Make IDNA return an empty string when the input is empty. Fixes #1163178.

Will backport to 2.4.

Lib/encodings/idna.py

@@ -149,6 +149,9 @@ class Codec(codecs.Codec):
             # IDNA is quite clear that implementations must be strict
             raise UnicodeError, "unsupported error handling "+errors
 
+        if not input:
+            return "", 0
+
         result = []
         labels = dots.split(input)
         if labels and len(labels[-1])==0:
@@ -166,6 +169,9 @@ class Codec(codecs.Codec):
         if errors != 'strict':
             raise UnicodeError, "Unsupported error handling "+errors
 
+        if not input:
+            return u"", 0
+
         # IDNA allows decoding to operate on Unicode strings, too.
         if isinstance(input, unicode):
             labels = dots.split(input)

Lib/test/test_codecs.py

@@ -630,6 +630,12 @@ class CodecTest(unittest.TestCase):
     def test_builtin(self):
         self.assertEquals(unicode("python.org", "idna"), u"python.org")
 
+    def test_stream(self):
+        import StringIO
+        r = codecs.getreader("idna")(StringIO.StringIO("abc"))
+        r.read(3)
+        self.assertEquals(r.read(), u"")
+
 class CodecsModuleTest(unittest.TestCase):
 
     def test_decode(self):

Misc/NEWS

@@ -193,6 +193,8 @@ Extension Modules
 Library
 -------
 
+- Bug #1163178: Make IDNA return an empty string when the input is empty.
+
 - Patch #848017: Make Cookie more RFC-compliant. Use CRLF as default output
   separator and do not output trailing semicola.