Fix packet order of FIN from SHUT_WR
#3562
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SHUT_WR
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robgjansen
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Apr 24, 2025
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robgjansen
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Good find!
If only we had a nice Rust TCP stack so we could throw this janky C stack in the trash :D
This test currently fails.
This should fix shadow#3100 and its associated regression test. This prevents FIN packets caused by a `SHUT_WR` from being sent before other packets with a lower sequence number.
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Every time I look at the rust tcp code, I remember how much work still needs to be done. Someday hopefully :) |
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Shadow assigns a priority to packets, and packets with a lower priority will be sent before other packets. Previously, shadow only assigned a priority to non-empty packets (here meaning containing a payload), and a priority of 0 to other packets. But this meant that empty packets like FIN (with a priority of 0) could be sent before other packets, even if the FIN had a higher sequence number. Shadow seems to have discarded these out-of-order FIN packets. See #3100 for an example.
This MR changes the legacy TCP code to always assign a non-zero priority if the packets has a sequence number, so that they won't be sent out of order. This (edit: partially; see #3100 (comment)) fixes (edit: <text to prevent github from closing the linked issue>) #3100, but there are still a lot of other shutdown-related bugs (see all the disabled tests in
src/test/socket/shutdown/test_shutdown.rs), soshutdown()still won't work 100% as expected.Related: #3558 (I think this MR fixes this shutdown issue as well, but it looks like there are still some other issues.)