nested content_tags escape inner html.. why?

Question

So, if I loop through and create a collection of li/a tags, I get as expected.. an array of these tags:

(1..5).to_a.map do
  content_tag(:li) do
    link_to(\"bo         


        

Answer 1

It happens because in Rails 3 the SafeBuffer class was introduced which wraps the String class and overrides the default escaping that would otherwise occur when concat is called.

In your case, the content_tag(:li) is outputting a proper SafeBuffer, but Array#join doesn't understand SafeBuffers and simply outputs a String. The content_tag(:ol) is then be called with a String as it's value instead of a SafeBuffer and escapes it. So it doesn't so much have to do with nesting as it does to do with join returning a String not a SafeBuffer.

Calling html_safe on a String, passing the String to raw, or passing the array to safe_join will all return a proper SafeBuffer and prevent the outer content_tag from escaping it.

Now in the case of passing false to the escape argument, this doesn't work when your passing a block to content tag because it is calling capture(&block) ActionView::Helpers::CaptureHelper which is used to pull in the template, or your case the output value of join, which then causes it to call html_escape on the string before it makes its way into the content_tag_string method.

  # action_view/helpers/tag_helper.rb
  def content_tag(name, content_or_options_with_block = nil, options = nil, escape = true, &block)
    if block_given?
      options = content_or_options_with_block if content_or_options_with_block.is_a?(Hash)
      # capture(&block) escapes the string from join before being passed
      content_tag_string(name, capture(&block), options, escape)
    else
      content_tag_string(name, content_or_options_with_block, options, escape)
    end
  end

  # action_view/helpers/capture_helper.rb
  def capture(*args)
    value = nil
    buffer = with_output_buffer { value = yield(*args) }
    if string = buffer.presence || value and string.is_a?(String)
      ERB::Util.html_escape string
    end
  end

Since value here is the return value from join, and join returns a String, it calls html_escape before the content_tag code even gets to it with it's own escaping.

Some reference links for those interested

https://github.com/rails/rails/blob/v3.1.0/actionpack/lib/action_view/helpers/capture_helper.rb

https://github.com/rails/rails/blob/v3.1.0/actionpack/lib/action_view/helpers/tag_helper.rb

http://yehudakatz.com/2010/02/01/safebuffers-and-rails-3-0/

http://railsdispatch.com/posts/security

Edit

Another way to handle this is to do a map/reduce instead of map/join since if reduce is not passed an argument it will use the first element and run the given operation using that object, which in the case of map content_tag will be calling the operation on a SafeBuffer.

content_tag(:ol) do
  (1..5).to_a.map do
    content_tag(:li) do
      link_to(...)
    end
  end.reduce(:<<)
  # Will concat using the SafeBuffer instead of String with join
end

As a one-liner

content_tag(:ul) { collection.map {|item| content_tag(:li) { link_to(...) }}.reduce(:<<) }

Add a little meta-spice to clean things up

ul_tag { collection.map_reduce(:<<) {|item| li_link_to(...) } }

Who needs html_safe... this is Ruby!