There were no signs of trouble until we noticed a mix of 200 and 500 HTTP statuses in Kukuruku's web server logs. We were a bit confused when we started to look into it. The weird thing was that the server responded with either 200 (OK) or 500 (Internal Server Error) statuses even to requests were going to the same URL. What would you blame first? In most cases caching is the first places that you might have to take a look into — some results may have been cached and cause issues for a set of users. But after looking through error log, it was obvious that the caching layer was operating correctly. The problem was somewhere in code, but the error message from logs was not that helpful. We started to think about the difference between user A and user B hitting the same URL. The first thought which came to our mind was authorization. But whole Kukuruku team checks the website tons of times through out a day. Someone would definitely notice the issue. In addition, Development Environment did not have any errors. The whole team was able to open the website in both logged in and logged out states.

Read more →

Looking through programming articles sometimes I see posts about creating your own HTTP server. I am most interested in C++ so I often read blogs about it. After looking them through you could easily write you own web server “on sockets” using boost.asio or something else. I also examined libevent and libev. Each of them has its advantages. Libevent is of great interest to me for developing a small HTTP server. Considering some innovations in C++11 the code becomes much more space-efficient and allows for the creation of a basic HTTP server in less than 40 lines.

The information of this post will be useful for those not familiar with libevent and those who want to quickly create an HTTP server. There’s nothing innovative in this post, so you can use it as material for working in the right direction.

libevent is better than libev and boost.asio because of its embedded HTTP server and some abstraction for operating with buffers. It also has a large set of helper functions. You can examine HTTP protocol by yourself by writing a simple FSN (finite state machine) or maybe through some other means. When working with libevent – it’s all there already. You can also go to a lower level and write your own parser for HTTP and perform the work with sockets on libevent. I liked the detail level of this library. If you want to do something quickly you’ll find a higher-level interface that is usually less flexible. When there are more serious requirements you can go down gradually, level by level. The library allows doing many things, such as: asynchronous input/output, work with the network, work with timers, rpc, etc. You can also use it to create both server-side and client-side software.

Read more →

I had to rebuild a pathfinding algorithm for our game recently. The previous one (Boost Concepts) was bad as any sidestep was dangerous. So I wanted to take a ready algorithm from a good source. That’s exactly when I remembered about boost as there’s functionality for working with graphs. Unfortunately “find a function, call it and everything will work” approach wasn’t meant to be realized. The library is focused on the maximum use flexibility which has badly affected its simplicity. But it’s better than creating it from scratch (then fixing it). I didn’t want to bother with other libraries, while boost has already been used in the project.

Read more →

In the previous articles of the series we’ve reviewed the adaptive process of the square game field for concepts of boost graphs. Now we’ll consider the process of finding the path in the square field. Implementation of boost search allows adapting the algorithm quite accurately. In this article we’ll provide just one example of such parameterization – an ability to create various lengths of graph edges.

Let’s begin with describing the parameter. We should create a map of edge weights. This map will meet requirements of ReadablePropertyMapConcept concept. It’s quite easy to implement. We should define several types and [] iterator. On the basis of the key-type edge the latter returns its length.

Read more →

I’ll briefly remind you of the task. There’s a two-dimensional game field consisting of squares. Some of them are vacant and others are occupied. We should find a path through vacant squares from one field position to another one. We implemented the search algorithm in Boost. But it requires our field to fit the graph definition. Or rather the class should meet the requirements of two concepts: boost::VertexListGraph and boost::IncidenceGraph. We don't want to change the interface of game field, as it’s not a graph for the remaining project and will never be one.

In the previous part we’ve reviewed attaching the external associative types that are necessary for interpreting the class as boost graph. Of course types only are not enough. We should also implement several functions with the assigned signature, and iterators which will help the library to handle the game field as a graph.

Read more →

Dear %username%,

I have recently come across several interesting and useful tools/libraries/events I would like to tell you about.

DC.js

This library allows creating great multi level/scalable cross-platform charts and diagrams providing instant feedback on user's interaction. A popular d3.js is in charge of the viewing process. crossfilter.js deals with the analysis of multi-dimensional data sets.

chart.renderlet(function(chart){
    // smooth the rendering through event throttling
    dc.events.trigger(function(){
        // focus some other chart to the range selected by user on this chart
        someOtherChart.focus(chart.filter());
    });
})

Read more →

Today we’re going to review an algorithm that was invented 11 years ago. Its “prototype” is a counting device with three thousand years of history.

Read more →

Rust is a system programming language. It runs blazingly fast, prevents almost all crashes and removes the ambiguities associated with sharing access to data. Mozilla developed it as a tool to create a new generation browser engine – Servo.

Read more →

Who This Article Is For

I would say that the article is mainly for people who already have an experience with some other programming languages, but they want to look around. Also, functional programming is a trending thing nowadays. So if you want to see what it actually is, welcome. If you are a complete beginner, it's still may be useful, as it's always good to know what's going on around the world of IT.

A Few Words about Elixir

A few years ago Jose Valim posted in his repository a project of the language that is built on top of Erlang VM — Elixir. In the article you’ll find extracts from the documentation and a few simple examples.

Read more →