A deep_reject method for hashes in Ruby

March 5th, 2015

Recently, while adding missing functionality for the i18n-js gem I’ve stumbled into a problem. I needed to have a method to “deep reject” keys in the hash. There are some examples in the wild doing that, but they all solve this problem by adding a new method to the Hash class. I wanted a generic method, which would take the hash as an argument.

After some head scratching, tinkering and tweaking, I’ve come up with a correct solution (at least I think it’s correct). Here it is:

def self.deep_reject(hash, &block)
  hash.each_with_object({}) do |(k, v), memo|
    unless block.call(k, v)
      if v.is_a?(Hash)
        memo[k] = deep_reject(v, &block)
        memo[k] = v

You use it like this:

hash = {:a => {:b => 1, :c => 2}}

result = deep_reject(hash) { |k, v| k == :b }

result # => {:a => {:c => 2}}

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Enabling I18n locale fallbacks in Rails

February 6th, 2015

This guide is valid for i18n version 0.7.0+ and Rails 4.1+

Strangely enough enabling custom locale fallbacks is harder than it should be. Here’s what you need to enable custom locale fallbacks with i18n gem.

First, you need to set config.i18n.fallbacks = true for all environments in a Rails application (config/environments/*.rb).

Then you need to have this in your config/application.rb:

# The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
# config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
config.i18n.default_locale = :en

# Enforce available locales
config.i18n.enforce_available_locales = true

# Custom I18n fallbacks
config.after_initialize do
  I18n.fallbacks = I18n::Locale::Fallbacks.new(at: :"de-DE", ch: :"de-DE", gb: :"en-US")

The above will enable custom fallbacks from at and ch locales to the German language and from gb locale to English. The enforce_available_locales bit is optional.

If you also use i18n-js to have your translated phrases available in javascript, here’s the exemplary fallbacks snippet you need to put inside your javascript code:

I18n.locales["at"] = ["de", "en"]
I18n.locales["ch"] = ["de", "en"]
I18n.locales["gb"] = ["en"]

Stubbing Time.now in Ruby

February 25th, 2013

Yeah, sure, we could do that. We could also use timecop. But both solutions seems overkill when all you need is to check if some attribute got updated with the result of `Time.now`. What you should do instead, is use the power of RSpec (or rspec-expectations to be more exact):

post.published_at.should be_within(1.second).of(Time.now)

Doesn’t it look just beautiful?

VI mode indicator in ZSH prompt

September 23rd, 2012

Here is my take on VI mode indicator in zsh’s prompt. This is useful only for people who use the vi mode (bindkey -v) in ZSH.


function zle-keymap-select {
  zle reset-prompt
zle -N zle-keymap-select

function zle-line-finish {
zle -N zle-line-finish

# Fix a bug when you C-c in CMD mode and you'd be prompted with CMD mode indicator, while in fact you would be in INS mode
# Fixed by catching SIGINT (C-c), set vim_mode to INS and then repropagate the SIGINT, so if anything else depends on it, we will not break it
# Thanks Ron! (see comments)
function TRAPINT() {
  return $(( 128 + $1 ))

And then it’s a matter of adding ${vim_mode} somewhere in your prompt. For example like this:


Other examples on the web use zle reset-prompt in the zle-line-init, which has a very nasty side effect of deleting last couple of lines on mode change (when going from ins to cmd mode) when using multi-line prompt. Using zle-line-finish works around that.

Also see my current ~/.zshrc, which includes those tweaks (and many others!).

ZSH vi mode with emacs keybindings

September 23rd, 2012

This is my attempt at bringing emacs-style keybindings to vi mode in ZSH:

bindkey -M viins '^a'    beginning-of-line
bindkey -M viins '^e'    end-of-line
bindkey -M viins '^k'    kill-line
bindkey -M viins '^r'    history-incremental-pattern-search-backward
bindkey -M viins '^s'    history-incremental-pattern-search-forward
bindkey -M viins '^p'    up-line-or-history
bindkey -M viins '^n'    down-line-or-history
bindkey -M viins '^y'    yank
bindkey -M viins '^w'    backward-kill-word
bindkey -M viins '^u'    backward-kill-line
bindkey -M viins '^h'    backward-delete-char
bindkey -M viins '^?'    backward-delete-char
bindkey -M viins '^_'    undo
bindkey -M viins '^x^r'  redisplay
bindkey -M viins '\eOH'  beginning-of-line # Home
bindkey -M viins '\eOF'  end-of-line       # End
bindkey -M viins '\e[2~' overwrite-mode    # Insert
bindkey -M viins '\ef'   forward-word      # Alt-f
bindkey -M viins '\eb'   backward-word     # Alt-b
bindkey -M viins '\ed'   kill-word         # Alt-d                    

bindkey -M vicmd '^a'    beginning-of-line
bindkey -M vicmd '^e'    end-of-line
bindkey -M vicmd '^k'    kill-line
bindkey -M vicmd '^r'    history-incremental-pattern-search-backward
bindkey -M vicmd '^s'    history-incremental-pattern-search-forward
bindkey -M vicmd '^p'    up-line-or-history
bindkey -M vicmd '^n'    down-line-or-history
bindkey -M vicmd '^y'    yank
bindkey -M vicmd '^w'    backward-kill-word
bindkey -M vicmd '^u'    backward-kill-line
bindkey -M vicmd '/'     vi-history-search-forward
bindkey -M vicmd '?'     vi-history-search-backward
bindkey -M vicmd '^_'    undo
bindkey -M vicmd '\ef'   forward-word                      # Alt-f
bindkey -M vicmd '\eb'   backward-word                     # Alt-b
bindkey -M vicmd '\ed'   kill-word                         # Alt-d
bindkey -M vicmd '\e[5~' history-beginning-search-backward # PageUp
bindkey -M vicmd '\e[6~' history-beginning-search-forward  # PageDown

You know, so that your muscle memory can rest in peace. Also see the commit adding the above emacs style keybindings to my dotfiles.

Testing CSRF protection in Rails

June 28th, 2012

Ever wanted to test your CSRF protection in a Rails app? For example, in a situation when you have a custom “remember me” cookie set and you need to overwrite Rails’ handle_unverified_request to clear it so it does not open a big security hole in your app? I know I did and it took me a while to find out how to do that, so I figured it would be good to write about it.

Here’s how to do it (in Test::Unit, but it’s the same for RSpec):

setup do
  # Enable CSRF protection in this test
  ActionController::Base.allow_forgery_protection = true

teardown do
  # Disable CSRF protection for all other tests
  ActionController::Base.allow_forgery_protection = false

Adding the above will make it so that the authenticity_token is added to each generated <form> element and will be required to be sent with each non GET request.

Heroku memory quota killing machine

April 4th, 2012

When I was migrating a suite of Exvo apps to Heroku‘s Cedar stack I’ve noticed a very strange behaviour. For two apps during first “run” the main process spun out of control, trying to consume way too much memory. After doing a manual restart everything went back to normal and the problem was basically gone (we haven’t seen it reoccuring).

Here is the log of such an out of control worker:

2012-04-02T11:52:32+00:00 heroku[worker.1]: Process running mem=550M(107.5%)
2012-04-02T11:52:32+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:52:52+00:00 heroku[worker.1]: Process running mem=811M(158.5%)
2012-04-02T11:52:52+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:53:12+00:00 heroku[worker.1]: Process running mem=858M(167.7%)
2012-04-02T11:53:12+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:53:32+00:00 heroku[worker.1]: Process running mem=1099M(214.8%)
2012-04-02T11:53:32+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:53:52+00:00 heroku[worker.1]: Process running mem=1539M(300.6%)
2012-04-02T11:53:52+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:54:12+00:00 heroku[worker.1]: Process running mem=1580M(308.7%)
2012-04-02T11:54:12+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:54:32+00:00 heroku[worker.1]: Process running mem=1709M(333.8%)
2012-04-02T11:54:32+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:54:53+00:00 heroku[worker.1]: Process running mem=2115M(413.1%)
2012-04-02T11:54:53+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:55:13+00:00 heroku[worker.1]: Process running mem=2301M(449.6%)
2012-04-02T11:55:13+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:55:33+00:00 heroku[worker.1]: Process running mem=2302M(449.6%)
2012-04-02T11:55:33+00:00 heroku[worker.1]: Error R14 (Memory quota exceeded)
2012-04-02T11:55:53+00:00 heroku[worker.1]: Process running mem=2747M(536.6%)
2012-04-02T11:55:53+00:00 heroku[worker.1]: Error R15 (Memory quota vastly exceeded)
2012-04-02T11:55:53+00:00 heroku[worker.1]: Stopping process with SIGKILL
2012-04-02T11:55:54+00:00 heroku[worker.1]: Process exited with status 137

This is just a worker, but I’ve observed the same for web processes as well. Be aware that as soon as your application starts serving R14/R15 errors it stops processing any new requests (they simply time out).

Previously: Introduction to Heroku H12 timeouts.

Uninitialized constant Gem::Deprecate

April 2nd, 2012

If you run into this problem, which by the way usually happens after upgrading the rubygems package (in my case it was to version 1.8.21), your best bet is to upgrade the gem from the backtrace of this error. In my case it was the old passenger version 3.0.9, which was causing this problem. Upgrading to 3.0.11 solved it.


March 3rd, 2012

This blog has been. But no more! Now restored from the dead (i.e. fresh installation and customization of the Kubrick template).

It seems that running and outdated WordPress installation is not a very bright idea. Who would have thought?

Oh WordPress and PHP…
how much I loathe thee!

Introduction to Heroku H12 timeouts

November 15th, 2011

At Exvo we were experiencing problems while trying to send an email to all of our 150K+ users. This lead to a careful investigation of what is exactly happening during this process. So we setup our loggers (heroku logs -t | tee output.log), run heroku consoles, increased to 20 dynos and 10 workers and begun the sending process.

It all started with a POST request to send those emails:

app[web.10]: Started POST ...

Which timed out and there was no:

app[web.10]: Completed 200 OK ...

or similar log entry later on, just silence.

This is Heroku’s killing machine in action. It silently kills every process, which runs for longer than 30 seconds (we’re using the Bamboo stack). This is more or less how Heroku deals with long running requests. I don’t blame them for this behavior, even though I very much dislike it. But I digress.

When Heroku kills such process it does so in a very nice way, i.e. it lets it finish its business first. In other words the process will continue in the background and after finishing it will just die/stop/restart. Our email collecting job (selecting 150K users from the database…) run uninterrupted for over 40 minutes. So this is the good part.

The bad part is that when this killed process is still running in the background the dyno which it was connected to will stop serving new requests until this process finally dies, but Heroku will keep sending new requests to it! This is observed by the infamous H12 timeouts:

heroku[router]: Error H12 (Request timeout) -> GET auth.exvo.com/users/sign_in dyno=web.10 queue= wait= service=30000ms status=503 bytes=0

Also notice the 503 error code (Unavailable), which is returned by the Heroku router.

So this is really bad as all sorts of different/random web requests will just keep failing without you knowing what’s going on.

So while I greatly appreciate that Heroku lets such processes still run in the background, I really don’t like that it still keeps sending traffic their way.

PS: Yes, sending emails should be done as a background action by the Heroku workers. I know. But it’s not. Yet.