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Attempt to overwrite without race condition #335

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Attempt to overwrite without race condition #335

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thatch
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@thatch thatch commented May 8, 2024

As explained in #332, there was previously a small window of time where the file is deleted before its new contents get written. Because reads don't happen with the lock held, this resulted in an empty-body cache hit when it shouldn't.

Fixes #332

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Attempt to overwrite without race condition
ef19577 
As explained in psf#332, there was previously a small window of time where the
file is deleted before its new contents get written.  Because reads don't
happen with the lock held, this resulted in an empty-body cache hit when it
shouldn't.

Fixes psf#332
@woodruffw woodruffw self-requested a review May 8, 2024 22:09
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Thanks @thatch! I'll try and give this a review in the coming days.

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thatch commented Jun 6, 2024

Any luck with testing?

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Any luck with testing?

Sorry for the delay -- I was out for a bit, and I'm catching up now. I'll do some testing tonight.

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woodruffw approved these changes Jun 13, 2024
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I did some local testing (on Linux) and didn't hit any issues with this.

I also went through the old _secure_open_write flags and confirmed that we shouldn't be missing anything important here -- the old flags should be irrelevant for our mkstemp use (since it defaults to binary mode and O_NOFOLLOW shouldn't be relevant for fresh temporary files).

As such, this LGTM! I'd like @frostming to also do a comb over it though 🙂

(I didn't test this locally on Windows, but my understanding is that os.replace is equally atomic there.)

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Race condition in FileCache that can result in empty body 200 response
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@thatch @woodruffw