Fix: Subscriptions can't be read if arrive when waiting for response of ping or publish

[rgorosito]

When I'm working with the library, I detect that some event was lost. After enabled debug, I've detected 2 situations:

1. Ping call processPacketsUntil which detect if call new message (appears in debug console), but can't be read in callback or readSubscription.
   My fix add a boolean attribute "new_message" (default false) in Adafruit_MQTT_Publish class. It is set to true inside processPacketsUntil. Later, in readSubscription, search if there are pending message. If so, return that message.
   Callback don't need to be modified because it call readSubscription.

2. Sometimes my program fail to publish a message and loss subscription arrived (detected in debug console). The fix was more easy and clean: replase readFullPacket with processPacketsUntil. This permit that a message arrive when waiting for response on QoS>0 and because processPacketsUntil has the expected packet type, the check in the type in buffer is not needed anymore.

Logs

1. PING

MQTT ping packet:
          [0xC0],   [0x00], 
Client sendPacket returned: 2
Read data:              2 [0x32], 
Packet Type:            2 [0x32],
Read data:                [0x1A], 
Packet Length:  26
Read data:                [0x00],   [0x14], e [0x65], s [0x73], p [0x70], - [0x2D], p [0x70], r [0x72],
        u [0x75], e [0x65], b [0x62], a [0x61], / [0x2F], l [0x6C], u [0x75], z [0x7A],
        / [0x2F], r [0x72], o [0x6F], j [0x6A], o [0x6F], 2 [0x32],   [0x00],   [0x1F],
        O [0x4F], N [0x4E],
Packet len: 28
        2 [0x32],   [0x1A],   [0x00],   [0x14], e [0x65], s [0x73], p [0x70], - [0x2D],
        p [0x70], r [0x72], u [0x75], e [0x65], b [0x62], a [0x61], / [0x2F], l [0x6C],
        u [0x75], z [0x7A], / [0x2F], r [0x72], o [0x6F], j [0x6A], o [0x6F], 2 [0x32],
          [0x00],   [0x1F], O [0x4F], N [0x4E],
Looking for subscription len 20
Found sub #4
Data len: 2
Data: ON
MQTT puback packet:
        2 [0x32],   [0x1A],   [0x00],   [0x14],
Client sendPacket returned: 4
Read data:                [0xD0],
Packet Type:              [0xD0],
Read data:                [0x00],
Packet Length:  0

message are parsed, but never read

2. PUBLISH

MQTT publish packet:
        2 [0x32], ' [0x27],   [0x00],   [0x17], e [0x65], s [0x73], p [0x70], - [0x2D],
        p [0x70], r [0x72], u [0x75], e [0x65], b [0x62], a [0x61], / [0x2F], f [0x66],
        e [0x65], e [0x65], d [0x64], s [0x73], / [0x2F], e [0x65], s [0x73], t [0x74],
        a [0x61], d [0x64], o [0x6F],   [0x00],   [0x0D], 1 [0x31], 9 [0x39], 2 [0x32],
        . [0x2E], 1 [0x31], 6 [0x36], 8 [0x38], . [0x2E], 0 [0x30], . [0x2E], 6 [0x36],
        1 [0x31],
Client sendPacket returned: 41
Read data:              2 [0x32],
Packet Type:            2 [0x32],
Read data:                [0x1A],
Packet Length:  26
Read data:                [0x00],   [0x14], e [0x65], s [0x73], p [0x70], - [0x2D], p [0x70], r [0x72],
        u [0x75], e [0x65], b [0x62], a [0x61], / [0x2F], l [0x6C], u [0x75], z [0x7A],
        / [0x2F], r [0x72], o [0x6F], j [0x6A], o [0x6F], 2 [0x32],   [0x00],   [0x03],
        O [0x4F], N [0x4E],
Publish QOS1+ reply:            2 [0x32],   [0x1A],   [0x00],   [0x14], e [0x65], s [0x73], p [0x70], - [0x2D],
        p [0x70], r [0x72], u [0x75], e [0x65], b [0x62], a [0x61], / [0x2F], l [0x6C],
        u [0x75], z [0x7A], / [0x2F], r [0x72], o [0x6F], j [0x6A], o [0x6F], 2 [0x32],
          [0x00],   [0x03], O [0x4F], N [0x4E],
Failed <--- return of publish is false
Read data:              @ [0x40],
Packet Type:            @ [0x40],
Read data:                [0x02],
Packet Length:  2
Read data:                [0x00],   [0x0D],
Packet len: 4
        @ [0x40],   [0x02],   [0x00],   [0x0D],

On publish waiting por ACK, ignore incomming messages and return an error because ACK come later.

[brentru]

@rgorosito Hi, thanks for submitting this PR. I agree completely with #2, thank you for adding it, it'll help the publish function be more selective with what its reading out.

In 1),

Ping call processPacketsUntil which detect if call new message (appears in debug console), but can't be read in callback or readSubscription.

I'm confused here.

The way the library currently works, ping is called which calls processPacketsUntil. processPacketsUntil waits for the broker to respond with a PINGRESP control packet. It should not obtain any other messages other than a PINGRESP. When would this not be the case?

[rgorosito]

The way the library currently works, ping is called which calls processPacketsUntil. processPacketsUntil waits for the broker to respond with a PINGRESP control packet. It should not obtain any other messages other than a PINGRESP. When would this not be the case?

the problem occurs when a new message reaches the subscriber between the ping that was sent and its response received. If you see the log 1:

out: PINGREQ [C0]
in: PUBLISH RECEPTION (sent from the mqtt server) [32]
out: PUBLISH ACK [32]
in: PINGRESP [D0]

[rgorosito]

How to reproduce:

Problem with ping:

• Create a sketch that subscribe to a topic and send PINGs once per second second (to increase the probability of occurrence)
• From another host, send messages in a loop
  you will see that some messages are not processed in readSubscription

Problem with publish:

• Create a sketch that subscribe to a topic and send messages to another topic once per second second (to increase the probability of occurrence)
• From another host, send messages in a loop
  you will see that some messages are not processed in readSubscription and son publish will return an error.

[brentru]

@rgorosito Ok, this does address a bug I've been having with this library. Requesting clarification + modifications before I merge in....

Also please bump the version number in the library.properties file so we can release.