var client_messages = 1;

var client_id_str = "-";

function getClientId(s) {

    if ( !s.fromUpstream ) {

        if ( s.buffer.toString().length == 0  ) { // Initial calls may

            s.log("No buffer yet");               // contain no data, so

            return s.AGAIN;                       // ask that we get called again

        } else if ( client_messages == 1 ) { // CONNECT is first packet from the client

            // CONNECT packet is 1, using upper 4 bits (00010000 to 00011111)

            var packet_type_flags_byte = s.buffer.charCodeAt(0);

            s.log("MQTT packet type+flags = " + packet_type_flags_byte.toString());

            if ( packet_type_flags_byte >= 16 && packet_type_flags_byte < 32 ) {

                // Calculate remaining length with variable encoding scheme

                var multiplier = 1;

                var remaining_len_val = 0;

                var remaining_len_byte;

                for (var remaining_len_pos = 1; remaining_len_pos < 5; remaining_len_pos++ ) {

                    remaining_len_byte = s.buffer.charCodeAt(remaining_len_pos);

                    if ( remaining_len_byte == 0 ) break; // Stop decoding on 0

                    remaining_len_val += (remaining_len_byte & 127) * multiplier;

                    multiplier *= 128;

                }

                // Extract ClientId based on length defined by 2-byte encoding

                var payload_offset = remaining_len_pos + 12; // Skip fixed head

                var client_id_len_msb = s.buffer.charCodeAt(payload_offset).toString(16);

                var client_id_len_lsb = s.buffer.charCodeAt(payload_offset + 1).toString(16);

                if ( client_id_len_lsb.length < 2 ) client_id_len_lsb = "0" + client_id_len_lsb;

                var client_id_len_int = parseInt(client_id_len_msb + client_id_len_lsb, 16);

                client_id_str = s.buffer.substr(payload_offset + 2, client_id_len_int);

                s.log("ClientId value  = " + client_id_str);

            } else {

                s.log("Received unexpected MQTT packet type+flags: " + packet_type_flags_byte.toString());

            }

        }

        client_messages++;

    }

    return s.OK;

}

function setClientId(s) {

    return client_id_str;

}