Note that the library is experimental, and the API is subject to change. See Implementation status for more information.

Kzmq is a Kotlin multi-platform ZeroMQ library. It supports four backend engines:

• CIO, a pure Kotlin coroutine-based implementation (using ktor-network),
• JeroMQ, a pure Java implementation of ZeroMQ,
• ZeroMQjs, a Node.JS addon implementation of ZeroMQ,
• Libzmq, the main native implementation of ZeroMQ.

Getting started

Simple example

Here is how you might implement a server that prints the messages it receives and responds to them with "Hello, world!":

import kotlinx.coroutines.*
import org.zeromq.*

suspend fun main() = coroutineScope {
  // Create a ZeroMQ context (with an auto-discovered engine)
  Context().use { context ->
    // Create a "Reply" socket to talk to clients
    context.createReply().apply {
      bind("tcp://localhost:5555")
    }.use { socket ->
      while (isActive) {
        // Suspend until a message is received
        val content = socket.receive {
            readFrame { readString() }
        }

        // Print the message
        println(content)

        // Send a response back
        socket.send {
            writeFrame("Hello, $content!")
        }
      }
    }
  }
}

More examples

For now, you can look at the test suite.

Documentation

You can generate the Kdoc documentation by running the dokkaHtmlMultiModule gradle task.

Engines

Kzmq supports four backend engines:

• CIO, a pure Kotlin coroutine-based implementation (using ktor-network),
• JeroMQ, a pure Java implementation of ZeroMQ,
• ZeroMQjs, a Node.JS addon implementation of ZeroMQ,
• Libzmq, the main native implementation of ZeroMQ.

The tables below might help you choose an engine depending on your needs.

We support auto-discovery of engines. See Using in your projects for more information.

Targets

Target/Engine	CIO	JeroMQ	ZeroMQjs	Libzmq
JVM	Y	Y
Node.JS			Y
Native	Y			Y

Transports

Transport/Engine	CIO	JeroMQ	ZeroMQjs	Libzmq
tcp://	Y	Y	Y	Y
ipc://	Y (♭)		Y	Y
inproc://	Y (♯)	Y (♯)	Y (♯)	Y (♯)

(♭) Supported on Native. Requires JVM >= 16 for the JVM target.

(♯) Each engine only supports the inproc transport with itself.

Protocol Version

Protocol/Engine	CIO	JeroMQ	ZeroMQjs	Libzmq
ZMTP 3.0	Y	Y	Y	Y
ZMTP 3.1	Y (♭)			Y (♭)

(♭) New ZMTP 3.1 sockets are not yet supported

Implementation status

Note that the library is experimental, and the API is subject to change.

Engine	CIO	JeroMQ	ZeroMQjs	Libzmq
Status	Experimental	Experimental	Experimental	Work in progress

Using in your projects

Note that the library is experimental, and the API is subject to change.

This library is published to Maven Central.

Gradle

Repository

• First, add the Maven Central repository if it is not already there:

repositories {
    mavenCentral()
}

• Add the API package to your commonMain source-set dependencies (or to a particular target source-set dependencies, if you only need it on that target):

kotlin {
    sourceSets {
        commonMain {
            dependencies {
                implementation("org.zeromq:kzmq-core:0.1.0")
                implementation("org.jetbrains.kotlinx:kotlinx-io-core:0.5.1")
            }
        }
    }
}

• Then add one or more engine packages to their corresponding source-sets.

In case you are lost, you can read more about multiplatform projects.

CIO engine

The CIO engine supports only the JVM and native targets. Add the CIO engine package to your commonMain source-set dependencies (or to a particular target source-set dependencies):

kotlin {
    sourceSets {
        commonMain {
            dependencies {
                implementation("org.zeromq:kzmq-engine-cio:0.1.0")
            }
        }
    }
}

JeroMQ engine

The JeroMQ engine supports only the JVM targets. Add the JeroMQ engine package to your jvmMain source-set dependencies:

kotlin {
    sourceSets {
        jvmMain {
            dependencies {
                implementation("org.zeromq:kzmq-engine-jeromq:0.1.0")
            }
        }
    }
}

ZeroMQ.js engine

The ZeroMQ.js engine supports only the Node.js targets. Add the ZeroMQ.js engine package to your jsMain source-set dependencies:

kotlin {
    sourceSets {
        jsMain {
            dependencies {
                implementation("org.zeromq:kzmq-engine-zeromqjs:0.1.0")
            }
        }
    }
}

Libzmq engine

The Libzmq engine supports only the native targets. Add the Libzmq engine package to your nativeMain source-set dependencies:

kotlin {
    sourceSets {
        nativeMain {
            dependencies {
                implementation("org.zeromq:kzmq-engine-libzmq:0.1.0")
            }
        }
    }
}

Building

Native build

In order to build for native targets, you need to have the development package for libzmq (e.g. zeromq-devel on Fedora, or libzmq3-dev on Ubuntu).