axiom-networking-legacy

Legacy iOS 12-25 NWConnection Patterns

These patterns use NWConnection with completion handlers for apps supporting iOS 12-25. If your app targets iOS 26+, use NetworkConnection with async/await instead (see axiom-network-framework-ref skill).

Pattern 2a: NWConnection with TLS (iOS 12-25)

Use when Supporting iOS 12-25, need TLS encryption, can't use async/await yet

Time cost 10-15 minutes

GOOD: NWConnection with Completion Handlers

import Network

// Create connection with TLS let connection = NWConnection( host: NWEndpoint.Host("mail.example.com"), port: NWEndpoint.Port(integerLiteral: 993), using: .tls // TCP inferred )

// Handle connection state changes connection.stateUpdateHandler = { [weak self] state in switch state { case .ready: print("Connection established") self?.sendInitialData() case .waiting(let error): print("Waiting for network: (error)") // Show "Waiting..." UI, don't fail immediately case .failed(let error): print("Connection failed: (error)") case .cancelled: print("Connection cancelled") default: break } }

// Start connection connection.start(queue: .main)

// Send data with pacing func sendData() { let data = Data("Hello, world!".utf8) connection.send(content: data, completion: .contentProcessed { [weak self] error in if let error = error { print("Send error: (error)") return } // contentProcessed callback = network stack consumed data // This is when you should send next chunk (pacing) self?.sendNextChunk() }) }

// Receive exact byte count func receiveData() { connection.receive(minimumIncompleteLength: 10, maximumLength: 10) { [weak self] (data, context, isComplete, error) in if let error = error { print("Receive error: (error)") return }

    if let data = data {
        print("Received \(data.count) bytes")
        // Process data...
        self?.receiveData() // Continue receiving
    }
}

}

Key differences from NetworkConnection

Must use [weak self] in all completion handlers to prevent retain cycles
stateUpdateHandler receives state, not async sequence
send/receive use completion callbacks, not async/await

When to use

Supporting iOS 12-15 (70% of devices as of 2024)
Codebases not yet using async/await
Libraries needing backward compatibility

Migration to NetworkConnection (iOS 26+)

stateUpdateHandler -> connection.states async sequence
Completion handlers -> try await calls
[weak self] -> No longer needed (async/await handles cancellation)

Pattern 2b: NWConnection UDP Batch (iOS 12-25)

Use when Supporting iOS 12-25, sending multiple UDP datagrams efficiently, need ~30% CPU reduction

Time cost 10-15 minutes

Background Traditional UDP sockets send one datagram per syscall. If you're sending 100 small packets, that's 100 context switches. Batching reduces this to ~1 syscall.

BAD: Individual UDP Sends (High CPU)

// WRONG — 100 context switches for 100 packets for frame in videoFrames { sendto(socket, frame.bytes, frame.count, 0, &addr, addrlen) // Each send = context switch to kernel }

GOOD: Batched UDP Sends (30% Lower CPU)

import Network

// UDP connection let connection = NWConnection( host: NWEndpoint.Host("stream-server.example.com"), port: NWEndpoint.Port(integerLiteral: 9000), using: .udp )

connection.stateUpdateHandler = { state in if case .ready = state { print("Ready to send UDP") } }

connection.start(queue: .main)

// Batch sending for efficiency func sendVideoFrames(_ frames: [Data]) { connection.batch { for frame in frames { connection.send(content: frame, completion: .contentProcessed { error in if let error = error { print("Send error: (error)") } }) } } // All sends batched into ~1 syscall // 30% lower CPU usage vs individual sends }

// Receive UDP datagrams func receiveFrames() { connection.receive(minimumIncompleteLength: 1, maximumLength: 65536) { [weak self] (data, context, isComplete, error) in if let error = error { print("Receive error: (error)") return }

    if let data = data {
        // Process video frame
        self?.displayFrame(data)
        self?.receiveFrames() // Continue receiving
    }
}

}

Performance characteristics

Without batch 100 datagrams = 100 syscalls = 100 context switches
With batch 100 datagrams = ~1 syscall = 1 context switch
Result ~30% lower CPU usage (measured with Instruments)

When to use

Real-time video/audio streaming
Gaming with frequent updates (player position)
High-frequency sensor data (IoT)

WWDC 2018 demo Live video streaming showed 30% lower CPU on receiver with user-space networking + batching

Pattern 2c: NWListener (iOS 12-25)

Use when Need to accept incoming connections, building servers or peer-to-peer apps, supporting iOS 12-25

Time cost 20-25 minutes

BAD: Manual Socket Listening

// WRONG — Manual socket management let sock = socket(AF_INET, SOCK_STREAM, 0) bind(sock, &addr, addrlen) listen(sock, 5) while true { let client = accept(sock, nil, nil) // Blocks thread // Handle client... }

GOOD: NWListener with Automatic Connection Handling

import Network

// Create listener with default parameters let listener = try NWListener(using: .tcp, on: 1029)

// Advertise Bonjour service listener.service = NWListener.Service(name: "MyApp", type: "_myservice._tcp")

// Handle service registration updates listener.serviceRegistrationUpdateHandler = { update in switch update { case .add(let endpoint): if case .service(let name, let type, let domain, _) = endpoint { print("Advertising as: (name).(type)(domain)") } default: break } }

// Handle incoming connections listener.newConnectionHandler = { [weak self] newConnection in print("New connection from: (newConnection.endpoint)")

// Configure connection
newConnection.stateUpdateHandler = { state in
    switch state {
    case .ready:
        print("Client connected")
        self?.handleClient(newConnection)
    case .failed(let error):
        print("Client connection failed: \(error)")
    default:
        break
    }
}

// Start handling this connection
newConnection.start(queue: .main)

}

// Handle listener state listener.stateUpdateHandler = { state in switch state { case .ready: print("Listener ready on port (listener.port ?? 0)") case .failed(let error): print("Listener failed: (error)") default: break } }

// Start listening listener.start(queue: .main)

// Handle client data func handleClient(_ connection: NWConnection) { connection.receive(minimumIncompleteLength: 1, maximumLength: 65536) { [weak self] (data, context, isComplete, error) in if let error = error { print("Receive error: (error)") return }

    if let data = data {
        print("Received \(data.count) bytes")

        // Echo back
        connection.send(content: data, completion: .contentProcessed { error in
            if let error = error {
                print("Send error: \(error)")
            }
        })

        self?.handleClient(connection) // Continue receiving
    }
}

}

When to use

Peer-to-peer apps (file sharing, messaging)
Local network services
Development/testing servers

Bonjour advertising

Automatic service discovery on local network
No hardcoded IPs needed
Works with NWBrowser for discovery

Security considerations

Use TLS parameters for encryption: NWListener(using: .tls, on: port)
Validate client connections before processing data
Set connection limits to prevent DoS

Pattern 2d: Network Discovery (iOS 12-25)

Use when Discovering services on local network (Bonjour), building peer-to-peer apps, supporting iOS 12-25

Time cost 25-30 minutes

BAD: Hardcoded IP Addresses

// WRONG — Brittle, requires manual configuration let connection = NWConnection(host: "192.168.1.100", port: 9000, using: .tcp) // What if IP changes? What if multiple devices?

GOOD: NWBrowser for Service Discovery

import Network

// Browse for services on local network let browser = NWBrowser(for: .bonjour(type: "_myservice._tcp", domain: nil), using: .tcp)

// Handle discovered services browser.browseResultsChangedHandler = { results, changes in for result in results { switch result.endpoint { case .service(let name, let type, let domain, _): print("Found service: (name).(type)(domain)") // Connect to this service self.connectToService(result.endpoint) default: break } } }

// Handle browser state browser.stateUpdateHandler = { state in switch state { case .ready: print("Browser ready") case .failed(let error): print("Browser failed: (error)") default: break } }

// Start browsing browser.start(queue: .main)

// Connect to discovered service func connectToService(_ endpoint: NWEndpoint) { let connection = NWConnection(to: endpoint, using: .tcp)

connection.stateUpdateHandler = { state in
    if case .ready = state {
        print("Connected to service")
    }
}

connection.start(queue: .main)

}

When to use

Peer-to-peer discovery (AirDrop-like features)
Local network printers, media servers
Development/testing (find test servers automatically)

Performance characteristics

mDNS-based (multicast DNS, no central server)
Near-instant discovery on same subnet
Automatic updates when services appear/disappear

iOS 26+ alternative

Use NetworkBrowser with Wi-Fi Aware for peer-to-peer without infrastructure
See Pattern 1d in axiom-network-framework-ref skill

Resources

Skills: axiom-networking, axiom-network-framework-ref, axiom-networking-migration

axiom-networking-legacy

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