Fix start_tls() loses StreamReader buffer data#103
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Vizonex merged 1 commit intoVizonex:mainfrom Dec 20, 2025
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…ng the connection
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@fizzi01 If the unittests fail know that it's caused by a rounding bug in uvloop and winloop and possibly libuv due to how it does math for getting timeouts. |
Owner
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@fizzi01 Thanks for the pull request btw. We don't get contributors here very often. I'll probably wind up optimizing this code in a later update since I've been trying to optimize the pure python portions for better performance. |
Vizonex
approved these changes
Dec 20, 2025
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What do these changes do?
This PR fixes a critical issue where buffered data in StreamReader is lost when upgrading a connection to TLS using StreamWriter.start_tls() or loop.start_tls(), causing the call to hang indefinitely. The issue exists in both asyncio (see python/cpython#142352) and uvloop.
The main focus is to verify and guarantee that any data buffered before upgrading a connection to TLS is not lost and is correctly transferred. These changes are effectively a port of python/cpython#142354 with absolutely no difference, except for the test that creates a TCP server, establishes a connection, buffers data, performs a TLS upgrade, and verifies that all messages (both pre-upgrade and post-upgrade) are received correctly.
Are there changes in behavior for the user?
No.
Is it a substantial burden for the maintainers to support this?
Nope.
Related issue number
Fixes #102
Checklist