couch-pubsub

A pub/sub tool that leverages the power of CouchDB clustering to provide a simple, reliable and distributed system out of the box.

Available for Node, the command line and even in the browser.

Installation

couch-pubsub can be used with Node, from the command line or directly in the browser.

Node

npm install couch-pubsub

Then:

var CouchPubSub = require('couch-pubsub');

Browser

npm install couch-pubsub

Then:

<script src="node_modules/couch-pubsub/dist/couch-pubsub.min.js"></script>

via CLI

npm install -g couch-pubsub

Usage

There are two main functions.

• Publish - write some data to a channel
• Subscribe - Get updates from a channel as they happen

There is also a utility function that allows you to fetch all events on a particular channel since a particular date.

Javascript (Node.js or Browser)

.publish( channel, str, [callback] )

To publish to the test-channel, you could do something like this:

var pubsub = new CouchPubSub({
  couch_host: "https://my-couch-db.com",
  couch_username: "username",
  couch_password: "password",
  couch_port: null // null for default
});

pubsub.publish("test-channel", "string that you want to publish", function(err, data) {
  
  // err - error writing to couchDB
  // data - the response from couchDB, contains _id and _rev of the doc
  
});

or if you don't want to handle the callback:

pubsub.publish("test-channel", "string that you want to publish");

.subscribe( opts )

If you wanted to listen for updates to this channel you could do something like this:

var pubsub = new CouchPubSub({
  couch_host: "https://my-couch-db.com",
  couch_username: "username",
  couch_password: "password",
  couch_port: null // null for default
});

var sub = pubsub.subscribe("test-channel");
sub.on('update', function (update) {
    
  // update - the value that was published (e.g. 'string that you want to publish' from above')
    
});

To get all updates since a particular date and keep on listening for future updates:

var sub = pubsub.subscribe({ channel: "test-channel", since: "2015-01-03 13:26:00"});
sub.on('update', function (update) {
    
  // update - the value that was published (e.g. 'string that you want to publish' from above')
    
});

.since( channel, date, callback )

To get all events since a particular date, as a one off event:

var pubsub = new CouchPubSub({
  couch_host: "https://my-couch-db.com",
  couch_username: "username",
  couch_password: "password",
  couch_port: null // null for default
});

var since = pubsub.since("test-channel", "2015-01-03 13:26:00", function(err, data) {
  
  // err - error retrieving previous events
  // data - array of previous events

});

Command line

To replicate the examples above on the command line you could do:

publish

couch-pubsub publish test-channel "string that you want to publish"
-> {"ok":true,"id":"7d6eaf1ddcd0f8f42f98d4a58ba3a527","rev":"1-9d78b84800709cf0d8446f2147c74d75"}

subscribe

couch-pubsub subscribe test-channel
-> "string that you want to publish"
-> "the next string that was published"
-> "the last string to be published"

If you want to subscribe but also retrieve all channel events since a particular date, you can add a date to the above comand.

couch-pubsub subscribe test-channel "2015-01-03 13:26:00"
-> "previous event 1"
-> "previous event 2"
-> "previous event 3"
-> "previous event 4"
-> "string that you want to publish"
-> "the next string that was published"
-> "the last string to be published"

You will need to supply your CouchDB credentials via environemnt variables:

export COUCH_PUBSUB_HOST="http://my-couch-db.com"
export COUCH_PUBSUB_USERNAME="username"
export COUCH_PUBSUB_PASSWORD="password"

TODO

I put this together pretty quickly and there are some things I want to add still, such as:

• Better error checking
• Some test coverage
• Probably more...