feat(native): integrate all native platforms via MQTT 3.1.1 over ktor-network

[Copilot]

Native targets (Linux, macOS, iOS, Windows, watchOS, tvOS) were completely absent — commented out in the build with no actual implementation. This PR enables them using ktor-network 3.4.1 (pure Kotlin, no system deps) as the transport layer with a hand-rolled MQTT 3.1.1 implementation.

Build changes

• Enable kotlin.native.ignoreDisabledTargets=true so unsupported targets are silently skipped per host
• Call applyDefaultHierarchyTemplate() and register all native targets: linuxX64, linuxArm64, mingwX64, macosX64/Arm64, iosArm64, iosSimulatorArm64, watchosArm32/64/SimulatorArm64, tvosArm64/SimulatorArm64
• Add ktor-network + ktor-network-tls (3.4.1) to nativeMain source set

Native implementation (NativeMkttClient)

• Full MQTT 3.1.1 over ktor TCP/TLS sockets, implementing the complete MkttClient interface
• QoS 0/1/2 including the full PUBREC → PUBREL → PUBCOMP exchange on both publish and receive paths
• Keep-alive PINGREQ loop, +/# topic-filter matching, and all MqttConnectionState transitions
• Coroutine-safe serialised writes via Mutex; all pending ACK Deferreds are cancelled on disconnect

ktor 3.x API compatibility

ByteReadChannel.readByte(), ByteWriteChannel.writeByte(), and writeFully() were removed in ktor 3.x. Replaced with:

• Reads: private readOneByte() helper using the still-available readFully(ByteArray, 0, 1)
• Writes: buildFullPacket() assembles the complete frame (fixed-header + variable-length remaining-length + payload) into a ByteArray via MqttBuffer, then written in one wc.write(size) { buf -> buf.write(packet, 0, packet.size) } call

val client = MkttClient(Dispatchers.Default) {
    brokerUrl = "broker.emqx.io"
    clientId  = "native-client"
    ssl       = true  // uses ktor-network-tls (OpenSSL / SecureTransport / SChannel)
}
client.connect()
client.subscribe("sensors/#", MqttQoS.AtLeastOnce).collect { println(it.payloadAsString()) }

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• download.jetbrains.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED --add-opens=java.base/java.time=ALL-UNNAMED -XX:MaxMetaspaceSize=2g -Xmx2g -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en (dns block)
• scans-in.gradle.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED --add-opens=java.base/java.time=ALL-UNNAMED -XX:MaxMetaspaceSize=2g -Xmx2g -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[gitguardian]

⚠️ GitGuardian has uncovered 1 secret following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secret in your pull request

GitGuardian id	GitGuardian status	Secret	Commit	Filename
29153006	Triggered	Generic Password	fb7cb34	src/nativeMain/kotlin/io/github/nicolasfara/NativeMqttProtocol.kt	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secret safely. Learn here the best practices.
3. Revoke and rotate this secret.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

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^{🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.}