Bad checksum passes FIXMessageDecoder validation

The FIXMessageDecoder.startsWith method has a bug, and the other functions in FIXMessageDecoder do not properly handle percolating the case back up to the caller. Specifically, if the pattern is matching against the end of a ByteBuffer it only matches the first character of the pattern. If the pattern doesn't match, there is no way to percolate a MessageDecoderResult.NOT_OK back up to the caller, it will just send back NEED_DATA.

It is best illustrated by running the following JUnit test

Paste into the FIXMessageDecoderTest class

public void testPatternMatching() throws Exception

{ decoder = new FIXMessageDecoder("UTF-16"); setUpBuffer("8=FIX.4.2\0019=12\00135=X\001108=30\0011wmyadz"); MessageDecoderResult decoderResult = decoder.decode(null, buffer, decoderOutput); assertEquals("wrong decoder result", MessageDecoderResult.NOT_OK, decoderResult); }