Allow superfluos padding base64 decoding

Author: msimacek

graalpython/com.oracle.graal.python.test/src/tests/test_binascii.py

@@ -70,6 +70,10 @@ def test_b2a_hex(self):
         b = self.type2test(b'helloo')
         self.assertEqual(binascii.hexlify(b), b'68656c6c6f6f')
 
+    def test_b2a_base64_padding(self):
+        b = self.type2test(b'cDXriAy/7i02kBeDkN0m2RIDz85w6pwuHkt2PZ4VmT2PQc1TZs8Ebvf6eKDFcD/S====')
+        self.assertEqual(binascii.a2b_base64(b), b'p5\xeb\x88\x0c\xbf\xee-6\x90\x17\x83\x90\xdd&\xd9\x12\x03\xcf\xcep\xea\x9c.\x1eKv=\x9e\x15\x99=\x8fA\xcdSf\xcf\x04n\xf7\xfax\xa0\xc5p?\xd2')
+
 class ArrayBinASCIITest(BinASCIITest):
     def type2test(self, s):
         return array.array('b', list(s))

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/BinasciiModuleBuiltins.java

@@ -171,9 +171,21 @@ PBytes doConvert(VirtualFrame frame, Object buffer,
         @TruffleBoundary
         private ByteSequenceStorage b64decode(byte[] data, int dataLen) {
             try {
+                // Remove superfluous padding, Java refuses it but CPython ignores it
+                int end;
+                for (end = dataLen - 1; end >= 0; end--) {
+                    if (data[end] != '=') {
+                        break;
+                    }
+                }
+                // The length without the padding
+                int unpaddedLen = end + 1;
+                // Round up to a multiple of 4 to get correct minimal padding. Clamp to dataLen in
+                // case the data is not padded correctly
+                int decodeLen = Math.min((unpaddedLen + 3) & ~3, dataLen);
                 // Using MIME decoder because that one skips over anything that is not the alphabet,
                 // just like CPython does
-                ByteBuffer result = Base64.getMimeDecoder().decode(ByteBuffer.wrap(data, 0, dataLen));
+                ByteBuffer result = Base64.getMimeDecoder().decode(ByteBuffer.wrap(data, 0, decodeLen));
                 return new ByteSequenceStorage(result.array(), result.limit());
             } catch (IllegalArgumentException e) {
                 throw PRaiseNode.raiseUncached(this, BinasciiError, e);