KMQTT

KMQTT is a Kotlin Multiplatform MQTT 3.1.1/5.0 Client and Broker, with the objective of targeting the most possible build targets.

Client features

❌ = To Do
✅ = Supported
➕ = Work In Progress

Platform	MQTT 3.1.1	MQTT 5.0	TCP	TLS	Websocket
JVM	✅	✅	✅	✅	✅
Windows X64	✅	✅	✅	✅	✅
Linux X64	✅	✅	✅	✅	✅
Linux ARM64	✅	✅	✅	✅	✅
Node.js	✅	✅	✅	✅	✅
iOS X64	✅	✅	✅	✅	✅
iOS ARM64	✅	✅	✅	✅	✅
iOS Simulator ARM64	✅	✅	✅	✅	✅
macOS X64	✅	✅	✅	✅	✅
macOS ARM64	✅	✅	✅	✅	✅
tvOS X64	✅	✅	✅	✅	✅
tvOS ARM64	✅	✅	✅	✅	✅
tvOS Simulator ARM64	✅	✅	✅	✅	✅
watchOS X64	✅	✅	✅	✅	✅
watchOS ARM32	✅	✅	✅	✅	✅
watchOS ARM64	✅	✅	✅	✅	✅
watchOS Simulator ARM64	✅	✅	✅	✅	✅

Broker features

❌ = To Do
✅ = Supported
➕ = Work In Progress

Platform	MQTT 3.1.1	MQTT 5.0	TCP	TLS	Websocket	Clustering
JVM	✅	✅	✅	✅	✅	➕
Windows X64	✅	✅	✅	✅	✅	❌
Linux X64	✅	✅	✅	✅	✅	❌
Linux ARM64	✅	✅	✅	✅	✅	❌
Node.js	✅	✅	✅	✅	✅	❌
macOS X64	✅	✅	✅	✅	✅	❌
macOS ARM64	✅	✅	✅	✅	✅	❌

Getting Started with the client

Library

Gradle

If you are getting an error saying that OpenSSL hasn't been found, please copy the correct file from https://github.com/davidepianca98/KMQTT/tree/master/kmqtt-common/src/nativeInterop in your project's main directory.

Kotlin Multiplatform plugin

On the Kotlin Multiplatform plugin you only need to require the dependency on the common source set and the platform specific parts will be automatically imported.

repositories {
    mavenCentral()
}

kotlin {
    jvm()
    mingwX64()
    macosX64()

    sourceSets {
        commonMain {
            dependencies {
                implementation("io.github.davidepianca98:kmqtt-common:0.4.8")
                implementation("io.github.davidepianca98:kmqtt-client:0.4.8")
            }
        }
    }
}

Single platform project

repositories {
    mavenCentral()
}
dependencies {
    implementation("io.github.davidepianca98:kmqtt-common-jvm:0.4.8")
    implementation("io.github.davidepianca98:kmqtt-client-jvm:0.4.8")
}

Replace jvm with js, linuxx64, linuxarm64, mingwx64, macosx64, macosarm64, iosarm64, iosX64, iossimulatorarm64, tvossimulatorarm64, tvosx64, tvosarm64, watchosarm32, watchosarm64, watchosx64, watchossimulatorarm64 based on the desired target.

Quick start code example

This code starts the MQTT client on port 1883 without TLS encryption. You can play with MQTTClient() constructor parameters to set the various settings

fun main() {
    val client = MQTTClient(
        MQTTVersion.MQTT5,
        "test.mosquitto.org",
        1883,
        null
    ) {
        println(it.payload?.toByteArray()?.decodeToString())
    }
    client.subscribe(listOf(Subscription("/randomTopic", SubscriptionOptions(Qos.EXACTLY_ONCE))))
    client.publish(false, Qos.EXACTLY_ONCE, "/randomTopic", "hello".encodeToByteArray().toUByteArray())
    client.run() // Blocking method, use step() if you don't want to block the thread
}

TLS code example

The certificates and key must be in PEM format, and they can be either a path to the PEM file or the actual PEM string. The password can be null if the private key has no protection.

fun main() {
    val client = MQTTClient(
        MQTTVersion.MQTT5,
        "test.mosquitto.org",
        8883,
        TLSClientSettings(
            serverCertificate = "mosquitto.org.crt",
        )
    ) {
        println(it.payload?.toByteArray()?.decodeToString())
    }
    client.subscribe(listOf(Subscription("/randomTopic", SubscriptionOptions(Qos.EXACTLY_ONCE))))
    client.publish(false, Qos.EXACTLY_ONCE, "/randomTopic", "hello".encodeToByteArray().toUByteArray())
    client.run() // Blocking method, use step() if you don't want to block the thread
}

Getting Started with the broker

Executables

You can download the executables for your platform under the release tab

Program Arguments

Argument	Default Value	Description
-h	127.0.0.1	Interface address to bind the server to
-p	1883	Server port to listen to
--max-connections	128	The maximum number of TCP connections to support
--key-store	null	The path to the PKCS12 keystore containing the private key and the certificate for TLS, if null TLS is disabled
--key-store-psw	null	The password of the PKCS12 keystore indicated in --key-store, if the keystore has no password set, don't set the option
--wsp	null	The WebSocket port to listen to

Library

Gradle

If you are getting an error saying that OpenSSL hasn't been found, please copy the correct file from https://github.com/davidepianca98/KMQTT/tree/master/kmqtt-common/src/nativeInterop in your project's main directory.

Kotlin Multiplatform plugin

On the Kotlin Multiplatform plugin you only need to require the dependency on the common source set and the platform specific parts will be automatically imported.

repositories {
    mavenCentral()
}

kotlin {
    jvm()
    mingwX64()
    macosX64()
    sourceSets {
        commonMain {
            dependencies {
                implementation("io.github.davidepianca98:kmqtt-common:0.4.8")
                implementation("io.github.davidepianca98:kmqtt-broker:0.4.8")
            }
        }
    }
}

Single platform project

repositories {
    mavenCentral()
}
dependencies {
    implementation("io.github.davidepianca98:kmqtt-common-jvm:0.4.8")
    implementation("io.github.davidepianca98:kmqtt-broker-jvm:0.4.8")
}

Replace jvm with js, linuxx64, linuxarm64, macosarm64, macosx64, mingwx64 based on the desired target.

Quick start code example

This code starts the MQTT broker on port 1883 without TLS encryption. You can play with Broker() constructor parameters to set the various settings

fun main() {
    Broker().listen()
}

TLS code example

The keystore must be in PKCS12 format, the keystore password can be null

fun main() {
    val broker = Broker(
        tlsSettings = TLSSettings(keyStoreFilePath = "keyStore.p12", keyStorePassword = "password"),
        port = 8883
    ).listen()
    broker.listen()
}

Authentication code example

fun main() {
    val broker = Broker(authentication = object : Authentication {
        override fun authenticate(clientId: String, username: String?, password: UByteArray?): Boolean {
            // TODO Implement your authentication method    
            return username == "user" && password?.toByteArray()?.decodeToString() == "pass"
        }
    })
    broker.listen() // Blocking method, use step() if you don't want to block the thread
}

Authorization code example

fun main() {
    val broker = Broker(authorization = object : Authorization {
        override fun authorize(
            clientId: String,
            username: String?,
            password: UByteArray?, // != null only if savePassword set to true in the broker constructor
            topicName: String,
            isSubscription: Boolean,
            payload: UByteArray?
        ): Boolean {
            // TODO Implement your authorization method    
            return topicName == "$clientId/topic"
        }
    })
    broker.listen() // Blocking method, use step() if you don't want to block the thread
}

Message interceptor code example

fun main() {
    val broker = Broker(packetInterceptor = object : PacketInterceptor {
        override fun packetReceived(clientId: String, username: String?, password: UByteArray?, packet: MQTTPacket) {
            when (packet) {
                is MQTTConnect -> println(packet.protocolName)
                is MQTTPublish -> println(packet.topicName)
            }
        }
    })
    broker.listen() // Blocking method, use step() if you don't want to block the thread
}

Internal publish code example

fun main() {
    val broker = Broker()
    broker.publish(
        retain = false,
        topicName = "test/",
        qos = Qos.AT_MOST_ONCE,
        properties = MQTTProperties(),
        "testPayload".toByteArray().toUByteArray()
    )
    broker.listen() // Blocking method, use step() if you don't want to block the thread
}

Other advanced functionality

MQTT5 Enhanced Authentication: set the enhancedAuthenticationProviders Broker constructor parameter, implementing the provider interface EnhancedAuthenticationProvider.

Session persistence: set the persistence Broker constructor parameter, implementing Persistence interface.

Bytes metrics: set the bytesMetrics Broker constructor parameter, implementing BytesMetrics interface.