Fix Base45 dropping trailing bytes on non-ASCII input

The Base45 encoder and decoder iterated with range(0, len(text), step)
while indexing into t = b(text). codext converts a bytes input to str
(UTF-8) before the codec runs, so for any non-ASCII content b(text) is
longer than text and len(text) stops the loop early, silently dropping
the trailing byte(s). For example encode(b'\xcf\xb1\x1b') returned
'OBQ' instead of 'OBQR0' and the value no longer round-tripped.

Iterate over len(t) (the actual byte sequence) instead. Output now
matches RFC 9285 and the reference base45 implementation, and encoding
round-trips for arbitrary byte input.

Author: gaoflow

src/codext/base/base45.py

@@ -34,7 +34,10 @@ def base45_encode(mode):
     b45 = _get_charset(B45, mode)
     def encode(text, errors="strict"):
         t, s = b(text), ""
-        for i in range(0, len(text), 2):
+        # iterate over the byte sequence (t), not len(text): when the input
+        # holds non-ASCII characters, b(text) is longer than text and using
+        # len(text) silently drops the trailing bytes
+        for i in range(0, len(t), 2):
             n = 256 * __ord(t[i])
             try:
                 n += __ord(t[i+1])
@@ -54,7 +57,7 @@ def base45_decode(mode):
     def decode(text, errors="strict"):
         t, s = b(text), ""
         ehandler = handle_error("base45", errors, decode=True)
-        for i in range(0, len(text), 3):
+        for i in range(0, len(t), 3):
             try:
                 n = b45[__chr(t[i])]
             except KeyError:

tests/test_base.py

@@ -211,6 +211,19 @@ def test_codec_base100(self):
         self.assertRaises(ValueError, codecs.decode, b(B100)[1:], "base100")
         self.assertIsNotNone(codecs.decode(b(B100) + b"\n", "base100", "ignore"))
 
+    def test_codec_base45(self):
+        # RFC 9285 test vectors
+        for s, b45 in [("AB", "BB8"), ("Hello!!", "%69 VD92EX0"), ("base-45", "UJCLQE7W581")]:
+            self.assertEqual(codecs.encode(s, "base45"), b45)
+            self.assertEqual(codecs.encode(b(s), "base45"), b(b45))
+            self.assertEqual(codecs.decode(b45, "base45"), s)
+            self.assertEqual(codecs.decode(b(b45), "base45"), b(s))
+        # a trailing non-ASCII byte must not be dropped (byte length, not str length, drives encoding)
+        self.assertEqual(codecs.encode(b"\xcf\xb1\x1b", "base45"), b"OBQR0")
+        self.assertEqual(codecs.decode(b"OBQR0", "base45"), b"\xcf\xb1\x1b")
+        for data in [b"\xff\xfe", b"hello", b"\x00", b"\x80\x81\x82\x83\x84"]:
+            self.assertEqual(codecs.decode(codecs.encode(data, "base45"), "base45"), data)
+
     def test_codec_base_generic(self):
         for n in range(2, 255):
             bn = "base{}_generic".format(n)