From df8ffd538aca3e3f6d897b46f5b4b9765da5c1c1 Mon Sep 17 00:00:00 2001
From: Dan Helfman <witten@torsion.org>
Date: Tue, 20 Oct 2009 20:49:06 -0700
Subject: [PATCH] Fix for problem with HTML differ that would actually hang the
 entire server when fed certain lengthy HTML strings. Unit tests included.

---
 controller/Html_differ.py           |  6 +++---
 controller/test/Test_html_differ.py | 13 +++++++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/controller/Html_differ.py b/controller/Html_differ.py
index b735598..330c951 100644
--- a/controller/Html_differ.py
+++ b/controller/Html_differ.py
@@ -82,9 +82,9 @@ class Html_differ( HTMLParser ):
     ( a, b ) = self.prepare_lists( a, b )
     return self.diff_lists( a, b )
 
-  SINGLE_TAG_PATTERN = re.compile( "<(\w+)(\s+[^>]*)*\s*/>" ) # e.g. '<br/>' or '<br />' or '<img src="foo" />'
-  START_TAG_PATTERN = re.compile( "<(\w+)(\s+[^>]*)*>" )      # e.g. '<i>' or '<a href="foo">'
-  END_TAG_PATTERN = re.compile( "</(\w+)>" )                  # e.g. '</i>' or '</a>'
+  SINGLE_TAG_PATTERN = re.compile( "<(\w+).*/>" ) # e.g. '<br/>' or '<br />' or '<img src="foo" />'
+  START_TAG_PATTERN = re.compile( "<(\w+).*>" )   # e.g. '<i>' or '<a href="foo">'
+  END_TAG_PATTERN = re.compile( "</(\w+)>" )      # e.g. '</i>' or '</a>'
 
   @staticmethod
   def track_open_tags( item, open_tags ):
diff --git a/controller/test/Test_html_differ.py b/controller/test/Test_html_differ.py
index cb7ca01..34b9529 100644
--- a/controller/test/Test_html_differ.py
+++ b/controller/test/Test_html_differ.py
@@ -1,3 +1,4 @@
+import time
 from controller.Html_differ import Html_differ
 
 
@@ -228,6 +229,18 @@ class Test_html_differ( object ):
     assert new_a == a
     assert new_b == b
 
+  def test_prepare_lists_with_style_and_timing( self ):
+    # An older version of the code took a really long time to parse certain
+    # lengthy style strings due to a backtracking regular expression, so check
+    # for that regression.
+    start_time = time.time()
+    a = [ 'foo ', 'bar ', 'baz ', 'quux' ]
+    b = [ 'foo ', 'bar ', 'baz ', '<span style="' + 'a: b' * 20 + '">' , 'quux' ]
+
+    result = self.differ.prepare_lists( a, b )
+
+    assert time.time() - start_time < 0.5
+
   def test_diff_lists_with_insert( self ):
     a = [ 'foo ', 'bar ', 'baz ', 'quux' ]
     b = [ 'foo ', 'bar ', 'whee ', 'baz ', 'quux' ]