From 45f005e930a2656be6e017a11b6e4e07bfcd2194 Mon Sep 17 00:00:00 2001 From: Jelle Zijlstra Date: Tue, 20 Oct 2026 10:19:50 -0700 Subject: [PATCH] gh-159739: Handle overlapping buffers in BytesIO.readinto (GH-159777) (cherry picked from commit 17df836e6d4ba3ce0a28cfe98efedf7c7b4f0e49) Co-authored-by: Jelle Zijlstra Co-authored-by: Jelle Zijlstra --- Lib/test/test_io/test_memoryio.py | 6 ++++++ .../Library/2026-10-19-20-38-17.gh-issue-159739.a81270.rst | 1 + Modules/_io/bytesio.c | 2 +- 3 files changed, 8 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.a81270.rst diff --git a/Lib/test/test_io/test_memoryio.py b/Lib/test/test_io/test_memoryio.py index 7f2eddd7ae7839e..2ee3a1d1562c8b4 100644 --- a/Lib/test/test_io/test_memoryio.py +++ b/Lib/test/test_io/test_memoryio.py @@ -859,6 +859,12 @@ class CBytesIOTest(PyBytesIOTest): ioclass = io.BytesIO UnsupportedOperation = io.UnsupportedOperation + def test_readinto_overlapping_buffer(self): + with self.ioclass(b'abcd') as stream: + with stream.getbuffer()[1:] as target: + self.assertEqual(stream.readinto(target), 3) + self.assertEqual(stream.getvalue(), b'aabc') + def test_getstate(self): memio = self.ioclass() state = memio.__getstate__() diff --git a/Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.a81270.rst b/Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.a81270.rst new file mode 100644 index 000000000000000..413fc0d7f18f680 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.a81270.rst @@ -0,0 +1 @@ +Fix :class:`io.BytesIO` reads into overlapping views of the same buffer. diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c index 9ea197d29f30960..17ae3a82acad2fe 100644 --- a/Modules/_io/bytesio.c +++ b/Modules/_io/bytesio.c @@ -670,7 +670,7 @@ _io_BytesIO_readinto_impl(bytesio *self, Py_buffer *buffer) assert(self->pos + len <= PY_SSIZE_T_MAX); assert(len >= 0); - memcpy(buffer->buf, PyBytes_AS_STRING(self->buf) + self->pos, len); + memmove(buffer->buf, PyBytes_AS_STRING(self->buf) + self->pos, len); self->pos += len; return PyLong_FromSsize_t(len);