Debugging performance issues in your Rails app can be a tough challenge.

To get more detailed insights consider using the rack-mini-profiler gem.

Setup with Unpoly

Add the following gems:

group :development do
  gem 'memory_profiler'
  gem 'rack-mini-profiler'
  gem 'stackprof'
end

Unpoly will interfere with the rack-mini-profiler widget, but configuring the following works okayish:

// rack-mini-profiler + unpoly
if (process...

There are two ways a logout in SAML can happen: Service Provider (SP) initiated and Identity Provider (IDP) initiated logout. I'll explain how to implement both flows with devise_saml_authenticatable.

Note

SAML also supports a SOAP and an Artifact binding to do this. This guide only refers to POST and Redirect bindings. devise_saml_authenticatable does not support SOAP and Artifact bindings.

SP initiated logout (using the Redirect Binding)

When the user clicks on Logout within the app, the app can trigger...

Developing or debugging SAML functionality can be a hassle, especially when you need to go back and forth with someone external who is managing the identity provider (IDP).
But you can setup a local keycloak server to act as your IDP to play around with. This might seam intimidating, but is actually quite simple when using docker and turning off some verification steps.

1. Start a keycloak instance using docker

`mkdir -p keycloak_data && docker run --network=host -e KEYCLOAK_ADMIN=admin -e KEYCLOAK_ADMIN...

If you need to make an HTTPS connection to a host which uses an expired certificate, do not disable certificate verifications entirely. Doing that enables e.g. man in the middle attacks.
If you accept only a single expired and known certificate, you are much less in trouble.

Setup

All the solutions described below use a verify_callback for the request's OpenSSL::X509::Store where you can specify a lambda to adjust its verification response.
Your callback must return either true or false and OpenSSL's verification result is...

tl;dr

Prefer request specs over end-to-end tests (Capybara) to joyfully test file downloads!

Why?

Testing file downloads via Capybara is not easy and results in slow and fragile tests. We tried different approaches and the best one is just okay.

Tests for file downloads via Capybara ...

• ... are slow,
• ... are fragile (breaks CI, breaks if Selenium driver changes, ...),
• ... need workarounds for your specia...

It's 2024 and we have tools like ffmpeg, imagemagick and GPT readily available. With them, it's easy to convert texts, images, audio and video clips into each other.

For the everyday use without any parameter tweaking I'm using a collection of tiny scripts in my ~/bin folder that can then be used as bash functions. And: It's faster to use the CLI than interacting with a website and cheaper to use the API than buying GPT plus.. :-)

Usage

• text-to-image "parmiggiano cheese wedding cake, digital art"
• `text-to-audio "Yesterday I ate ...

I recently built a screen with a very high and wide table in the center. This posed some challenges:

• Giving the table a horizontal scroll bar is very unergonomic, since the scrollbar might be far off screen.
• Making the whole page scrollable looks bad, since I don't want the rest of the UI to scroll.
• Giving the table its own vertical scrollbar and a limited height would have solved it, but felt weird, since the table was 90% of the page.

What I ended up doing is reusing the horizontal page scrollbar (which is naturally fixed at t...

Example

I, [2024-01-21T06:22:17.484221 #2698200]  INFO -- : [4cdad7a4-8617-4bc9-84e9-c40364eea2e4] test
I, [2024-01-21T06:22:17.484221 #2698200]  INFO -- : [4cdad7a4-8617-4bc9-84e9-c40364eea2e4] more
I, [2024-01-21T06:22:17.484221 #2698200]  INFO -- : [6e047fb3-05df-4df7-808e-efa9fcd05f87] test
I, [2024-01-21T06:22:17.484221 #2698200]  INFO -- : [6e047fb3-05df-4df7-808e-efa9fcd05f87] more
I, [2024-01-21T06:22:17.484221 #2698200]  INFO -- : [53a240c1-489e-4936-bbeb-d6f77284cf38] nope
I, [2024-01-21T06:22:17.484221 #2698200]  INFO -- ...

Getting an entire test suite green can be a tedious task which involves frequent switches between the CLI that is running tests back to the IDE where its cause can be fixed.

The following bash aliases helped me speed up that process:

alias show-next-failure="bundle exec rspec --next-failure"
alias open-next-failure="show-next-failure || show-next-failure --format json  | jq -r '.examples[0]' | jq '\"--line \" + (.line_number|tostring) + \" \" + .file_path' | xargs echo | xargs rubymine"

There is a lot going on above but the gist...

Getting CSS (and JS) live reloading to work in a esbuild / Rails project is a bit of a hassle, but the following seems to work decently well.

We assume that you already use a standard "esbuild in Rails" setup, and have an esbuild watcher running that picks up your source code in app/assets and compiles to public/assets; if not change the paths below accordingly.

Basic idea

We will

• use the guard-livereload gem as the livereload server (which send updates to the browser),
• use the livereload-js npm package in the browser to con...

Every modern Rails app should have a Content Security Policy enabled.

Very compatible default

The following "default" is a minimal policy that should

• "just work" for almost all applications
• give you most of the benefits of a CSP

In your config/initializers/content_security_policy.rb, set

Rails.application.config.content_security_policy do |policy|
  policy.object_src :none
  policy.script_src :unsafe_eval, :strict_dynamic, :https # Browsers with support for "'strict-dynamic'" will ignore "https:"
  po...

While upgrading CarrierWave from version 0.11.x to 3.x, we encountered some very nasty fails. Below are the basic changes you need to perform and some behavior you may eventually run into when upgrading your application. This aims to save you some time understanding what happens under the hood to possibly discover problems faster as digging deeply into CarrierWave code is very fun...

Whitelists and blacklists

The following focuses on extension allowlisting, but it is the exact same thing for content type allowlisting with the `content_ty...

All direct child directories of app are automatically added to the eager- and autoload paths. They do NOT create a module for namespacing. This is intuitive, since there normally is no module Model, or module Controller. If you want to add a new base directory, there's no additional config needed.

Example

app
├── controllers
├── helpers
├── inputs # No config needed 
├── mailers
├── models
├── uploaders # No config needed
├── util # No config needed
└── workers # No config needed

Sometimes it's handy to group files wit...

The git doc states on the difference of these two commands:

• git-restore[1] is about restoring files in the working tree from either the index or another commit. This command does not update your branch. The command can also be used to restore files in the index from another commit.
• git-reset[1] is about updating your branch, moving the tip in order to add or remove commits from the branch. This operation changes the commit history.

git reset can also be used to restore th...

There are multiple ways to redirect URLs to a different URL in Rails, and they differ in small but important nuances.

Imagine you want to redirect the following url https://www.example.com/old_location?foo=bar to https://www.example.com/new_location?foo=bar.

Variant A

You can use ActionController::Redirecting#redirect_to in a controller action

class SomeController < ActionController::Base
  def old_location
    redirect_to(new_location_url(params.permit(:foo))) 
  end
end

This will:

• It will redirect with a 302 st...

Rails' url_for is useful for generating routes from a Hash, but can lead to an open redirect vulnerability.

Your application's generated route methods with a _url suffix are also affected because [they use url_for unter the hood](https://github.com/rails/rails...

Rails' Strong Parameters enable you to allow only specific values from request params to e.g. avoid mass assignment.

Usually, you say something like params.permit(:email, :password) and any extra parameters would be ignored, e.g. when calling to_h.
This is excellent and you should definitely use it.

What is permit! and why is it dangerous?

However, there is also params.permit! whic...

You can tell npm to install a package globally with npm -g install @puppeteer/browsers. However, it seems that its not possible that npx can run commands from global packages without referencing the global package path.

Example

Installing @puppeteer/browsers globally:

$ npm -g install @puppeteer/browsers

The globally installed package @puppeteer/browsers can not be access via npx:

$ npx --no-install @puppeteer/browsers

npm ERR! canceled # Error message when package is not installed

But it is installed g...