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;
        }