConnectionDelegate
    func connectionOpened(connection: NetworkConnection)
    {
        log.info("Server connection opened")
        self.delegate?.connectionOpened(id: connection.id)
    }
    
    func connectionClosed(connection: NetworkConnection)
    {
        self.connectionsByID.removeValue(forKey: connection.id)
        log.info("Server connection closed (\(connection))")
    }
    
    func connectionError(connection: NetworkConnection, error: Error)
    {
        log.error("Server connection error: \(error) (\(connection))")
    }
    
    func connectionReceivedData(connection: NetworkConnection, data: Data)
    {
        self.delegate?.connectionReceivedData(id: connection.id, data: data)
    }
}

Thanks your code :)
Can I use your code in my commercial app?

Sure, go ahead. I've updated the license.