Issue #5640: Fix _multibytecodec so that CJK codecs don't repeat

error replacement returned by codec error callbacks twice in
IncrementalEncoder and StreamWriter.

Lib/test/test_multibytecodec.py

@@ -112,6 +112,10 @@ class Test_IncrementalEncoder(unittest.TestCase):
         self.assertRaises(UnicodeEncodeError, encoder.encode, '\u0123')
         self.assertEqual(encoder.encode('', True), b'\xa9\xdc')
 
+    def test_issue5640(self):
+        encoder = codecs.getincrementalencoder('shift-jis')('backslashreplace')
+        self.assertEqual(encoder.encode('\xff'), b'\\xff')
+        self.assertEqual(encoder.encode('\n'), b'\n')
 
 class Test_IncrementalDecoder(unittest.TestCase):
 

Misc/NEWS

@@ -58,6 +58,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #5640: Fix _multibytecodec so that CJK codecs don't repeat
+  error substitutions from non-strict codec error callbacks in
+  incrementalencoder and StreamWriter.
+
 - Issue #5656: Fix the coverage reporting when running the test suite with
   the -T argument.
 

Modules/cjkcodecs/multibytecodec.c

@@ -506,7 +506,6 @@ multibytecodec_encode(MultibyteCodec *codec,
 		outleft = (Py_ssize_t)(buf.outbuf_end - buf.outbuf);
 		r = codec->encode(state, codec->config, &buf.inbuf, inleft,
 				  &buf.outbuf, outleft, flags);
-		*data = buf.inbuf;
 		if ((r == 0) || (r == MBERR_TOOFEW && !(flags & MBENC_FLUSH)))
 			break;
 		else if (multibytecodec_encerror(codec, state, &buf, errors,r))
@@ -536,6 +535,7 @@ multibytecodec_encode(MultibyteCodec *codec,
 		if (_PyBytes_Resize(&buf.outobj, finalsize) == -1)
 			goto errorexit;
 
+	*data = buf.inbuf;
 	Py_XDECREF(buf.excobj);
 	return buf.outobj;