Align Apple platform floors and fix watchOS compilation

.github/workflows/ci.yml

@@ -41,6 +41,38 @@ jobs:
       - name: Test
         run: swift test
 
+  # ── Apple platform floors ──────────────────────────────────────────────────
+  # Build-only cross-compiles that validate the platform floors declared in
+  # Package.swift. Catches APIs that are unavailable on a platform (e.g.
+  # NetService on watchOS) or newer than a declared floor — neither of which
+  # the native macOS build can see.
+  #
+  # Versionless triples pick up the deployment target from Package.swift.
+  # visionOS needs an explicit version in the triple because SwiftPM
+  # synthesizes an invalid default (xros10.13) for a versionless xros triple;
+  # keep it in sync with the .visionOS floor in Package.swift.
+  apple-platforms:
+    name: ${{ matrix.platform.name }} (build only)
+    runs-on: macos-15
+    timeout-minutes: 15
+    strategy:
+      fail-fast: false
+      matrix:
+        platform:
+          - { name: iOS,      triple: arm64-apple-ios,      sdk: iphoneos }
+          - { name: tvOS,     triple: arm64-apple-tvos,     sdk: appletvos }
+          - { name: watchOS,  triple: arm64-apple-watchos,  sdk: watchos }
+          - { name: visionOS, triple: arm64-apple-xros1.0,  sdk: xros }
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build
+        run: >
+          swift build
+          --triple ${{ matrix.platform.triple }}
+          --sdk "$(xcrun --sdk ${{ matrix.platform.sdk }} --show-sdk-path)"
+
   # ── Linux ──────────────────────────────────────────────────────────────────
   linux:
     name: Linux

Package.swift

@@ -4,11 +4,11 @@ import PackageDescription
 let package = Package(
     name: "mdns-swift",
     platforms: [
-        .macOS(.v15),
-        .iOS(.v18),
-        .tvOS(.v18),
-        .watchOS(.v11),
-        .visionOS(.v2),
+        .macOS(.v14),
+        .iOS(.v17),
+        .tvOS(.v17),
+        .watchOS(.v10),
+        .visionOS(.v1),
     ],
     products: [
         .library(name: "MDNSCore",  targets: ["MDNSCore"]),

Sources/MDNSApple/AppleServiceDiscovery.swift

@@ -83,6 +83,26 @@ public final class AppleServiceDiscovery: ServiceDiscovery, @unchecked Sendable
         self.logger = logger
     }
 
+    // MARK: - TXT Encoding
+
+    /// Encode TXT key/value pairs into RFC 6763 wire format: each entry is a
+    /// length byte followed by the UTF-8 bytes of `"key=value"`.
+    ///
+    /// Hand-rolled because `NetService.data(fromTXTRecord:)` is unavailable on
+    /// watchOS (and deprecated everywhere else). Keys are sorted so the output
+    /// is deterministic; entries longer than 255 bytes are truncated, matching
+    /// the Linux responder's TXT encoding. An empty dictionary yields empty
+    /// `Data`, which `DNSServiceRegister` accepts as "no TXT record".
+    static func txtRecordData(_ records: [String: String]) -> Data {
+        var out = Data()
+        for (key, value) in records.sorted(by: { $0.key < $1.key }) {
+            let bytes = Array("\(key)=\(value)".utf8)
+            out.append(UInt8(min(bytes.count, 255)))
+            out.append(contentsOf: bytes.prefix(255))
+        }
+        return out
+    }
+
     // MARK: - ServiceDiscovery
 
     public func advertise(service: ServiceRecord) async throws {
@@ -96,9 +116,8 @@ public final class AppleServiceDiscovery: ServiceDiscovery, @unchecked Sendable
             DNSServiceRefDeallocate(ref)
         }
 
-        // Build TXT record payload using the NetService helper for correct wire encoding.
-        let txtDict = service.txtRecords.mapValues { $0.data(using: .utf8) ?? Data() }
-        let txtData = NetService.data(fromTXTRecord: txtDict)
+        // Build the TXT record payload in RFC 6763 wire format.
+        let txtData = Self.txtRecordData(service.txtRecords)
 
         // Build the regtype string.
         // DNSServiceRegister natively supports comma-separated subtypes:

Tests/MDNSAppleTests/AppleServiceDiscoveryTests.swift

@@ -1,6 +1,7 @@
 // AppleServiceDiscoveryTests.swift
 // Copyright 2026 Monagle Pty Ltd
 
+import Foundation
 import Testing
 import MDNSCore
 
@@ -9,7 +10,7 @@ import MDNSCore
 // This file verifies that the MDNSApple module compiles and types are correct.
 
 #if canImport(Network)
-import MDNSApple
+@testable import MDNSApple
 
 @Suite("AppleServiceDiscovery Compile-time Tests")
 struct AppleServiceDiscoveryTests {
@@ -28,4 +29,31 @@ struct AppleServiceDiscoveryTests {
         _ = e2
     }
 }
+
+@Suite("TXT Record Encoding")
+struct TXTRecordEncodingTests {
+
+    @Test("Entries are length-prefixed key=value, sorted by key")
+    func wireFormat() {
+        let data = AppleServiceDiscovery.txtRecordData(["id": "AA:BB", "c#": "1"])
+        var expected = Data()
+        expected.append(4)
+        expected.append(contentsOf: Array("c#=1".utf8))
+        expected.append(8)
+        expected.append(contentsOf: Array("id=AA:BB".utf8))
+        #expect(data == expected)
+    }
+
+    @Test("Empty dictionary encodes as empty data")
+    func emptyRecords() {
+        #expect(AppleServiceDiscovery.txtRecordData([:]).isEmpty)
+    }
+
+    @Test("Entries longer than 255 bytes are truncated")
+    func oversizedEntry() {
+        let data = AppleServiceDiscovery.txtRecordData(["k": String(repeating: "x", count: 300)])
+        #expect(data.count == 256)
+        #expect(data.first == 255)
+    }
+}
 #endif