CommonMarker

Ruby wrapper for libcmark, the reference parser for CommonMark. It passes all of the C tests, and is therefore spec-complete.

Installation

Add this line to your application's Gemfile:

gem 'commonmarker'

And then execute:

$ bundle

Or install it yourself as:

$ gem install commonmarker

Usage

Converting to HTML

Call render_html on a string to convert it to HTML:

require 'commonmarker'
CommonMarker.render_html('Hi *there*', :default)
# <p>Hi <em>there</em></p>\n

The second argument is optional--see below for more information.

Generating a document

You can also parse a string to receive a Document node. You can than print that node to HTML, iterate over the children, and other fun node stuff. For example:

require 'commonmarker'

doc = CommonMarker.render_doc('*Hello* world', :default)
puts(doc.to_html) # <p>Hi <em>there</em></p>\n

doc.walk do |node|
  puts node.type # [:document, :paragraph, :text, :emph, :text]
end

The second argument is optional--see below for more information.

Example: walking the AST

require 'commonmarker'

# parse the files specified on the command line
doc = CommonMarker.render_doc("# The site\n\n [GitHub](https://www.github.com)")

# Walk tree and print out URLs for links
doc.walk do |node|
  if node.type == :link
    printf("URL = %s\n", node.url)
  end
end

# Capitalize all regular text in headers
doc.walk do |node|
  if node.type == :header
    node.walk do |subnode|
      if subnode.type == :text
        subnode.string_content = subnode.string_content.upcase
      end
    end
  end
end

# Transform links to regular text
doc.walk do |node|
  if node.type == :link
    node.insert_before(node.first_child)
    node.delete
  end
end

Creating a custom renderer

You can also derive a class from CommonMarker's HtmlRenderer class. This produces slower output, but is far more customizable. For example:

class MyHtmlRenderer < CommonMarker::HtmlRenderer
  def initialize
    super
    @headerid = 1
  end
  def header(node)
    block do
      out("<h", node.header_level, " id=\"", @headerid, "\">",
               :children, "</h", node.header_level, ">")
      @headerid += 1
    end
  end
end

# this renderer prints directly to STDOUT, instead
# of returning a string
myrenderer = MyHtmlRenderer.new
print(myrenderer.render(doc))

# Print any warnings to STDERR
renderer.warnings.each do |w|
  STDERR.write("#{w}\n")
end

Options

CommonMarker accepts the same options that CMark does, as symbols:

• :default - The default rendering.
• :sourcepos - Include source position in rendered HTML.
• :hardbreaks - Treat \n as hardbreaks (by adding <br/>).
• :normalize - Attempt to normalize the HTML.
• :smart - Use smart punctuation (curly quotes, etc.).
• :validate_utf8 - Replace illegal sequences with the replacement character U+FFFD.
• :safe - Suppress raw HTML and unsafe links.

For a single option, pass it in as a symbol argument:

require 'commonmarker'
CommonMarker.render_html("\"Hello,\" said the spider.", :smart)
# <p>“Hello,” said the spider.</p>\n

To have multiple options applied, pass in an array of symbols:

require 'commonmarker'
CommonMarker.render_html("\"Hello,\" said the spider.\n\"'Shelob' is my name.\"", [:hardbreaks, :smart])
# <p>“Hello,” said the spider.</br>“‘Shelob’ is my name.”</p>

For more information on these options, see the CMark documentation.

Hacking

After cloning the repo:

script/bootstrap
bundle exec rake compile

If there were no errors, you're done! Otherwise, make sure to follow the CMark dependency instructions.

Benchmarks

Some rough benchmarks:

$ bundle exec rake benchmark

input size = 11063727 bytes

redcarpet
  0.070000   0.020000   0.090000 (  0.079641)
github-markdown
  0.070000   0.010000   0.080000 (  0.083535)
commonmarker with to_html
  0.100000   0.010000   0.110000 (  0.111947)
commonmarker with ruby HtmlRenderer
  1.830000   0.030000   1.860000 (  1.866203)
kramdown
  4.610000   0.070000   4.680000 (  4.678398)