File syn_mqtt.c¶

Lightweight MQTT 3.1.1 client implementation — fully non-blocking.

#include "../port/syn_port_system.h"
#include "../util/syn_assert.h"
#include "../util/syn_pack.h"
#include "syn_mqtt.h"
#include <string.h>

Public Functions¶

Type	Name
SYN_Status	syn_mqtt_init (SYN_MqttClient * client, const char * host, uint16_t port, const char * client_id, const char * username, const char * password, uint16_t keep_alive_s, uint8_t * rx_buf, size_t rx_buf_size, uint8_t * tx_buf, size_t tx_buf_size) Initialize the MQTT client.
SYN_Status	syn_mqtt_ping (SYN_MqttClient * client) Transmit an explicit MQTT PINGREQ packet.
SYN_Status	syn_mqtt_publish (SYN_MqttClient * client, const char * topic, const void * payload, size_t len, uint8_t qos, bool retain) Publish a message to a topic.
SYN_Status	syn_mqtt_subscribe (SYN_MqttClient * client, const char * topic, uint8_t qos) Subscribe to a topic.
SYN_PT_Status	syn_mqtt_task (SYN_PT * pt, SYN_Task * task) Cooperative task for driving the MQTT client.

Public Static Functions¶

Type	Name
size_t	encode_remaining_len (uint8_t * buf, uint32_t len) Encode MQTT remaining length into variable-length bytes.
void	handle_publish (SYN_MqttClient * c, const uint8_t * payload, uint32_t len, uint8_t qos_bits) Handle an incoming PUBLISH packet.
void	poll_rx (SYN_MqttClient * c) Non-blocking receive state machine poll.
void	process_packet (SYN_MqttClient * c) Dispatch a fully received MQTT packet.
bool	send_mqtt_connect (SYN_MqttClient * c) Build and send an MQTT CONNECT packet.
bool	send_mqtt_ping (const SYN_MqttClient * c) Send an MQTT PINGREQ packet.

Macros¶

Type	Name
define	MQTT_ACK_TIMEOUT_MS `5000`
define	MQTT_RECV_TIMEOUT_MS `5000`

Public Functions Documentation¶

function syn_mqtt_init¶

Initialize the MQTT client.

SYN_Status syn_mqtt_init (
    SYN_MqttClient * client,
    const char * host,
    uint16_t port,
    const char * client_id,
    const char * username,
    const char * password,
    uint16_t keep_alive_s,
    uint8_t * rx_buf,
    size_t rx_buf_size,
    uint8_t * tx_buf,
    size_t tx_buf_size
)

Configures broker destination, client ID, authentication credentials, keep-alive timing parameters, and network packet buffers.

Parameters:

client Pointer to client context.
host Broker network address string.
port Broker port number.
client_id MQTT client identity string.
username Authentication username (or NULL).
password Authentication password (or NULL).
keep_alive_s Keep-alive timeout parameter in seconds.
rx_buf Receive buffer storage.
rx_buf_size Receive buffer capacity.
tx_buf Transmit buffer storage.
tx_buf_size Transmit buffer capacity.

Returns:

SYN_OK on successful configuration, or error parameter code.

function syn_mqtt_ping¶

Transmit an explicit MQTT PINGREQ packet.

SYN_Status syn_mqtt_ping (
    SYN_MqttClient * client
)

Note: PINGREQ packets are sent automatically by syn_mqtt_task based on the configured keep_alive_s interval. This function allows manual pinging on demand.

Parameters:

client Pointer to client context.

Returns:

SYN_OK on success, SYN_ERROR if not connected or transmit failed.

function syn_mqtt_publish¶

Publish a message to a topic.

SYN_Status syn_mqtt_publish (
    SYN_MqttClient * client,
    const char * topic,
    const void * payload,
    size_t len,
    uint8_t qos,
    bool retain
)

Non-blocking publish command. For QoS 0, queued directly. For QoS 1, tracks acknowledgement state.

Parameters:

client Pointer to client context.
topic Topic name to target.
payload Data payload to send.
len Payload size in bytes.
qos Quality of service level (0 or 1).
retain Retain flag on broker.

Returns:

SYN_OK on queued, or error status if payload bounds exceeded.

function syn_mqtt_subscribe¶

Subscribe to a topic.

SYN_Status syn_mqtt_subscribe (
    SYN_MqttClient * client,
    const char * topic,
    uint8_t qos
)

Formats and queues a subscription request for transmission.

Parameters:

client Pointer to client context.
topic Topic filter string.
qos Requested quality of service.

Returns:

SYN_OK on success.

function syn_mqtt_task¶

Cooperative task for driving the MQTT client.

SYN_PT_Status syn_mqtt_task (
    SYN_PT * pt,
    SYN_Task * task
)

Yields during connection, socket polling, keep-alive pinging, and packet parsing loops. Runs within the cooperative scheduler context.

Parameters:

pt Cooperative protothread handle.
task Corresponding task control block.

Returns:

PT_WAITING or PT_EXITED status.

Public Static Functions Documentation¶

function encode_remaining_len¶

Encode MQTT remaining length into variable-length bytes.

static size_t encode_remaining_len (
    uint8_t * buf,
    uint32_t len
)

Parameters:

buf Output buffer (at least 4 bytes).
len Length value to encode.

Returns:

Number of bytes written.

function handle_publish¶

Handle an incoming PUBLISH packet.

static void handle_publish (
    SYN_MqttClient * c,
    const uint8_t * payload,
    uint32_t len,
    uint8_t qos_bits
)

Parameters:

c MQTT client.
payload Raw payload (after fixed header).
len Payload length.
qos_bits QoS flags from the fixed header.

function poll_rx¶

Non-blocking receive state machine poll.

static void poll_rx (
    SYN_MqttClient * c
)

Reads available bytes with timeout=0. Advances through RX phases: IDLE → REMAINING_LEN → PAYLOAD / DISCARD → IDLE

Parameters:

c MQTT client.

function process_packet¶

Dispatch a fully received MQTT packet.

static void process_packet (
    SYN_MqttClient * c
)

Parameters:

c MQTT client context.

function send_mqtt_connect¶

Build and send an MQTT CONNECT packet.

static bool send_mqtt_connect (
    SYN_MqttClient * c
)

Parameters:

c MQTT client.

Returns:

true on success.

function send_mqtt_ping¶

Send an MQTT PINGREQ packet.

static bool send_mqtt_ping (
    const SYN_MqttClient * c
)

Parameters:

c MQTT client.

Returns:

true on success.

Macro Definition Documentation¶

define MQTT_ACK_TIMEOUT_MS¶

#define MQTT_ACK_TIMEOUT_MS `5000`

Timeout for ACK responses (ms).

define MQTT_RECV_TIMEOUT_MS¶

#define MQTT_RECV_TIMEOUT_MS `5000`

Timeout for incomplete packet reception (ms).

The documentation for this class was generated from the following file src/syntropic/net/syn_mqtt.c