Extensions in Scratch let you add additional blocks to the palette. I’ve written about how to create extensions before, but in this post I want to share my latest extension which adds MQTT support.
I don’t have a particular Scratch project in mind for this yet, but publishing and subscribing to an MQTT broker from a Scratch project would allow multiple web browsers each running Scratch to communicate with each other. I’m sure there are some fun things this could be used for.
Overview
Extending WebSphere MQ to include support for WebSockets, allowing messaging to web browsers, including mobile browsers, without any additional client software
Background
I’ve talked about MQTT before – a lightweight messaging protocol that I’ve used both on personal projects and my day job.
From mqtt.org:
It is useful for connections with remote locations where a small code footprint is required and/or network bandwidth is at a premium.
I’ve used it in CurrentCost projects, mobile apps and with small and embedded computers like my Slug.
But in all cases, I’ve needed MQTT client software to talk to the messaging server. Whether writing in C, C#, Java or Python, I’ve needed a client library to get me started, something that knows the sequence of packets that make up the MQTT protocol.
It’d be useful to have a zero-install MQTT client: an MQTT client app delivered over the web, without the user needing to install any additional client libraries, or resort to Java applets.
What this does
One possible way to do this could be WebSockets. Part of HTML5, this is a protocol that describes how to do two-way messaging between web servers and web browsers. And I mean proper two-way communication, including push-notification from the server to the browser, without resorting to hacks or kludges like long polling or hidden iframes.
It’s an emerging protocol, still in draft form, but there are a few implementations around so there are already a few browsers that know how to manage WebSockets.
We’ve been exploring recently how this could work with MQTT – the aim was to build in support for WebSockets into an MQTT messaging server: IBM WebSphere MQ (WMQ).
I’ve mentioned WebSphere MQ before, as back in the dim-and-distant past (well, five or six years ago) I used to be a developer of it.
It’s one of the server implementations that support the MQTT protocol.
By adding support for WebSockets to it, it means that WMQ could send and receive messages to web browsers. It means a web app could be a fully-fledged MQTT client.
Overview
How to receive push notifications using MQTT in an Android mobile application
Background
I’ve written before about MQTT as a technology for doing push notifications to mobile. When I wrote that, I gave an example Android project. However, it was the first time I’d ever done Android development, and while it was an okay Java MQTT sample, it was a poor Android sample – I didn’t know anything about how Android works as a platform.
I’ve since written other Android MQTT apps, such as a hackday app for pushing updates from websites to your phone and learnt a lot about how to do it properly. Well… if not properly, at least a little better.
But Google is still directing people to my old, and probably unhelpful, sample. So it’s about time that I share something more useful.
I’ve put the full source for a sample implementation below. (Note that I’m using the Java J2EE client library from ibm.com). Hopefully the comments in it are clear enough, but here are a few of the key points.
What do the following have in common?
Weather Channel Max – an iPhone weather app. StockWatch – an iPhone stock prices app. CNN Mobile – an iPhone news app. FlightTrack – an iPhone flight updates app. Tweetie – an iPhone twitter app.
They are all apps which provide users with updates to their phone when some information changes. The information in question is different. But they’re all ways for users to get information that they are interested in, while they are on the move.
Having a dedicated hard-coded app for each type of data is great for information that a large number of people are interested in.
For example, there are enough people who are interested in the weather that it’s worth having an app dedicated to it.
But what if you want updates for information that isn’t so widely needed? What about niche interests?
We’re all different. There is going to be something that you’re interested in that not everyone else is. Or at least a particular set of interests that noone else exactly shares.
People’s needs and interests are almost infinitely varied, so we can’t come up with enough applications to meet everyone’s unique needs. Particularly for more esoteric topics, which are too long tail to each justify a specific mobile app.
For these situations, we need something generic that individual users can customise.
This was an idea I played with on the last IBM HackDay. I managed to get a proof-of-concept working on the day, but not had the chance to share it before now.
What I tried to create was:
I’ve recorded a video of it running. (Difficult to see without full-screen – sorry!)
To summarise, the steps involved are:
Friday was the seventh IBM Hack Day, and I again got the chance to spend a day playing with some random ideas.
As Hack Days go, I had a surprisingly productive day! I had four ideas on the day:
In this post, I’ll describe what I did for the last of these ideas: writing a client app for the wiki that comes with IBM’s Lotus Connections.
The idea
In the same way that I am writing this post in an offline blogging client, I wanted the same for using wikis: read and make changes to a wiki while offline, with changes uploaded to the online wiki the next time you are online.
This wasn’t a new idea. In fact, I tried it at IBM HackDay 4 back in 2007 but the wiki we used at work at the time had no API access for retrieving or updating wiki pages. So I sort of gave up and forgot about the idea.
But now I use Lotus Connections wikis at work. And Lotus Connections does have an API – an AtomPub API that gives you feeds to know when pages are changed, and a way to publish changes.
So I decided to revisit the idea.
The “finished” (ish) hack
It’s still very rough around the edges (this was a HackDay – I wrote the client code in under a day!) but it already shows the basic idea.
The top left view shows the list of your wikis.
Clicking on this fills the list below – a list of pages in the selected wiki. Clicking on a page in that list opens the contents of the page in the main view on the right.
Update (1 Feb 2011): I’ve shared some better sample code for Android
Last weekend, I went to Imperial College for Over The Air: a conference for mobile developers.
I gave a talk at the event on how to write a mobile application that uses push notifications. It was pretty well received, so I’d thought I’d share it here, too.
I’ve made some notes below to cover roughly what I said at the event. Any comments or questions (or corrections if you spot any!) are very welcome. 🙂
Update (24/10/2009): I revisited this presentation to address some of the feedback that I got on battery life implications of using MQTT.