Tasmota/lib/arduino-mqtt-2.3.3.02/README.md

# arduino-mqtt

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This library bundles the [lwmqtt](https://github.com/256dpi/lwmqtt) MQTT 3.1.1 client and adds a thin wrapper to get an Arduino like API.

Download the latest version from the [release](https://github.com/256dpi/arduino-mqtt/releases) section. Or even better use the builtin Library Manager in the Arduino IDE and search for "MQTT".

The library is also available on [PlatformIO](https://platformio.org/lib/show/617/MQTT). You can install it by running: `pio lib install "MQTT"`. 

## Compatibility

The following examples show how you can use the library with various Arduino compatible hardware:

- [Arduino Yun & Yun-Shield](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoYun/ArduinoYun.ino) ([Secure](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoYunSecure/ArduinoYunSecure.ino))
- [Arduino Ethernet Shield](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoEthernetShield/ArduinoEthernetShield.ino)    
- [Arduino WiFi Shield](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoWiFiShield/ArduinoWiFiShield.ino)
- [Adafruit HUZZAH ESP8266](https://github.com/256dpi/arduino-mqtt/blob/master/examples/AdafruitHuzzahESP8266/AdafruitHuzzahESP8266.ino) ([Secure](https://github.com/256dpi/arduino-mqtt/blob/master/examples/AdafruitHuzzahESP8266Secure/AdafruitHuzzahESP8266Secure.ino))
- [Arduino/Genuino WiFi101 Shield](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoWiFi101/ArduinoWiFi101.ino) ([Secure](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoWiFi101Secure/ArduinoWiFi101Secure.ino))
- [Arduino MKR GSM 1400](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoMKRGSM1400/ArduinoMKRGSM1400.ino) ([Secure](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ArduinoMKRGSM1400Secure/ArduinoMKRGSM1400Secure.ino))
- [ESP32 Development Board](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ESP32DevelopmentBoard/ESP32DevelopmentBoard.ino) ([Secure](https://github.com/256dpi/arduino-mqtt/blob/master/examples/ESP32DevelopmentBoardSecure/ESP32DevelopmentBoardSecure.ino))

Other shields and boards should also work if they provide a [Client](https://www.arduino.cc/en/Reference/ClientConstructor) based network implementation.

## Notes

- The maximum size for packets being published and received is set by default to 128 bytes. To change the buffer sizes, you need to use `MQTTClient client(256)` instead of just `MQTTClient client` on the top of your sketch. The passed value denotes the read and write buffer size.

- On the ESP8266 it has been reported that an additional `delay(10);` after `client.loop();` fixes many stability issues with WiFi connections.

- To use the library with shiftr.io, you need to provide the token key (username) and token secret (password) as the second and third argument to `client.connect(name, key, secret)`. 

## Example

The following example uses an Arduino MKR1000 to connect to shiftr.io. You can check on your device after a successful connection here: https://shiftr.io/try.

```c++
#include <SPI.h>
#include <WiFi101.h>
#include <MQTT.h>

const char ssid[] = "ssid";
const char pass[] = "pass";

WiFiClient net;
MQTTClient client;

unsigned long lastMillis = 0;

void connect() {
  Serial.print("checking wifi...");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    delay(1000);
  }

  Serial.print("\nconnecting...");
  while (!client.connect("arduino", "try", "try")) {
    Serial.print(".");
    delay(1000);
  }

  Serial.println("\nconnected!");

  client.subscribe("/hello");
  // client.unsubscribe("/hello");
}

void messageReceived(String &topic, String &payload) {
  Serial.println("incoming: " + topic + " - " + payload);
}

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, pass);

  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
  // You need to set the IP address directly.
  client.begin("broker.shiftr.io", net);
  client.onMessage(messageReceived);

  connect();
}

void loop() {
  client.loop();

  if (!client.connected()) {
    connect();
  }

  // publish a message roughly every second.
  if (millis() - lastMillis > 1000) {
    lastMillis = millis();
    client.publish("/hello", "world");
  }
}
```

## API

Initialize the object using the hostname of the broker, the brokers port (default: `1883`) and the underlying Client class for network transport:

```c++
void begin(const char hostname[], Client &client);
void begin(const char hostname[], int port, Client &client);
```

- Specify port `8883` when using secure clients for encrypted connections.
- Local domain names (e.g. `Computer.local` on OSX) are not supported by Arduino. You need to set the IP address directly.

The hostname and port can also be changed after calling `begin()`:

```c++
void setHost(const char hostname[]);
void setHost(const char hostname[], int port);
```

Set a will message (last testament) that gets registered on the broker after connecting. `setWill()` has to be called before calling `connect()`:

```c++
void setWill(const char topic[]);
void setWill(const char topic[], const char payload[]);
void setWill(const char topic[], const char payload[], bool retained, int qos);
void clearWill();
```

Register a callback to receive messages:

```c++
void onMessage(MQTTClientCallbackSimple);
// Callback signature: void messageReceived(String &topic, String &payload) {}

void onMessageAdvanced(MQTTClientCallbackAdvanced);
// Callback signature: void messageReceived(MQTTClient *client, char topic[], char payload[], int payload_length) {}
```

- The set callback is mostly called during a call to `loop()` but may also be called during a call to `subscribe()`, `unsubscribe()` or `publish() // QoS > 0` if messages have been received before receiving the required acknowledgement. Therefore, it is strongly recommended to not call `subscribe()`, `unsubscribe()` or `publish() // QoS > 0` directly in the callback.

Set more advanced options:

```c++
void setOptions(int keepAlive, bool cleanSession, int timeout);
```

- The `keepAlive` option controls the keep alive interval in seconds (default: 10).
- The `cleanSession` option controls the session retention on the broker side (default: true).
- The `timeout` option controls the default timeout for all commands in milliseconds (default: 1000). 

Connect to broker using the supplied client id and an optional username and password:

```c++
bool connect(const char clientId[]);
bool connect(const char clientId[], const char username[]);
bool connect(const char clientId[], const char username[], const char password[]);
```

- This functions returns a boolean that indicates if the connection has been established successfully.

Publishes a message to the broker with an optional payload:

```c++
bool publish(const String &topic);
bool publish(const char topic[]);
bool publish(const String &topic, const String &payload);
bool publish(const String &topic, const String &payload, bool retained, int qos);
bool publish(const char topic[], const String &payload);
bool publish(const char topic[], const String &payload, bool retained, int qos);
bool publish(const char topic[], const char payload[]);
bool publish(const char topic[], const char payload[], bool retained, int qos);
bool publish(const char topic[], const char payload[], int length);
bool publish(const char topic[], const char payload[], int length, bool retained, int qos);
```

Subscribe to a topic:

```c++
bool subscribe(const String &topic);
bool subscribe(const String &topic, int qos); 
bool subscribe(const char topic[]);
bool subscribe(const char topic[], int qos);
```

Unsubscribe from a topic:

```c++
bool unsubscribe(const String &topic);
bool unsubscribe(const char topic[]);
```

Sends and receives packets:

```c++
bool loop();
```

- This function should be called in every `loop`.

Check if the client is currently connected:

```c++
bool connected();
```

Access low-level information for debugging:

```c++
lwmqtt_err_t lastError();
lwmqtt_return_code_t returnCode();
```

- The error codes can be found [here](https://github.com/256dpi/lwmqtt/blob/master/include/lwmqtt.h#L11).
- The return codes can be found [here](https://github.com/256dpi/lwmqtt/blob/master/include/lwmqtt.h#L243).

Disconnect from the broker:

```c++
bool disconnect();
```

## Release Management

- Update version in `library.properties`.
- Create release on GitHub.