Network.framework API Reference

Overview

Network.framework is Apple's modern networking API that replaces Berkeley sockets, providing smart connection establishment, user-space networking, built-in TLS support, and seamless mobility. Introduced in iOS 12 (2018) with NWConnection and evolved in iOS 26 (2025) with NetworkConnection for structured concurrency.

Evolution timeline

• 2018 (iOS 12) NWConnection with completion handlers, deprecates CFSocket/NSStream/SCNetworkReachability
• 2019 (iOS 13) User-space networking (30% CPU reduction), TLS 1.3 default
• 2025 (iOS 26) NetworkConnection with async/await, TLV framing built-in, Coder protocol, Wi-Fi Aware discovery

Key capabilities

• Smart connection establishment Happy Eyeballs (IPv4/IPv6 racing), proxy evaluation (PAC), VPN detection, WiFi Assist fallback
• User-space networking ~30% lower CPU usage vs sockets, memory-mapped regions, reduced context switches
• Built-in security TLS 1.3 by default, DTLS for UDP, certificate pinning support
• Mobility Automatic network transition handling (WiFi ↔ cellular), viability notifications, Multipath TCP
• Performance ECN (Explicit Congestion Notification), service class marking, TCP Fast Open, UDP batching

When to use vs URLSession

• URLSession HTTP, HTTPS, WebSocket, simple TCP/TLS streams → Use URLSession (optimized for these)
• Network.framework UDP, custom protocols, low-level control, peer-to-peer, gaming, streaming → Use Network.framework

Related Skills

• Use axiom-networking for anti-patterns, common patterns, pressure scenarios
• Use axiom-networking-diag for systematic troubleshooting of connection failures

When to Use This Skill

Use this skill when:

• Planning migration from BSD sockets, CFSocket, NSStream, or SCNetworkReachability
• Understanding API differences between NWConnection (iOS 12-25) and NetworkConnection (iOS 26+)
• Implementing all 12 WWDC 2025 examples (TLS connection, TLV framing, Coder protocol, NetworkListener, Wi-Fi Aware)
• Choosing protocols (TCP, UDP, TLS, QUIC) for your use case
• Peer-to-peer discovery setup with NetworkBrowser and Wi-Fi Aware
• Optimizing performance with user-space networking, batching, pacing
• Migrating from completion handlers to async/await (NWConnection → NetworkConnection)

API Evolution

Timeline

NWConnection (iOS 12-25) vs NetworkConnection (iOS 26+)

Recommendation

• New apps targeting iOS 26+: Use NetworkConnection (cleaner, safer)
• Apps supporting iOS 12-25: Use NWConnection (backward compatible)
• Migration: Both APIs coexist, migrate incrementally

NetworkConnection (iOS 26+) Complete Reference

4.1 Creating Connections

NetworkConnection uses declarative protocol stack composition.

Example 1: Basic TLS Connection (WWDC 4:04)

import Network

// Basic connection with TLS (TCP and IP inferred)
let connection = NetworkConnection(
    to: .hostPort(host: "www.example.com", port: 1029)
) {
    TLS()
}

// Send and receive with async/await
public func sendAndReceiveWithTLS() async throws {
    let outgoingData = Data("Hello, world!".utf8)
    try await connection.send(outgoingData)

    let incomingData = try await connection.receive(exactly: 98).content
    print("Received data: \(incomingData)")
}

Key points

• TLS() infers TCP() and IP() automatically
• No explicit connection.start() needed (happens on first send/receive)
• Async/await eliminates callback nesting

Example 2: Custom IP Options (WWDC 4:41)

// Customize IP fragmentation
let connection = NetworkConnection(
    to: .hostPort(host: "www.example.com", port: 1029)
) {
    TLS {
        TCP {
            IP()
                .fragmentationEnabled(false) // Disable IP fragmentation
        }
    }
}

When to customize IP

• .fragmentationEnabled(false) — For protocols that handle fragmentation themselves (QUIC)
• .ipVersion(.v6) — Force IPv6 only (testing)

Example 3: Custom Parameters (WWDC 5:07)

// Constrained paths (low data mode) + custom IP
let connection = NetworkConnection(
    to: .hostPort(host: "www.example.com", port: 1029),
    using: .parameters {
        TLS {
            TCP {
                IP()
                    .fragmentationEnabled(false)
            }
        }
    }
    .constrainedPathsProhibited(true) // Don't use cellular in low data mode
)

Common parameters

• .constrainedPathsProhibited(true) — Respect low data mode
• .expensivePathsProhibited(true) — Don't use cellular/hotspot
• .multipathServiceType(.handover) — Enable Multipath TCP

Endpoint Types

// Host + Port
.hostPort(host: "example.com", port: 443)

// Service (Bonjour)
.service(name: "MyPrinter", type: "_ipp._tcp", domain: "local.", interface: nil)

// Unix domain socket
.unix(path: "/tmp/my.sock")

Protocol Stack Composition

// TLS over TCP (most common)
TLS()

// QUIC (TLS + UDP, multiplexed streams)
QUIC()

// UDP (datagrams)
UDP()

// TCP (stream, no encryption)
TCP()

// WebSocket over TLS
WebSocket {
    TLS()
}

// Custom framing
TLV {
    TLS()
}

4.2 State Machine

NetworkConnection transitions through these states:

setup
  ↓
preparing (DNS, TCP handshake, TLS handshake)
  ↓
┌─ waiting (no network, retrying)
│    ↓
└→ ready (can send/receive)
     ↓
  failed (error) or cancelled

Monitoring States

// Option 1: Async sequence (monitor in background)
Task {
    for await state in connection.states {
        switch state {
        case .preparing:
            print("Connecting...")
        case .waiting(let error):
            print("Waiting for network: \(error)")
        case .ready:
            print("Connected!")
        case .failed(let error):
            print("Failed: \(error)")
        case .cancelled:
            print("Cancelled")
        @unknown default:
            break
        }
    }
}

Key states

• .preparing DNS lookup, TCP SYN, TLS handshake
• .waiting No network available, framework retries automatically
• .ready Connection established, can send/receive
• .failed Unrecoverable error (server refused, TLS failed, timeout)
• .cancelled Task cancelled or connection.cancel() called

4.3 Send/Receive Patterns

Send: Basic

how to use axiom-network-framework-ref
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How to use axiom-network-framework-ref on Cursor
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Prerequisites
Before installing skills in Cursor, ensure your development environment meets these requirements:
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›Node.js version 16.0+ with npm package manager (verify with node --version)
›Active project directory or workspace where you want to add axiom-network-framework-ref
2
Execute installation command
Execute the skills CLI command in your project's root directory to begin installation:
$npx skills add https://github.com/charleswiltgen/axiom --skill axiom-network-framework-refcopy
The skills CLI fetches axiom-network-framework-ref from GitHub repository charleswiltgen/axiom and configures it for Cursor.
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4
Verify installation
Confirm successful installation by checking the skill directory location:
.cursor/skills/axiom-network-framework-ref
Reload or restart Cursor to activate axiom-network-framework-ref. Access the skill through slash commands (e.g., /axiom-network-framework-ref) or your agent's skill management interface.
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