MQTT API

This Library is a high-performance [MQTT] library for IoT publish/subscribe communications.

The library supports MQTT version 3.1.1 and has the following features:

• Supports connect, publish, subscribe, ping and disconnect messages.
• Message quality of service for reliable delivery.
• Retained messages.
• TLS encryption with ALPN over port 443.
• High message throughput with exceptionally low overhead.
• Wait for delivery or acknowledgement options.
• Auto reconnect on network failures.
• Parallelism via fiber coroutines.

Extensions

Mqtt	MQTT Protocol.

Functions

Mqtt *	mqttAlloc(cchar *clientId, MqttEventProc proc)
	Allocate an MQTT object.
int	mqttConnect(Mqtt *mq, RSocket *sock, int flags, MqttWaitFlags waitFlags)
	Establish a session with the MQTT broker.
int	mqttDisconnect(Mqtt *mq)
	Send a disconnection packet.
void	mqttFree(Mqtt *mq)
	Free an Mqtt instance.
cchar *	mqttGetError(struct Mqtt *mq)
	Returns an error message for error code, error.
Ticks	mqttGetLastActivity(Mqtt *mq)
	Return the time of last I/O activity.
bool	mqttIsConnected(Mqtt *mq)
	Return true if the MQTT instance is connected to a peer.
int	mqttMsgsToSend(Mqtt *mq)
	Get the number of messages in the queue.
int	mqttPing(Mqtt *mq)
	Ping the broker.
int	mqttPublish(Mqtt *mq, cvoid *msg, ssize size, int qos, MqttWaitFlags waitFlags, cchar *topic, ...)
	Publish an application message to the MQTT broker.
int	mqttPublishRetained(Mqtt *mq, cvoid *msg, ssize size, int qos, MqttWaitFlags waitFlags, cchar *topic, ...)
	Publish a retained message to the MQTT broker.
void	mqttSetMessageSize(Mqtt *mq, int size)
	Set the maximum message size.
void	mqttSetWill(Mqtt *mq, cchar *topic, cvoid *msg, ssize length)
	Set the will and testament message.
int	mqttSubscribe(Mqtt *mq, MqttCallback callback, int maxQos, MqttWaitFlags waitFlags, cchar *topic, ...)
	Subscribe to a topic.
int	mqttSubscribeMaster(Mqtt *mq, int maxQos, MqttWaitFlags waitFlags, cchar *topic, ...)
	Perform a master subscription.
int	mqttUnsubscribe(Mqtt *mq, cchar *topic, MqttWaitFlags wait)
	Unsubscribe from a topic.

Typedefs

Mqtt	MQTT instance.
MqttCallback	Message receipt callback.
MqttEventProc	MQTt event callback.
MqttHdr	Fixed header of a packet.
MqttMsg	Mqtt message.
MqttRecv	A struct used to deserialize/interpret an incoming packet from the broker.

Defines

#define	MQTT_BUF_SIZE   4096
	Receive buffer size.
#define	MQTT_EVENT_ATTACH   1
	Attach a socket.
#define	MQTT_EVENT_CONNECTED   2
	A new connection was established.
#define	MQTT_EVENT_DISCONNECT   3
	Connection closed.
#define	MQTT_EVENT_TIMEOUT   4
	The idle connection has timed out.
#define	MQTT_INLINE_BUF_SIZE   128
	Size of inline buffer.
#define	MQTT_KEEP_ALIVE   (20 * 60 * TPS)
	Default connection keep alive time.
#define	MQTT_MAX_MESSAGE_SIZE   256 * 1024 * 1024
	Max message size.
#define	MQTT_MSG_TIMEOUT   (30 * TPS)
	Default message timeout.
#define	MQTT_PROTOCOL_LEVEL   0x04
	Protocol version 3.1.1.
#define	MQTT_TIMEOUT   (MAXINT)
	Default connection timeout in msec.
#define	MQTT_TOPIC_SIZE   128
	Max topic size.
#define	MQTT_PROTOCOL_LEVEL   0x04
	Protocol version 3.1.1.

Mqtt

Mqtt

MQTT Protocol.

API Stability:

Evolving.

Fields:

RBuf *		buf	I/O read buffer.
uint		connected	Mqtt is currently connected flag.
int		error	Mqtt error flag.
char *		errorMsg	Mqtt error message.
uint		freed	Safe free detection.
MqttMsg		head	Head of message queue.
char *		id	Client ID.
Ticks		keepAlive	Server side keep alive duration in seconds.
REvent		keepAliveEvent	Keep alive event.
Ticks		lastActivity	Time of last I/O activity.
int		mask	R library wait event mask.
char *		masterTopic	Master subscription topic.
int		maxMessage	Maximum message size.
int		msgTimeout	Message timeout for retransmit.
int		nextId	Next message ID.
char *		password	Username for connect.
MqttEventProc		proc	Notification event callback
uint		processing	ProcessMqtt is running.
RSocket *		sock	Underlying socket transport.
uint		subscribedApi	Reserved.
Ticks		throttle	Throttle delay in msec.
Ticks		throttleLastPub	Time of last publish or throttle.
Ticks		throttleMark	Throttle sending until Time.
Ticks		timeout	Inactivity timeout for on-demand connections.
RList *		topics	List of subscribed topics.
char *		username	Password for connect.
char *		willMsg	Will and testament message.
ssize		willMsgSize	Size of will message.
char *		willTopic	Will and testament topic.

Mqtt * * mqttAlloc (cchar *clientId, MqttEventProc proc)

Allocate an MQTT object.

Parameters:

clientId	Unique client identifier string.
proc	Event notification callback procedure.

API Stability:

Evolving.

int mqttConnect (Mqtt *mq, RSocket *sock, int flags, MqttWaitFlags waitFlags)

Establish a session with the MQTT broker.

Description:

This call established a new MQTT connection to the broker using the supplied socket. The MQTT object keeps a reference to the socket. If the socket is closed or freed by the caller, the caller must call mqttDisconnect.

Parameters:

mq	The Mqtt object.
sock	The underlying socket to use for communications.
flags	Additional MqttConnectFlags to use when establishing the connection. These flags are for forcing the session to start clean: MQTT_CONNECT_CLEAN_SESSION, the QOS level to publish the will and testament messages with, and whether or not the broker should retain the will_message, MQTT_CONNECT_WILL_RETAIN.
waitFlags	Wait flags. Set to MQTT_WAIT_NONE, MQTT_WAIT_SENT or MQTT_WAIT_ACK.

Returns:

Zero if successful.

API Stability:

Evolving.

int mqttDisconnect (Mqtt *mq)

Send a disconnection packet.

Description:

This will not close the socket. The peer, upon receiving the disconnection will close the connection.

Returns:

Zero if successful.

API Stability:

Evolving.

cchar * * mqttGetError (struct Mqtt *mq)

Returns an error message for error code, error.

Parameters:

mq	Mqtt object.

Returns:

The associated error message.

API Stability:

Evolving.

Ticks mqttGetLastActivity (Mqtt *mq)

Return the time of last I/O activity.

Returns:

The time in Ticks of the last I/O.

API Stability:

Evolving.

bool mqttIsConnected (Mqtt *mq)

Return true if the MQTT instance is connected to a peer.

Parameters:

mq	The MQTT mq.

Returns:

True if connected.

API Stability:

Prototype.

int mqttMsgsToSend (Mqtt *mq)

Get the number of messages in the queue.

Parameters:

mq	The MQTT mq.

Returns:

The number of messages in the queue.

API Stability:

Evolving.

int mqttPing (Mqtt *mq)

Ping the broker.

Parameters:

mq	The MQTT mq.

Returns:

Zero if successful.

API Stability:

Evolving.

int mqttPublish (Mqtt *mq, cvoid *msg, ssize size, int qos, MqttWaitFlags waitFlags, cchar *topic, ...)

Publish an application message to the MQTT broker.

Parameters:

mq	The Mqtt object.
msg	The data to be published.
size	The size of application_message in bytes.
qos	Quality of service. 0, 1, or 2.
waitFlags	Wait flags. Set to MQTT_WAIT_NONE, MQTT_WAIT_SENT or MQTT_WAIT_ACK.
topic	Printf style topic string.
...	Topic args.

Returns:

Zero if successful.

int mqttPublishRetained (Mqtt *mq, cvoid *msg, ssize size, int qos, MqttWaitFlags waitFlags, cchar *topic, ...)

Publish a retained message to the MQTT broker.

Parameters:

mq	The Mqtt object.
msg	The data to be published.
size	The size of application_message in bytes.
qos	Quality of service. 0, 1, or 2.
waitFlags	Wait flags. Set to MQTT_WAIT_NONE, MQTT_WAIT_SENT or MQTT_WAIT_ACK.
topic	Printf style topic string.
...	Topic args.

Returns:

Zero if successful.

API Stability:

Evolving.

void mqttSetMessageSize (Mqtt *mq, int size)

Set the maximum message size.

Description:

AWS supports a smaller maximum message size.

Parameters:

mq	The MQTT mq.
size	The maximum message size.

API Stability:

Evolving.

void mqttSetWill (Mqtt *mq, cchar *topic, cvoid *msg, ssize length)

Set the will and testament message.

Parameters:

mq	The MQTT mq.
topic	Will message topic.
msg	Message to send.
length	Message size.

API Stability:

Evolving.

int mqttSubscribe (Mqtt *mq, MqttCallback callback, int maxQos, MqttWaitFlags waitFlags, cchar *topic, ...)

Subscribe to a topic.

Parameters:

mq	Mqtt object.
callback	Function to invoke on receipt of messages.
maxQos	Maximum quality of service message to receive.
waitFlags	Wait flags. Set to MQTT_WAIT_NONE, MQTT_WAIT_SENT or MQTT_WAIT_ACK.
topic	Printf style topic string.
...	Topic args.

Returns:

Zero if successful.

API Stability:

Evolving.

int mqttSubscribeMaster (Mqtt *mq, int maxQos, MqttWaitFlags waitFlags, cchar *topic, ...)

Perform a master subscription.

Description:

To minimize the number of active MQTT subscriptions, this call can establish a master subscription. Subsequent subscriptions using this master topic as a prefix will not incurr an MQTT protocol subscription. But will be processed off the master subscription locally.

Parameters:

mq	Mqtt object.
maxQos	Maximum quality of service message to receive. This is used for all local subscriptions using this master.
waitFlags	Wait flags. Set to MQTT_WAIT_NONE, MQTT_WAIT_SENT or MQTT_WAIT_ACK.
topic	Printf style topic string.
...	Topic args.

Returns:

Zero if successful.

API Stability:

Prototype.

int mqttUnsubscribe (Mqtt *mq, cchar *topic, MqttWaitFlags wait)

Unsubscribe from a topic.

Parameters:

mq	The MQTT mq.
topic	The name of the topic to unsubscribe from.
wait	Wait flags.

Returns:

Zero if successful.

API Stability:

Evolving.

Functions

void mqttFree (Mqtt *mq)

Free an Mqtt instance.

Parameters:

mq	Mqtt instance allocated via mqttAlloc

Typedefs

typedef void(* MqttCallback) (struct MqttRecv *resp).

Message receipt callback.

Parameters:

resp	Message received structure.

API Stability:

Evolving.

typedef void(* MqttEventProc) (struct Mqtt *mq, int event).

MQTt event callback.

Parameters:

mq	Mqtt object created via mqttAlloc
event	Event type, set to MQTT_EVENT_CONNECT, MQTT_EVENT_DISCONNECT or MQTT_EVENT_STOPPING.

API Stability:

Evolving.

Mqtt

MQTT instance.

API Stability:

Evolving.

Fields:

RBuf *		buf	I/O read buffer.
uint		connected	Mqtt is currently connected flag.
int		error	Mqtt error flag.
char *		errorMsg	Mqtt error message.
uint		freed	Safe free detection.
MqttMsg		head	Head of message queue.
char *		id	Client ID.
Ticks		keepAlive	Server side keep alive duration in seconds.
REvent		keepAliveEvent	Keep alive event.
Ticks		lastActivity	Time of last I/O activity.
int		mask	R library wait event mask.
char *		masterTopic	Master subscription topic.
int		maxMessage	Maximum message size.
int		msgTimeout	Message timeout for retransmit.
int		nextId	Next message ID.
char *		password	Username for connect.
MqttEventProc		proc	Notification event callback
uint		processing	ProcessMqtt is running.
RSocket *		sock	Underlying socket transport.
uint		subscribedApi	Reserved.
Ticks		throttle	Throttle delay in msec.
Ticks		throttleLastPub	Time of last publish or throttle.
Ticks		throttleMark	Throttle sending until Time.
Ticks		timeout	Inactivity timeout for on-demand connections.
RList *		topics	List of subscribed topics.
char *		username	Password for connect.
char *		willMsg	Will and testament message.
ssize		willMsgSize	Size of will message.
char *		willTopic	Will and testament topic.

MqttHdr

Fixed header of a packet.

API Stability:

Evolving.

Fields:

int		flags	Packet control flags.
int		length	Size in of the variable portion after fixed header and packet length.

MqttMsg

Mqtt message.

API Stability:

Internal.

Fields:

uchar *		buf	External message text buffer for large messages.
uchar *		end	End of message.
uchar *		endbuf	End of message buffer.
RFiber *		fiber	Message fiber to process the message.
int		id	Message sequence ID.
uchar		inlineBuf[MQTT_INLINE_BUF_SIZE]	Inline message text buffer for small message efficiency.
struct MqttMsg *		next	Next message in the queue.
struct MqttMsg *		prev	Previous message in the queue.
int		qos	Message quality of service.
Ticks		sent	Time the message was sent.
uchar *		start	Start of message.
MqttMsgState		state	Message send status.
MqttPacketType		type	Message packet type.
MqttWaitFlags		wait	Message wait for send flags.

MqttRecv

A struct used to deserialize/interpret an incoming packet from the broker.

API Stability:

Evolving.

Fields:

MqttConnCode		code	Connection response code.
cuchar *		codes	Array of return codes for subscribed topics.
char *		data	Published message.
int		dataSize	Size of data.
uchar		dup	Set to 0 on first attempt to send packet.
uint		hasSession	Connection using an existing session.
struct MqttHdr		hdr	MQTT message fixed header.
int		id	Message ID.
MqttTopic *		matched	Matched topic.
struct Mqtt *		mq	Message queue.
int		numCodes	Size of codes.
uchar		qos	Quality of service.
uchar		retain	Message is retained.
char *		topic	Topic string.
int		topicSize	Size of topic.