Block Size - retrieved as negative with Snappy codec.

I am using the snappy codec, the bytes from 0x4fc1 to 0x4fd0,represent 16 byte sync block

16 byte sync >>    1c 21 91 44 35 f6 7a 76 e1 a6 ce 8f cc bf 11 29

After that there are two bytes showing 32 and 37 – which are avro long values using zigzag variable encoding.  those decode to 25 and -28. Now the block size reads as negative.

The Avro tool fail to read the block with following error.

AvroRuntimeException —  java.io.exception: Block size invalid or too large for this implemenation: -28.

Also i the sync 16 bytes are missing from the end of the file.   Any idea what's wrong and how we can fix the same.