Perform ACM-triggered cloud connection migration without a disconnect

[avtolstoy]

TODO

Add stress test

Problem

After performing an initial cloud connection, ACM will re-evaluate this decision (if there are multiple network interfaces available) and might decide to migrate the connection. This is currently performed by disconnect, session move and re-connect.

Solution

This instead can be performed without tearing down the cloud connection and just re-binding the underlying socket + indicating to the comms layer that session move + ping needs to be performed.

This PR also fixes slo/connect_time test with test runner-forced network (--network=X option).

Log

Having connected to the cloud over cellular, migrating to a connection over wifi:

0000016932 [comm.coap] TRACE: ACK 0.00  size=4 token= id=12
0000017690 [comm.coap] TRACE: Sending CoAP message
0000017704 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=13
0000017942 [comm.coap] TRACE: Received CoAP message
0000017956 [comm.coap] TRACE: ACK 0.00  size=4 token= id=13
0000018724 [comm.coap] TRACE: Sending CoAP message
0000018737 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=14
0000018981 [comm.coap] TRACE: Received CoAP message
0000018995 [comm.coap] TRACE: ACK 0.00  size=4 token= id=14
0000019759 [comm.coap] TRACE: Sending CoAP message
0000019773 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=15
0000020030 [comm.coap] TRACE: Received CoAP message
0000020044 [comm.coap] TRACE: ACK 0.00  size=4 token= id=15
0000020794 [comm.coap] TRACE: Sending CoAP message
0000020808 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=16
0000020828 [system.cm] INFO: Ethernet: 0/0 packets (0 tx errors) 0/0 bytes received, avg rtt: 0, mask=0000, score=4294967295
0000020861 [system.cm] INFO: WiFi: 10/10 packets (0 tx errors) 1813/1943 bytes received, avg rtt: 183, mask=03ff, score=183
0000020894 [system.cm] INFO: Cellular: 10/10 packets (0 tx errors) 2529/2659 bytes received, avg rtt: 271, mask=03ff, score=271
0000020929 [system.cm] TRACE: Using best network: WiFi
0000020945 [system.cm] TRACE: Best network interface for cloud connection changed (to WiFi) - move the cloud session
0000020976 [system] INFO: Attempting to move cloud connection to interface 5
0000020998 [system] INFO: Re-bound cloud socket to iface 5 ("wl4")
0000021016 [comm] INFO: Moving connection (session move + ping)
0000021034 [comm.dtls] INFO: session cmd (CLS,DIS,MOV,LOD,SAV): 2
0000021052 [comm] INFO: Forcing a cloud ping
0000021064 [comm.coap] TRACE: Sending CoAP message
0000021079 [comm.coap] TRACE: CON 0.00  size=4 token= id=17
0000021285 [comm.dtls] INFO: session cmd (CLS,DIS,MOV,LOD,SAV): 4
0000021303 [comm.coap] TRACE: Received CoAP message
0000021317 [comm.coap] TRACE: ACK 0.00  size=4 token= id=17
0000021830 [comm.coap] TRACE: Sending CoAP message
0000021843 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=18
0000022042 [comm.coap] TRACE: Received CoAP message
0000022057 [comm.coap] TRACE: ACK 0.00  size=4 token= id=18
0000022864 [comm.coap] TRACE: Sending CoAP message
0000022878 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=19
0000023076 [comm.coap] TRACE: Received CoAP message
0000023091 [comm.coap] TRACE: ACK 0.00  size=4 token= id=19
0000023899 [comm.coap] TRACE: Sending CoAP message
0000023912 [comm.coap] TRACE: CON POST /E/blah size=20 token= id=20
0000024146 [comm.coap] TRACE: Received CoAP message
0000024161 [comm.coap] TRACE: ACK 0.00  size=4 token= id=20

References

Links to the Community, Docs, Other Issues, etc..

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[sergeuz]

Any reason not to return the actual error code instead of UNKNOWN if this fails?

[avtolstoy]

🤷 fixed. And added one session use.

[sergeuz]

😅