do {
            if (readn(this.in, this.sbuf, 0, 4) < 4) {
                return null;
            }
        } while (this.sbuf[0] == (byte) 0x85); /* Dodge NetBIOS keep-alive */
        /* read smb header */
        if (readn(this.in, this.sbuf, 4, SmbConstants.SMB1_HEADER_LENGTH) < SmbConstants.SMB1_HEADER_LENGTH) {
            return null;
        }