Add test for HTTP2 CONNECT termination #3655
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howardjohn
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May 1, 2024
See hyperium/hyper#3652. What I have found is the final reference to a stream being dropped after the `maybe_close_connection_if_no_streams` but before the `inner.poll()` completes can lead to the connection dangling forever without any forward progress. No streams/references are alive, but the connection is not complete and never wakes up again. This seems like a classic TOCTOU race condition. In this fix, I check again at the end of poll and if this state is detected, wake up the task again. Wth the test in hyperium/hyper#3655, on my machine, it fails about 5% of the time: ``` 1876 runs so far, 100 failures (94.94% pass rate). 95.197349ms avg, 1.097347435s max, 5.398457ms min ``` With that PR, this test is 100% reliable ``` 64010 runs so far, 0 failures (100.00% pass rate). 44.484057ms avg, 121.454709ms max, 1.872657ms min ``` Note: we also have reproduced this using `h2` directly outside of `hyper`, which is what gives me confidence this issue lies in `h2` and not `hyper`.
This was referenced May 1, 2024
seanmonstar
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May 2, 2024
See hyperium/hyper#3652. What I have found is the final reference to a stream being dropped after the `maybe_close_connection_if_no_streams` but before the `inner.poll()` completes can lead to the connection dangling forever without any forward progress. No streams/references are alive, but the connection is not complete and never wakes up again. This seems like a classic TOCTOU race condition. In this fix, I check again at the end of poll and if this state is detected, wake up the task again. Wth the test in hyperium/hyper#3655, on my machine, it fails about 5% of the time: ``` 1876 runs so far, 100 failures (94.94% pass rate). 95.197349ms avg, 1.097347435s max, 5.398457ms min ``` With that PR, this test is 100% reliable ``` 64010 runs so far, 0 failures (100.00% pass rate). 44.484057ms avg, 121.454709ms max, 1.872657ms min ``` Note: we also have reproduced this using `h2` directly outside of `hyper`, which is what gives me confidence this issue lies in `h2` and not `hyper`.
seanmonstar
approved these changes
May 3, 2024
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Thank you! I was waiting to release |
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Ah makes sense. Thanks! |
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For #3652.
In #3647, I thought I tracked down the root cause of #3652. However, with the help of @seanmonstar in #3652 (comment) I realized that this was too forcefully terminating the connection even if things other than SendRequest were still alive. I also realized the original test case I wrote was just wrong and failed to properly reproduce the issue.
This adds a test that properly reproduces the issue. On my machine, it fails about 5% of the time:
With further investigation, I believe this bug actually originates in
h2itself. hyperium/h2#772. With that PR, this test is 100% reliable