mdns-swift

Shared mDNS/DNS-SD service discovery for Swift — used by matter-swift and hap-swift.

Overview

mdns-swift is a pure-Swift mDNS/DNS-SD service discovery library (RFC 6762) with platform-specific backends:

• Apple platforms — NWBrowser for browsing/resolving, DNSServiceRegister for advertising (supports DNS-SD subtypes required by Matter commissioning)
• Linux — Pure-Swift RFC 6762 responder over SwiftNIO; no system daemon dependency

The library is intentionally protocol-agnostic. Consumers define their own service types via ServiceType extensions:

// In matter-swift
extension ServiceType {
    public static let commissionable: ServiceType = "_matterc._udp"
    public static let operational:    ServiceType = "_matter._tcp"
}

// In hap-swift
extension ServiceType {
    public static let hapAccessory: ServiceType = "_hap._tcp"
}

Quick Start

Add mdns-swift to your Package.swift:

dependencies: [
    .package(url: "https://github.com/acumen-dev/mdns-swift.git", from: "1.0.0")
]

Advertise a service

import MDNSCore
#if canImport(Network)
import MDNSApple
let discovery: any ServiceDiscovery = AppleServiceDiscovery()
#else
import MDNSLinux
let discovery: any ServiceDiscovery = LinuxServiceDiscovery()
#endif

try await discovery.advertise(service: ServiceRecord(
    name: "My Bridge",
    serviceType: "_hap._tcp",
    host: "",
    port: 51826,
    txtRecords: ["id": "AA:BB:CC:DD:EE:FF", "c#": "1"]
))

Browse for services

for await record in discovery.browse(serviceType: "_hap._tcp") {
    print("Found: \(record.name) (port \(record.port))")
}

Resolve to a network address

let address = try await discovery.resolve(record)
print("Connecting to \(address.host):\(address.port)")

Module Architecture

Module	Purpose	Platforms
MDNSCore	ServiceDiscovery protocol, ServiceRecord, ServiceType, NetworkAddress. Zero platform dependencies.	All
MDNSApple	AppleServiceDiscovery using Network.framework + dnssd.	Apple only
MDNSLinux	LinuxServiceDiscovery using SwiftNIO + pure-Swift RFC 6762 codec.	All (primary target: Linux)

MDNSCore
    ↑
├── MDNSApple   (Apple platforms)
└── MDNSLinux   (Linux / cross-platform)

Service Types

ServiceType is a RawRepresentable struct backed by the DNS-SD string (e.g. "_hap._tcp"). It conforms to ExpressibleByStringLiteral and Hashable, so consumers add typed static members via Swift extensions:

extension ServiceType {
    static let myService: ServiceType = "_myservice._tcp"
}

// Both of these work:
discovery.browse(serviceType: .myService)
discovery.browse(serviceType: "_myservice._tcp")

Platform Requirements

Platform	Minimum Version
macOS	15.0
iOS	18.0
tvOS	18.0
watchOS	11.0
visionOS	2.0
Linux	Swift 6.1+ (Ubuntu 24.04 tested)

Dependencies

• swift-log 1.0+ — all targets
• swift-nio 2.65+ — MDNSLinux only

License

Licensed under the Apache License, Version 2.0. See LICENSE.md for details.