arduino-mqtt
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256dpi
ESP32DevelopmentBoardSecure example has LWMQTT_BUFFER_TOO_SHORT error
The ESP32DevelopmentBoardSecure example sketch for the ESP32 fails to receive the first message after connect and sits in an endless re-connecting loop.
Inserting the getLastError() call before the re-connect shows an error of -1 (LWMQTT_BUFFER_TOO_SHORT) - in order to get the example to run I have to initialise the client with a much larger buffer: MQTTClient client(1024);
If the buffer is smaller than this, the example doesn't work for me.
The first message I receive is always bonkers accordng to the serial output:
checking wifi....
connecting...
connected!
incoming: /hello - 01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789
incoming: /hello - world
incoming: /hello - world
The first message you see is from someone that published a retained message in the "try" namespace on shiftr.io. Sure, not an ideal experience, but theres nothing we can do about it... 🤷♂️
Perhaps we can immediately publish a blank retained message (The topic can only have a single retained message) and that should prevent us from receiving the "bad" retained message that requires a large buffer.
I think a simple client.publish("/hello", "", true); should make the example code more reliable for people.
I can do a PR if you think this is acceptable?
Yes, let's do that. The client.publish("/hello", "", 1, true) should be placed right before the subscribe to ensure the retained message has been reset before subscribing. Also a comment should explain why it is needed and that the program may still crash if the "adversary" is online and sending. Would you be able to update all examples?