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binder: add unit tests for Inbound. Use them to repro & fix an edge case in delivery - #13032
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dbgalur
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@kannanjgithub, could you consider this for approval? My colleague has reviewed it for Android. |
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Perhaps Eric will have a moment to consider this for approval during pacific business hours. |
…getDelegate() Permits fake/mock implementations in tests that aren't actually backed by an IBinder at all. TAG=agy CONV=a7051e19-0fc1-42a4-8b24-5c2e3373aa0c
It's hard to unit test Inbound in isolation because of its many hard-coded concrete dependencies. However, without unit tests, we can't safely refactor Inbound to fix this either! Introduce ClientInboundTest and ServerInboundTest, which bootstrap a way out of this mess by creating an Inbound indirectly via a dummy BinderTransport. TAG=agy CONV=a7051e19-0fc1-42a4-8b24-5c2e3373aa0c
Inbound's queuedTransactionData holds message fragments from the peer that haven't yet been assembled and delivered to the application. Binder transactions are sent in index order and must contain at least one of: a prefix, part/all of a message, and a suffix. When a transaction with message data arrives before its predecessors (according to index), Inbound's enqueueTransactionData() reserves slots for those predecessors in queuedTransactionData. After each predecessor transaction trickles in, enqueueTransactionData() checks whether it completes the message, which can then be delivered. There's an edge case, though, where a late-arrival transaction contains just the prefix with no message data at all. In that case, Inbound remove()s the queuedTransactionData slot it previously reserved and carries on without considering that this prefix-only transaction might have completed the first message! And if that was the final transaction in the stream, Inbound will never call lookForCompleteMessage() again, leaving the stream stuck forever with a complete but undelivered message.
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Regression testing this bug fix required building unit tests for Inbound (it currently has none). We'll rely on these tests for other, bigger, upcoming changes like #12747 and #9010.
Will not squash please review each commit individually.