1amageek/swift-mDNS

Features

• Pure Swift - No C dependencies, works on all Swift platforms
• High Performance - Zero-copy parsing, inline IP address storage, DNS name compression
• RFC Compliant - Implements RFC 1035 (DNS), RFC 6762 (mDNS), RFC 6763 (DNS-SD)
• Modern Swift - Uses Swift 6 concurrency with actors and Sendable types
• Type Safe - Strongly typed DNS records, questions, and messages

Requirements

• Swift 6.2+
• macOS 15+ / iOS 18+ / tvOS 18+ / watchOS 11+ / visionOS 2+

Installation

Add swift-mDNS to your Package.swift:

dependencies: [
    .package(url: "https://github.com/1amageek/swift-mDNS.git", from: "1.0.0")
]

Then add mDNS to your target dependencies:

.target(
    name: "YourTarget",
    dependencies: ["mDNS"]
)

Usage

Service Browsing

import mDNS

let browser = ServiceBrowser()
try await browser.start()

// Browse for HTTP services
try await browser.browse(for: "_http._tcp.local.")

for await event in browser.events {
    switch event {
    case .found(let service):
        print("Found: \(service.name) at \(service.hostName ?? "unknown"):\(service.port ?? 0)")
    case .updated(let service):
        print("Updated: \(service.name)")
    case .removed(let service):
        print("Removed: \(service.name)")
    case .error(let error):
        print("Error: \(error)")
    }
}

Service Advertising

import mDNS

let advertiser = ServiceAdvertiser()
try await advertiser.start()

let service = Service(
    name: "My Web Server",
    type: "_http._tcp",
    port: 8080,
    txtRecord: TXTRecord(["path": "/api", "version": "1.0"])
)

try await advertiser.register(service)

// Later, to unregister:
try await advertiser.unregister(service)

Low-Level DNS Message Handling

import mDNS

// Create a query
let query = try DNSMessage.mdnsQuery(for: "_http._tcp.local.")
let encoded = query.encode()

// Decode a response
let message = try DNSMessage.decode(from: receivedData)
for answer in message.answers {
    print("\(answer.name) \(answer.type) TTL=\(answer.ttl)")

    switch answer.rdata {
    case .ptr(let serviceName):
        print("  PTR -> \(serviceName)")
    case .srv(let srv):
        print("  SRV -> \(srv.target):\(srv.port)")
    case .txt(let strings):
        print("  TXT -> \(strings)")
    case .a(let addr):
        print("  A -> \(addr)")
    case .aaaa(let addr):
        print("  AAAA -> \(addr)")
    default:
        break
    }
}

Working with DNS Names

import mDNS

// Create from string
let name = try DNSName("_http._tcp.local.")

// Use string literal
let name2: DNSName = "_printer._tcp.local."

// Case-insensitive comparison
let name3: DNSName = "_HTTP._TCP.LOCAL."
print(name == name3)  // true

// Encode to wire format
let encoded = name.encode()

// Decode from wire format
let (decoded, bytesConsumed) = try DNSName.decode(from: data, at: 0)

Working with IP Addresses

import mDNS

// IPv4
let ipv4 = IPv4Address(192, 168, 1, 100)
let ipv4FromString = IPv4Address(string: "192.168.1.100")
print(ipv4.description)  // "192.168.1.100"

// IPv6
let ipv6 = IPv6Address(hi: 0xfe80_0000_0000_0000, lo: 0x0000_0000_0000_0001)
let ipv6FromString = IPv6Address(string: "fe80::1")
print(ipv6.description)  // "fe80::1"

Performance

swift-mDNS is optimized for high throughput with minimal memory allocations.

Benchmark Results

Measured on Apple Silicon (M-series):

| Operation | Throughput | Latency | |-----------|------------|---------| | IPv4Address creation | 202M ops/sec | 5 ns | | IPv6Address creation | 479M ops/sec | 2 ns | | IPv4Address equality | 113M ops/sec | 9 ns | | IPv4Address parsing | 513K ops/sec | 1.9 μs | | DNSName decoding | 3.2M ops/sec | 0.31 μs | | DNSName encoding | 230K ops/sec | 4.3 μs | | DNSName equality | 512K ops/sec | 2.0 μs | | DNSMessage query decoding | 1.15M ops/sec | 0.87 μs | | DNSMessage query encoding | 202K ops/sec | 5.0 μs | | DNSMessage response decoding | 300K ops/sec | 3.3 μs | | DNSMessage response encoding | 73K ops/sec | 13.7 μs | | End-to-end roundtrip | 170K ops/sec | 5.9 μs |

Optimization Techniques

• Zero-copy parsing: DNS messages are parsed directly from UnsafeRawBufferPointer without intermediate allocations
• Zero-copy NIO integration: Direct ByteBuffer encoding/decoding without Data conversion
• Inline IP storage: IPv4/IPv6 addresses use stack-allocated tuples instead of heap-allocated Data
• DNS name compression: Repeated name suffixes are compressed to 2-byte pointers (RFC 1035)
• ContiguousArray: Write buffer uses ContiguousArray<UInt8> for better cache locality
• ASCII case-insensitive comparison: DNS name equality uses byte-level comparison without string allocation
• Non-copyable buffers: ReadBuffer and WriteBuffer use ~Copyable to prevent accidental copies

Running Benchmarks

swift test --filter Benchmark

API Reference

Core Types

| Type | Description | |------|-------------| | DNSName | DNS domain name with label encoding and compression pointer support | | DNSQuestion | DNS query with QU bit support for mDNS unicast responses | | DNSResourceRecord | Resource record with cache-flush bit support | | DNSRecordData | Typed RDATA (A, AAAA, PTR, SRV, TXT, HINFO, NSEC) | | DNSMessage | Complete DNS message with header and all sections | | IPv4Address | IPv4 address with inline storage | | IPv6Address | IPv6 address with inline storage |

High-Level Types

| Type | Description | |------|-------------| | Service | Represents a discovered or advertised DNS-SD service | | TXTRecord | Key-value TXT record attributes (case-insensitive keys) | | ServiceBrowser | Actor for browsing services via mDNS | | ServiceAdvertiser | Actor for advertising services via mDNS |

DNS Record Types

| Type | Value | Description | |------|-------|-------------| | .a | 1 | IPv4 address | | .aaaa | 28 | IPv6 address | | .ptr | 12 | Domain name pointer | | .srv | 33 | Service location | | .txt | 16 | Text strings | | .hinfo | 13 | Host information | | .nsec | 47 | Next secure record | | .any | 255 | Any record type (queries only) |

DNS-SD Service Discovery Flow

1. PTR Query: Query for _service._protocol.local. to get service instances
2. PTR Response: Returns ServiceName._service._protocol.local.
3. SRV/TXT Query: Query for the service instance name
4. SRV Response: Returns hostname and port
5. TXT Response: Returns service attributes
6. A/AAAA Query: Query for the hostname
7. A/AAAA Response: Returns IP addresses

mDNS Protocol Details

• Multicast Address: 224.0.0.251 (IPv4) / ff02::fb (IPv6)
• Port: 5353
• Message ID: Always 0 for mDNS
• Cache-Flush Bit: High bit of class field indicates cache flush
• QU Bit: High bit of question class requests unicast response
• Goodbye: TTL=0 indicates record withdrawal

References

• RFC 1035 - Domain Names - Implementation and Specification
• RFC 6762 - Multicast DNS
• RFC 6763 - DNS-Based Service Discovery
• RFC 2782 - DNS SRV Records

License

MIT License

Package Metadata

Repository: 1amageek/swift-mDNS

Stars: 5

Forks: 1

Open issues: 0

Default branch: main

Primary language: swift

README: README.md