@Override
    public long readInt64() throws IOException
    {
        if (offset + 2 > limit && !readable(2))
            throw new ProtostuffException("Truncated message.");

        final int size = buffer[offset++] | (buffer[offset++] << 8);

        if (size == 0)
            return 0;

        if (offset + size > limit && !readable(size))
            throw new ProtostuffException("Truncated message.");

        final long number = parseLong(buffer, offset, size, 10);

        offset += size;

        return number;
    }
Returns true if there are {@code minimum} bytes available for reading.
<p>
The caller is responsible that the arg {@code minimum} is not larger than the buffer size.
protostuff-kvp/src/main/java/io/protostuff/KvpInput.java