Sources/SophaxChatCore/Network/LanDiscovery.swift

1// LanDiscovery.swift
2// SophaxChatCore
3//
4// mDNS/Bonjour discovery — enables automatic iOS ↔ Android peer discovery
5// on the same WiFi network, without any central server.
6//
7// Both platforms advertise "_sophaxchat._tcp." on port 25519.
8// On discovery, the resolved address is passed to the delegate which
9// initiates a TCP connection. From there the normal Hello / X3DH handshake
10// takes over — this file is transport-only, no crypto.
11
12import Foundation
13
14public protocol LanDiscoveryDelegate: AnyObject {
15    /// Called when a peer's TCP address has been resolved. Implementor should
16    /// call `ChatManager.connectViaTCP(address:)` with the provided address.
17    func lanDiscovery(didFind address: String)
18}
19
20public final class LanDiscovery: NSObject {
21
22    // _sophaxchat._tcp. on port 25519 (Curve25519 homage — same as TCPTransport)
23    private static let serviceType = "_sophaxchat._tcp."
24    private static let port: Int32 = 25519
25
26    private var netService: NetService?
27    private var browser: NetServiceBrowser?
28    private var myServiceName: String?
29
30    /// Active resolved services — keyed by service name to avoid duplicate TCP connects.
31    private var resolved = Set<String>()
32
33    public weak var delegate: LanDiscoveryDelegate?
34
35    public override init() { super.init() }
36
37    // MARK: - Public
38
39    /// Start advertising and browsing. Call from the main thread (or ChatManager's queue).
40    public func start(peerID: String) {
41        myServiceName = peerID
42
43        // Advertise ourselves so others can find us
44        let svc = NetService(
45            domain: "local.",
46            type:   Self.serviceType,
47            name:   peerID,
48            port:   Self.port
49        )
50        svc.delegate = self
51        svc.publish()
52        netService = svc
53
54        // Browse for others
55        let b = NetServiceBrowser()
56        b.delegate = self
57        b.searchForServices(ofType: Self.serviceType, inDomain: "local.")
58        browser = b
59    }
60
61    public func stop() {
62        netService?.stop()
63        browser?.stop()
64        netService = nil
65        browser = nil
66        resolved.removeAll()
67    }
68}
69
70// MARK: - NetServiceBrowserDelegate
71
72extension LanDiscovery: NetServiceBrowserDelegate {
73
74    public func netServiceBrowser(
75        _ browser: NetServiceBrowser,
76        didFind service: NetService,
77        moreComing: Bool
78    ) {
79        // Skip ourselves
80        guard service.name != myServiceName else { return }
81        // Skip peers we've already connected to this session
82        guard !resolved.contains(service.name) else { return }
83
84        service.delegate = self
85        service.resolve(withTimeout: 5.0)
86    }
87
88    public func netServiceBrowser(
89        _ browser: NetServiceBrowser,
90        didRemove service: NetService,
91        moreComing: Bool
92    ) {
93        resolved.remove(service.name)
94    }
95
96    public func netServiceBrowser(
97        _ browser: NetServiceBrowser,
98        didNotSearch errorDict: [String: NSNumber]
99    ) {
100        // Browse error — non-fatal, discovery will be absent until next restart
101    }
102}
103
104// MARK: - NetServiceDelegate
105
106extension LanDiscovery: NetServiceDelegate {
107
108    public func netServiceDidPublish(_ sender: NetService) {
109        // Advertising confirmed — no action needed
110    }
111
112    public func netService(_ sender: NetService, didNotPublish errorDict: [String: NSNumber]) {
113        // Publication failure (e.g., port already in use) — non-fatal
114    }
115
116    public func netServiceDidResolveAddress(_ sender: NetService) {
117        // `hostName` is the resolved mDNS hostname (e.g. "iPhone.local")
118        guard let host = sender.hostName else { return }
119        resolved.insert(sender.name)
120        delegate?.lanDiscovery(didFind: "\(host):\(sender.port)")
121    }
122
123    public func netService(_ sender: NetService, didNotResolve errorDict: [String: NSNumber]) {
124        // Resolution failure — non-fatal, peer will be re-discovered on next browse cycle
125    }
126}