Emcute cannot create a double-byte name

[ouyangkan]

Description

When I used the emcute routine, the sub had a double-byte name and I could not accept pub from the PC.

Steps to reproduce the issue

1.Compile main in examples\emcute_mqttsn. Burn write stm32f4.
2.Connect to my server
3.sub a
4.pub a (Pub was successful, but my device did not receive the message)
5.sub asd
6.pub asd(Success to send and receive)

Versions

RIOT-2019.10

[ouyangkan]

1.I wrote in the emcute thread：
for(int i=0; i<len; i++) { printf("rbuf[%d] = %x\n", i, rbuf[i]); }
2.When I sub a，I get:

sub a
2019-11-05 07:01:24,962 # sub a
2019-11-05 07:01:24,962 # rbuf[0] = 8
2019-11-05 07:01:24,963 # rbuf[1] = 13
2019-11-05 07:01:24,964 # rbuf[2] = 0
2019-11-05 07:01:24,966 # rbuf[3] = 0
2019-11-05 07:01:24,966 # rbuf[4] = 2
2019-11-05 07:01:24,967 # rbuf[5] = 12
2019-11-05 07:01:24,968 # rbuf[6] = 34
2019-11-05 07:01:24,968 # rbuf[7] = 0
2019-11-05 07:01:24,969 # Now subscribed to a

3.When I pub a, I get:

pub a asd
2019-11-05 07:02:52,354 # pub a asd
2019-11-05 07:02:52,355 # rbuf[0] = 7
2019-11-05 07:02:52,356 # rbuf[1] = b
2019-11-05 07:02:52,357 # rbuf[2] = 0
2019-11-05 07:02:52,358 # rbuf[3] = 2
2019-11-05 07:02:52,363 # rbuf[4] = 12
2019-11-05 07:02:52,364 # rbuf[5] = 35
2019-11-05 07:02:52,365 # rbuf[6] = 0
2019-11-05 07:02:52,365 # rbuf[0] = a
2019-11-05 07:02:52,366 # rbuf[1] = c
2019-11-05 07:02:52,370 # rbuf[2] = 2
2019-11-05 07:02:52,371 # rbuf[3] = 61
2019-11-05 07:02:52,372 # rbuf[4] = 61
2019-11-05 07:02:52,372 # rbuf[5] = 0
2019-11-05 07:02:52,373 # rbuf[6] = 0
2019-11-05 07:02:52,389 # rbuf[7] = 61
2019-11-05 07:02:52,390 # rbuf[8] = 73
2019-11-05 07:02:52,391 # rbuf[9] = 64

4.0x61 is the ascall code for 'a'.
I suspect MQTT creates topic_id directly with topic_name when topic_name is less than two bytes.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you want me to ignore this issue, please mark it with the "State: don't stale" label. Thank you for your contributions.