Ashish Datta, Author at {5} Setfive - Talking to the World

As has become tradition, Mary Meeker of Kleiner Perkins published her anual “Internet trends” report a couple of days ago. As always, its a great read and you should check it out here. Digging through the slides, a couple of things jumped out to me personally:

Tablets are far from dead

Over the past few months, there’s been a slew of blog posts bemoaning the death of the tablet. Arguments basically ranged from the point that tablet hardware is too immature to the fact that most people don’t have a strong table usecase. Looking at the report though, the # of shipped tablets is clearly exploding and is trending upwards. That said, the report doesn’t break out what kinds of tablets are being shipped – we’ll have to check in with Ben Evans for that.

Print media spend is heavily over indexed

If I worked in print media, slide 15 would be giving me some serious heartburn. Compared to other channels, print is receiving a disproportionate percentage of ad spend compared to how much time consumer spend consuming print media. Obvious outcome here is that advertising dollars are going to continue to shift digital, with mobile picking up the biggest chunk. The buying spree around mobile ad networks is already signalling this shift with the clear example being Twitter buying MoPub.

Music is changing

There was a flurry of attention and armchair quarterbacking around Apple’s acquisition of Beats and slide 50 highlights how music is changing. With consumers favoring streaming over purchasing, the market opportunity for “winning” music is certainly shrinking. Couple that with streaming services being available on multiple devices and the Apple/Beats deal looks even stranger. In any case, the future will definitely be streamed.

The battle for the living room is heating up

Looks like the hotly anticipated “battle for the living room” is heating up. With the proliferation of set top boxes like the Roku and AmazonTV along with release of next gen game consoles, consumers are changing how they consume traditional TV. Coupled with “apps” like HBO Go, there are fewer reasons to avoid “cutting the cord” and abandoning traditional cable TV service. Obviously the content owners still hold the keys but as Netflix proved with House of Cards, making awesome TV as an outsider isn’t impossible.

Anyway, as always would love any thoughts or comments!

Last weekend, the boys and I were at a bar and we started playing on one of those “parlor game” machines. If you’re unfamiliar, they’re basically a computer with a touch screen in a glorified case. They’re loaded up with dozens of games like “spot the difference”, traditional casino games, and of course X-rated versions of everything. As we were burning cash playing, we started thinking out loud that the game would be “cooler” if you could actually win money back. Games like this do exist in Vegas but they’re consequently heavily regulated by gambling related laws. As we were discussing this, someone mentioned building the game using Bitcoin in hopes of skirting gambling regulations. So, how could you go about building a real world game using Bitcoin for payments?

Hardware

The natural choice here would be to run with a WiFi enabled RaspberryPi along with a capacitive touchscreen. I’ve never done any work with touchscreens but it looks like TigerDirect has 22″ Planar ones for under $300. Couple that with a WiFi RaspberryPi kit for $50 and we should be in business for <$500. You could obviously grab a smaller screen but go big or go home right?

Authentication

Now things get interesting. Philosophically, I think you do want to enforce authentication so that users can save scores, carry a BTC balance, and generally make the experience “stickier”. The straightforward approach would be to offer a traditional sign up using an email address and password but that would totally sacrifice leveraging social media. Allowing users to easily “sign in” with Twitter or Facebook would allow you leverage their social graphs to find their friends and drive awareness of the game. An issue I’ve run into in the past is that “kiosks” always ask you to enter you Facebook or Twitter credentials directly on the kiosk – which is a non-starter for most people.

So how can we avoid this? The big idea is that you really just need the user’s OAuth tokens for whatever service they want to use – not their credentials. To do this, you’d need to either distribute an app or have a website where the user could “sign in” while already logged in on Facebook or Twitter on their mobile phone. Then, you’d be able to capture their OAuth tokens and log them in to the kiosk.

Getting the Bitcoin

Ok, so the user is logged in, now we need to get them some Bitcoin to play with. I think what you’d want to do is generate a wallet for each authenticated user and let them transfer in to an address as need be. So since their account is unfunded, they’d be presented with a QR code for an address that they can use to fund it. Another interesting idea would be to let users buy BTC in cash from the bartender which would in turn automatically fund their account. To support this, you’d need an app or website where the bartender could transfer BTC into the user’s wallet after receiving cash on site.

In terms of software to facilitate this, it seems like bitcoinj would be the best option. Written in Java, bitcoinj is a “client node only” implementation of the Bitcoin protocol that allows it to run without a full local copy of the Blockchain. Because of this, bitcoinj will run in resource constrained environments like the RaspberryPi. In addition, bitcoinj supports “simplified payment verification” so you’d be able to clear transactions instantly without waiting for confirmations to settle.

The Games

Graphically and conceptually, the games are all pretty straightforward so your best bet is probably implementing with JavaScript with HTML and CSS. The benefits would be you’re development cycles would be short and you’d be able to develop the games independently of the device itself. With HTML5 hitting it’s stride, you’d also be able to enable “multiplayer” versions using WebSockets.

One interesting consideration is that without being able to definitely vouch for the physical security of the kiosk how can you verify that the running code is authentic?

Sending the Bitcoin

The final step in the dance (and what makes it special) is allowing the user to cash BTC out of their account. I think you’d want to offer the option of allowing the use to generate a “send to” address if they have a mobile wallet and also allow them to cash out in person. If they can generate a “send to” address, they’d have to use the kiosk to scan a QR code where their BTC balance would get sent. To facilitate this, you’d need a webcam attached to the RaspberryPi and then use something like ZXing to decode the data in the QR code.

For the “in-person” option, you’d need to build out functionality to allow the bartender to initiate a transfer from the user’s wallet back to the bar from the web or mobile app. After it settles, they’d simply hand the user back some cash and the account would be settled.

Is this legal?

Therein lays the rub. It probably is but I’m not 100% sure. Eliminating the option to exchange BTC for cash might help the case for legality. Along with that, if you can side step “making odds” as well it might help your case. Would love any thoughts on this!

One of the nicest features of Symfony2 is the Request/Response paradigm for processing a HTTP request and then sending a response back to a client. At a high level, Symfony’s HttpFoundation component provides an object oriented abstraction to easily deal with HTTP requests and generate responses to send back to a client. Assuming application code correctly uses HttpFoundation, it will only interact with request variables through the Request class, as opposed to $_REQUEST, and only send output using the Response class, as opposed to an “echo”. Because of this contract, the framework as a whole makes it easy to manipulate responses before they’re sent back to a client.

A typical use case that leverages this would be logging API responses before they’re sent back to a client. As much as an API might be RESTful, at some point it’s easier to debug things when you can see the responses that clients have been receiving. OK great so how do you do it? It’s actually pretty straightforward, just create a class to receive the “kernel.terminate” event and register it as a service with the appropriate tags:

And then create the class where you want to manipulate or log the requests:

And that’s about it!

Note: Per Andras’ comment below the event has been switched to “kernel.terminate”.

A couple of weeks ago, we picked up a RaspberryPi for the office and started brainstorming ideas for cool hacks for it. One of the ideas that was floated was using the Pi as a server for some sort of multiplayer JavaScript game. I’ve actually never written a game before so I figured it would be an interesting project. We ended up trying to use node-qt for graphics along with ws to receive input via websockets but the refresh rate of Qt was just to low. A story for another time.

Anyway, so back to ping pong. One of the things we wanted to avoid was writing our own code to manage the game objects, we really wanted to use a game engine for this. The only caveat we had was that the engine had to be UI agnostic since we were planning to output graphics on Qt instead of a HTML5 Canvas. After looking around, most of the JavaScript game engines have strong dependencies on Canvas so we started looking at other options. The two strongest options were Box2JS and ChipmunkJS. We decided to go with ChipmunkJS in part because it was handwritten while Box2JS was automatically converted from ActionScript so the resulting code is harder to follow.

Getting ChipmunkJS setup is relatively painless, just include the file and you’re off to the races. Since we were looking to eventually use Qt, we tried our best to cleanly separate the Chipmunk code from what we’d be using to draw the objects on the screen. Because of that, it’s pretty easy to follow what’s going on with the Chipmunk code. If you take a look at cpPong.js it basically initializes the physics space and then starts the game.

With the physics space setup, the next step is setting up the drawing. Following the Chipmunk demo’s lead, I added specific “draw” methods to the Prototypes of each shape. Doing this, allows you to just iterate over each shape in the scene and call “draw” to have it appear on Canvas or Qt. Check out pong.html to see how we added the draw methods to the shapes. And that’s about it! The only other interesting part is using “requestAnimationFrame” to avoid using setTimeout to update the scene.

There’s a live demo running here and of course the code on GitHub.

Any questions or comments welcome!

I was poking around the ThoughtBot blog a couple of days ago and ran across a post titled Refactoring Ruby Iteration Patterns to the Database. At a high level, the post was summarizing how you can take an ActiveRecord aggregation (a sum in this case) and run it in directly in your RDMS with SQL. Not really rocket science, but it was a keen reminder of how ORMs often mask over much of the power of “regular” SQL. This isn’t a specific criticism of ActiveRecord, it’s an issue with every ORM from Doctrine to Hybernate.

We’ve actually been writing some straight SQL lately, mostly for analytics work, so I had the team shoot over their favorite “maybe hidden” SQL feature. Since life is better with examples, the sample use cases and queries are written against a schema describing the “items” found on a “receipt” which are optionally related to a “category”. The SQL to create the schema is:

Note: SQLFiddle is unfortunately down right now or I’d add this as a fiddle. Anyway, if you have the schema setup feel free to run the queries as you go down the list.

Order rows by fixed ordering of a column

At some point, you might find yourself needing to sort a list of rows by a column in an arbitrarily enforced order. For example, say on our item table, you needed to sort the rows by the “quadrant” column such that WE was first, followed by AX, and finally BT.

Turns out, it’s possible to specify an arbitrary ordering using the ORDER BY FIELD statement:

Check that a LEFT JOIN relation exists

If you’re only running JOINs on columns with foreign key relations this isn’t an issue, but what happens if you need to run a JOIN where a FK doesn’t necessarily exist? In our example, lets say you wanted to select only the items which had a corresponding row in the “receipt” table.

The most straightforward way to accomplish this is generally to check that the JOIN’ed column on the related table isn’t NULL:

Assign an aggregate value to a variable and re-use

One of the SQL features that’s usually glossed over or ignored in web development is the ability to create variables and then reuse them in subsequent statements. With this schema, an example would be calculating the “% of total spend” for the individual items – most people would run one query to generate the total and then a separate query to calculate the % of spend. For something trivial like this it doesn’t matter but if you were involving complex WHERE predicates it could be a nice performance boost.

The syntax for variables is relatively easy and it’s actually a powerful concept:

Add synthetic “pseudo” columns using variables

This one is a Matt Daum favorite and pretty handy. Looking at the example, say that you wanted to assign a “sequence” value to each item depending on their rank order based on “total” within their “category_id”. In plain English, for each “category_id” you want to assign the most expensive item a “1”, the second most a “2”, and so on.

This seems straightforward, but try and construct a result set using only a GROUP BY or some combination of sub queries, I’ll wait. Turns out, the easiest way to accomplish this is to use variables to construct a “pseudo” column that increments and resets when the category changes.

Select only GROUP’ed rows that fulfill a second clause

Sorry for the terrible description, an example will make it clearer. Given our schema, lets say you wanted to select *only* the most expensive items per category, how could you set about doing it? The obvious approach would be using some combination of GROUP BY and MAX but unfortunately because of the semantics of GROUP BY that wont work as expected.

A better approach, is to leverage an INNER JOIN along with MAX() to only select the rows that match the max total per category:

The caveat here is that you’re really selecting the highest total, so if two rows have the same total you’re not guaranteed which one you’ll end up with. This approach also scales out, in the sense that you can add additional INNER JOINs to limit the resultset in situations where you’re getting tripped up by GROUP BYs and ORDER BYs.

Anyway, as always, we’d love to hear your favorite tips and tricks in the comments!

Author: Ashish Datta

Four takeaways from Mary Meeker’s 2014 Internet trends