Receive offline messages mqtt

问题

I'm using mosquitto as broker and paho(python) as client. I'm trying to make subscriber to receive offline messages.

For that I made following changes:

• Fixed client ID
• qos level 2

but, still the subscriber is not able to receive messages.

any help?

Thanks, Rahul

回答1:

In order to have your client as a durable client and receive messages that were sent to topics when it was offline, you need to meet the following criteria:

1. Fixed client ID (as you've done)
2. Always connect with clean_session=False
3. Subscriptions must be made with QoS>0
4. Messages published must have QoS>0

The mistake that I make most frequently is to forget either one of points 3 and 4, so I'm publishing with QoS=0 or subscribing with QoS=0, either of which would cause messages not to be stored.

You could also look at the queue_qos0_messages option to tell the broker to store QoS=0 messages as well. Note that this is an implementation detail that may be specific to mosquitto.

回答2:

Check if you have set the retain flag to true when publishing message to topic, with retain=true, new connected client which subscribes the topic will receive the retained message.

来源：https://stackoverflow.com/questions/34150452/receive-offline-messages-mqtt