Simple, flexible message hub using websockets
Last updated a month ago by poelstra .
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MHub message server and client


MHub is a simple, flexible message bus using a JSON-based protocol. It natively supports websockets, but also 'plain' TCP ports.

Because both the protocol and the messages use JSON, this makes it very powerful, yet still simple enough to be directly implemented in e.g. a microcontroller.

It can be used as a lightweight Javascript-only alternative to e.g. RabbitMQ or MQTT.

This project provides:

  • a message broker (mhub-server) for loosely coupling software components
  • accompanying command-line tools (mhub-client) for interacting with the server and
  • a library for communicating with the server using Javascript.

Packages using MHub

It's successfully powering my home automation for a few years now.



The purpose of an MHub server (mhub-server) is to pass messages between connected clients.

A message consists of a topic and optionally data and/or headers.

The topic of a message typically represents e.g. a command or event, like clock:arm, twitter:add or /home/lights/kitchen.

Data can be the countdown time, tweet to add, light value, etc. It can be anything that's valid in JSON.

Headers are for more advanced uses of the system, e.g. to support sending messages between multiple brokers, but also e.g. to mark certain messages to be persistent (i.e. any future subscriber will also receive it, see HeaderStore below).

Publish / subscribe (pubsub)

MHub (like many other message busses) supports the concept of publishing messages and subscribing to topics (aka 'pubsub').

For example, a client that subscribes to all messages with the topic pattern twitter:*, will receive messages published by other clients with topics such as twitter:add or twitter:remove.

Any client can both publish messages and subscribe to other messages. (Note: messages sent by a client will also be received by that client if it matches one of its subscriptions).

The topic format is free-form, and pattern matching is done by minimatch. So, depending on the needs and preferences of your applicatino, topics can look like someThing, some:thing, some/thing, /some/thing/, etc.

For example, in my home automation system I'm using topics like:

  • /home/lights/kitchen, /home/lights/table, etc: dimmer values for lights
  • /home/scene: string value with the name of a scene to switch to (e.g. "dinner", "off", etc)
  • /dev/rfhub/rx, /dev/rfhub/tx: received RF events and RF commands to be transmitted (for controlling lights)

Nodes and bindings

An MHub server (mhub-server) instance contains one or more nodes, on which messages can be published or retrieved.

In many cases, the default node will suffice, but to allow for more flexibility on larger systems, it is possible to define additional nodes.

For example, this mechanism can be used to:

  • route tweets to an 'unmoderated' node first, pass through some moderator system, then send them through to a 'moderated' node (which then can have bindings to other nodes that are interested in these tweets, e.g. display nodes).
  • route a subset of all messages from an mhub-server on the local network to an mhub-server on the Internet, e.g. for consumption by a public website.
  • route team scores to both a video overlay display and dedicated score displays in other areas, but only route the show/hide commands of the scores view to the video overlay, such that the dedicated displays keep displaying their scores.
  • create a firehose node that emits all 'non-confidential' messages for display on a public screen somewhere (we're targetting tech-events, right?).

For such larger systems, it is a good idea to assign every application instance in the system (video display controller, video display, pit area display controller, pit area display, scores subsystem, etc.) its own node.

Bindings then make it possible to selectively route certain messages (based on their topic) between different nodes. A binding (optionally based on a topic pattern, like subscriptions), forwards all (matching) messages from its source node to its destination node.

These bindings can either directly be specified in the mhub-server configuration (for routing between nodes on the same server), or through an external program such as mhub-relay (for routing between nodes on the same, and/or different servers).

Basic installation and usage

To install and run the server:

npm install -g mhub

You'll now have an MHub server listening on port 13900 for websocket connections, and 13902 for 'raw' TCP connections.

Start an mhub-client in listen mode on the default node:

mhub-client -l

In another terminal, publish some messages:

mhub-client -t /some/topic
mhub-client -t /some/topic -d 42
mhub-client -t /some/topic -d '"a message"'
mhub-client -t /some/topic -d '{"some": "object"}'
mhub-client -t /some/topic -d 123 -h '{"keep": true}'

Note how the data and header parameters accepts any JSON input, so it must be properly quoted on the shell.

You'll see them turn up in the first terminal as:

Message { topic: '/some/topic', data: undefined, headers: {} }
Message { topic: '/some/topic', data: 42, headers: {} }
Message { topic: '/some/topic', data: 'a message', headers: {} }
Message { topic: '/some/topic', data: { some: 'object' }, headers: {} }
Message {
  topic: '/some/topic',
  data: { persistent: 'message' },
  headers: { keep: true } }
Message { topic: '/some/topic', data: 123, headers: { keep: true } }

If you restart the listening MHub client (mhub-client -l), you'll now immediately get:

Message { topic: '/some/topic', data: 123, headers: { keep: true } }

Note how the message with 'keep: true' is automatically redelivered. Read more about this at the HeaderStore node type, below.

mhub-client commandline interface

The mhub-client commandline tool can be used to both listen for messages, or to publish messages. See mhub-client --help for available commandline parameters:

$ mhub-client --help
Listen mode:
  mhub-client [-n <nodename>] -l [-p <topic_pattern>] [-o <output_format>]
Post mode:
  mhub-client [-n <nodename>] -t <topic> [-d <json_data>] [-h <json_headers>]
Pipe mode:
  mhub-client [-n <nodename>] -t <topic> -i <input_format> [-h <json_headers>]

Use -s [protocol://]<host>[:<port>] to specify a custom server/port.
To use SSL/TLS, use e.g. -s wss://your_host.
For self-signed certs, see --insecure.

  --help          Show help                                            [boolean]
  -s, --socket    WebSocket to connect to, specify as [protocol://]host[:port],
                  e.g. ws://localhost:13900, or wss://localhost:13900
                                [string] [required] [default: "localhost:13900"]
  -n, --node      Node to subscribe/publish to, e.g. 'test'
                                        [string] [required] [default: "default"]
  -l, --listen    Select listen mode                                   [boolean]
  -p, --pattern   Topic subscription pattern as glob, e.g. 'twitter:*'  [string]
  -o, --output    Output format, can be: human, text, jsondata, json
                                                     [string] [default: "human"]
  -t, --topic     Message topic                                         [string]
  -d, --data      Optional message data as JSON object, e.g. '"a string"' or '{
                  "foo": "bar" }'                                       [string]
  -h, --headers   Optional message headers as JSON object, e.g. '{ "my-header":
                  "foo" }'                                              [string]
  -i, --input     Read lines from stdin, post each line to server.
                  <input_format> can be: text, json                     [string]
  --insecure      Disable server certificate validation, useful for testing
                  using self-signed certificates                       [boolean]
  --key           Filename of TLS private key (in PEM format)           [string]
  --cert          Filename of TLS certificate (in PEM format)           [string]
  --ca            Filename of TLS certificate authority (in PEM format) [string]
  --passphrase    Passphrase for private key                            [string]
  --pfx           Filename of TLS private key, certificate and CA certificates
                  (in PFX or PKCS12 format). Mutually exclusive with --key,
                  --cert and --ca.                                      [string]
  --crl           Filename of certificate revocation list (in PEM format)
  --ciphers       List of ciphers to use or exclude, separated by :     [string]
  -U, --username  Username                                              [string]
  -P, --password  Password. Note: sent in plain-text, so only use on secure
                  connection. Also note it may appear in e.g. `ps` output.
  -v, --version   Show version number                                  [boolean]

Listening for messages

Using mhub-client, listen mode is initiated with the -l parameter.

In the default (human-friendly) format, short messages are printed on a single line, but larger messages will wrap across multiple lines. See below for options to change this.

To simply listen for all messages on the default topic, use:

mhub-client -l

To listen for all messages on another node use e.g.:

mhub-client -l -n somenode

To only receive messages with a certain topic use e.g.:

mhub-client -l -n ping -p 'ping:*'

(Tip: use the bundled mhub-ping program to do a quick round-trip time measurement.)

By default, all messages are printed in a somewhat human-readable format, which is not suitable for consumption by other programs. However, a number of output options are available to simplify this:

  • human (default): Outputs raw messages, but mostly without quotes
  • text: Outputs just the data field of a message as text. Useful when listening to a single topic that only contains string data. Note: if data is an object, it will still be printed in human-readable format, and may thus span multiple lines.
  • json: Outputs the full message as JSON. Every message is guaranteed to be printed on its own line, and contains all info in the message (topic, headers and data).
  • jsondata: Outputs just the data field of a message. Every message is guaranteed to be printed on its own line. Useful when listening to just a single topic with complex data.

Publishing single messages

Publishing a single message can be done by specifying the -t option (and not passing -l nor -i).

To publish a message without data to the default topic, use e.g.:

mhub-client -t test:something

Again, the -n option can be used to specify a custom node.

mhub-client -n ping -t ping:request

To pass data (and/or headers) to a message, it needs to be specified as JSON. This means that e.g. a number can be specified directly as e.g. 42, but a string needs to be enclosed in double-quotes (e.g. "something"). Note that shells typically parse these quotes too, so they will need to be escaped.

For example:

# On *nix shell:
mhub-client -t my:topic -d '"some string"'
mhub-client -t my:topic -d '{ "key": "value" }'
# On Windows command prompt:
mhub-client -t my:topic -d """some string"""
mhub-client -t my:topic -d "{ ""key"": ""value"" }"

Publishing multiple messages / streaming from other programs

It is possible to 'stream' messages to the bus by using the -i option. Available input formats are:

  • text: Every line of the input is sent as a string in the message's data field.
  • json: Every line of the input is parsed as a JSON object, and used as the message's data field.

Example to stream tweets into an mhub-server, using the tweet command from node-tweet-cli.

tweet login
tweet stream some_topic --json | mhub-client -t twitter:add -i json

Advanced message routing and transformations

The above examples all use the bundled commandline tools to achieve simple message routing.

For more advanced scenario's you can use e.g.:

  • MHub for Node-RED: a visual programming tool for the Internet of Things
  • mhub-relay: allows you to connect to one or more MHub servers, subscribe to nodes, optionally transform messages (using simple JavaScript functions), and publish them to other nodes.

Customizing server nodes and bindings

To customize the available nodes and bindings, create a copy of server.conf.json, edit it to your needs and start the server as:

mhub-server -c <config_filename>

Note: the pattern in a binding can be omitted, in which case everything will be forwarded.

Note: don't edit the server.conf.json file directly, because any changes to it will be lost when you upgrade mhub. Edit a copy of the file instead.

Debug logging

To assist in debugging message routing, start the server as:

mhub-server -l debug

Or set the logging option in the config file to "debug":

// In server.conf.json:
    "logging": "debug" // or: none, fatal, error, warning, info (default)

This will show incoming commands, message routing and outgoing commands, and adds timestamps to each line.

Note: enabling debug mode will slow down message processing, especially on a Windows console. Don't expect your 60fps mouse tracking to work then.

Node types

MHub supports different types of nodes.

The default configuration has a node named default, which is configured as a HeaderStore. This is likely all you need for many applications.

You can configure custom nodes in the nodes property of the server configuration as an object of { node_name: node_definition } pairs as:

// In server.conf.json:
    "nodes": {
        "nodename1": "TypeWithoutOptions",
        "nodename2": {
            "type": "TypeWithOptions",
            "options": {
                /* configuration options for this type of node */
    /* rest of configuration file */

For examples, see the packaged server.conf.example.json.

Currently available node types and their options:

  • Exchange: Simplest node type. Broadcasts any incoming message to all subscribed clients (taking their pattern into account, of course).
  • HeaderStore: Forwards all messages (like Exchange), but depending on a message's keep header, can also store messages when new subscribers arrive later, also when the server is restarted. This is useful for storing the last state of a switch, (simple) configuration data (e.g. URLs of JSON APIs), etc. If a message's keep header is true, the message will be stored, overwriting any previously stored message for its topic. If keep is false, previous message for this topic is cleared (but message is still forwarded). Note: if keep is not present, message will be forwarded, but any previously stored message (if any) will NOT be affected.
    • persistent?: boolean: Whether to persist this queue to disk (default true)
  • Queue: Forwards incoming messages to all subscribed clients (like an Exchange), but also stores a configurable number of messages. A new subscriber will receive all currently stored messages. Useful for e.g. chat applications, list last X tweets, etc. Optionally, a pattern can be given to limit which message topics will be remembered. Additionally, the queue can be persisted to disk, such that it survives mhub-server restarts. Configuration options:
    • capacity?: number: Number of messages to keep (default 10)
    • pattern?: string | string[]: Which messages (filtered by topic) to keep (default all)
    • persistent?: boolean: Whether to persist this queue to disk (default false)
  • TopicStore: Forwards all messages, but also stores the last message for each topic. New subscribers will receive that last message (and any future state) of the topics. Useful for storing (simple) configuration data (e.g. URLs of JSON APIs), initializing all connecting displays to the same state, etc. To 'delete' a topic from storage, send a message without any data (payload). Note: this means that a message will always need to have some sort of data in order to be stored by a TopicStore. Note: this node is deprecated in favor of the HeaderStore. Again, a topic pattern can be given, and the queue can be persisted to disk.
    • pattern?: string | string[]: Which messages (filtered by topic) to keep (default all)
    • persistent?: boolean: Whether to persist this queue to disk (default false)
  • ConsoleDestination: Debug helper that logs all messages published to it, to the console.
  • PingResponder: Useful to measure round-trip response times. When it receives a message with topic ping:request, it will respond with a message with topic ping:response and the same payload as it received in the request. This type of node is set up by default in the packages configuration, on a node called ping.
  • TestSource: Source of periodic test messages. Configured by default in the packaged configuration as node blib.
    • topic?: string: Topic for the test messages (default "blib")
    • interval?: number: Delay between messages (in ms, default 5000)

For backward compatibility, it's also possibly for nodes to be an array of node names, in which case all these nodes are created as Exchange nodes.

Configuring transports (protocols / ports)

mhub-server natively supports a JSON-based protocol, which is by default served over WebSockets (port 13900). It can also be configured for websockets over https on port 13901.

Additionally, the same JSON-based protocol is also available on a 'raw' TCP (by default on port 13902), where each protocol command/response is transferred as one UTF-8 encoded JSON string per line, each line terminated by a newline (\n, ASCII code 10). This allows easy integration with platforms that don't support WebSockets.

To configure which ports and transports mhub-server uses, use the listen field in server.conf.json. It accepts either a single object or an array of objects that describe one or more transports to be used.

See the configuration file and the next section for examples on setting it up.

Using TLS / SSL

To enable TLS / SSL on the server (wss:// instead of ws://), you can change your server configuration to look like:

// In server.conf.json:
    "listen": [
            "type": "websocket",
            "port": 13901,
            "key": "key.pem",
            "cert": "cert.pem"
    /* rest of configuration follows */

Note that the recommended port for MHub over secure websockets is 13901. Also note that it is possible to enable both transports simultaneously by passing more than one configuration object to the listen array.

This will still allow any client to connect. To only allow trusted clients to connect, use something like:

// In server.conf.json:
    "listen": [
            "type": "websocket",
            "port": 13901,
            "key": "key.pem",
            "cert": "cert.pem",
            "ca": "ca.pem", // Can be omitted to use system's default
            "requestCert": true,
            "rejectUnauthorized": true
    /* rest of configuration follows */

See for details on the supported options. Options that accept a Buffer (or array of Buffers) need to be specified as filename(s) in the configuration file.

For testing purposes, it can be useful to look at certificates for localhost. When using these, use { "type": "websocket", "port": 13901, "key": "privkey.pem", "cert": "fullchain.pem" }.

On mhub-client, to enable TLS, specify a wss:// URL. To use client certificates, either pass --key, --cert and --ca options, or the --pfx option.

Note: when using a self-signed server certificate, the client will refuse to connect ([Error: self signed certificate] code: 'DEPTH_ZERO_SELF_SIGNED_CERT'). In that case, either pass the server's certificate to --ca, or (for testing purposes), use the --insecure option to ignore these errors.

Access control

By default, everyone is allowed to connect, publish and subscribe to all available MHub nodes and topics.

MHub supports simple username/password authentication to lock this down.

It is advised to only use these on secure (e.g. wss://) connections, as the username and password are sent in plain text.


To configure users, add a users key to server.conf.json. It can either be a string which points to a JSON file (relative paths resolved to the location of the config file) containing an object of { "username": "password" } pairs, or such an object can be directly given in the config file itself.

Example for inline users:

// server.conf.json
    "users": {
        "martin": "somePassword"

Example for linking to a users file:

// server.conf.json
    "users": "/path/to/users.json"
// users.json
    "martin": "somePassword"

The commandline tools (mhub-client, mhub-ping) support -U and -P options to pass a username and password. Be advised that the commandline (and thus password) may be visible to other users on the system through e.g. ps. The MHub client library has a login() method.


Then, add a rights section to server.conf.json that specifies the rights (publish, subscribe) for each user, and the anonymous user (denoted by the empty string).

Rights can be specified per user, as:

  • a boolean: true (allow everything) or false (allow nothing, which is the default)
  • an object with permissions per action (publish, subscribe), which can again be specified as:
    • a boolean (allow/deny publish/subscribe in general)
    • a map of node-permissions, which again can be given as:
      • a boolean (allow/deny everything on this node, deny being the default already)
      • a topic pattern, or array of patterns to allow

For example:

// server.conf.json
    "rights": {
        "": { // Anonymous/guest
            "subscribe": true,
            "publish": false
        "admin": true, // allow everything
        "martin": {
            "subscribe": true, // allow all subscriptions
            "publish": {
                "someNode": true, // allow publishing all topics to node "someNode"
                "otherNode": "/some/**", // allow e.g. "/some/foo/bar" on "otherNode"
                "default": ["/some/**", "/other"] // allow e.g. "/some/foo/bar" and "/other"

Note: for backward compatibility and ease of use in the simple case, if both users and rights are omitted, everyone will have publish and subscribe rights! (If only one of them is given, no-one has access.)

When a user tries to publish to a node/topic without having access, the command will return an error (i.e. it will not silently fail).

When a user tries to subscribe to a node that is explicitly denied (or the user is not allowed to subscribe at all), the subscribe will fail. This also prevents a user from finding out whether a certain node exists, at all.

However, when a user subscribes to a node which is protected by a pattern, the subscribe will succeed, although depending on the subscription pattern, no message may ever be received on it.

For example:

// In server.conf.json:
    "rights": {
        "testUser": {
            "subscribe": {
                "node1": false,
                "node3": true,
                "node4": "/foo/**",
                "node5": ["/foo/**", "/bar"]
// Examples (note: no pattern means match everything)
client.subscribe("node1") -> access denied
client.subscribe("node2") -> access denied
client.subscribe("node3") -> ok, can receive everything on this node
client.subscribe("node4") -> ok, but will only receive topics matching "/foo/**"
client.subscribe("node4", "/foo/bar/baz") -> ok, will only match "/foo/bar/baz"
client.subscribe("node4", "/bar") -> ok, but will never match anything
client.subscribe("node5", "/bar") -> ok, will only match "/bar"

Using MHub client from Javascript

In Node.JS, simply npm install --save mhub in your package, then require the client interface as e.g.:

// ES6
import MClient from "mhub";
// ES5 (commonjs)
var MClient = require("mhub").MClient;

Example usage of subscribing to a node and sending a message:

var MClient = require("mhub").MClient;
var client = new MClient("ws://localhost:13900");
client.on("message", function(message) {
    console.log(message.topic,, message.headers);
client.connect().then(function() {
    client.subscribe("blib"); // or e.g. client.subscribe("blib", "my:*");
    client.publish("blib", "my:topic", 42, { some: "header" });

When an error occurs (e.g. the connection is lost), the error will be emitted on the error event.

It is possible (and advisable) to also listen for the close event to reconnect (after some time) to the server in case the connection is lost. Note: any subscriptions will have to be recreated upon reconnection.

For use in the browser, a native WebSocket version is available as import MHubClient from "mhub/dist/src/browserclient");, which can then be bundled using e.g. browserify or webpack. This client has the same interface as the Node.JS version, and will be moved to its own package at a later stage.

API doc for MClient:

 * MHub client.
 * Allows subscribing and publishing to MHub server nodes.
 * @event open() Emitted when connection was established.
 * @event close() Emitted when connection was closed.
 * @event error(e: Error) Emitted when there was a connection, server or protocol error.
 * @event message(m: Message) Emitted when message was received (due to subscription).
export declare class MClient extends events.EventEmitter {
    private _transactions;
    private _seqNo;
    private _socket;
    private _url;
    private _options;
    private _idleTimer;
    private _connected;
     * Create new connection to MServer.
     * @param url Websocket URL of MServer, e.g. ws://localhost:13900
     * @param options Optional TLS settings and other options (see
     *        for the TLS settings, and `MClientOptions` for other options)
    constructor(url: string, options?: MClientOptions);
     * Current Websocket, if any.
     * @return {ws} Websocket or `undefined`
    readonly socket: ws;
    readonly url: string;
     * Connect to the MServer.
     * If connection is already active or pending, this is a no-op.
     * Note: a connection is already initiated when the constructor is called.
    connect(): Promise<void>;
     * Disconnect from MServer.
     * Pending requests will be rejected with an error.
     * If already disconnected, this becomes a no-op.
     * Note: any existing subscriptions will be lost.
     * Optionally pass an error to signal abrupt failure,
     * forcefully terminating the connection.
     * The same error will be used to reject any pending
     * requests.
     * @param error (optional) Error to emit, reject transactions with, and
     *              forcefully close connection.
    close(error?: Error): Promise<void>;
     * Login to server using username/password.
     * Warning: the username and password are sent in plain text.
     * Only use this on secure connections such as wss://.
     * @param username Username.
     * @param password Password.
    login(username: string, password: string): Promise<void>;
     * Subscribe to a node. Emits the "message" event when a message is received for this
     * subscription.
     * @param nodeName Name of node in MServer to subscribe to (e.g. "default")
     * @param pattern  Optional pattern glob (e.g. "namespace:*"), matches all messages if not given
     * @param id       Optional subscription ID sent back with all matching messages
    subscribe(nodeName: string, pattern?: string, id?: string): Promise<void>;
     * Unsubscribe `pattern` (or all if omitted) from given `node` and `id`.
     * Subscription id "default" is used if `id` is omitted.
     * @param nodeName Name of node in MServer to unsubscribe from (e.g. "default")
     * @param pattern  Optional pattern glob (e.g. "/some/foo*"). Unsubscribes all (on `node` and `id`)
     *                 if omitted.
     * @param id       Subscription ID, or "default"
    unsubscribe(nodeName: string, pattern?: string, id?: string): Promise<void>;
     * Publish message to a node.
     * @param nodeName Name of node in MServer to publish to (e.g. "default")
     * @param topic Message topic
     * @param data  Message data
     * @param headers Message headers
    publish(nodeName: string, topic: string, data?: any, headers?: Headers): Promise<void>;
     * Publish message to a node.
     * @param nodeName Name of node in MServer to publish to (e.g. "default")
     * @param message Message object
    publish(nodeName: string, message: Message): Promise<void>;
     * Ping server.
     * Mostly used to check whether connection is still alive.
     * Note that the client will automatically send pings in the
     * absence of other communication, so there should be no need to
     * manually send pings.
     * @param timeout (optional) Timeout in milliseconds before rejecting
     *                the promise with an error, or infinite if not given.
    ping(timeout?: number): Promise<void>;

 * Options to be passed to MClient constructor.
export interface MClientOptions extends TlsOptions {
     * When true, will not automatically connect in the
     * constructor. Connect explicitly using `#connect()`.
    noImplicitConnect?: boolean;
     * Number of milliseconds of idleness (i.e. no data
     * transmitted or received) before sending a ping to
     * the server. If it doesn't respond within that same
     * interval, the connection is closed with an error.
     * Use 0 to disable.
    keepalive?: number;

export interface TlsOptions {
    pfx?: string | Buffer;
    key?: string | string[] | Buffer | Buffer[];
    passphrase?: string;
    cert?: string | string[] | Buffer | Buffer[];
    ca?: string | string[] | Buffer | Buffer[];
    crl?: string | string[] | Buffer | Buffer[];
    ciphers?: string;
    honorCipherOrder?: boolean;
    requestCert?: boolean;
    rejectUnauthorized?: boolean;
    NPNProtocols?: string[] | Buffer;
    ALPNProtocols?: string[] | Buffer;

API doc for Message (implemented as a class for convenient construction):

 * Headers are key-value pairs that carry meta-information
 * about a message.
export interface Headers {
    [name: string]: string | boolean | number;

 * Interface describing what a 'raw' object should look like
 * if it is to be converted to a Message using `Message.fromObject()`.
export interface MessageLike {
    topic: string;
    data?: any;
    headers?: Headers;

 * Message to be sent or received over MHub network.
export declare class Message {
     * Create a Message object from a plain object, by taking its topic, data and
     * headers properties.
     * Note that the data is not deep-cloned.
     * @param o Input object. Must at least contain a `.topic` property.
     * @return New `Message` instance, with given topic, same data, and clone of headers.
    static fromObject(o: MessageLike): Message;
     * Topic of message.
     * Can be used to determine routing between pubsub Nodes.
    topic: string;
     * Optional message data, can be null.
     * Must be JSON serializable.
    data: any;
     * Optional message headers.
    headers: Headers;
     * Construct message object.
     * Note: headers are cloned, but data is NOT cloned, so don't change data after you've
     * passed it to the pubsub framework!
    constructor(topic: string, data?: any, headers?: Headers);
     * Perform a shallow clone of the message.
     * I.e. the new message will share the same `data` as the source message,
     * so be careful when the data is an object: making changes to it will be
     * reflected in the old and new message.
     * The headers (if any) are cloned into a new headers object.
     * @return New message with same topic, same data and shallow clone of headers.
    clone(): Message;
     * Validate correctness of message properties, e.g. that topic is a string,
     * and header is either undefined or key-values.
    validate(): void;

Note: Message is not directly used on the wire, it is only used to pass to e.g. client.publish() and received for subscriptions. Use e.g. Message.fromObject() to convert a plain (JSON) object into an instance of Message.

Integrating MHub server into your application

It's possible, and easy, to integrate an MHub server into your own application. For example, to have a websocket server hosted on the same port as your API webserver.

See src/example/custom-server.ts for a fully functional example.

Basically, you instantiate a Hub, and connect transports (TCP, websocket, etc.) to it, like:

const authenticator = new PlainAuthenticator(); // or your own Authenticator implementation
const hub = new Hub(authenticator);
hub.add(new HeaderStore("default"));
await hub.init();

const httpServer = http.createServer();
// ... insert your Express API code here ...

const wss = new ws.Server({ server: httpServer });
let connectionId = 0;
wss.on("connection", (conn: ws) =>
    new WSConnection(hub, conn, "websocket" + this.connectionId++)


There's also a LocalClient which behaves exactly like a 'normal' networked client, but directly connects to the hub. This allows easy access to the hub from e.g. your API backend code.

Wire protocol

MHub typically uses JSON messages over websockets, or a line-based TCP socket.

Both transports transfer UTF-8 encoded JSON strings. In the case of WebSockets, these are already packetized by the WebSocket protocol. In case of 'raw' TCP sockets, each string is sent or received per line, separated by newlines (\n, ASCII code 10).

Every 'raw' JSON message is an object, with a type field to distinguish different commands and responses to/from MHub.

The currently supported commands and responses are documented in src/protocol.ts, but here's a quick how-to on basic communication.

Minimal publish command

The minimal command to publish an MHub message, is e.g.:

    "type": "publish",
    "node": "default",
    "topic": "myTopic"

This will post a message without data (payload), and without any feedback from the server (except if an error occurs).

To post a message with data, add the data field:

    "type": "publish",
    "node": "default",
    "topic": "clock:arm",
    "data": {
        "countdown": 150

Sequence numbers / acks

You'll typically want to know whether your message was received in good order, so in order to do that, you can add a seq field (sequence number) to the message. Note that the sequence number should be a unique number (at least unique across any outstanding requests).

For example, when sending:

    "type": "publish",
    "node": "default",
    "topic": "myTopic",
    "seq": 0

the server will respond with:

    "type": "puback",
    "seq": 0

or with e.g.

    "type": "error",
    "message": "some error message here",
    "seq": 0

When sending a command with a sequence number, the server will always respond with a response having that same sequence number (either an ack, or an error).

The only cases where the server will never send a sequence number are:

  • messages received on a subscription (you'll get your subscription ID instead)
  • errors that are not (or could not be) related to a specific command
  • gratuitous pingack's, which may be sent by a future implementation of the server to check whether the connection is still alive

Subscribing to nodes

To start receiving messages, you can subscribe to a node. To simply receive all messages from node test, the minimal message would be:

    "type": "subscribe",
    "node": "test"

The server will then start sending you responses such as:

    "type": "message",
    "topic": "myTopic",
    "headers": {},
    "subscription": "default"

Again, it's probably best to include a sequence number in the subscribe command in order to get feedback about its success or failure.

It's also possible to set a pattern, such that only matching topics will be forwarded to the client.

Additionally, it's possible to provide an id in the subscribe command that will be echoed as the subscription field in each message response. This is useful if different parts of your application have different subscriptions, and you want to route these responses to the relevant part of your application. (Note: the same ID can be used for multiple subscriptions, e.g. to subscribe to different nodes.)

For example:

    "type": "subscribe",
    "node": "test",
    "pattern": "my*",
    "id": "someID",
    "seq": 1

Use the unsubscribe command to unsubscribe from some or all previously subscribed patterns. Like subscribe, you can use node, pattern, id and seq. See src/protocol.ts for a detailed description of the exact behaviour.


All feedback and contributions are welcome!

Be sure to Star the package if you like it, leave me a mail, submit an issue, etc.

git clone
cd mhub
npm install
npm test
# or run `npm run watch` for continuous compilation+running

The package is developed in Typescript, which adds strong typing on top of plain Javascript. It should mostly be familiar to Javascript developers.

You can edit the .ts files with any editor you like, but to profit from things like code-completion and inline documentation, I recommend using Visual Studio Code. If you like SublimeText, use e.g. Microsoft's Typescript plugin.

For other editors, to get automatic compilation and live-reload, run npm watch.

Please run npm test (mainly tslint for now, other tests still pending...) before sending a pull-request.


The list below shows notable changes between each release. For details, see the version tags at GitHub.

2.1.0 (2020-04-21):

  • authentication: Allow asynchronous authentication backend (#19), thanks to @rikkertkoppes
  • server: Export most types to allow easy embedding of MHub (server) in your own app, add docs and example source code on how to do it
  • all: Upgrade dependencies to latest versions (incl Typescript)

2.0.0 (2019-07-20):

  • all: Switch to native promises (breaking change because any returned promise now e.g. doesn't have methods like .return() or .delay() anymore)

1.0.1 (2019-07-19):

  • package: Update WS and other packages to address security warnings.

1.0.0 (2019-06-05):

  • protocol: Add unsubscribe command
  • server: Implement HeaderStore and use it for default node
  • server: Remove test nodes from server.conf.json, but keep ping and heartbeat (renamed from blib).
  • all: various bugfixes and huge refactoring of the code base, thanks @rikkertkoppes!

0.9.1 (2017-08-18):

  • mhub-server: Fix TLS server on newer versions of Node.

0.9.0 (2017-08-12):

  • mhub-server: Add fine-grained permission control: publish/subscribe rights per node/topic(-pattern)
  • mhub-server: Switch to micromatch iso minimatch (mostly drop-in, but may have subtle changes for intricate patterns)
  • message: clone() and fromObject() now make shallow clone of headers (NOT data)
  • client: Add preliminary browser client (import MHubClient from "dist/src/browserclient"). Note: API may change, will likely move to dedicated package in future.
  • all: Update to TS 2.4.2, enabled strict null-checks

0.8.0 (2017-02-25):

  • protocol: Add plaintext username/password authentication
  • mhub-server: Add users and publish/subscribe permissions
  • MClient: connect() and close() now return promises
  • MClient: fix closing while DNS lookup still in progress

0.7.1 (2017-01-20):

  • mhub-server: Handle multiple simultaneous lines received on raw tcp socket

0.7.0 (2016-11-11):

  • mhub-server / MClient: implement ping command
  • mhub-server: better handling of unknown messages
  • MClient: Events now emitted asynchronously
  • MClient: unhandled errors in event handlers will crash your program
  • MClient: automatic (configurable) keep-alive checking (e.g. for network disconnects)
  • MClient: don't emit close when connection was never established (e.g. on connection failure)
  • MClient: option to not start connecting in constructor

0.6.0 (2016-10-29):

  • mhub-server: Add logging option to config file, defaults to info, deprecates verbose
  • mhub-server: Add -l <level> commandline option to override log level
  • MClient: Fix crash when tlsOptions object isn't given
  • MClient: Only emit generic error event when it's not specific to a certain request, allows to gracefully handle e.g. subscription to non-existing node
  • MClient: Use ts-promise instead of native Promises

0.5.0 (2016-07-23):

  • mhub-server: 'Raw' TCP support added (line-based JSON), default on port 13902
  • mhub-server: Multi-transport support added (e.g. websockets + secure websockets + raw TCP)
  • Default / recommended port for secure websockets changed to 13901
  • mhub-server: TopicState renamed (again) to TopicStore, old name still works

0.4.0 (2016-07-19):

  • mhub-server: TopicQueue was renamed to TopicState to better reflect its meaning
  • mhub-server: No longer send acks when no sequence number was given in the request
  • Document all protocol commands/responses and their fields in src/protocol.ts and provide quick how-to in Readme

0.3.4 (2016-07-16):

  • mhub-server: Implement various node types (Exchange (old default), Queue, TopicQueue)
  • mhub-server: Implement optional persistent storage for queues

0.3.3 (2016-07-04):

  • Add TLS support
  • mhub-server: Move port option to listen option (old one still works, but is deprecated)
  • mhub-server: Add verbose option to config (default true)

0.3.2 (2016-06-30):

  • Rename m{client,ping,server} to mhub-{client,ping,server} (old names still work, but are deprecated)
  • Publish TS sources in NPM package (for source-map-support)
  • Upgrade dependencies

0.3.1 (2016-02-09):

  • Add "-v" option for version number
  • Fix sequence number logic in MClient
  • Upgrade ws to fix "invalid compressed data" errors

0.3.0 (2016-01-03):

  • Update to latest TS module resolution
  • Add Message#clone()
  • Implement message ACKs
  • ES6 imports/exports
  • Move FLL-specific scripts into separate package
  • Improve Readme

0.2.1 (2015-04-18):

  • First public version


Licensed under the MIT License, see LICENSE.txt.

Copyright (c) 2015 Martin Poelstra

Current Tags

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