Sometimes you just want to have a small web server that serves files to test something.

Serve the current directory

On Ruby 1.9.2+ you can do the following ("." for current directory).

ruby -run -ehttpd . -p8000

Python 2.x offers a similar way.

python -m SimpleHTTPServer 8000 .

This is the same way with Python 3.x

python -m http.server

In both cases your web server is single-threaded and will block when large files are being downloaded from you.

For solutions in many other languages, see the [big list of http s…

When you need to create a locale for a language variant (like Austrian for German), you probably don't want to duplicate your entire de.yml file only to change a few minor exceptions for our Austrian friends.

Luckily, the I18n gem used by Rails has a fallback feature where you can make one locale file fall back to another if no translation is available.

In the example above you would have a config/locales/de_DE.yml:

de_DE:
    # hundreds of translations here

… and another …

For newer Ubuntu versions we currently need to install the patch level version 1.8.7-p375, otherwise the dev dependencies from openssl will cause the installation to fail.

For a project that specifies the Ruby version 1.8.7 in the .ruby-version the rbenv autoswitch will not work. You have several options how you can solve this problem:

• Install rbenv-aliases, which will alias your Ruby 1.8.7-p375 …

This card shows basic techniques for fixing a flaky integration test suite that sometimes passes and sometimes fails. "Integration test" is a test script that remote-controls a web browser with tools like Selenium WebDriver.

Although the examples in this card use Cucumber and Selenium, the techniques are applicable to all languages and testing tools.

Why tests are flaky

Your tests probably look like this:

When I click on A
When I click on B
When I click on C
Then I should see effects of C

A test like this works fine most of t…

I had an issue with icons from an icon font aligning differently on Linux, iOS and Windows (seemingly browser-independent). With vertical-align:middle, they aligned properly on Linux, iOS and macOS, whereas with a vertical-align of -18%, it looked good on Windows and iOS, but not Linux.

Further investigation showed that not only icons, but also normal capital letters aligned differently. No setting of vertical-align could fix this, neither top, bottom, middle, nor additional paddings or margins. It seems like browsers take the…

In a JavaScript console, type this:

> 9112347935156469760
9112347935156470000

Ooops.

This occurs because JavaScript uses double precision floats to store numbers.

So according to IEEE floating point definition only numbers between -(2^53 - 1) (-9007199254740991) and 2^53 - 1 (9007199254740991) can safely be represented in JavaScript.

Note that ECMAScript 6 will probably also offer [Number.MAX_SAFE_INTEGER](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference…

Compatible changes:

• Add preload_association at instance level. Example: user.preload_associations(:posts)
• Add support for polymorphic associations in traverse_association.

This is a small example on how you can check if your Postgres index can be used by a specific query in you Rails application. For more complex execution plans it might still be a good idea to use the same path of proof.

1. Identify the query your application produces

puts User.order(:last_name, :created_at).to_sql
# => SELECT "users".* FROM "users" ORDER BY "users"."last_name" ASC, "users"."created_at" ASC

2. Add an index in your migration and migrate

add_index :users, [:last_name, :created_at]

3. Test the…

Web applications can be used by multiple users at the same time. A typical application server like Passenger has multiple worker processes for a single app. In a distributed deployment setup like we use at makandra you will even have multiple application servers, each with their own worker pool.

This means that your code needs to deal with concurrent data access. The two main tools we use to cope with concurrency are database transactions and distributed locks. These two are not interchangeable. You ca…

From time to time we update the underlying rubocop version in our makandra-rubocop gem. This often results in breaking changes in the cops configuration.

The upgrade process is described in the Changelog. Normally you will only see the new cops that were added by the rubocop upstream. They will result in new offenses in your project and need to be fixed.

For this release we want to encourage you to enable the Rails cops, too. This is how you co…

In Rspec 3 the DSL like describe is exposed globally by default. Therefore it is not necessary to write Rspec.describe.

However, there is a config option to disable this beavior, which also disables the old should-syntax:

RSpec.configure do |config|
  config.disable_monkey_patching!
end

In order to still use describe without Rspec, you can set expose_dsl_globally = true after disable_monkey_patching!:

```
RSpec.configure do |con…

When installing gems, a lot of time is spent building locally installed documentation that you probably never use.

We recommend you disable documentation generation for gem install by default.
Note that Bundler won't install documentation, so this advice applies only when installing gems manually.

If you don't already have it, create a ~/.gemrc file. The gemrc is a Yaml file, so add the following line to add default switches to the gem command.

gem: --no-document

(If you do n…

When a Rails controller action should handle both HTML and JSON responses, do not use request.xhr? to decide that. Use respond_to.

I've too often seen code like this:

def show
  # ...
  if request.xhr?
    render json: @user.as_json
  else
     # renders default HTML view
  end
end

This is just plain wrong. Web browsers often fetch JSON via XHR, but they (should) also send the correct Accept HTTP header to tell the server the data they expect to receive.

If you say request.xhr? as a means for "…