Modifying attributes with Hpricot

If you’re processing HTML with Hpricot and want to change the attributes on a tag in a search block, beware that the attributes method on an element returns a copy of the actual attributes. In order to change the real attribute on the element, you need to set raw_attributes on it. Here’s what I had to do, boiled down to the scum on the pan:

doc = Hpricot(html)
doc.search("img").each do |element|
  # do some processing here, calculating the new attribute value
  # ...
  element.raw_attributes = element.attributes.merge("src" => new_src)
end
# now save the tweaked document
file.write(doc.to_html)