Ensure that we send MRP acks to incoming messages as needed. #19398
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There were two ways we could fail to send an ack to an incoming reliable message: 1) If we found no matching handler, and hence created an ephemeral exchange to handle the message, but the message was unencrypted. In this case our ephemeral exchange would return true for IsEncryptionRequired(), because it would default to an ApplicationExchangeDispatch, and we would never call into ExchangeContext::HandleMessage. 2) If ExchangeMessageDispatch::MessagePermitted returned false for the message. In particular, for an ApplicationExchangeDispatch, this would happen for all the handshake messages except StatusReport. The fix for issue 1 is to ensure we always call into HandleMEssage if we manage to allocate an exchange. If there is an encryption mismatch, which only matters when the exchange is non-ephemeral, we close the exchange first to prevent event delivery to the delegate. The fix for issue 2 is to move the MRP processing out of ExchangeMessageDispatch and into ExchangeContext, and to move the MessagePermitted check so the only thing it prevents is delivery of the message to the delegate, not any other processing by the exchange. Fixes project-chip#10515
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PR #19398: Size comparison from 0adc4f3 to fa18784 Increases (27 builds for cc13x2_26x2, efr32, esp32, k32w, linux, mbed, nrfconnect, p6, telink)
Decreases (14 builds for cc13x2_26x2, cyw30739, esp32, linux, telink)
Full report (30 builds for cc13x2_26x2, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, p6, telink)
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There were two ways we could fail to send an ack to an incoming reliable message:
If we found no matching handler, and hence created an ephemeral exchange to
handle the message, but the message was unencrypted. In this case our ephemeral
exchange would return true for IsEncryptionRequired(), because it would default
to an ApplicationExchangeDispatch, and we would never call into
ExchangeContext::HandleMessage.
If ExchangeMessageDispatch::MessagePermitted returned false for the message.
In particular, for an ApplicationExchangeDispatch, this would happen for all the
handshake messages except StatusReport.
The fix for issue 1 is to ensure we always call into HandleMEssage if we manage
to allocate an exchange. If there is an encryption mismatch, which only matters
when the exchange is non-ephemeral, we close the exchange first to prevent event
delivery to the delegate.
The fix for issue 2 is to move the MRP processing out of ExchangeMessageDispatch
and into ExchangeContext, and to move the MessagePermitted check so the only
thing it prevents is delivery of the message to the delegate, not any other
processing by the exchange.
Fixes #10515
Problem
See above.
Change overview
See above.
Testing
Introduced a 10-second sleep in CASE StatusReport processing, which without these changes caused acks to the resent Sigma3 or Sigma2Resume message to be dropped. Verified that with these changes those acks are sent correctly. That exercises problem 1.
In addition to the above, added StatusReport to the list of disallowed messages in
ApplicationExchangeDispatch::MessagePermittedand verified that without the changes to fix problem 2 above acks failed to be sent, but with the changes in this PR acks were sent correctly.