fastbuffer.rb

module ActiveSupport
  module FastSafeBuffer
    [
      :capitalize, :chomp, :chop, :delete, :downcase, :gsub, :lstrip,
      :next, :reverse, :rstrip, :slice, :squeeze, :strip, :sub,
      :succ, :swapcase, :tr, :tr_s, :upcase, :prepend
    ].each do |unsafe_method|
      if String.new.respond_to? unsafe_method
        module_eval <<-EVAL
          def #{unsafe_method}!(*)
            @html_safe = false
            super
          end
        EVAL
      end
    end

    def [](*args)
      return super if args.size < 2
      super.add_safety(self)
    end

    def safe_concat(value)
      raise ActiveSupport::SafeBuffer::SafeConcatError unless html_safe?
      concat(value)
    end

    def safe!
      @html_safe = true
    end

    def initialize_copy(other)
      super
      safe! if other.html_safe?
    end

    def clone_empty
      self[0, 0].add_safety(self)
    end

    def concat(value)
      if html_safe? and value.html_safe?
        super(value)
      else
        super(ERB::Util.h(value))
      end
    end
    alias << concat

    def +(other)
      dup.concat(other)
    end

    def dup
      super.add_safety(self, true)
    end

    def html_safe?
      !!@html_safe
    end

    def to_s
      self
    end

    def encode_with(coder)
      coder.represent_scalar nil, to_str
    end

    def to_yaml(*args)
      return super() if defined?(YAML::ENGINE) && !YAML::ENGINE.syck?
      to_str.to_yaml(*args)
    end
  end
end

class String
  def add_safety(from = nil, force = false)
    unless @_extended_html_safe and !force
      @_extended_html_safe = true
      self.extend ::ActiveSupport::FastSafeBuffer
      safe! if from == true or from.html_safe?
    end
    self
  end

  def html_safe
    add_safety(true)
  end
end