@Override
    public byte[] readByteArray() throws IOException
    {
        final int length = readRawVarint32();
        if (length < 0)
            throw ProtobufException.negativeSize();

        if (offset + length > limit)
            throw ProtobufException.misreportedSize();

        final byte[] copy = new byte[length];
        System.arraycopy(buffer, offset, copy, 0, length);

        offset += length;

        return copy;
    }
Read an {@code sint64} field value from the internal buffer.
protostuff-core/src/main/java/io/protostuff/ByteArrayInput.java