Issue #19619: Blacklist non-text codecs in method API

str.encode, bytes.decode and bytearray.decode now use an
internal API to throw LookupError for known non-text encodings,
rather than attempting the encoding or decoding operation and
then throwing a TypeError for an unexpected output type.

The latter mechanism remains in place for third party non-text
encodings.

Backported changeset d68df99d7a57.

1 files changed, 42 insertions, 0 deletions

diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index 1a199f7..a8b3da0 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -4,6 +4,7 @@ import locale
 import sys
 import unittest
 import warnings
+import encodings
 
 from test import support
 
@@ -2408,6 +2409,47 @@ class TransformCodecTest(unittest.TestCase):
             sout = reader.readline()
             self.assertEqual(sout, b"\x80")
 
+    def test_text_to_binary_blacklists_binary_transforms(self):
+        # Check binary -> binary codecs give a good error for str input
+        bad_input = "bad input type"
+        for encoding in bytes_transform_encodings:
+            fmt = (r"{!r} is not a text encoding; "
+                   r"use codecs.encode\(\) to handle arbitrary codecs")
+            msg = fmt.format(encoding)
+            with self.assertRaisesRegex(LookupError, msg) as failure:
+                bad_input.encode(encoding)
+            self.assertIsNone(failure.exception.__cause__)
+
+    def test_text_to_binary_blacklists_text_transforms(self):
+        # Check str.encode gives a good error message for str -> str codecs
+        msg = (r"^'rot_13' is not a text encoding; "
+               r"use codecs.encode\(\) to handle arbitrary codecs")
+        with self.assertRaisesRegex(LookupError, msg):
+            "just an example message".encode("rot_13")
+
+    def test_binary_to_text_blacklists_binary_transforms(self):
+        # Check bytes.decode and bytearray.decode give a good error
+        # message for binary -> binary codecs
+        data = b"encode first to ensure we meet any format restrictions"
+        for encoding in bytes_transform_encodings:
+            encoded_data = codecs.encode(data, encoding)
+            fmt = (r"{!r} is not a text encoding; "
+                   r"use codecs.decode\(\) to handle arbitrary codecs")
+            msg = fmt.format(encoding)
+            with self.assertRaisesRegex(LookupError, msg):
+                encoded_data.decode(encoding)
+            with self.assertRaisesRegex(LookupError, msg):
+                bytearray(encoded_data).decode(encoding)
+
+    def test_binary_to_text_blacklists_text_transforms(self):
+        # Check str -> str codec gives a good error for binary input
+        for bad_input in (b"immutable", bytearray(b"mutable")):
+            msg = (r"^'rot_13' is not a text encoding; "
+                   r"use codecs.decode\(\) to handle arbitrary codecs")
+            with self.assertRaisesRegex(LookupError, msg) as failure:
+                bad_input.decode("rot_13")
+            self.assertIsNone(failure.exception.__cause__)
+
 
 @unittest.skipUnless(sys.platform == 'win32',
                      'code pages are specific to Windows')