CODEC-305: Fix byte-skipping in Base16 decoding

Author: ab

src/main/java/org/apache/commons/codec/binary/Base16.java

@@ -169,34 +169,33 @@ void decode(final byte[] data, int offset, final int length, final Context conte
 
         // we must have an even number of chars to decode
         final int charsToProcess = availableChars % BYTES_PER_ENCODED_BLOCK == 0 ? availableChars : availableChars - 1;
+        final int end = offset + dataLen;
 
         final byte[] buffer = ensureBufferSize(charsToProcess / BYTES_PER_ENCODED_BLOCK, context);
 
         int result;
-        int i = 0;
         if (dataLen < availableChars) {
             // we have 1/2 byte from previous invocation to decode
             result = (context.ibitWorkArea - 1) << BITS_PER_ENCODED_BYTE;
             result |= decodeOctet(data[offset++]);
-            i = 2;
 
             buffer[context.pos++] = (byte)result;
 
             // reset to empty-value for next invocation!
             context.ibitWorkArea = 0;
         }
 
-        while (i < charsToProcess) {
+        final int loopEnd = end - 1;
+        while (offset < loopEnd) {
             result = decodeOctet(data[offset++]) << BITS_PER_ENCODED_BYTE;
             result |= decodeOctet(data[offset++]);
-            i += 2;
             buffer[context.pos++] = (byte)result;
         }
 
         // we have one char of a hex-pair left over
-        if (i < dataLen) {
+        if (offset < end) {
             // store 1/2 byte for next invocation of decode, we offset by +1 as empty-value is 0
-            context.ibitWorkArea = decodeOctet(data[i]) + 1;
+            context.ibitWorkArea = decodeOctet(data[offset]) + 1;
         }
     }
 

src/test/java/org/apache/commons/codec/binary/Base16Test.java

@@ -577,4 +577,25 @@ public void testLenientDecoding() {
         final byte[] decoded = b16.decode(StringUtils.getBytesUtf8(encoded));
         assertArrayEquals(new byte[] {(byte)0xaa, (byte)0xbb, (byte)0xcc, (byte)0xdd}, decoded);
     }
+
+    @Test
+    public void testOddEvenDecoding() {
+        final String encoded = "4142434445";
+
+        final BaseNCodec.Context context = new BaseNCodec.Context();
+        final Base16 base16 = new Base16();
+
+        final byte[] encodedBytes = StringUtils.getBytesUtf8(encoded);
+
+        // pass odd, then even, then odd amount of data
+        base16.decode(encodedBytes, 0, 3, context);
+        base16.decode(encodedBytes, 3, 4, context);
+        base16.decode(encodedBytes, 7, 3, context);
+
+        final byte[] decodedBytes = new byte[context.pos];
+        System.arraycopy(context.buffer, context.readPos, decodedBytes, 0, decodedBytes.length);
+        final String decoded = StringUtils.newStringUtf8(decodedBytes);
+
+        assertEquals("ABCDE", decoded);
+    }
 }