Even though this code is written in 2011, as of April 2015, i'm still using this gem myself. Any feature request, bugfix or issues will be handled.

A bbcode parser gem you can include in your rails app to parse bbcode-formatted strings to HTML or any other format you like.

The bbcode gem consists of 4 parts:

• The Tokenizer-class, which converts the bbcode-formatted string to a stream of tokens.
• The Parser-class, which attempts to pair bbcode tags to bbcode elements.
• The Handler-class, which converts bbcode elements anyway you like.
• The Helpers-module, which adds a method to String, allowing you to convert bbcode-formatted strings with a registered handler.

Additionally, a HtmlHandler class is available. This class is a Handler designed to convert bbcode elements to HTML more easily.

Add the gem to the gemfile of your project: gem "th-bbcode", "~> 0.4.0"

Create and register a handler. In this example, I'm creating a HtmlHandler and I'm going to register it as :html.

require 'rubygems'
require 'bundler/setup'
require 'bbcode'

Bbcode::Base.register_handler :html, Bbcode::HtmlHandler.new(
  :b => :strong,
  :i => :em,
  :url => [ :a, { :href => "%{0}" } ],
  :txt => ->(element){ "#{element.content.source}" },
  :img => ->(element){ %(<img src="#{CGI.escapeHTML(element.content.source)}">) },
  :admin => ->(element, locals){ locals[:is_admin] ? element.content : "" },
  :color => [ :span, { :style => "color: %{0};" } ]
)

That's it! You can now parse any string as bbcode and convert it to html with the :html-handler like this:

"[b]Hello, bold world![/]".as_bbcode.to :html
# => <strong>Hello, bold world!</strong>
"[admin]Hello, admin![/]".as_bbcode.to :html, :is_admin => true
# => Hello, admin!
"[admin]Hello, admin![/]".as_bbcode.to :html, :is_admin => false
# => 

If you're using this gem in a rails project, I would recommend registering your handlers in an initializer.

See examples in spec/ folder for detailed examples of usage.

• Parsing regular bbcode tags like [b] and [/b].
• Parsing anonymous closing bbcode tags like [/].
• Parsing bbcode tags with arguments like [a=foo, bar], [a foo=1 bar:2], [a=foo, bar bar:1 foo=2] and [a="foo" b='bar'].
• Parsing nested bbcode elements like [b]bold[i]and italic[/]only bold[/], which might result to <b>bold<i>and italic</i>only bold</b>.
• Parsing incorrectly nested bbcode elements like [b]bold[i]and italic[/b]only italic[/], which might result to <b>bold<i>and italic</i></b><i>only italic</i>.
• Passing variables to the handler and accessing them to the element handler callbacks.

You might want to convert URLs in the message to be converted to a hyperlink, or you might want smileys in your bbcode message. This can be done by defining a :"#text"-handler in your Handler or HtmlHandler.

I personally used WillScanString's StringScanner class to achieve this:

# Requires the will_scan_string gem
require "will_scan_string"

string_scanner = WillScanString::StringScanner.new
string_scanner.register_replacement "<", "&lt;"
string_scanner.register_replacement ">", "&gt;"
string_scanner.register_replacement "&", "&amp;"
string_scanner.register_replacement "\"", "&quot;"
string_scanner.register_replacement /(?:\r\n|\r|\n)/, "<br>"
string_scanner.register_replacement /[^\s@]+@[^\s@]/, ->(email){ %(<a href="mailto:#{CGI.escapeHTML(email)}">#{CGI.escapeHTML(email)}</a>) }

# +handler+ is your Bbcode::HtmlHandler or Bbcode::Handler instance
handler.register_element_handler :"#text", ->(text){ string_scanner.replace(text) }

The above example converts newlines to <br>-tags, escapes HTML entities and converts e-mail addresses to clickable mailto hyperlinks.

Note: By overwriting the :"#text"-handler in the HtmlHandler, html entities are no longer replaced automatically: You need to escape them in your handler callback yourself. Failing to do so might expose your website to XSS vulnerabilities.

Although this bbcode parser gem was primary designed for converting bbcode to HTML, it is possible to use another parser or tokenizer while still using the same handlers.

Using another tokenizer allows you to parse anything as if it were to be bbcode. This feature is still in development, but a nice example is my own ycode gem. This gem can be found here: https://github.com/tobyhinloopen/y-code

• An easier way to handle text around bbcode tags to, for example, add smileys and wrap hyperlinks to URLs. Currently, the only way to achieve this is by adding a :"#text"-handler to your handler and adding the functionality yourself. (note: See the above note regarding WillScanString)
• An easier way to include the content, source or content-source in the HtmlHandler-class.
• Review handleability of element interrupts.
• Review regular expression matching bbcode tags to allow tags having names containing characters other than A-Z, 0-9, _ and -, possibly based on the current registered tags.
• Add CDATA-like feature for bbcode tags to allow tags to be ignored within certain elements. Useful for [code]-tags.
• Add a default handler with the most common bbcode tags.