message-client

Note

The project is currently being hosted on a private gitlab account and being transferred to github at some point. So for now please forgive the empty GIT repo. Please use the GIT repo to log any issues you might be having.

Install

Install this package with NPM

npm install message-client

What is this?

This is a lightweight message client to be used when communicating with micro-services. The library is easy to use. It uses rabbitmq as the message transport. So you need to have a rabbitmq instance running. Get one at heroku or use AWS to provision one.

You before you start make sure you have your RABBIT_HOST environment variable set. This should be in the following format:

ampq://[username[:password:]@]host[:port]

Take advantage of being able to use the same rabbitmq server for multiple different projects. Simply set the CONTEXT environment variable of your application. By default your context will be set to local.*. So if you look at your rabbitmq queues

Every 2.0s: rabbitmqctl list_queues                                               b3df0772fafc: Thu Nov 30 20:56:18 2017

Listing queues
local.test      0
local.test3     0

Usage

The library is very simple to use. Take a look at this code example:

 
const MessageClient = require("message-client")
    , client = new MessageClient("api")
 
client.tell("notifications", { user: "userid", message: "this is the sample message" })
 
client.ask("notifications", { type: "request", message: "test message"})
    .then( response => {
        console.log(response.content)
    }).catch(error => {
        console.error(error)
    })
 
client.on("message", function(content, message) {
    console.log("I got a message", content)
    switch(content.type) {
        case "request" : {
            client.reply("sending a string back", message)
            break
        }
        case "superrequest": {
            client.reply({ message: "sending back an object"}, message)
            break
        }
        default : {
            throw new Error ("An unexpected message type was requested")
        }
    }
})

As you can see, three interfaces are provided. tell, ask, on and reply. Tell is for fire and forget requests. Ask is when you wish to communicate with a service and want a reply back. Ask returns a promise.

On for now only allows you to listen for messages. Errors will be added soon. You can also reply to messages. You must include the original message when replying, otherwise it will not know what message it is replying to.

More Notes

• Don't worry about message compression. All messages are compressed with MessagePack.
• Be careful of long running or slow Ask calls. For now the library will timeout after 30 seconds and reject the promise. Make sure you handle all rejected promises.
• Do not reply to a message more than once.

Todo

• Add a value to specify the timeout of a request
• Allow for streaming data between services