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Installation | Usage | Contributors and developers | Learn more about nteract

enchannel-zmq-backend offers the ZeroMQ backend implementation for enchannel.

Technical overview

As a refresher for the reader, enchannel details nteract's lightweight, implementation-flexible specification for communication between a user frontend and a backend, such as a language kernel. The enchannel specification offers a simple description of "what" messages may be passed between frontends and backends, while leaving a developer freedom in "how" to achieve message communication.

enchannel-zmq-backend takes a classic design approach using ZeroMQ, the foundation messaging protocol for the Jupyter project. enchannel-zmq-backend implements backend support for the messaging channels described in the Jupyter messaging specification. This spec explains how front end clients should communicate with backend language kernels which implement the Jupyter messaging specification.

Our backend

enchannel-zmq-backend implements the "how" to communicate messages to and from a backend.

We provide functions to create RxJS Subjects (two way Observables for four of the channels described in the Jupyter messaging specification):

  • shell
  • control
  • iopub
  • stdin

That's it. Functions for four channels; simplicity in action.


Prerequisite: Node.js and npm

npm install enchannel-zmq-backend


Creating messaging channels

To get access to all of the channels for messaging (shell, control, iopub, and stdin), import and use the createChannels function:

import { createChannels } from 'enchannel-zmq-backend'

The createChannels function accepts two things:

  • an identity

    You'll want to set up your identity, relying on the node uuid package:

    const uuidv4 = require('uuid/v4');
    const identity = uuidv4();
  • a runtime object, such as a kernel (which matches the on-disk JSON). Using spawnteract with this project helps streamline spawning a kernel.

    const runtimeConfig = {
      stdin_port: 58786,
      ip: '',
      control_port: 58787,
      hb_port: 58788,
      signature_scheme: 'hmac-sha256',
      key: 'dddddddd-eeee-aaaa-dddd-dddddddddddd',
      shell_port: 58784,
      transport: 'tcp',
      iopub_port: 58785

To create the channels object:

const channels = createChannels(identity, runtimeConfig)
const { shell, iopub, stdin, control } = channels;

enchannel-zmq-backend also offers four convenience functions to easily create the messaging channels for control, stdin, iopub, and shell :

import {
} from 'enchannel-zmq-backend';

Creating a subject for the shell channel:

const shell = createShellSubject(identity, runtimeConfig)

Subscribing to messages

Here's an example about how to subscribe to iopub messages:

const iopub = createIOPubSubject(identity, runtimeConfig);
var subscription = iopub.subscribe(msg => {

// later, run subscription.unsubscribe()

Since these channels are RxJS Observables, you can use filter, map, scan and many other RxJS operators:

iopub.filter(msg => msg.header.msg_type === 'execute_result')
     .map(msg =>
     .subscribe(x => { console.log(`DATA! ${util.inspect(x)}`)})

Sending messages to the kernel

Executing code will rely on sending an execute_request to the shell channel.

var message = {
  header: {
    msg_id: `execute_9ed11a0f-707e-4f71-829c-a19b8ff8eed8`,
    username: 'rgbkrk',
    session: '00000000-0000-0000-0000-000000000000',
    msg_type: 'execute_request',
    version: '5.0',
  content: {
    code: 'print("woo")',
    silent: false,
    store_history: true,
    user_expressions: {},
    allow_stdin: false,

Currently, you'll need to have at least one subscription activated before you can send on a channel.

> shell.subscribe(console.log)
> Message {
   { username: 'rgbkrk',
     msg_type: 'execute_reply',
     msg_id: '0f6d37f3-56a2-41fd-b3ed-90cc189ac423',
     version: '5.1',
     session: '40472e70-e008-48d1-9537-55837a905c05',
     date: '2016-01-12T00:39:44.686986' },
   { username: 'rgbkrk',
     session: '00000000-0000-0000-0000-000000000000',
     version: '5.0',
     msg_id: 'execute_9ed11a0f-707e-4f71-829c-a19b8ff8eed8',
     msg_type: 'execute_request' },
   { dependencies_met: true,
     engine: '34d73425-4f04-4b57-9bc7-b46e3100e1fd',
     status: 'ok',
     started: '2016-01-12T00:39:44.684534' },
   { status: 'ok',
     execution_count: 60,
     user_expressions: {},
     payload: [] } }

Contributors and developers

ZeroMQ Dependency

If you plan to contribute to this project or extend it, you will need to have ZeroMQ installed on your system. The easiest way to do this is to install nteract's zmq-prebuilt[] binary for your operating system.

Install a local development environment

To set up a development environment, you'll need to install:

Then, fork and clone this repo:

git clone
cd enchannel-zmq-backend
npm install

Develop! We welcome new and first time contributors.

Learn more about nteract

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