private static int unsignedByte(ByteBuffer buffer, int index) {
        return buffer.get(index) & 0x0FF;
    }
Verify a packet to see whether it is a valid SSL packet.

@param buffer Encrypted SSL packet.
@return Verification result, one of {@link #PACKET_NOT_ENOUGH}, {@link #PACKET_NOT_ENCRYPTED},
and {@link #PACKET_SSL}.
netbare-core/src/main/java/com/github/megatronking/netbare/ssl/SSLUtils.java