Mist is a simple pub/sub based on the idea that messages are tagged. To subscribe, a client simply constructs a list of tags that it is interested in, and all messages that are tagged with all of those tags are sent to that client.

A client can not only be a subscriber (with multiple active subscriptions), but also a publisher. Clients will receive messages for any tags they are subscribed, except message publish by themselves.

Mist comes with two sets of available commands out of the box. Basic commands and Admin commands. It also has the ability to accept custom commands and handlers.

You can connect to mist with something like netcat; once connected you can simply type commands:

>> nc 127.0.0.1 1445
{"command":"publish", "tags":["hello"], "data":"world!"}

Basic command are what provide the core functionality of mist. They allow you subscribe to and publish messages, see all of your active subscriptions and also unsubscribe from any tags you no longer want to receive messages for.

If mist is started with an authenticator and a token then a client has the chance to validate that token on connect. Once validated mist adds some additional admin commands that allow the creation of token/tag combos that provide a layer of authentication when using basic commands.

All communications within mist are sent and received as JSON encoded/decoded messages:

Message struct {
  Command string   `json:"command"`
  Tags    []string `json:"tags"`
  Data    string   `json:"data,omitempty"`
  Error   string   `json:"error,omitempty"`
}

Each Message has a set of tags and data. Tags can take any form you like, as they are just an array of strings.

{
  "tags": ["company:pagodabox", "product:mist", "repo:#nanopack"],
  "data": "Mist is awesome!"
}

Think of tags as a way to filter out messages you don't want to receive; the more tags that are added to a subscription the more direct a message has to be:

Message that are published to clients as the result of a subscription are delivered in this format:

{"command":"<command>", "tags":["<tag>", "<tag>"], "data":"<data>"}

A few things to not about how mist handles data:

• Data flowing through mist is not touched or verified in anyway, however, it MUST NOT contain a newline character as this will break the mist protocol.

• Messages are not guaranteed to be delivered, if the client is running behind on processing messages, newer messages could be dropped.

• Messages are not stored, if no client is available to receive the message, then it is dropped.

Out of the box mist supports three different types of servers (TCP, HTTP, and Websocket). By default, when mist starts, it will start one of each.

TCP server listening at '127.0.0.1:1445'...
HTTP server listening at '127.0.0.1:8080'...
WS server listening at '127.0.0.1:8888'...

When starting mist, you can specify any number and type of server you'd like as long as it follows the string URI protocol (If a listener is passed that mist doesn't support it will skip).

Also, if mist doesn't support a server you need it allows you to register custom servers that can be used on startup.

(scheme:[//[user:pass@]host[:port]][/]path[?query][#fragment])

./mist --server --listeners "tcp://127.0.0.1:1445", "http://127.0.0.1:8080", "ws://127.0.0.1:8888"

Mist also provides support for authentication. This means that during startup you can provide mist with an authenticator and a token. Once enabled, any client that connects to the server has an opportunity (as the first command) to provide the authentication token to "unlock" admin commands for that connection.

./mist --server --authenticator memory:// --token TOKEN

Notice that when an authenticator is provided, a token must also be provided otherwise the server will not start.

Like listeners, mist allows for the registration of custom authenticators.

(scheme:[//[user:pass@]host[:port]][/]path[?query][#fragment])

When connecting to an authenticated server, to enter "admin" mode, the very first communication across the wire must be the auth command.

>> nc 127.0.0.1 1445
{"command":"auth", "data":"TOKEN"}

Failing to authenticate will still allow the connection to proceed, however no "admin" commands will be allowed on the connection.

Out of the box mist provides a CLI, a TCP client, and the ability to connect via Websocket Clients

The CLI provides a built-in TCP client that can be used to connect with any running mist

Usage:
  mist [flags]
  mist [command]

Available Commands:
  ping        Ping a running mist server
  subscribe   Subscribe tags
  publish     Publish a message

Flags:
      --authenticator string   Setting enables authentication, storing tokens in the authenticator provided
      --config string          Path to config file
      --listeners value        A comma delimited list of servers to start (default [tcp://127.0.0.1:1445,ws://127.0.0.1:8888])
      --log-level string       Output level of logs (TRACE, DEBUG, INFO, WARN, ERROR, FATAL) (default "INFO")
      --server                 Run mist as a server
      --token string           Auth token for connections
  -v, --version                Display the current version of this CLI

Use "mist [command] --help" for more information about a command.

Here is an example of a TCP client written in Golang that will connect with mist and handle messages:

package main

import (
	"fmt"
	"os"
	"time"

	"github.com/nanopack/mist/clients"
)

func main() {
	client, err := clients.New("127.0.0.1:1445")
	if err != nil {
		os.Exit(1)
	}

	// example commands (not handling errors for brevity)
	client.Ping()
	client.Subscribe([]string{"hello"})
	client.Publish([]string{"hello"}, "world")
	client.List()
	// client.Unsubscribe([]string{"hello"})

	// do stuff with messages
	for {
		select {
		case msg := <-client.Messages():
			fmt.Printf("MSG: %#v\n", msg)
		case <-time.After(time.Second * 1):
			// do something if messages are taking too long
		}
	}

	// do stuff with messages (alternate)
	// for msg := range client.Messages() {
	// 	fmt.Printf("MSG: %#v\n", msg)
	// }
}

Since mist just uses a JSON message protocol internally, sending messages via websocket is easy.

NOTE: If authentication is enabled you'll need to provide a token when connecting the websocket:

• As a Header: X-AUTH-TOKEN: token
• As a query param: x-auth-token=token

NOTE: If using WSS you'll need to accept the generated cert via the browser https://localhost:8082/subscribe/websocket prior to chrome console letting you run the following javascript.

  // connect the websocket
  var ws = new WebSocket("ws://localhost:8080/subscribe/websocket?x-auth-token=token")

  // handle responses from the server
  ws.onmessage = function(me){
    console.log("Response!", me.data)
  }

  // ping
  ws.send(JSON.stringify({"command": "ping"}))

  // subscribe
  ws.send(JSON.stringify({"command": "subscribe", "tags": ["hello", "world"]}))

  // unsubscribe
  ws.send(JSON.stringify({"command": "unsubscribe", "tags": ["hello", "world"]}))

  // list
  ws.send(JSON.stringify({"command": "list"}))

To run mist as a server, using the following command will start mist as a daemon:

mist --server

If you need to override any default config options you can pass the path to a config file:

mist --config /path/to/config

authenticator: memory://
listeners:
  - tcp://127.0.0.1:1445
log-level: INFO
token: TOKEN
server: true

Or you can just pass any configuration options as flags:

mist --server --log-level DEBUG

Contributions to mist are welcome and encouraged. Mist is a Nanobox project and contributions should follow the Nanobox Contribution Process & Guidelines.