Johan Sørensen

Rails tip: validating Markdown

Wednesday March 30, 2005

I’ve been doing a bunch of work on Collaboa in the past few nights, mainly bringing it up to date with the latest Rails and a general major overhaul.

One of the problems with previous versions was the there was no validation of user inputted Markdown and since BlueCloth has a habit of blowing up in the face of users whenever the syntax isn’t complete. Left out backticks, for inline code, are in particular troublesome.

So I wanted to check that the syntax was proper through Rails’ validation methods before saving anything and giving the user he ability to fix his syntax errors. The following was the simplest solution I came up with.

protected
  def validate
    errors.add("content", "has #{invalid_markdown_syntax(self.content)}") »
          unless invalid_markdown_syntax(self.content).nil?
  end
  
private
  def invalid_markdown_syntax(text)               
    begin
      BlueCloth.new(text).to_html
      return nil
    rescue BlueCloth::FormatError => e
      return e
    end
  end	

Since I want to display the syntax error to the user, I’ll have to return the error that BlueCloth raised so I can display it in the validation failure message and return nothing (nil) if BlueCloth didn’t choke on anything. This way the following text will be displayed on Markdown formatting errors (typing ``foo` is something BlueCloth will usually choke on): "Content has bad markdown format near “foo”: No “`” found before end".

UPDATE Jeremy stepped up and offered a much better solution to the problem, which follows the “Ruby Way” (and/or Rails way) of dealing with it, see the comments below

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