luamqtt

https://xhaskx.github.io/luamqtt/
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luamqtt is a pure-lua client for MQTT versions 3.1.1 and 5.0, enabling Lua applications to...
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### Simple MQTT Client Example in Lua

Source: https://xhaskx.github.io/luamqtt/examples/simple.lua.html

This snippet demonstrates how to create an MQTT client, connect to a broker, subscribe to a topic, publish a message, and handle incoming messages. It uses the `mqtt.client` constructor and event handlers for connection, message reception, and errors. The `mqtt.run_ioloop` function is used to process network events.

```lua
-- load mqtt module
local mqtt = require("mqtt")

-- create mqtt client
local client = mqtt.client{
	-- NOTE: this broker is not working sometimes; comment username = "..." below if you still want to use it
	-- uri = "test.mosquitto.org",
	uri = "mqtt.flespi.io",
	-- NOTE: more about flespi tokens: https://flespi.com/kb/tokens-access-keys-to-flespi-platform
	username = "stPwSVV73Eqw5LSv0iMXbc4EguS7JyuZR9lxU5uLxI5tiNM8ToTVqNpu85pFtJv9",
	clean = true,
}
print("created MQTT client", client)

client:on{
	connect = function(connack)
		if connack.rc ~= 0 then
			print("connection to broker failed:", connack:reason_string(), connack)
			return
		end
		print("connected:", connack) -- successful connection

		-- subscribe to test topic and publish message after it
		assert(client:subscribe{ topic="luamqtt/#", qos=1, callback=function(suback)
			print("subscribed:", suback)

			-- publish test message
			print('publishing test message "hello" to "luamqtt/simpletest" topic...')
			assert(client:publish{
				topic = "luamqtt/simpletest",
				payload = "hello",
				qos = 1
			})
		end})
	end,

	message = function(msg)
		assert(client:acknowledge(msg))

		print("received:", msg)
		print("disconnecting...")
		assert(client:disconnect())
	end,

	error = function(err)
		print("MQTT client error:", err)
	end,
}

print("running ioloop for it")
mqtt.run_ioloop(client)

print("done, ioloop is stopped")

```

--------------------------------

### Synchronous MQTT Client Example

Source: https://xhaskx.github.io/luamqtt/examples/sync.lua.html

This snippet demonstrates how to create and use a synchronous MQTT client. It connects to a broker, subscribes to a topic, publishes a message, and handles incoming messages. Note that in synchronous mode, background PINGREQ and automatic reconnects are not available.

```lua
-- load mqtt module
local mqtt = require("mqtt")

-- create mqtt client
local client = mqtt.client{
	-- NOTE: this broker is not working sometimes; comment username = "..." below if you still want to use it
	-- uri = "test.mosquitto.org",
	uri = "mqtt.flespi.io",
	-- NOTE: more about flespi tokens: https://flespi.com/kb/tokens-access-keys-to-flespi-platform
	username = "stPwSVV73Eqw5LSv0iMXbc4EguS7JyuZR9lxU5uLxI5tiNM8ToTVqNpu85pFtJv9",
	clean = true,
}
print("created MQTT client", client)

client:on{
	connect = function(connack)
		if connack.rc ~= 0 then
			print("connection to broker failed:", connack:reason_string(), connack)
			return
		end
		print("connected:", connack) -- successful connection

		-- subscribe to test topic and publish message after it
		assert(client:subscribe{ topic="luamqtt/#", qos=1, callback=function(suback)
			print("subscribed:", suback)

			-- publish test message
			print('publishing test message "hello" to "luamqtt/simpletest" topic...')
			assert(client:publish{
				topic = "luamqtt/simpletest",
				payload = "hello",
				qos = 1
			})
		end})
	end,

	message = function(msg)
		assert(client:acknowledge(msg))

		print("received:", msg)
		print("disconnecting...")
		assert(client:disconnect())
	end,

	error = function(err)
		print("MQTT client error:", err)
	end,

	close = function()
		print("MQTT conn closed")
	end
}

-- run io loop for client until connection close
-- please note that in sync mode background PINGREQ's are not available, and automatic reconnects too
print("running client in synchronous input/output loop")
mqtt.run_sync(client)

print("done, synchronous input/output loop is stopped")

```

--------------------------------

### ioloop_mt:get

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Retrieves the default ioloop instance, optionally creating it if it doesn't exist.

```APIDOC
## ioloop_mt:get

### Description
Returns default ioloop instance

### Parameters:
* autocreate (boolean) - Automatically create ioloop instance (default: true)
* args (table) - Arguments for creating ioloop instance (optional)

### Returns:
* ioloop_mt - ioloop instance
```

--------------------------------

### MQTT v5.0 Client Connection and Messaging

Source: https://xhaskx.github.io/luamqtt/examples/mqtt5-simple.lua.html

This snippet demonstrates how to create an MQTT v5.0 client, connect to a broker, subscribe to a topic, publish a message, and handle incoming messages. It includes setting up connection and message callbacks, and managing client lifecycle.

```lua
local mqtt = require("mqtt")

-- create mqtt client
local client = mqtt.client{
	uri = "mqtt.flespi.io",
	-- NOTE: more about flespi tokens: https://flespi.com/kb/tokens-access-keys-to-flespi-platform
	username = "stPwSVV73Eqw5LSv0iMXbc4EguS7JyuZR9lxU5uLxI5tiNM8ToTVqNpu85pFtJv9",
	clean = true,
	version = mqtt.v50,
}
print("created MQTT v5.0 client:", client)

client:on{
	connect = function(connack)
		if connack.rc ~= 0 then
			print("connection to broker failed:", connack:reason_string(), connack)
			return
		end
		print("connected:", connack) -- successful connection

		-- subscribe to test topic and publish message after it
		assert(client:subscribe{
			topic = "luamqtt/#",
			qos = 1,
			callback = function(suback)
				print("subscribed:", suback)

				-- publish test message
				print('publishing test message "hello" to "luamqtt/simpletest" topic...')
				assert(client:publish{
					topic = "luamqtt/simpletest",
					payload = "hello",
					qos = 1,
					properties = {
						payload_format_indicator = 1,
						content_type = "text/plain",
					},
					user_properties = {
						hello = "world",
					},
				})
			end
		})
	end,

	message = function(msg)
		assert(client:acknowledge(msg))

		print("received:", msg)
		print("disconnecting...")
		assert(client:disconnect())
	end,

	error = function(err)
		print("MQTT client error:", err)
	end,
}

print("running ioloop for it")
mqtt.run_ioloop(client)

print("done, ioloop is stopped")

```

--------------------------------

### create

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Creates and initializes a new MQTT client instance. Accepts arguments similar to the client_mt:__init method.

```APIDOC
## create (...)

### Description
Create, initialize and return new MQTT client instance.

### Parameters
* **...** - See arguments of client_mt:__init(args)

### Returns
client_mt - MQTT client instance

### See also:
client_mt:__init
```

--------------------------------

### client_mt:start_connecting

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Initiates the connection process to the MQTT broker.

```APIDOC
## client_mt:start_connecting ()

### Description
Start connecting to broker.

### Returns
true on success or false and error message on failure
```

--------------------------------

### client_mt:start_connecting

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Initiates the process of connecting to the MQTT broker. This method should be called after client initialization to establish the network connection.

```APIDOC
## client_mt:start_connecting ()

### Description
Start connecting to broker.
```

--------------------------------

### create

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Creates, initializes, and returns a new MQTT client instance. This is the primary function for obtaining a client object.

```APIDOC
## create (...)

### Description
Create, initialize and return new MQTT client instance.

### Parameters:
* ... - Arguments for client creation, passed to `client_mt:__init`.
```

--------------------------------

### mqtt.client

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.html

Creates a new MQTT client instance. The parameters are the same as for `mqtt.client.create`.

```APIDOC
## mqtt.client

### Description
Create new MQTT client instance.

### Parameters:
* ... Same as for mqtt.client.create(...)

### See also:
__init
```

--------------------------------

### client_mt:__init

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Creates and initializes a new MQTT client instance. It allows configuration of connection details, authentication, and session parameters.

```APIDOC
## client_mt:__init (args)

### Description
Create and initialize MQTT client instance.

### Parameters:
* args (table) - MQTT client creation arguments table
  * uri (string) - MQTT broker uri to connect. Expecting "host:port" or "host" format, in second case the port will be selected automatically: 1883 port for plain or 8883 for secure network connections
  * clean (boolean) - clean session start flag
  * version (number) - MQTT protocol version to use, either 4 (for MQTT v3.1.1) or 5 (for MQTT v5.0). Also you may use special values mqtt.v311 or mqtt.v50 for this field.
  * id (string) - MQTT client ID, will be generated by luamqtt library if absent (_optional_)
  * username (string) - username for authorization on MQTT broker (_optional_)
  * password (string) - password for authorization on MQTT broker; not acceptable in absence of username (_optional_)
  * secure (boolean|table) - use secure network connection, provided by luasec lua module; set to true to select default params: { mode="client", protocol="tlsv1_2", verify="none", options="all" } or set to luasec-compatible table, for example with cafile="...", certificate="...", key="..." (_default_ false)
  * will (table) - will message table with required fields { topic="...", payload="..." } and optional fields { qos=1...3, retain=true/false } (_optional_)
  * keep_alive (number) - time interval for client to send PINGREQ packets to the server when network connection is inactive (_default_ 60)
  * reconnect (boolean|number) - force created MQTT client to reconnect on connection close. Set to number value to provide reconnect timeout in seconds It's not recommended to use values < 3 (_default_ false)
  * connector (table) - connector table to open and send/receive packets over network connection. default is require("mqtt.luasocket"), or require("mqtt.luasocket_ssl") if secure argument is set (_optional_)
  * ssl_module (string) - module name for the luasec-compatible ssl module, default is "ssl" may be used in some non-standard lua environments with own luasec-compatible ssl module (_default_ "ssl")

### Returns:
* client_mt (table) - MQTT client instance table
```

--------------------------------

### ioloop_mt:__init

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Initializes a new ioloop instance with optional arguments for network operation timeouts and sleep intervals.

```APIDOC
## ioloop_mt:__init

### Description
Initialize ioloop instance

### Parameters:
* args (table) - ioloop creation arguments table
  * timeout (number) - network operations timeout in seconds (default: 0.005)
  * sleep (number) - sleep interval after each iteration (default: 0)
  * sleep_function (function) - custom sleep function to call after each iteration (optional)

### Returns:
* ioloop_mt - ioloop instance
```

--------------------------------

### mqtt.get_ioloop

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.html

Returns the default ioloop instance.

```APIDOC
## mqtt.get_ioloop

### Description
Returns default ioloop instance.

### Parameters:
None
```

--------------------------------

### mqtt.run_sync

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.html

Runs a synchronous input/output loop for a single MQTT client. This function opens the client's connection, but the client reconnect feature and keep-alive will not work.

```APIDOC
## mqtt.run_sync

### Description
Run synchronous input/output loop for only one given MQTT client. Provided client's connection will be opened. Client reconnect feature will not work, and keep_alive too.

### Parameters:
* cl MQTT client instance to run
```

--------------------------------

### mqtt.run_ioloop

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.html

Runs the default ioloop for the given MQTT clients or functions.

```APIDOC
## mqtt.run_ioloop

### Description
Run default ioloop for given MQTT clients or functions.

### Parameters:
* ... MQTT clients or lopp functions to add to ioloop

### See also:
* mqtt.ioloop.get
* mqtt.ioloop.run_until_clients
```

--------------------------------

### Asynchronous MQTT Ping-Pong with Copas

Source: https://xhaskx.github.io/luamqtt/examples/copas-example.lua.html

This snippet demonstrates a ping-pong communication pattern using two LuaMQTT clients within the Copas ioloop. It requires the 'mqtt', 'copas', and 'mqtt.ioloop' modules. The 'ping' client sends a sequence of messages, and the 'pong' client receives and acknowledges them. Ensure a valid Flespi token is provided for authentication.

```lua
-- example of using luamqtt inside copas ioloop: http://keplerproject.github.io/copas/index.html

local mqtt = require("mqtt")
local copas = require("copas")
local mqtt_ioloop = require("mqtt.ioloop")

local num_pings = 10 -- total number of ping-pongs
local timeout = 1 -- timeout between ping-pongs
local suffix = tostring(math.random(1000000)) -- mqtt topic suffix to distinct simultaneous running of this script

-- NOTE: more about flespi tokens: https://flespi.com/kb/tokens-access-keys-to-flespi-platform
local token = "stPwSVV73Eqw5LSv0iMXbc4EguS7JyuZR9lxU5uLxI5tiNM8ToTVqNpu85pFtJv9"

local ping = mqtt.client{
	uri = "mqtt.flespi.io",
	username = token,
	clean = true,
	version = mqtt.v50,
}

local pong = mqtt.client{
	uri = "mqtt.flespi.io",
	username = token,
	clean = true,
	version = mqtt.v50,
}

ping:on{
	connect = function(connack)
		assert(connack.rc == 0)
		print("ping connected")

		for i = 1, num_pings do
			copas.sleep(timeout)
			print("ping", i)
			assert(ping:publish{ topic = "luamqtt/copas-ping/"..suffix, payload = "ping"..i, qos = 1 })
		end

		copas.sleep(timeout)

		print("ping done")
		assert(ping:publish{ topic = "luamqtt/copas-ping/"..suffix, payload = "done", qos = 1 })
		ping:disconnect()
	end,
	error = function(err)
		print("ping MQTT client error:", err)
	end,
}

pong:on{
	connect = function(connack)
		assert(connack.rc == 0)
		print("pong connected")

		assert(pong:subscribe{ topic="luamqtt/copas-ping/"..suffix, qos=1, callback=function(suback)
			assert(suback.rc[1] > 0)
			print("pong subscribed")
		end })
	end,

	message = function(msg)
		print("pong: received", msg.payload)
		assert(pong:acknowledge(msg))

		if msg.payload == "done" then
			print("pong done")
			pong:disconnect()
		end
	end,
	error = function(err)
		print("pong MQTT client error:", err)
	end,
}

print("running copas loop...")

copas.addthread(function()
	local ioloop = mqtt_ioloop.create{ sleep = 0.01, sleep_function = copas.sleep }
	ioloop:add(ping)
	ioloop:run_until_clients()
end)

copas.addthread(function()
	local ioloop = mqtt_ioloop.create{ sleep = 0.01, sleep_function = copas.sleep }
	ioloop:add(pong)
	ioloop:run_until_clients()
end)

copas.loop()

print("done, copas loop is stopped")

```

--------------------------------

### client_mt:open_connection

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Opens the network connection to the MQTT broker. This is a low-level method, typically managed internally by `start_connecting`.

```APIDOC
## client_mt:open_connection ()

### Description
Open network connection to the broker.
```

--------------------------------

### client_mt:open_connection

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Opens the network connection to the MQTT broker.

```APIDOC
## client_mt:open_connection ()

### Description
Open network connection to the broker.

### Returns
true on success or false and error message on failure
```

--------------------------------

### Packet Creation and Utility Functions

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Functions for creating MQTT packet headers, checking QoS and Packet IDs, generating the next Packet ID, and combining packet data.

```APIDOC
## make_header (ptype, flags, len)

### Description
Creates the bytes of the MQTT fixed packet header. For MQTT v3.1.1: **2.2 Fixed header**, For MQTT v5.0: **2.1.1 Fixed Header**.

### Parameters
* `ptype` number - MQTT packet type.
* `flags` number - MQTT packet flags.
* `len` number - MQTT packet length.

### Returns
string - Bytes of the fixed packet header.
```

```APIDOC
## check_qos (val)

### Description
Checks if the given value is a valid PUBLISH message QoS value.

### Parameters
* `val` number - QoS value.

### Returns
boolean - True for a valid QoS value, otherwise false.
```

```APIDOC
## check_packet_id (val)

### Description
Checks if the given value is a valid Packet Identifier. For MQTT v3.1.1: **2.3.1 Packet Identifier**, For MQTT v5.0: **2.2.1 Packet Identifier**.

### Parameters
* `val` number - Packet ID value.

### Returns
boolean - True for a valid Packet ID value, otherwise false.
```

```APIDOC
## next_packet_id ([curr])

### Description
Returns the next Packet Identifier value relative to the given current value. If current is nil, returns 1 as the first possible Packet ID. For MQTT v3.1.1: **2.3.1 Packet Identifier**, For MQTT v5.0: **2.2.1 Packet Identifier**.

### Parameters
* `curr` number - current Packet ID value (optional).

### Returns
number - Next Packet ID value.
```

```APIDOC
## packet_id_required (args)

### Description
Checks if the Packet Identifier field is required for the given packet.

### Parameters
* `args` table - Arguments for creating the packet.

### Returns
boolean - True if Packet Identifier is required for the packet.
```

```APIDOC
## combine (...)

### Description
Combines several data parts into one.

### Parameters
* `...` combined_packet_mt/string - Any amount of strings of combined_packet_mt tables to combine into one packet.

### Returns
table - Combined_packet_mt table suitable to append packet parts or to stringify it into raw packet bytes.
```

```APIDOC
## packet_tostring (packet)

### Description
Renders a packet to its string representation.

### Parameters
* `packet` packet_mt table - The packet table to convert to a string.

### Returns
string - Human-readable string representation of the packet.
```

--------------------------------

### client_mt:send_connect

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends the CONNECT packet over the opened network connection to establish the MQTT session.

```APIDOC
## client_mt:send_connect ()

### Description
Send CONNECT packet into opened network connection.

### Returns
true on success or false and error message on failure
```

--------------------------------

### client_mt:subscribe

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Subscribes to one or more topics with specified Quality of Service (QoS) levels. Supports MQTT v5.0 specific flags and properties for advanced configurations. An optional callback can be provided to be notified when the subscription is created.

```APIDOC
## client_mt:subscribe (args)

### Description
Subscribes to topics with specified QoS levels. Supports MQTT v5.0 flags and properties. An optional callback can be provided.

### Parameters
#### Path Parameters
* **args** (table) - Subscription arguments
  * **topic** (string) - Topic to subscribe
  * **qos** (number) - QoS level for subscription (default: 0)
  * **no_local** (boolean) - MQTT v5.0 only: no_local flag
  * **retain_as_published** (boolean) - MQTT v5.0 only: retain_as_published flag
  * **retain_handling** (boolean) - MQTT v5.0 only: retain_handling flag
  * **properties** (table) - MQTT v5.0 only: properties for subscribe operation (optional)
  * **user_properties** (table) - MQTT v5.0 only: user properties for subscribe operation (optional)
  * **callback** (function) - Callback function when subscription is created (optional)

### Returns
packet id on success or false and error message on failure
```

--------------------------------

### mqtt table

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.html

The module table containing protocol version constants and the library version.

```APIDOC
## mqtt

### Description
Module table.

### Fields:
* v311 number MQTT v3.1.1 protocol version constant
* v50 number MQTT v5.0 protocol version constant
* _VERSION string luamqtt library version string

### See also:
mqtt.const
```

--------------------------------

### client_mt:on

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Adds functions as handlers for specified MQTT events. This allows the client to react to various occurrences like connection, message reception, etc.

```APIDOC
## client_mt:on (...)

### Description
Add functions as handlers of given events.

### Parameters:
* ... - (event_name, function) or { event1 = func1, event2 = func2 } table
```

--------------------------------

### make_string

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Encodes a UTF-8 string into bytes, prefixed with its length as a uint16, adhering to MQTT specifications.

```APIDOC
## make_string (str)

### Description
Create bytes of the UTF-8 string value according to the MQTT spec. Basically it's the same string with its length prefixed as uint16 value. For MQTT v3.1.1: **1.5.3 UTF-8 encoded strings** , For MQTT v5.0: **1.5.4 UTF-8 Encoded String**.

### Parameters
* **str** (string) - string value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### client_mt:publish

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Publishes a message to a specified topic. Supports QoS levels, retain and duplicate flags, and optional payload. MQTT v5.0 properties and an acknowledgment callback are also supported.

```APIDOC
## client_mt:publish (args)

### Description
Publishes a message to a broker.

### Parameters
#### Path Parameters
* **args** (table) - Publish operation arguments
  * **topic** (string) - Topic to publish message
  * **payload** (string) - Publish message payload (optional)
  * **qos** (number) - QoS level for message publication (default: 0)
  * **retain** (boolean) - Retain message publication flag (default: false)
  * **dup** (boolean) - Dup message publication flag (default: false)
  * **properties** (table) - Properties for publishing message (optional)
  * **user_properties** (table) - User properties for publishing message (optional)
  * **callback** (function) - Callback to call when published message is acknowledged (optional)

### Returns
true or packet id on success or false and error message on failure
```

--------------------------------

### make_uint16_nonzero

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Creates bytes for a 2-byte value, enforcing that the value must be non-zero.

```APIDOC
## make_uint16_nonzero (value)

### Description
Make bytes for 2-byte value with nonzero check.

### Parameters
* **value** (number) - integer value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### make_uint32

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Creates bytes for a uint32 value, used for larger integer fields within MQTT packets.

```APIDOC
## make_uint32 (val)

### Description
Create bytes of the uint32 value.

### Parameters
* **val** (number) - integer value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### ioloop_mt:run_until_clients

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Continuously runs the ioloop until at least one client is active or has pending operations.

```APIDOC
## ioloop_mt:run_until_clients

### Description
Run ioloop until at least one client are in ioloop
```

--------------------------------

### client_mt:publish

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Publishes a message to a specified MQTT topic on the broker. This is a core function for sending data through MQTT.

```APIDOC
## client_mt:publish (args)

### Description
Publish message to broker.

### Parameters:
* args (table) - Arguments for publishing. Expected to contain topic and payload information.
```

--------------------------------

### ioloop_mt:add

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Adds an MQTT client or a loop function to the ioloop instance for event processing.

```APIDOC
## ioloop_mt:add

### Description
Add MQTT client or a loop function to the ioloop instance

### Parameters:
* client (client_mt or function) - MQTT client or a loop function to add to ioloop

### Returns:
* boolean - true on success or false and error message on failure
```

--------------------------------

### make_uint8_0_or_1

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Creates bytes for a 1-byte value that must be either 0 or 1, used for specific boolean-like flags in MQTT.

```APIDOC
## make_uint8_0_or_1 (value)

### Description
Make bytes for 1-byte value with only 0 or 1 value allowed.

### Parameters
* **value** (number) - integer value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### make_uint8

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Creates bytes for a uint8 value. This is a fundamental operation for encoding MQTT messages.

```APIDOC
## make_uint8 (val)

### Description
Create bytes of the uint8 value.

### Parameters
* **val** (number) - integer value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### client_mt:auth

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends an AUTH packet to authenticate the client on the broker, specifically for MQTT v5.0. Supports setting a reason code and MQTT v5.0 properties.

```APIDOC
## client_mt:auth ([rc=0[, properties[, user_properties]]])

### Description
Send AUTH packet to authenticate client on broker, in MQTT v5.0 protocol.

### Parameters
#### Path Parameters
* **rc** (number) - Authenticate Reason Code (default: 0)
* **properties** (table) - Properties for PUBACK/PUBREC packets (optional)
* **user_properties** (table) - User properties for PUBACK/PUBREC packets (optional)

### Returns
true on success or false and error message on failure
```

--------------------------------

### make_var_length

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Encodes an integer into a variable-length byte sequence, crucial for fields like Remaining Length in MQTT packets.

```APIDOC
## make_var_length (len)

### Description
Create bytes of the integer value encoded as variable length field For MQTT v3.1.1: **2.2.3 Remaining Length** , For MQTT v5.0: **2.1.4 Remaining Length**.

### Parameters
* **len** (number) - integer value to be encoded

### Returns
string bytes of the value
```

--------------------------------

### client_mt:auth

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends an AUTH packet to authenticate the client on the broker, specifically for MQTT v5.0 protocol. Used for authentication flows that occur after the initial connection.

```APIDOC
## client_mt:auth ([rc=0[, properties[, user_properties]]])

### Description
Send AUTH packet to authenticate client on broker, in MQTT v5.0 protocol.

### Parameters:
* rc (number) - Reason code for authentication, defaults to 0.
* properties (table) - Optional properties for the AUTH packet.
* user_properties (table) - Optional user properties for the AUTH packet.
```

--------------------------------

### client_mt:unsubscribe

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Unsubscribes from specified topics. An optional callback can be provided to be notified when the subscription is removed from the broker. Supports MQTT v5.0 properties.

```APIDOC
## client_mt:unsubscribe (args)

### Description
Unsubscribes from specified topics. An optional callback can be provided to be notified when the subscription is removed.

### Parameters
#### Path Parameters
* **args** (table) - Unsubscription arguments
  * **topic** (string) - Topic to unsubscribe
  * **properties** (table) - Properties for unsubscribe operation (optional)
  * **user_properties** (table) - User properties for unsubscribe operation (optional)
  * **callback** (function) - Callback function when subscription is removed (optional)

### Returns
packet id on success or false and error message on failure
```

--------------------------------

### client_mt:unsubscribe

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Unsubscribes the client from a specified MQTT topic. An optional callback can be provided to be executed once the unsubscription is confirmed by the broker.

```APIDOC
## client_mt:unsubscribe (args)

### Description
Unsubscribe from specified topic, and calls optional callback when subscription will be removed on broker.

### Parameters:
* args (table) - Arguments for unsubscription. Expected to contain topic information.
```

--------------------------------

### client_mt:send_connect

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends the CONNECT packet into the opened network connection. This is a low-level method, usually called after the network connection is established.

```APIDOC
## client_mt:send_connect ()

### Description
Send CONNECT packet into opened network connection.
```

--------------------------------

### make_var_length_nonzero

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Creates bytes for a variable-length encoded value, ensuring the value is non-zero.

```APIDOC
## make_var_length_nonzero (value)

### Description
Make bytes for variable length value with nonzero value check.

### Parameters
* **value** (number) - integer value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### make_uint16

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Creates bytes for a uint16 value, commonly used for fields like packet identifiers or string lengths.

```APIDOC
## make_uint16 (val)

### Description
Create bytes of the uint16 value.

### Parameters
* **val** (number) - integer value to convert to bytes

### Returns
string bytes of the value
```

--------------------------------

### client_mt:subscribe

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Subscribes the client to a specified MQTT topic. It returns the SUBSCRIBE packet ID and can optionally call a callback function once the subscription is confirmed by the broker.

```APIDOC
## client_mt:subscribe (args)

### Description
Subscribe to specified topic. Returns the SUBSCRIBE packet id and calls optional callback when subscription will be created on broker.

### Parameters:
* args (table) - Arguments for subscription. Expected to contain topic information.
```

--------------------------------

### Packet Parsing Functions

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Functions for initiating packet parsing and parsing specific packet types.

```APIDOC
## start_parse_packet (read_func)

### Description
Starts parsing a new packet.

### Parameters
* `read_func` function - Function to read data from the network connection.

### Returns
1. number - Packet type.
2. number - Flags.
3. table - Input, a table with fields "read_func" and "available" representing a stream-like object to read already received packet data in chunks.
4. OR false and error_message on failure.
```

```APIDOC
## parse_packet_connect (read_func[, version])

### Description
Parses a CONNECT packet using the provided read_func.

### Parameters
* `read_func` function - Function to read data from the network connection.
* `version` number - The MQTT protocol version (optional).
```

--------------------------------

### ioloop_mt:iteration

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Performs a single iteration of the ioloop, processing network events for connected clients.

```APIDOC
## ioloop_mt:iteration

### Description
Perform one ioloop iteration
```

--------------------------------

### parse_packet_connect_input

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Parses a CONNECT packet from a stream-like input table. It can optionally validate against a specific protocol version.

```APIDOC
## parse_packet_connect_input (input[, version])

### Description
Parse CONNECT packet from already received stream-like packet input table.

### Parameters
#### Path Parameters
* **input** (table) - a table with fields "read_func" and "available" representing a stream-like object
* **version** (number) - expected protocol version constant or nil to accept both versions (_optional_)

### Returns
packet on success or false and error message on failure
```

--------------------------------

### client_mt:send_pingreq

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends a PINGREQ packet to the broker to maintain the connection.

```APIDOC
## client_mt:send_pingreq ()

### Description
Send PINGREQ packet.

### Returns
true on success or false and error message on failure
```

--------------------------------

### client_mt:send_pingreq

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends a PINGREQ (ping request) packet to the broker. This is used to keep the connection alive and check if the broker is still responsive.

```APIDOC
## client_mt:send_pingreq ()

### Description
Send PINGREQ packet.
```

--------------------------------

### client_mt:close_connection

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Immediately closes the established network connection without sending a graceful DISCONNECT packet. Use this for abrupt connection termination.

```APIDOC
## client_mt:close_connection ([reason])

### Description
Immediately close established network connection, without graceful session finishing with DISCONNECT packet.

### Parameters:
* reason (any) - Optional reason for closing the connection.
```

--------------------------------

### ioloop_mt:remove

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Removes an MQTT client or a loop function from the ioloop instance.

```APIDOC
## ioloop_mt:remove

### Description
Remove MQTT client or a loop function from the ioloop instance

### Parameters:
* client (client_mt or function) - MQTT client or a loop function to remove from ioloop

### Returns:
* boolean - true on success or false and error message on failure
```

--------------------------------

### client_mt:close_connection

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Immediately closes the established network connection without a graceful session finishing with a DISCONNECT packet. An optional reason string can be provided.

```APIDOC
## client_mt:close_connection ([reason])

### Description
Immediately close established network connection, without graceful session finishing with DISCONNECT packet.

### Parameters
#### Path Parameters
* **reason** (string) - The reason string of connection close (optional)

### Returns
N/A (This method performs an action, return value not specified)
```

--------------------------------

### client_mt:acknowledge

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Acknowledges a received message, typically a PUBLISH message. Supports setting a reason code and MQTT v5.0 properties for PUBACK/PUBREC packets.

```APIDOC
## client_mt:acknowledge (msg[, rc=0[, properties[, user_properties]]])

### Description
Acknowledge given received message.

### Parameters
#### Path Parameters
* **msg** (packet_mt) - PUBLISH message to acknowledge
* **rc** (number) - Reason code for PUBACK/PUBREC in MQTT v5.0 (default: 0)
* **properties** (table) - Properties for PUBACK/PUBREC packets (optional)
* **user_properties** (table) - User properties for PUBACK/PUBREC packets (optional)

### Returns
true on success or false and error message on failure
```

--------------------------------

### client_mt:disconnect

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends a DISCONNECT packet to the broker and gracefully closes the network connection. This is the standard way to terminate an MQTT session.

```APIDOC
## client_mt:disconnect ([rc=0[, properties[, user_properties]]])

### Description
Send DISCONNECT packet to the broker and close the connection.

### Parameters:
* rc (number) - Reason code for disconnection, defaults to 0.
* properties (table) - Optional properties for the disconnect packet.
* user_properties (table) - Optional user properties for the disconnect packet.
```

--------------------------------

### client_mt:disconnect

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Sends a DISCONNECT packet to the broker and gracefully closes the connection. Supports setting a reason code and MQTT v5.0 properties.

```APIDOC
## client_mt:disconnect ([rc=0[, properties[, user_properties]]])

### Description
Send DISCONNECT packet to the broker and close the connection.

### Parameters
#### Path Parameters
* **rc** (number) - Disconnect Reason Code in MQTT v5.0 (default: 0)
* **properties** (table) - Properties for PUBACK/PUBREC packets (optional)
* **user_properties** (table) - User properties for PUBACK/PUBREC packets (optional)

### Returns
true on success or false and error message on failure
```

--------------------------------

### Parsing Functions

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.protocol.html

Functions for parsing various data types from a read function, including strings, integers of different sizes, and variable-length fields.

```APIDOC
## parse_string (read_func)

### Description
Reads string (or bytes) using the provided read_func function.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. string - Parsed string (or bytes) on success.
2. OR false and error message on failure.
```

```APIDOC
## parse_uint8 (read_func)

### Description
Parses a uint8 value using the provided read_func.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

```APIDOC
## parse_uint8_0_or_1 (read_func)

### Description
Parses a uint8 value using the provided read_func, allowing only 0 or 1.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

```APIDOC
## parse_uint16 (read_func)

### Description
Parses a uint16 value using the provided read_func.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

```APIDOC
## parse_uint16_nonzero (read_func)

### Description
Parses a non-zero uint16 value using the provided read_func.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

```APIDOC
## parse_uint32 (read_func)

### Description
Parses a uint32 value using the provided read_func.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

```APIDOC
## parse_var_length (read_func)

### Description
Parses a variable-length field value using the provided read_func. For MQTT v3.1.1: **2.2.3 Remaining Length**, For MQTT v5.0: **2.1.4 Remaining Length**.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

```APIDOC
## parse_var_length_nonzero (read_func)

### Description
Parses a non-zero variable-length field value using the provided read_func. For MQTT v3.1.1: **2.2.3 Remaining Length**, For MQTT v5.0: **2.1.4 Remaining Length**.

### Parameters
* `read_func` function - Function to read some bytes from the network layer.

### Returns
1. number - Parsed value.
2. OR false and error message on failure.
```

--------------------------------

### client_mt:acknowledge

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Acknowledges a received message. This is typically used in scenarios requiring message confirmation, especially with QoS levels higher than 0.

```APIDOC
## client_mt:acknowledge (msg[, rc=0[, properties[, user_properties]]])

### Description
Acknowledge given received message.

### Parameters:
* msg (table) - The received message to acknowledge.
* rc (number) - Return code, defaults to 0.
* properties (table) - Optional properties for the acknowledgment.
* user_properties (table) - Optional user properties for the acknowledgment.
```

--------------------------------

### client_mt:off

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.client.html

Removes a previously added function handler for a specified event. This is used to stop the client from reacting to certain events.

```APIDOC
## client_mt:off (event, func)

### Description
Remove given function handler for specified event.

### Parameters:
* event (string) - event name to remove handler
* func (function) - handler function to remove
```

--------------------------------

### ioloop_mt:can_sleep

Source: https://xhaskx.github.io/luamqtt/modules/mqtt.ioloop.html

Determines if the ioloop can sleep, based on whether any network operations timed out in the current iteration.

```APIDOC
## ioloop_mt:can_sleep

### Description
Perform sleep if no one of the network operation in current iteration was not timeouted
```
Tokens:
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