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How do I subscribe to MQTT topic?
You can subscribe to multiple topics using two wildcard characters (+ and #) as discussed in the understanding MQTT topics tutorial. All subscriptions are acknowledged by the broker using a subscription acknowledge message that includes a packet identifier that can be used to verify the success of the subscription.
What is subscribe in MQTT?
To receive messages on topics of interest, the client sends a SUBSCRIBE message to the MQTT broker. This subscribe message is very simple, it contains a unique packet identifier and a list of subscriptions. Packet Identifier The packet identifier uniquely identifies a message as it flows between the client and broker.
What is MQTT subscribe?
Is there a tool to subscribe to MQTT topics?
MQTT.fx is a GUI utility implemented with JavaFX that is available for Windows, Linux and macOS. This tool allows us to connect with an MQTT server, subscribe to topic filters, see the received messages and publish messages to topics.
How does the MQTT broker decide which message to send?
As we have already mentioned, the MQTT broker uses the topic of a message to decide which client receives which message. We also look at SYS-topics, which are special topics that reveal information about the broker itself. Be sure to watch our video about MQTT topics at the end of this blog post. Let’s get started.
An MQTT topic filter with the format $share/ {ShareName}/ {filter} indicates a shared subscription. For more information, refer to Shared Subscriptions. An MQTT topic filter starting with $noexport indicates that the event broker should not export shared subscriptions.
When do you use wildcard characters in MQTT?
Wildcard Characters in MQTT Topic Subscriptions When the “+” or “#” characters are used in topic subscriptions they function as wildcards, which affects the topic matches that can occur from the subscription.