Les Hill — Truncating HTML

We recently needed to show a truncated version of existing HTML content. Although there are several issues¹ when dealing with HTML content, our specific concern was maintaining the integrity of the HTML. Some quick googling led to a nice helper written by Henrik Nyh last year. We tweaked the original a bit to append the ellipsis within the tag at the truncation point and truncate at a word (or tag) boundary. Here it is, enjoy.

 1 # By Henrik Nyh <http://henrik.nyh.se> 2008-01-30.
 2 # Free to modify and redistribute with credit.
 3 # Word truncation and fixes by Les Hill <http://blog.leshill.org> 2009-06-02
 4 #
 5 
 6 require "rubygems"
 7 require "hpricot"
 8 
 9 module TextHelper
10 
11   # Like the Rails _truncate_ helper but doesn't break HTML tags or entities.
12   def truncate_html(text, max_length = 30, ellipsis = "...")
13     return if text.nil?
14     doc = Hpricot(text.to_s)
15     doc.inner_text.chars.length > max_length ? doc.truncate(max_length, ellipsis).inner_html : text.to_s
16   end
17 
18   def self.truncate_at_space(text, max_length, ellipsis = '...')
19     l = [max_length - ellipsis.length, 0].max
20     stop = text.rindex(' ', l) || 0
21     (text.length > max_length ? text[0...stop] + ellipsis : text).to_s
22   end
23 end
24 
25 module HpricotTruncator
26   module NodeWithChildren
27     def truncate(max_length, ellipsis)
28       return self if inner_text.chars.length <= max_length
29       truncated_node = dup
30       truncated_node.name = name
31       truncated_node.raw_attributes = raw_attributes
32       truncated_node.children = []
33       each_child do |node|
34         break if max_length <= 0
35         node_length = node.inner_text.chars.length
36         truncated_node.children << node.truncate(max_length, ellipsis)
37         max_length = max_length - node_length
38       end
39       truncated_node
40     end
41   end
42 
43   module TextNode
44     def truncate(max_length, ellipsis)
45       self.content = TextHelper.truncate_at_space(content, max_length, ellipsis)
46       self
47     end
48   end
49 
50   module IgnoredTag
51     def truncate(max_length, ellipsis)
52       self
53     end
54   end
55 end
56 
57 Hpricot::Doc.send(:include,       HpricotTruncator::NodeWithChildren)
58 Hpricot::Elem.send(:include,      HpricotTruncator::NodeWithChildren)
59 Hpricot::Text.send(:include,      HpricotTruncator::TextNode)
60 Hpricot::BogusETag.send(:include, HpricotTruncator::IgnoredTag)
61 Hpricot::Comment.send(:include,   HpricotTruncator::IgnoredTag)

¹ For example: preventing XSS attacks, maintaining coherent styling.