Memory exception in MQTTAsync_freeCommand

[vortex314]

Describe the bug
The mqtt stack seems to fail when I send very rapidly about 20 published messages, I'm connecting a joystick that at initialization sends all buttons and axis info.
https://github.com/vortex314/joystick2mqtt
To Reproduce
Not alsways reproducible
Expected behavior
No crash
Screenshots
If applicable, add screenshots to help explain your problem.

** Environment (please complete the following information):**
Linux pcdell 5.4.0-54-generic #60-Ubuntu SMP Fri Nov 6 10:37:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Additional context
Sources in https://github.com/vortex314/joystick2mqtt
Stack trace
ut/js0 I | 00:06:04.158 | pcdell | Joystick2Mqtt.cpp: 291 | axis : 6 = 0
ut/js0 I | 00:06:04.158 | pcdell | Mqtt.cpp: 172 | MQTT PUB : src/pcdell/js0/axis6 = 0
ut/js0 I | 00:06:04.158 | pcdell | Joystick2Mqtt.cpp: 291 | axis : 7 = 0
ut/js0 I | 00:06:04.158 | pcdell | Mqtt.cpp: 172 | MQTT PUB : src/pcdell/js0/axis7 = 0
free(): invalid pointer
Aborted (core dumped)
lieven@pcdell:/workspace/joystick2mqtt/Debug$ gdb joystick2mqtt core
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Reading symbols from joystick2mqtt...
[New LWP 127717]
[New LWP 127714]
[New LWP 127716]
[New LWP 127715]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `./joystick2mqtt ../src/joystick2mqtt.json'.
Program terminated with signal SIGABRT, Aborted.
--Type for more, q to quit, c to continue without paging--
#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
50 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
[Current thread is 1 (Thread 0x7f7876255700 (LWP 127717))]
(gdb) bt
#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1 0x00007f78773d1859 in __GI_abort () at abort.c:79
#2 0x00007f787743c3ee in __libc_message (action=action@entry=do_abort, fmt=fmt@entry=0x7f7877566285 "%s\n") at ../sysdeps/posix/libc_fatal.c:155
#3 0x00007f787744447c in malloc_printerr (str=str@entry=0x7f78775644ae "free(): invalid pointer") at malloc.c:5347
#4 0x00007f7877445cac in _int_free (av=, p=, have_lock=0) at malloc.c:4173
#5 0x000055a8ff6d4f70 in Internal_heap_unlink (file=file@entry=0x55a8ff6dde6d "src/MQTTAsync.c", line=line@entry=1726, p=p@entry=0x7f78700220c8) at src/Heap.c:260
#6 0x000055a8ff6d5198 in myfree (file=file@entry=0x55a8ff6dde6d "src/MQTTAsync.c", line=line@entry=1726, p=p@entry=0x7f78700220c8) at src/Heap.c:282
#7 0x000055a8ff6bf15f in MQTTAsync_freeCommand (command=command@entry=0x7f78700220c8) at src/MQTTAsync.c:1726
#8 0x000055a8ff6c241e in MQTTAsync_cycle (rc=0x7f7876254e0c, timeout=, sock=0x7f7876254e10) at src/MQTTAsync.c:4705
#9 MQTTAsync_receiveThread (n=) at src/MQTTAsync.c:2712
#10 0x00007f78777a3609 in start_thread (arg=) at pthread_create.c:477
#11 0x00007f78774ce293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

[icraggs]

A client library trace, as described in the readme might help to illustrate a bit more about what's going on. Just at the normal level, not maximum. Even if you can't trace the error situation, it might give me an idea of the circumstances.

[vortex314]

Hi Ian, as I also refactored my code, I was not able to reproduce the issue. Sorry for the inconvenience. Lieven

[icraggs]

Thanks for letting me know.