Remove client side session expiry timer #767
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I thought that the client needs to have session expiry timer to erase inflight messages. So I implemented the session expiry timer for the client. However, I found the following clause in the spec. --- https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901078 If the Server accepts a connection with Clean Start set to 1, the Server MUST set Session Present to 0 in the CONNACK packet in addition to setting a 0x00 (Success) Reason Code in the CONNACK packet [MQTT-3.2.2-2]. https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901048 The Client can avoid implementing its own Session expiry and instead rely on the Session Present flag returned from the Server to determine if the Session had expired. If the Client does implement its own Session expiry, it needs to store the time at which the Session State will be deleted as part of its Session State. --- That means the client can remove the session expiry timer depends on broker side session existance that is reported by session_present flag on CONNACK packet. The spac also said that as follows. It is the session state mismatching between the client and the broker. If they have the timers individually, then it could happen. It is a kind of clock skew. Depending on session_present can automatically avoid this issue. So, I decided removing from session expiry timer from the client and use session_present flag to erase the inflight messages. It is a better design. --- https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901078 If the Client does not have Session State and receives Session Present set to 1 it MUST close the Network Connection [MQTT-3.2.2-4]. If it wishes to restart with a new Session the Client can reconnect using Clean Start set to 1. If the Client does have Session State and receives Session Present set to 0 it MUST discard its Session State if it continues with the Network Connection [MQTT-3.2.2-5]. ---
The published messages during offline should be sent only if the session exists in the broker. If offline publish is sent after session has been expired is a protocol error.
Codecov Report
@@ Coverage Diff @@
## master #767 +/- ##
==========================================
- Coverage 85.19% 85.19% -0.01%
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Files 61 61
Lines 8694 8645 -49
==========================================
- Hits 7407 7365 -42
+ Misses 1287 1280 -7 |
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