92 lines
3.3 KiB
Markdown
92 lines
3.3 KiB
Markdown
## MQTT Client
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MQTT Client is a library that can publish strings to a topic of a MQTT broker.
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For using it you have to include the library
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[Cooperative Multitasking](https://bitbucket.org/amotzek/cooperative-multitasking) too.
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#### Example
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The following example publishes the string `"Hello"` to the topic `"amotzek/hello"`
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of the broker broker.hivemq.com repeatedly. The message can be observed in HiveMQs
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[Websockets client](http://www.hivemq.com/demos/websocket-client/).
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The example assumes that you connect to the internet via `Wifi101`, so you need the
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SSID and the password of your WLAN. You also need an Arduino board that is compatible
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with `Wifi101`, e.g. the MKR1000. If your board connects to the internet in a
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different way, you have to pass a different client (for example an `EthernetClient`)
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to the constructor of `MQTTClient`.
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#include <Client.h>
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#include <WiFi101.h>
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#include <CooperativeMultitasking.h>
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#include <MQTTClient.h>
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char ssid[] = "...";
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char pass[] = "...";
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char host[] = "broker.hivemq.com";
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char clientid[] = "...";
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char username[] = "...";
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char password[] = "...";
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char topicname[] = "amotzek/hello";
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CooperativeMultitasking tasks;
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WiFiClient wificlient;
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MQTTClient mqttclient(&tasks, &wificlient, host, 1883, clientid, username, password);
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MQTTTopic topic(&mqttclient, topicname);
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void setup() {
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Serial.begin(9600);
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//
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while (!Serial) {
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delay(1000);
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}
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//
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WiFi.begin(ssid, pass);
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delay(10000); // wait until WiFi connection is established
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}
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void loop() {
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if (mqttclient.connect()) {
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topic.publish("Hello");
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//
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while (tasks.available()) {
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tasks.run(); // receive connect acknowledgement, send publish, receive publish acknowledgement
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}
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//
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mqttclient.disconnect();
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}
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//
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switch (WiFi.status()) {
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case WL_CONNECT_FAILED:
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case WL_CONNECTION_LOST:
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case WL_DISCONNECTED: WiFi.begin(ssid, pass); // reconnect WiFi if necessary
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}
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//
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delay(30000);
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}
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#### Details
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To create an instance of class `MQTTClient` you need a reference to an instance of class
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`CooperativeMultitasking`, a reference to an instance of a network connection (e.g. from
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`WiFi101` or `Ethernet`), the host name of the MQTT broker, its port number (typically
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1883) and a client id. If the broker requires that, you also have to pass a user name and
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a password.
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To create an instance of class `MQTTTopic` you have to pass a reference to an instance of
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`MQTTClient` and the topic name.
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The method `connect()` of `MQTTClient` creates a network connection to the broker.
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You can publish a string by calling the method `publish("...")` of `MQTTTopic`. The
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method can be called independently of an established connection to the MQTT broker. It
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will delay publishing your message until a connection becomes available.
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The message is published with QoS 1. That means that `MQTTClient` waits for a publish
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acknowledgement from the MQTT broker. If the acknowledgement does not arrive in time,
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`MQTTClient` retries publishing the message up to 15 times until it gives up.
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`connect` and `publish` work asynchronously. They create tasks that are managed by the
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instance of `CooperativeMultitasking`. That's why you have to call it's method `run()`
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until all tasks are finished.
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