TMqttPacket

Create method

class function Create(AKind: TMqttPacketKind): TMqttPacket; static;

Returns an empty packet of the given kind, with ProtocolLevel 4 and CleanSession True; everything else is zero or empty. Start every packet with it rather than with Default(TMqttPacket).

Packet := TMqttPacket.Create(mkPingReq);

Kind field

Kind: TMqttPacketKind;

The packet type. Decides which of the other fields mean anything.

Dup field

Dup, Retain: Boolean;

PUBLISH: the duplicate flag, set when a message is sent again. Must be False at quality 0.

Retain field

Dup, Retain: Boolean;

PUBLISH: the retain flag.

QoS field

QoS: TMqttQoS;

PUBLISH: the quality of service.

Topic field

Topic: string;

PUBLISH: the topic name. It may not be empty or contain wildcards.

Payload field

Payload: TBytes;

PUBLISH: the application bytes. May be empty.

PacketId field

PacketId: Word;

The packet identifier, 1 to 65535, of PUBLISH above quality 0, PUBACK, PUBREC, PUBREL, PUBCOMP, SUBSCRIBE, SUBACK, UNSUBSCRIBE and UNSUBACK. 0 is invalid for these, and the encoder refuses it.

ClientId field

ClientId, Username, WillTopic: string;

CONNECT: the client identifier.

Username field

ClientId, Username, WillTopic: string;

CONNECT: the user name; sent only when HasUsername is True.

WillTopic field

ClientId, Username, WillTopic: string;

CONNECT: the will topic; sent only when HasWill is True.

Password field

Password, WillPayload: TBytes;

CONNECT: the password, as bytes (it may be binary); sent only when HasPassword is True.

WillPayload field

Password, WillPayload: TBytes;

CONNECT: the will message.

HasUsername field

HasUsername, HasPassword, HasWill, WillRetain, CleanSession: Boolean;

CONNECT: a user name is present.

HasPassword field

HasUsername, HasPassword, HasWill, WillRetain, CleanSession: Boolean;

CONNECT: a password is present. MQTT 3.1.1 requires HasUsername too; the encoder refuses a password alone.

HasWill field

HasUsername, HasPassword, HasWill, WillRetain, CleanSession: Boolean;

CONNECT: a will is present.

WillRetain field

HasUsername, HasPassword, HasWill, WillRetain, CleanSession: Boolean;

CONNECT: the will is to be retained.

CleanSession field

HasUsername, HasPassword, HasWill, WillRetain, CleanSession: Boolean;

CONNECT: start a fresh session. Create sets it to True.

WillQoS field

WillQoS: TMqttQoS;

CONNECT: the quality of the will.

KeepAlive field

KeepAlive: Word;

CONNECT: the keep-alive period in seconds; 0 turns it off.

ProtocolLevel field

ProtocolLevel: Byte;

CONNECT: 4 for MQTT 3.1.1. Create sets it to 4.

SessionPresent field

SessionPresent: Boolean;

CONNACK: the broker kept a session from before.

ReturnCode field

ReturnCode: Byte;

CONNACK: 0 accepted; 1 to 5 refused. TAtlasMqttCodec.ConnAckText turns a code into words.

Filters field

Filters: TArray<string>;

SUBSCRIBE and UNSUBSCRIBE: the topic filters; at least one.

FilterQoS field

FilterQoS: TArray<TMqttQoS>;

SUBSCRIBE: the requested quality for each filter, in the same order.

Granted field

Granted: TArray<Byte>;

SUBACK: per filter, the granted quality 0, 1 or 2, or $80 (TAtlasMqttCodec.SubscribeFailure) for a refusal.

Encode a PUBLISH

Topic a/b, quality 1, identifier 10, payload hi. The result is the eleven bytes 32 09 00 03 61 2F 62 00 0A 68 69.

uses
  System.SysUtils, Atlas.MqttCodec;

function EncodedPublish: TBytes;
var
  Packet: TMqttPacket;
begin
  Packet := TMqttPacket.Create(mkPublish);
  Packet.Topic := 'a/b';
  Packet.QoS := qosAtLeastOnce;
  Packet.PacketId := 10;
  Packet.Payload := TEncoding.UTF8.GetBytes('hi');
  Result := TAtlasMqttCodec.Encode(Packet);
end;