public byte[] getFileData() throws IOException {
	    byte[] data = source.getPayload();
	    CRC32 check=new CRC32();
	    // todo: see how much this crc check is slowing us down
	    check.update(data);
	    if(check.getValue() != this.crc32.getValue()) {
	        throw new IOException("CRC mismatch reloading file");
	    }
	    return data;
	}