Fix #1070: bytes_to_read buffer size for Python 3.14#1074
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Fixes pyinvoke#1070. On Python 3.14, fcntl.ioctl rejects undersized mutable buffers (cpython#144206). `bytes_to_read()` was passing a 2-byte buffer to FIONREAD, which writes a C int (typically 4 bytes). The same bug was fixed for `_pty_size` in pyinvoke#1038, but `bytes_to_read` was missed. This worked by accident on <=3.13 thanks to CPython's 1024-byte static copy buffer that masked the size mismatch. CPython 3.14 tightened the check, so `Connection.run()` from a TTY-attached process on 3.14 now crashes with SystemError: buffer overflow in `handle_stdin`. Fix: pass a 4-byte buffer (`b"\x00\x00\x00\x00"`) and unpack as a signed int (`struct.unpack('i', ...)`) instead of signed short (`'h'`). Tests: tests/terminals/test_bytes_to_read.py covers: - buffer passed to ioctl is 4 bytes - result is the int parsed from the 4-byte C int - FIONREAD returning 0 is correctly handled - non-TTY fallback still returns 1 Test runs: - New tests: 3/3 pass - Full non-pty, non-runner suite: 774 passed (no regressions) - Pre-existing pty/runner failures in this sandbox are env-specific (no real TTY, no /dev/tty) and unrelated to this change Fixes pyinvoke#1070 Refs: AI-2138
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Fixes #1070.
Bug
On Python 3.14, fcntl.ioctl rejects undersized mutable buffers (cpython#144206).
bytes_to_read()was passing a 2-byte buffer to FIONREAD, which writes a C int (typically 4 bytes). Same root cause as the bug fixed in #1038 for_pty_size, butbytes_to_readwas missed.Worked by accident on <=3.13 thanks to CPython's 1024-byte static copy buffer. On 3.14,
Connection.run()from a TTY-attached process crashes with SystemError: buffer overflow inhandle_stdin.Fix
Pass a 4-byte buffer and unpack as a signed int:
Tests
tests/terminals/test_bytes_to_read.py— 3 cases:Refs: AI-2138