Offline-First Solutions

Glynn Bird, Developer Advocate, IBM Cloud Data Services

@glynn_bird

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Image Credit: Joan Touzet (@wohali), ASF Member, CouchDB PMC Member

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Frameworks

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Image Credit: Device landscape by Jeremy Keith, on Flickr

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Not just mobile first…

Image Credit: NASA New Horizons

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Offline First

Offline-First

Offline, online and somewhere in-between

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The Eight Fallacies of Distributed Computing 1.  The network is reliable 2.  Latency is zero

3.  Bandwidth is infinite

4.  The network is secure

5.  Topology doesn't change

6.  There is one administrator

7.  Transport cost is zero

8.  The network is homogeneous

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Text Credit: The Eight Fallacies of Distributed Computing by Peter Deutsch | Image Credit: Pneumatic Central by Sleestak, on Flickr

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Offline-first is the only way to achieve a true, 100%

always-on user experience.*

*assuming the device is reliable

Benefits of Offline First

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•  Better, faster user experience, both offline and online •  Allow your users to work offline or with limited connectivity •  Potentially saves battery life and bandwidth usage

Offline Patterns & Anti-Patterns •  Don't return an error for no reason •  Do let users view cached/saved data

•  Do synchronize data when connected

•  Consider letting your users decide when to sync

•  Think about the UX of users seeing stale data

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Difficulties of Offline First

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Image credit http://www.sneakerheadvc.com/wp-content/uploads/2012/02/Apple_iSync1.png

Introducing PouchDB

PouchDB •  A database in your web browser •  Can synchronize with any

database that implements the CouchDB Replication Protocol

•  Makes create, read, update and delete operations extremely quickly

•  Free, open-source

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JSON Documents

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{ type: "Feature", geometry: { type: "Point", coordinates: [ -71.1028, 42.3691 ] }, properties: { session_id: "3486b13f9b82800e367f", timestamp: 1422928591717 } }

Limited data types •  string

•  number

•  boolean

•  array

•  object

Getting started with PouchDB

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<script src="https://cdn.jsdelivr.net/pouchdb/3.6.0/pouchdb.min.js"></script> <script type="javascript">

var db = new PouchDB("smart-meter"); </script>

Adding documents - callbacks

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db.post({ date: "2014-11-12T23:27:03.794Z",

kilowatt_hours: 14

}, function(err, data) {

console.log(err,data); });

Adding documents - promises

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db.post({ date: "2014-11-12T23:27:03.794Z",

kilowatt_hours: 14

}).then(function() {

console.log("Document created"); }).catch(function(error) {

console.log(error);

});

Adding documents - bring your own id

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var db = new PouchDB("smart-meter"); var obj = {

_id: "abc123",

timestamp: "2014-11-12T23:27:03.794Z",

kilowatt_hours: 14 };

db.put(obj, callback);

https://github.com/bradley-holt/offline-first/blob/master/pouchdb/04-create-document-put.js

Getting a document

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db.get("abc123", callback);

// calls back with // {

// _id: "abc123", // _rev: "1-27695d5f483ac267d03ad0e3cb54bd2c",

// timestamp: "2014-11-12T23:27:03.794Z",

// kilowatt_hours: 14

// }

Getting multiple documents

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db.allDocs({include_docs:true}, callback);

// calls back with // {

// "offset": 0, // "total_rows": 24,

// "rows": [{...},{...}]

// }

Querying

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•  Primary Index •  MapReduce

•  PouchDB-find plugin

•  PouchDB-quick search plugin

Querying a Database with PouchDB Find •  Based on Cloudant Query (Mango) •  MongoDB-style query language

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Image Credit: Mango with section on a white background by bangdoll, on Flickr

db.find({

selector:{

name:'Mario'

debut:{'$gt':1990}

},

fields:['_id','lastname'],

sort:['lastname']

})...

Replicating a PouchDB Database

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var db = new PouchDB("smart-meter");

var remoteDb = new PouchDB("https://bradley-holt.cloudant.com/smart-meter");

db.replicateTo(remoteDb);

https://github.com/bradley-holt/offline-first/blob/master/pouchdb/08-replicate-database.js

Bidirectionally Replicating a PouchDB Database

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db.sync(remoteDb).on("change", function(info) {

// Replication has written a new document

console.log(info);

}).on("complete", function(info) {

// Replication has completed or been cancelled

console.log(info);

});

https://github.com/bradley-holt/offline-first/blob/master/pouchdb/09-replicate-database-bidirectional.js

Listening for Database Changes

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var changes = remoteDb.changes({

since: "now"

}).on("change", function(change) {

// A document has changed

console.log(change);

}).on("complete", function(info) {

// changes() was canceled

console.log(info);

});

https://github.com/bradley-holt/offline-first/blob/master/pouchdb/11-database-changes.js

PouchDB Framework Adapters

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Apache CouchDB

Apache CouchDB •  JSON document database •  HTTP API

•  Master-master replication

•  Free, open-source

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IBM Cloudant •  Globally distributed data layer for

web and mobile applications •  Run as-a-service •  MongoDB-style queries

•  Advanced geospatial capabilities

•  Full text search indexing

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PouchDB and CouchDB Replication

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CouchDB Replication Protocol •  One-off, one way operation •  Peer-to-peer (masterless)

•  Incremental

•  Conflict detection

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Going Offline

HTML5 Offline Application Cache •  Enables fully-functional offline

web apps

•  Stores files and assets for offline browsing

•  Makes page loads very fast, even when online

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Cache Manifest File

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<html manifest="example.appcache"> … </html>

CACHE MANIFEST # v1 - 2015-01-08 index.html logo.png app.css app.js

Service Workers (Beta)

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Client-side scripting framework for • programmable cache

• sync

• push messaging

• geo-fencing

• background tasks

https://jakearchibald.github.io/isserviceworkerready/

Cross-Origin Resource Sharing (CORS) •  Enable Cross-Origin Resource

Sharing (CORS) on remote database

•  Browsers place security restrictions on cross-site HTTP requests

•  If you run into a problem, remember this warning!

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Image Credit: Grunge Warning Sign - Do Not Read This Sign by Nicolas Raymond, on Flickr

Hybrid or Responsive Mobile Web Apps

Hybrid Mobile Web Apps •  Native mobile web apps built with

HTML5, CSS and JavaScript

•  Good for: •  Fully-featured, cross-platform native apps

•  High-fidelity prototypes

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Responsive Mobile Web Apps •  HTML5, CSS and JavaScript mobile

web apps

•  Responsive design

•  Enhanced to enable offline usage

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Examples

Pro Forma •  Define fields you want to collect •  Renders form saving data to

PouchDB

•  Replicates data to Cloudant

•  Demo https://glynnbird.github.io/proforma/

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MD •  Offline word processor •  Saves Markdown documents to

PouchDB

•  Replicates data to Cloudant

•  Demo http://mddoc.mybluemix.net/

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Gutenberg •  Offline e-book reader •  Replicates book list from server

•  Each book is a Cloudant database

•  Demo http://glynnbird.github.io/gutenberg/

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www.glynnbird.com •  My home page •  Cloudant database of articles

•  Replicated to PouchDB

•  Appcache for offline first

•  http://www.glynnbird.com/

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Volt •  Password vault in a Chrome

extension

•  Data stored in encrypted in PouchDB

•  Optional back to CouchDB/Cloudant

•  https://github.com/glynnbird/volt

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Location Tracker •  Stores data locally in PouchDB •  Front end built with AngularJS

•  Authentication logic built with Node.js

•  User interface built with Leaflet

•  Replicates location data to Cloudant

•  More info: https://cloudant.com/location-tracker/

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Glynn Bird Developer Advocate, Cloud Data Services glynn.bird@uk.ibm.com @glynn_bird github.com/glynnbird www.glynnbird.com

Image Credits

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•  Joan Touzet (@wohali), ASF Member, CouchDB PMC Member <https://twitter.com/wohali/status/595689720933445632>

•  Device landscape by Jeremy Keith, on Flickr <https://www.flickr.com/photos/adactio/6153481666>

•  NASA New Horizons <https://www.nasa.gov/sites/default/files/thumbnails/image/nh-surface.jpg>

•  Pneumatic Central by Sleestak, on Flickr <https://www.flickr.com/photos/dlanod/235990854>

•  Mango with section on a white background by bangdoll, on Flickr <https://www.flickr.com/photos/bangdoll/5665235102>

•  Grunge Warning Sign - Do Not Read This Sign by Nicolas Raymond, on Flickr <https://www.flickr.com/photos/80497449@N04/7417352980>