@@ -28,6 +28,7 @@
 __author__ = '[email protected] (Neil Fraser)'
 
 import re
+import struct
 import sys
 import time
 import urllib
@@ -1135,6 +1136,14 @@ def diff_levenshtein(self, diffs):
 levenshtein += max(insertions, deletions)
 return levenshtein
 
+@classmethod
+def is_high_surrogate(cls, c):
+return 0xd800 <= struct.unpack('>H', c)[0] <= 0xdbff
+
+@classmethod
+def is_low_surrogate(cls, c):
+return 0xdc00 <= struct.unpack('>H', c)[0] <= 0xdfff
+
 def diff_toDelta(self, diffs):
 """Crush the diff into an encoded string which describes the operations
 required to transform text1 into text2.
@@ -1148,15 +1157,32 @@ def diff_toDelta(self, diffs):
 Delta text.
 """
 text = []
+last_end = None
 for (op, data) in diffs:
+if 0 == len(data):
+continue
+
+encoded = data.encode('utf-16be')
+this_top = encoded[0:2]
+this_end = encoded[-2:]
+
+if self.is_high_surrogate(this_end):
+last_end = this_end
+encoded = encoded[0:-2]
+
+if last_end and self.is_high_surrogate(last_end) and self.is_low_surrogate(this_top):
+encoded = last_end + encoded
+
+if 0 == len(encoded):
+continue
+
 if op == self.DIFF_INSERT:
 # High ascii will raise UnicodeDecodeError. Use Unicode instead.
-data = data.encode("utf-8")
-text.append("+" + urllib.quote(data, "!~*'();/?:@&=+$,# "))
+text.append("+" + urllib.quote(encoded.decode('utf-16be').encode('utf-8'), "!~*'();/?:@&=+$,# "))
 elif op == self.DIFF_DELETE:
-text.append("-%d" % len(data))
+text.append("-%d" % (len(encoded) // 2))
 elif op == self.DIFF_EQUAL:
-text.append("=%d" % len(data))
+text.append("=%d" % (len(encoded) // 2))
 return "\t".join(text)
 
 def diff_fromDelta(self, text1, delta):

@@ -441,6 +441,86 @@ def testDiffDelta(self):
 # Convert delta string into a diff.
 self.assertEquals(diffs, self.dmp.diff_fromDelta(text1, delta))
 
+diffs = [(self.dmp.DIFF_EQUAL, u"\ud83d\ude4b\ud83d"), (self.dmp.DIFF_INSERT, u"\ude4c\ud83d"), (self.dmp.DIFF_EQUAL, u"\ude4b")]
+delta = self.dmp.diff_toDelta(diffs)
+self.assertEquals("=2\t+%F0%9F%99%8C\t=2", delta)
+
+# Unicode: split surrogates
+# Inserting similar surrogate pair at beginning
+self.assertEquals(
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_INSERT, u'\U0001F171'),
+(self.dmp.DIFF_EQUAL, u'\U0001F170\U0001F171')
+]),
+self.dmp.diff_toDelta(self.dmp.diff_main(
+u'\U0001F170\U0001F171',
+u'\U0001F171\U0001F170\U0001F171'
+))
+)
+
+# Inserting similar surrogate pair in the middle
+self.assertEquals(
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_EQUAL, u'\U0001F170'),
+(self.dmp.DIFF_INSERT, u'\U0001F172'),
+(self.dmp.DIFF_EQUAL, u'\U0001F171')
+]),
+self.dmp.diff_toDelta(self.dmp.diff_main(
+u'\U0001F170\U0001F171',
+u'\U0001F170\U0001F172\U0001F171'
+))
+)
+
+# Deleting similar surogate pair at the beginning
+self.assertEquals(
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_DELETE, u'\U0001F171'),
+(self.dmp.DIFF_EQUAL, u'\U0001F170\U0001F171')
+]),
+self.dmp.diff_toDelta(self.dmp.diff_main(
+u'\U0001F171\U0001F170\U0001F171',
+u'\U0001F170\U0001F171'
+))
+)
+
+# Deleting similar surogate pair in the middle
+self.assertEquals(
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_EQUAL, u'\U0001F170'),
+(self.dmp.DIFF_DELETE, u'\U0001F172'),
+(self.dmp.DIFF_EQUAL, u'\U0001F171')
+]),
+self.dmp.diff_toDelta(self.dmp.diff_main(
+u'\U0001F170\U0001F172\U0001F171',
+u'\U0001F170\U0001F171'
+))
+)
+
+# Swap surrogate pair
+self.assertEquals(
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_DELETE, u'\U0001F170'),
+(self.dmp.DIFF_INSERT, u'\U0001F171')
+]),
+self.dmp.diff_toDelta(self.dmp.diff_main(
+u'\U0001F170',
+u'\U0001F171'
+))
+)
+
+# Swap surrogate pair, force the invalid diff groups
+self.assertEquals(
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_INSERT, u'\U0001F170'),
+(self.dmp.DIFF_DELETE, u'\U0001F171')
+]),
+self.dmp.diff_toDelta([
+(self.dmp.DIFF_EQUAL, u'\ud83c'),
+(self.dmp.DIFF_INSERT, u'\udd70'),
+(self.dmp.DIFF_DELETE, u'\udd71')
+])
+)
+
 # Verify pool of unchanged characters.
 diffs = [(self.dmp.DIFF_INSERT, "A-Z a-z 0-9 - _ . ! ~ * ' ( ) ; / ? : @ & = + $ , # ")]
 text2 = self.dmp.diff_text2(diffs)