Our Blog

Implementing Background Fetch in iOS 7

By Kamil Ciemniewski
March 11, 2014

With the iOS7 being out and gaining market share, great features it introduced are becoming available to more and more users.

One such new feature is a set of so-called “background modes”.

States the application can be in, in iOS

To explain this new set of modes, let me give you a really quick intro to what modes are.

In iOS, at a given point in time, an app can be in one of the following states:

Not running

There is no process for the app in the system.

Inactive

The app is running in the foreground but currently is not receiving any events. (It may be executing other code though.) An app usually stays in this state only briefly as it transitions to a different state.

Active

The application is running and is receiving user input. The main user interface is visible on the display.

Background

The application is running. It’s not receiving user input. Its code is being executed but it will be switched to the suspended state very soon by the system.

Suspended

The app remains in memory, but it’s not being executed. It remains dormant until a user chooses to activate it again or a system switches it back to a background state to allow it to process certain kinds of data.

Background modes …

Interchange table hacking

By Jeff Boes
March 11, 2014

Interchange has a powerful but terribly obscure table administration tool called the Table Editor. You can create, update, and delete rows, and even upload whole spreadsheets of data, but the Table Editor isn’t the most flexible thing in the world, so sometimes it just flat-out refuses to do what you want.

So you trick it.

A client wanted to upload data to a table that had a single-column primary key (serial), but also had a unique three-column key that was only used in the upload process (because the uploaded data was intended to replace rows with identical three-column combinations). Example:

In the table:

code: 243
field1: AAA
field2: BBB
field3: CCC
data-fields: ...

In the spreadsheet:

field1  field2  field3  data-fields...
 AAA     BBB     CCC     ...

In the database definition for this table, I had to add a secondary key definition for Interchange’s use:

Database  my_table  COMPOSITE_KEY  field1 field2 field3

in addition to the original key:

Database  my_table  KEY  code

Here’s the problem this presents: when you add a COMPOSITE_KEY to a table, the table editor refuses to show per-row checkboxes that allow you to delete rows. I thought I might have to write a custom admin …

md+lvm expansion from RAID 1 to RAID 5

By Josh Williams
March 9, 2014

VHS is on the way out, or so they tell me. A little while back I unearthed the family’s collection of old tape recordings, and have been digitizing everything in an effort to preserve all the old youth sports games and embarassing birthday parties. There’s no way I’m going to let my brother forget those. It’s a lot of video, and that takes up quite a bit of space. Between that, HD videos recorded more recently, Postgres test databases and source datasets, server backups, and so on, the 3TB of space on my local file server was quickly running out.

I know, right? My first hard drive was 40MB, in two 20MB partitions. And we were glad for that space!

Back in the present, now it was time to add another hard drive. This (otherwise) tiny rooted plug server contained two 3TB USB hard drives in a RAID-1 configuration through the Linux md module. On top of that is lvm. lvm itself could have been used for the RAID-1, but has the disadvantage of not being able to optimize multiple reads, whereas md can allow both disks in the mirror serve different reads at the same time.

I bought a third disk of the same model, so it could be added in to a RAID-5 configuration. These being big USB drives, …

Amazon Payments — Caveat Developer

By Carl Bailey
March 6, 2014

A client of ours needed me to install Amazon Payments for them. Now there are several shopping carts for which Amazon Payments can be installed as an option, and I assume they work just fine. This client was not so lucky, and I had to roll my own.

Amazon starts with a JavaScript widget that asks you to log in or create an Amazon account. The widget returns an order reference ID:

<div id="payWithAmazonDiv" style="padding-top: 1.2em;">
  <br />
   <img src="https://payments.amazon.com/gp/widgets/button?sellerId=[Amazonseller id]&size=large&color=orange" 
        style="cursor: pointer;"/>
</div>

<script type="text/javascript">
 var amazonOrderReferenceId;
 new OffAmazonPayments.Widgets.Button ({
   sellerId: '[Amazon seller id]',
   useAmazonAddressBook: true,
   onSignIn: function(orderReference) {
     amazonOrderReferenceId = orderReference.getAmazonOrderReferenceId();
      window.location = 'https://www.yoursite.com/nextpage.html?session=' +
                        amazonOrderReferenceId;
   },
   onError: function(error) {
     // your error handling code
     alert('Amazon …

Ansiblizing SSH Keys

By Cas Rusnov
March 3, 2014

It is occasionally the case that several users share a particular account on a few boxes, such as in a scenario where a test server and a production server share a deployment account, and several developers work on them. In these situations the preference is to authenticate the users with their ssh keys through authorized_keys on the account they are sharing, which leads to the problem of keeping the keys synchronized when they are updated and changed. We add the additional parameter that perhaps any given box will have a few users of the account that aren’t shared by the others, but otherwise allow a core of developers to access them. Now extend this scenario across hundreds of machines, and the maintenance becomes difficult or impossible when updating any of the core accounts. Obviously this is a job for a remote management framework like Ansible.

Our Example Scenario

We have developers Alice, Bob and Carla which need access to every box. We have additional developers Dwayne and Edward that only need access to one box each. We have a collection of servers: dev1, dev2, staging and prod. All of the servers have an account called web_deployment.

The authorized_keys for …

JavaScript Namespacing with the Rails Asset Pipeline

By Steph Skardal
March 3, 2014

Since the release of Rails 3 [a while back], I’ve had a lot of use with the asset pipeline. There can be minor headaches associated with it, but ultimately, the process of combining, minifying, and serving a single gzipped JavaScript and CSS file is a great gain in terms of reducing requests to speed up your web application. It’s a behavior that I’ve wanted to emulate in other platforms that I’ve used (including Interchange).

One headache that might come up from the asset pipeline is that JavaScript functions from various parts of the application might have the same name, and may override existing functions of the same name. The last defined function will be the one that executes. I’ve come up with a common pattern to avoid this headache, described below:

Set the Body ID

First, I set the body tag in my application layout file to be related to the controller and action parameters. Here’s what it looks like:

<body id="<%= "#{params[:controller].gsub(/\//, '_')}_#{params[:action]}" %>">
...
</body>

If I was less lazy, I could create a helper method to spit out the id.

Shared JS

I create a shared.js file, which contains JavaScript shared …

Liquid Galaxy at the Economist World Ocean Summit

By Dave Jenkins
March 3, 2014

The Liquid Galaxy with image capture equipment

End Point had the distinct privilege of providing a Liquid Galaxy to the Economist World Ocean Summit held in Half Moon Bay, California last week. Originally conceived as a Google Earth and Google Street View platform, the Liquid Galaxy is rapidly becoming a premiere display for ocean content as well. Google is partnering with NGOs and corporations that are actively working toward ocean sustainability. Together, these organizations capture and categorize a great deal of ocean content, with most of that content publicly available via Street View. Some of this equipment was on display next to the Liquid Galaxy: a Trekker camera for remote areas and an underwater camera provided by the Catlin Seaview Survey for capturing hi-definition panoramas underwater.

This deployment used a custom configuration with six large HDTVs arrayed in a curved 3x2 panorama. The Liquid Galaxy is able to show this content as a single large surface with geometrically-adjusted angles. In short, it’s like a bay window on a submarine. Viewers are able to navigate to different locations through a touchscreen interface, and then rotate and zoom in on detailed …

DBD::Pg prepared statement change

By Greg Sabino Mullane
February 28, 2014

One of the changes in the recently released DBD::Pg version 3 (in addition to the big utf8 change), is the addition of a new attribute, pg_switch_prepared. This accompanies a behavior change in the use of prepare/execute. DBD::Pg will now postpone creating a server-side PREPARE statement until the second time a query is run via the execute() method.

Technically, DBD::Pg will use PQexecParams (part of the underlying libpq system that DBD::Pg uses) the first time a statement is executed, and switch to using PQexecPrepared the second time the statement is executed (by calling PQprepare first). When it actually switches is controlled by the pg_switch_prepared attribute, which defaults to 2 (the behavior above). You can set it to 0 or 1 to always use PQexecPrepared (as the older versions did), or you can set it to -1 to always use PQexecParams and avoid creating prepared statements entirely.

The typical flow of events in a DBI script is to create a statement handle via the prepare() method, then call the execute() time with varying arguments as many times as needed.

#!perl

use strict;
use warnings;
use DBI;

my $DSN = 'DBI:Pg:dbname=postgres';
my $dbh = DBI->connect($DSN, …