End Point


Welcome to End Point's blog

Ongoing observations by End Point people.

Impressions from Open Source work with Elixir

Some time ago I started working on the Elixir library that would allow me to send emails as easily as ActionMailer known from the Ruby world does.

The beginnings were exciting — I got to play with a very clean and elegant new language which Elixir is. I also quickly learned about the openness of the Elixir community. After hacking some first draft-like version and posting it on GitHub and Google groups — I got a very warm and thorough code review from the language’s author José Valim! That’s just impressive and it made me even more motivated to help out the community by getting my early code into a better shape.

Coding the ActionMailer like library in a language that was born 3 years ago doesn’t sound like a few hours job — there’s lots of functionality to be covered. An email’s body has to be somehow compiled from the template but also the email message has to be transformed to the form in which the SMTP server can digest and relay it. It’s also great if the message’s body can be encoded with „quoted printable” — this makes even the oldest SMTP server happy. But there’s lots more: connecting with external SMTP servers, using the local in-Elixir implementation, ability to test etc…

Fortunately Elixir’s built on top of the Erlang’s „Virtual Machine” - BEAM - which makes you able to use its libraries — a lot of them. For the huge part of the functionality I needed to cover I chose the great gen_smtp library (https://github.com/Vagabond/gen_smtp). This allowed me to actually send emails to SMTP servers and have them properly encoded. With the focus on developer’s productivity, Elixir made me come up with the nice set of other features that you can check out here: https://github.com/kamilc/mailman

This serves as a shout out blog post for the Elixir ecosystem and community. The friendliness that it radiates with makes open source work like this very rewarding. I invite you to make your contributions as well — you’ll like it.

Simple cross-browser communication with ROS

ROS and RobotWebTools have been extremely useful in building our latest crop of distributed interactive experiences. We're continuing to develop browser-fronted ROS experiences very quickly based on their huge catalog of existing device drivers. Whether a customer wants their interaction to use a touchscreen, joystick, lights, sound, or just about anything you can plug into the wall, we now say with confidence: "Yeah, we can do that."

A typical ROS system is made out of a group ("graph") of nodes that communicate with (usually TCP) messaging. Topics for messaging can be either publish/subscribe namespaces or request/response services. ROS bindings exist for several languages, but C++ and Python are the only supported direct programming interfaces. ROS nodes can be custom logic processors, aggregators, arbitrators, command-line tools for debugging, native Arduino sketches, or just about any other imaginable consumer of the data streams from other nodes.

The rosbridge server, implemented with rospy in Python, is a ROS node that provides a web socket interface to the ROS graph with a simple JSON protocol, making it easy to communicate with ROS from any language that can connect to a web socket and parse JSON. Data is published to a messaging topic (or topics) from any node in the graph and the rosbridge server is just another subscriber to those topics. This is the critical piece that brings all the magic of the ROS graph into a browser.

A handy feature of the rosbridge JSON protocol is the ability to create topics on the fly. For interactive exhibits that require multiple screens displaying synchronous content, topics that are only published and subscribed between web socket clients are a quick and dirty way to share data without writing a "third leg" ROS node to handle input arbitration and/or logic. In this case, rosbridge will act as both a publisher and a subscriber of the topic.

To develop a ROS-enabled browser app, all you need is an Ubuntu box with ROS, the rosbridge server and a web socket-capable browser installed. Much has been written about installing ROS (indigo), and once you've installed ros-indigo-ros-base, set up your shell environment, and started the ROS core/master, a rosbridge server is two commands away:

$ sudo apt-get install ros-indigo-rosbridge-suite
$ rosrun rosbridge_server rosbridge_websocket

While rosbridge is running, you can connect to it via ws://hostname:9090 and access the ROS graph using the rosbridge protocol. Interacting with rosbridge from a browser is best done via roslibjs, the JavaScript companion library to rosbridge. All the JavaScripts are available from the roslibjs CDN for your convenience.

<script type="text/javascript"
<script type="text/javascript"

From here, you will probably want some shared code to declare the Ros object and any Topic objects.

//* The Ros object, wrapping a web socket connection to rosbridge.
var ros = new ROSLIB.Ros({
  url: 'ws://localhost:9090' // url to your rosbridge server

//* A topic for messaging.
var exampleTopic = new ROSLIB.Topic({
  ros: ros,
  name: '/com/endpoint/example', // use a sensible namespace
  messageType: 'std_msgs/String'

The messageType of std_msgs/String means that we are using a message definition from the std_msgs package (which ships with ROS) containing a single string field. Each topic can have only one messageType that must be used by all publishers and subscribers of that topic.

A "proper" ROS communication scheme will use predefined message types to serialize messages for maximum efficiency over the wire. When using the std_msgs package, this means each message will contain a value (or an array of values) of a single, very specific type. See the std_msgs documentation for a complete list. Other message types may be available, depending on which ROS packages are installed on the system.

For cross-browser application development, a bit more flexibility is usually desired. You can roll your own data-to-string encoding and pack everything into a single string topic or use multiple topics of appropriate messageType if you like, but unless you have severe performance needs, a JSON stringify and parse will pack arbitrary JavaScript objects as messages just fine. It will only take a little bit of boilerplate to accomplish this.

 * Serializes an object and publishes it to a std_msgs/String topic.
 * @param {ROSLIB.Topic} topic
 *       A topic to publish to. Must use messageType: std_msgs/String
 * @param {Object} obj
 *       Any object that can be serialized with JSON.stringify
function publishEncoded(topic, obj) {
  var msg = new ROSLIB.Message({
    data: JSON.stringify(obj)

 * Decodes an object from a std_msgs/String message.
 * @param {Object} msg
 *       Message from a std_msgs/String topic.
 * @return {Object}
 *       Decoded object from the message.
function decodeMessage(msg) {
  return JSON.parse(msg.data);

All of the above code can be shared by all pages and views, unless you want some to use different throttle or queue settings on a per-topic basis.

On the receiving side, any old anonymous function can handle the receipt and unpacking of messages.

exampleTopic.subscribe(function(msg) {
  var decoded = decodeMessage(msg);
  // do something with the decoded message object

The sender can publish updates at will, and all messages will be felt by the receivers.

// Explicitly declare that we intend to publish on this Topic.

setInterval(function() {
  var mySyncObject = {
    time: Date.now(),
    myFavoriteColor: 'red'
  publishEncoded(exampleTopic, mySyncObject);
}, 1000);

From here, you can add another layer of data shuffling by writing message handlers for your communication channel. Re-using the EventEmitter2 class upon which roslibjs depends is not a bad way to go. If it feels like you're implementing ROS messaging on top of ROS messaging.. well, that's what you're doing! This approach will generally break down when communicating with other non-browser nodes, so use it sparingly and only for application layer messaging that needs to be flexible.

 * Typed messaging wrapper for a std_msgs/String ROS Topic.
 * @param {ROSLIB.Topic} topic
 *       A std_msgs/String ROS Topic for multiplexed messaging.
 * @constructor
function RosTypedMessaging(topic) {
  this.topic = topic;
RosTypedMessaging.prototype.__proto__ = EventEmitter2.prototype;

 * Handles an incoming message from the topic by firing an event.
 * @param {Object} msg
 * @private
RosTypedMessaging.prototype.handleMessage_ = function(msg) {
  var decoded = decodeMessage(msg);
  var type = decoded.type;
  var data = decoded.data;
  this.emit(type, data);

 * Sends a typed message to the topic.
 * @param {String} type
 * @param {Object} data
RosTypedMessaging.prototype.sendMessage = function(type, data) {
  var msg = {type: type, data: data};
  publishEncoded(this.topic, msg);

//* Example implementation of RosTypedMessaging.
var myMessageChannel = new RosTypedMessaging(exampleTopic);

myMessageChannel.on('fooo', function(data) {
  console.log('fooo!', data);

setInterval(function() {
  var mySyncObject = {
    time: Date.now(),
    myFavoriteColor: 'red'
  myMessageChannel.sendMessage('fooo', mySyncObject);
}, 1000);

If you need to troubleshoot communications or are just interested in seeing how it works, ROS comes with some neat command line tools for publishing and subscribing to topics.

### show messages on /example/topicname
$ rostopic echo /example/topicname

### publish a single std_msgs/String message to /example/topicname
$ rostopic pub -1 /example/topicname std_msgs/String "foo!"

To factor input, arbitration or logic out of the browser, you could write a roscpp or rospy node acting as a server. Also worth a look are ROS services, which can abstract asynchronous data requests through the same messaging system.

Liquid Galaxy for Google.org at SXSW

End Point enjoyed an opportunity to work with Google.org, who bought a Liquid Galaxy to show their great efforts, at last week's SXSW conference in Austin. Google.org has a number of projects worldwide, all focused on how tech can bring about unique and inventive solutions for good. To showcase some of those projects, Google asked us to develop presentations for the Liquid Galaxy where people could fly to a given location, read a brief synopsis of the grantee organizations, and view presentations which included virtual flight animations, map overlays, and videos of the various projects.

Some of the projects included are as follows:
  • Charity:Water - The charity: water presentation included scenes featuring multi screen video of Scott Harrison (Founder/CEO) and Robert Lee (Director of Special Programs), and an animated virtual tour of charity: water well sites in Ethiopia.
  • World Wildlife Fund - The World Wildlife Fund presentation featured a virtual tour of the Bouba N’Djida National Park, Cameroon putting the viewer into the perspective of a drone patrolling the park for poachers. Additional scenes in the presentation revealed pathways of transport for illegal ivory from the park through intermediate stops in Nigeria and Hong Kong before reaching China.
  • Samasource - The Samasource presentation showed slums where workers start and the technology centers they are able to migrate to while serving a global network of technology clients.

But the work didn’t stop there! Google.org was also sharing the space with the XPrize opening gala on Monday night. For this event, we drew up a simple game where attendees could participate in various events around the room, receive coded answers at each station, and then enter their code into the Liquid Galaxy touchscreen. If successful, the 7-screen display whisked them to the Space Port in the Mojave, then into orbit. If the wrong code was entered, the participant got splashed into the Pacific Ocean. It was great fun!

The SXSW engagement is the latest in an ongoing campaign to bring attention to global challenges and how Google.org is helping solve those challenges. End Point enjoys a close working relationship with Google and Google.org. We relish the opportunity to bring immersive and inviting displays that convey a wealth of information to viewers in such an entertaining and engrossing manner.

This event ran for 2 days at the Trinity Hall venue just 1 block from the main SXSW convention center in downtown Austin, Texas.

Simple AngularJS Page

The best thing in AngularJS is the great automation of actualizing the data in the html code.

To show how easy Angular is to use, I will create a very simple page using AngularJS and Github.

Every Github user can get lots of notifications. All of them can be seen at Github notification page. There is also the Github API, which can be used for getting the notification information, using simple http requests, which return jsons.

I wanted to create a simple page with a list of notifications. With information if the notification was read (I used "!!!" for unread ones). And with automatical refreshing every 10 minutes.

To access the Github API, first I generated an application token on the Github token page. Then I downloaded a file from the AngularJS page, and a Github API javascript wrapper.

Then I wrote a simple html file:


      <body ng-app="githubChecker">

Github Notifications

!!! {{ n.subject.title }}
</body> </html>

This is the basic structure. Now we need to have some angular code to ask Github for the notifications and fill that into the above html.

The code is also not very complicated:

  var githubChecker = angular.module('githubChecker', []);

  githubChecker.controller("mainController", ['$scope', '$interval', function($scope, $interval){

    $scope.notifications = [];

    var github = new Github({
      username: "USERNAME",
      token:    "TOKEN",
      auth:     "oauth"
    var user = github.getUser();

    var getNotificationsList = function() {
      user.notifications(function(err, notifications) {
        $scope.notifications = notifications;


    $interval(getNotificationsList, 10*60*1000);


First of all I've created an Angular application object. That object has one controller, in which I created a Github object, which gives me a nice way to access the Github API.

The function getNotificationsList calls the Github API, gets a response, and just stores it in the $scope.notifications object.

Then the angular's magic comes into play. When the $scope fields are updated, angular automatically updates all the declarations in the html page. This time it is not so automatic, as I had to call the $scope.$apply() function to trigger it. It will loop through the $scope.notifications and update the html.

For more information about the Angular, and the commands I used, you can check the AngularJS Documentation.

Mobile-friendly sites or bust!

A few weeks ago, Google announced that starting on April 21 it will expand its “use of mobile-friendliness as a ranking signal” which “will have a significant impact in our search results”.

The world of search engine optimization and online marketing is aflutter about this announcement, given that even subtle changes in Google’s ranking algorithm can have major effects to improve or worsen any particular site’s ranking. And the announcement was made less than two months in advance of the announced date of the change, so there is not much time to dawdle.

Google has lately been increasing its pressure on webmasters (is that still a real term‽) such as with its announcement last fall of an accelerated timetable for sunsetting SSL certificates with SHA-1 signatures. So far these accelerated changes have been a good thing for most people on the Internet.

In this case, Google provides an easy Mobile-Friendly Site Test that you can run on your sites to see if you need to make changes or not:


So get on it and check those sites! I know we have a few that we can do some work on.

Advanced Product Filtering in Ecommerce

One of my recent projects for Paper Source has been to introduce advanced product filtering (or faceted filtering). Paper Source runs on Interchange, a perl-based open source ecommerce platform that End Point has been involved with (as core developers & maintainers) for many years.

In the case of Paper Source, personalized products such as wedding invitations and save the dates have advanced filtering to filter by print method, number of photos, style, etc. Advanced product filtering is a very common feature in ecommerce systems with a large number of products that allows a user to narrow down a set of products to meet their needs. Advanced product filtering is not unlike faceted filtering offered by many search engines, which similarly allows a user to narrow down products based on specific tags or facets (e.g. see many Amazon filters on the left column). In the case of Paper Source, I wrote the filtering code layered on top of the current navigation. Below I'll go through some of the details with small code examples.

Data Model

The best place to start is the data model. A simplified existing data model that represents product taxonomy might look like the following:

Basic data model linking categories to products.

The existing data model links products to categories via a many-to-many relationship. This is fairly common in the ecommerce space – while looking at a specific category often identified by URL slug or id, the products tied to that category will be displayed.

And here's where we go with the filtering:

Data model with filtering layered on top of existing category to product relationship.

Some notes on the above filtering data model:

  • filters contains a list of all the files. Examples of entries in this table include "Style", "Color", "Size"
  • filters_categories links filters to categories, to allow finite control over which filters show on which category pages, in what order. For example, this table would link category "Shirts" to filters "Style", "Color", "Size" and the preferred sort order of those filters.
  • filter_options includes all the options for a specific filter. Examples here for various options include "Large", "Medium", and "Small", all linked to the "Size" filter.
  • filter_options_products links filter options to a specific product id with a many to many relationship.

Filter Options Exclusivity

One thing to consider before coding are the business rules pertaining to filter option exclusivity. If a product is assigned to one filter option, can it also have another filter option for that same filter type? IE, if a product is marked as blue, can it also be marked as red? When a user filters by color, can they filter to select products that are both blue and red? Or, if a product is is blue, can it not have any other filter options for that filter? In the case of Paper Source product filtering, we went with the former, where filter options are not exclusive to each other.

A real-life example of filter non-exclusivity is how Paper Source filters wedding invitations. Products are filtered by print method and style. Because some products have multiple print methods and styles, non-exclusivity allows a user to narrow down to a specific combination of filter options, e.g. a wedding invitation that is both tagged as "foil & embossed" and "vintage".

URL Structure

Another thing to determine before coding is the URL structure. The URL must communicate the current category of products and current filter options (or what I refer to as active/activated filters).

I designed the code to recognize one component of the URL path as the category slug, and the remaining paths to map to the various filter option url slugs. For example, a URL for the category of shirts is "/shirts", a URL for large shirts "/shirts/large", and the URL for large blue shirts "/shirts/blue/large". The code not only has to accept this format, but it also must create consistently ordered URLs, meaning, we don't want both "/shirts/blue/large" and "/shirts/large/blue" (representing the same content) to be generated by the code. Here's what simplified pseudocode might look like to retrieve the category and set the activated filters:

my @url_paths = split('/', $request_url); #url paths is e.g. /shirts/blue/large
my $category_slug = shift(@url_paths)
# find Category where slug = $category_slug
# redirect if not found
# @url_paths is active filters

Applying the Filtering

Next, we need a couple things to happen:

  • If there is an activated filter for any filter option, apply it.
  • Generate URLs to toggle filter options.

First, all products are retrieved in this category with a query like this:

SELECT products.*,
  COALESCE((SELECT GROUP_CONCAT(fo.url_slug) FROM filters_options_item foi 
    JOIN filters_options fo ON fo.id = foi.filter_option_id 
    WHERE foi.product_id = products.id), '') AS filters
FROM products 
JOIN categories_products cp ON cp.product_id = products.id
JOIN categories c ON c.id = cp.category_id
WHERE c.url_slug = ?

Next is where the code gets pretty hairy, so instead I'll try to explain with pseudocode:

#@filters = all applicable filters for current category
# loop through @filters
  # loop through filter options for this filter
  # filter product results to include any selected filter options for this filter
  # if there are no filter options selected for this filter, include all products
  # build the url for each filter option, to toggle the filter option (on or off)
# loop through @filters (yes, a second time)
  # loop through filter options for this filter
  # count remaining products for each filter option, if none, set filter option to inactive
  # build the final url for each filter option, based on all filters turned on and off

My pseudocode shows that I iterate through the filters twice, first to apply the filter and determine the base URL to toggle each filter option, and second to count the remaining filtered products and build the URL to toggle each filter. The output of this code is a) a set of filtered products and b) a set of ordered filters and filter options with corresponding counts and links to toggle on or off.

Here's a more specific example:

  • Let's say we have a set of shirts, with the following filters & options: Style (Long Sleeve, Short Sleeve), Color (Red, Blue), Size (Large, Medium, Small).
  • A URL request comes in for /shirts/blue/large
  • The code recognizes this is the shirts category and retrieves all shirts.
  • First, we look at the style filter. No style filter is active in this request, so to toggle these filters on, the activation URLs must include "longsleeve" and "shortsleeve". No products are filtered out here.
  • Next, we look at the color filter. The blue filter option is active because it is present in the URL. In this first loop, products not tagged as blue are removed from the set of products. To toggle the red option on, the activation URL must include "red", and to toggle the blue filter off, the URL must not include "blue", which is set here.
  • Next, we look at the size filter. Products not tagged as large are removed from the set of products. Again, the large filter has to be toggled off in the URL because it is active, and the medium and small filter need to be toggled on.
  • In the second pass through filters, the remaining items applicable to each filter option are counted, for long sleeve, short sleeve, red, medium, and small options. And the URLs are built to turn on and off all filter options (e.g. applying the longsleeve filter will yield the URL "/shirts/longsleeve/blue/large", applying the red filter will yield the URL "/shirts/blue/red/large", turning off the blue filter will yield the URL "/shirts/large").

The important thing to note here is the double pass through filters is required to build non-duplicate URLs and to determine the product count after all filter options have been applied. This isn't simple logic, and of course changing the business rules like exclusivity will change the loop behavior and URL logic.

Alternative Approaches

Finally, a few notes regarding alternative approaches here:

  • Rather than going with the blacklist approach described here, one could go with a whitelist approach where a set of products is built up based on the filter options set.
  • Filtering could be done entirely via AJAX, in which case URL structure may not be a concern.
  • If the data is simple enough, products could potentially be filtered in the database query itself. In our case, this wasn't feasible since we generate product filter option details from a number of product attributes, not just what is shown in the simplified product filter data model above.

wroclove.rb a.k.a. "The best Java conference in Ruby world"

Time and Date: 13-15th March 2015
Place: Wrocław University

Amongst many Ruby and Rails talks on this conference, there were some not related to Ruby at all. Since 2013 I have observed a growing number of functional programming topics and concerns. Even the open discussion was mainly devoted not to OOP but to concepts like Event Sourcing or patterns similar to those promoted by Erlang or Clojure.

So let's enumerate the best moments.

First of all, the "ClojureScript + React.js" presented by Norbert Wójtowicz. The link below points to the presentation that was recorded on Lambda Days. It is a fascinating talk about gigantic technology leap that is going to have a impact on the whole OOP world.

Nicolas Dermine presented Overtone's implemented mostly in Ruby that's called Sonic Pi which lets you basically write code that plays music. It is a great tool from which to learn programming and to use to have fun in the same time. It is also a great tool for teachers (both - music and programming).

There was also a fascinating talk about some aspects of social engineering in sourcing the requirements from your customers. It was presented by Alberto Brandolini, and the technique is called Event Storming.