changemate

Changemate is a change notification service and framework. At present it only supports responding to the _changes feed of a couch database, but will be expanded in time to support other change notification formats.

Supported Notifiers

CouchDB

The couchdb notifier is the first cab off the rank, as it is required for steelmesh. The couchdb notifier hooks into the continuous changes feed for a couchdb instance.

var changemate = require('changemate');
var counter = 0;
var notifier = changemate('<:couch:> https://fluxant.cloudant.com/seattle_neighbourhood');
 
notifier
  .on('connect', function() {
    console.log('connected');
  })
  .on('change', function(data) {
    console.log('got change id: ' + data.id + ', seq: ' + data.seq + ', counter: ' + (++counter));
  })
  .on('close', function() {
    console.log('disconnected from server');
  });
 

Supported Options:

• since - the change_sequence to get changes since
• include_docs - whether or not document fragments should be included with the change data

State Management

You can see by running the example above, that the changes for the feed are read from since=0 each time. While this is good for the purpose of the example, it's unlikely to be the desired behaviour in your application.

Changemate does not offer a checkpoint persistence mechanism, but does provide checkpoint information so that you can store that information yourself and use it:

var changemate = require('changemate');
var counter = 0;
var notifier;
var _checkpoint;
 
function _createNotifier() {
  // reset the counter
  counter = 0;
 
  console.log(_checkpoint);
 
  // create the notifier
  notifier = changemate(
    '<:couch:> https://fluxant.cloudant.com/seattle_neighbourhood', // target
    {}, // options
    _checkpoint // checkpoint
  );
 
  notifier.on('change', function(data, checkpoint) {
    // save the checkpoint
    _checkpoint = checkpoint;
 
    console.log('got change id: ' + data.id + ', seq: ' + data.seq + ', counter: ' + (++counter));
    if (counter >= 100) {
      notifier.close();
      _createNotifier();
    }
  });
}
 
// create the notifier
_createNotifier();
 

In the example above, we are collecting the checkpoint data that is passed through in the change event. Additionally, we are closing the notifier for every 100 updates, and creating a new notifier with the checkpoint data that has been captured in previous events.

To make the sample above persist across sessions, the checkpoint information could be save to a local JSON file or similar and reloaded the next time the script ran to start from next required update.

License(s)

MIT

Copyright (c) 2016 Damon Oehlman [e-mail]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.