s3-poller

Fetch a JSON object from S3. Poll it for updates. Refetch it only if it has changed.

Usage

Fairly self-documenting. See index.js comments for nitty-gritty. Here are the basics:

const poller = new Poller({
    bucket: 'my-bucket',
    key: 'path/to/some.json'
});
 
poller.getCurrentValue(); // undefined
poller.getLastModified(); // undefined
 
await poller.getObject(); // fetch from S3
await poller.getObject(); // already cached; returns cached copy
 
assert(poller.getCurrentValue() === await poller.getObject());
 
poller.getLastModified(); // Date
 
await poller.getUpdate(); // fetch from S3, even if cached, but only if modified since last fetch
 
poller.onUpdate(listenerFunction, another, yetAnother, ...); // call you back when updates happen
poller.poll(60 * 60 * 1000); // check every hour
 
poller.offUpdate(another, yetAnother); // remove these listeners
 
poller.poll(2 * 60 * 60 * 1000); // change polling inteval, same listeners
 
poller.cancelPoll(); // stop polling, listeners stay registered
 
poller.removeListeners(); // remove all listeners

(await is ES7-speak for Promises. You don't need ES7, you can just use .then() etc.)

Useful constructor options:

• bucket, key - obvious, required
• initialValue - preset the interally cached value
• lastModified - preset the last modified date
• updateInterval - preset the update interval (ms), AND start polling immediately
• updateListener - add an update listener; you can give an array of listeners too
• s3Config - this gets passed into the AWS.S3() constructor call

This thing will barf if the object it receives isn't JSON. You can catch that error from getObject() or getUpdate(). Polling just discards the error for the time being.

Legal

Copyright (c) 2016 Datanalytics, Inc. d/b/a Juristat.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at:

http://www.apache.org/licenses/LICENSE-2.0