slodown

slodown is the ultimate user input rendering pipeline.

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I love Markdown. I love syntax highlighting. I love oEmbed. And last but not least, I love whitelist-based HTML sanitizing. slodown rolls all of these into one, and then some.

Here's what slodown does by default:

  • render extended Markdown into HTML. It uses the kramdown library, so yes, footnotes are supported!
  • add syntax highlighting to Markdown code blocks through CodeRay.
  • support super-easy rich media embeds, sloblog.io-style. Just point the Markdown image syntax at, say, a Youtube video, and slodown will fetch the complete embed code through the magic of ruby-oembed.
  • auto-link contained URLs using Rinku, which is smart enough to not auto-link URLs contained in, say, code blocks.
  • sanitize the generated HTML using the white-list based sanitize gem.

slodown is an extraction from sloblog.io. It is very easy to extend or modify, as it's just a plain old Ruby class you can inherit from.

Installation

Add this line to your application's Gemfile:

gem 'slodown'

And then execute:

$ bundle

Or install it yourself as:

$ gem install slodown

Usage

For every piece of user input that needs to be rendered, create an instance of Slodown::Formatter with the source text and use it to perform some or all transformations on it. Finally, call #to_s to get the rendered output.

Examples:

# let's create an instance to work with
formatter = Slodown::Formatter.new(text)

# just extract metadata
formatter.extract_metadata.to_s

# just render Markdown to HTML
formatter.markdown.to_s

# just auto-link contained URLs
formatter.autolink.to_s

# just sanitize HTML tags
formatter.sanitize.to_s

# you can chain multiple operations
formatter.markdown.sanitize.to_s

# this is the whole deal:
formatter.extract_metadata.markdown.autolink.sanitize.to_s

# which is the same as:
formatter.complete.to_s

Metadata

Slodown allows metadata, such as the creation date, to be defined in the text to be processed:

#+title: Slodown
#+created_at: 2014-03-01 13:51:12 CET
# Installation

Add this line to your application's Gemfile:

    gem 'slodown'

...

Metadata can be accessed with Slodown::Formatter#metadata:

formatter.metadata[:title] # => "Slodown"

OEmbed support

Slodown extends the Markdown image syntax to support OEmbed-based embeds. Anything supported by the great OEmbed gem will work. Just supply the URL:

![youtube video](https://www.youtube.com/watch?v=oHg5SJYRHA0)

Some OEmbed providers will return IFRAME-based embeds. If you want to control which hosts are allowed to have IFRAMEs on your site, override the Formatter#allowed_iframe_hosts method to return a regular expression that will be matched against the IFRAME source URL's host. Please note that this will also apply to IFRAME HTML tags added by the user directly.

Hints

  • If you want to add more transformations or change the behavior of the #complete method, just subclass Slodown::Formatter and go wild. :-)
  • Markdown transformations, HTML sanitizing, oEmbed handshakes and other operations are pretty expensive operations. For sake of performance (and stability), it is recommended that you cache the generated output in some manner.
  • Eat more Schnitzel.

TODOs

  • More/better specs. slodown doesn't have a lot of functionality of its own, passing most of its duties over to the beautiful rendering gems it uses, but I'm sure there's still an opportunity or two for it to break, so, yeah, I should be adding some specs.
  • Better configuration for the HTML sanitizer. Right now, in order to change the sanitizing behavior, you'll need to inherit a new class from Slodown::Formatter and override its #sanitize_config method. Regarding the contents of the hash this method returns, please refer to the sanitize documentation.

Contributing

Just like with my other gems, I am trying to keep slodown as sane (and small) as possible. If you want to contribute code, please talk to me before writing a patch or submitting a pull request! I'm serious about keeping things focused and would hate to cause unnecessary disappointment. Thank you.

If you're still set on submitting a pull request, please consider the following:

  1. Create your pull request from a feature branch.
  2. The pull request must only contain changes related to the feature.
  3. Please include specs where it makes sense.
  4. Absolutely no version bumps or similar.

Version History

0.2.0

  • Slodown is now whitelisting all domains for possible iframe/embed-based media embeds by default. If you don't want this, you can override Formatter#allowed_iframe_hosts to return a regular expression that will match against the embed URL's host.
  • Bumped minimum required version of kramdown to 1.5.0 for all the nice new syntax highlighter integrations it offers (and changes required due to deprecated/changed options.)
  • Support for Twitter oEmbed (using an unfortunately deprecated API, nonetheless.)
  • Added Slodown::Formatter#kramdown_options, returning a hash of kramdown configuration options. Overload this in order to customize the formatter's behavior.

0.1.3

  • first public release