gh-146379: Avoid StreamReader BufferError with active memoryview exports#146380

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MadLongTom wants to merge 2 commits intopython:mainfrom

MadLongTom:fix-streamreader-bufferror

Open

gh-146379: Avoid StreamReader BufferError with active memoryview exports#146380
MadLongTom wants to merge 2 commits intopython:mainfrom
MadLongTom:fix-streamreader-bufferror

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MadLongTom commentedMar 24, 2026•
edited by bedevere-appbot
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Description

Summary

This PR fixesBufferError inasyncio.StreamReader when a memoryview export exists on the internal buffer andStreamReader performs in-placebytearray mutation.

Problem

CurrentStreamReader logic includes in-place mutations (slice delete / clear). If a memoryview is active,bytearray resizing raises:

BufferError: Existing exports of data: object cannot be re-sized

Changes

UpdateStreamReader buffer-consumption paths to avoid in-place resize operations.
Use replacement assignment patterns that do not mutate exportedbytearray objects in place.
Apply the fix consistently across:
- read
- readline
- readuntil
- readexactly

Tests

Added regression tests for each affected method with an active memoryview on the internal buffer.
Added coverage for both normal consume paths and EOF/error paths.
Verified tests fail before fix and pass after fix.

Behavioral impact

No API change.
No semantic change to returned data.
Fixes crashes under valid runtime scenarios where memoryview exports exist.

Checklist

Added/updated tests
Ran relevant test suite successfully
Added NEWS entry if required by core team guidance
Linked issue in title/body and followed CPython contribution workflow

Fixes#146379

Issue:asyncio.StreamReader raises BufferError with active memoryview #146379

pythongh-146379: Fix StreamReader BufferError with active memoryview …

f2a893a

…exportsStreamReader methods (read, readline, readuntil, readexactly) raiseBufferError when a memoryview is held on the internal buffer, becausebuffer mutations (take_bytes, del slice, clear) cannot resize abytearray with active exports.Add _consume_buffer() helper that tries take_bytes() first, thenfalls back to non-mutating object replacement when BufferError israised. Replace all buffer-consumption call sites in StreamReaderto use _consume_buffer().Also fix readline's LimitOverrunError handler which still useddel-slice and .clear() instead of take_bytes().Add 7 regression tests covering all affected methods with an activememoryview on the internal buffer.