Issue #23099: Closing io.BytesIO with exported buffer is rejected now to

prevent corrupting exported buffer.

Doc/library/io.rst

@@ -563,7 +563,8 @@ than raw I/O does.
 .. class:: BytesIO([initial_bytes])
 
    A stream implementation using an in-memory bytes buffer.  It inherits
-   :class:`BufferedIOBase`.
+   :class:`BufferedIOBase`.  The buffer is discarded when the
+   :meth:`~IOBase.close` method is called.
 
    The argument *initial_bytes* contains optional initial :class:`bytes` data.
 
@@ -584,7 +585,7 @@ than raw I/O does.
 
       .. note::
          As long as the view exists, the :class:`BytesIO` object cannot be
-         resized.
+         resized or closed.
 
       .. versionadded:: 3.2
 
@@ -592,6 +593,7 @@ than raw I/O does.
 
       Return :class:`bytes` containing the entire contents of the buffer.
 
+
    .. method:: read1()
 
       In :class:`BytesIO`, this is the same as :meth:`read`.
@@ -858,7 +860,8 @@ Text I/O
 
 .. class:: StringIO(initial_value='', newline='\\n')
 
-   An in-memory stream for text I/O.
+   An in-memory stream for text I/O.  The text buffer is discarded when the
+   :meth:`~IOBase.close` method is called.
 
    The initial value of the buffer (an empty string by default) can be set by
    providing *initial_value*.  The *newline* argument works like that of
@@ -870,9 +873,7 @@ Text I/O
 
    .. method:: getvalue()
 
-      Return a ``str`` containing the entire contents of the buffer at any
+      Return a ``str`` containing the entire contents of the buffer.
-      time before the :class:`StringIO` object's :meth:`close` method is
-      called.
 
    Example usage::
 

Lib/_pyio.py

@@ -833,8 +833,14 @@ class BytesIO(BufferedIOBase):
     def getbuffer(self):
         """Return a readable and writable view of the buffer.
         """
+        if self.closed:
+            raise ValueError("getbuffer on closed file")
         return memoryview(self._buffer)
 
+    def close(self):
+        self._buffer.clear()
+        super().close()
+
     def read(self, size=None):
         if self.closed:
             raise ValueError("read from closed file")

Lib/test/test_memoryio.py

@@ -398,14 +398,19 @@ class BytesIOMixin:
         # raises a BufferError.
         self.assertRaises(BufferError, memio.write, b'x' * 100)
         self.assertRaises(BufferError, memio.truncate)
+        self.assertRaises(BufferError, memio.close)
+        self.assertFalse(memio.closed)
         # Mutating the buffer updates the BytesIO
         buf[3:6] = b"abc"
         self.assertEqual(bytes(buf), b"123abc7890")
         self.assertEqual(memio.getvalue(), b"123abc7890")
-        # After the buffer gets released, we can resize the BytesIO again
+        # After the buffer gets released, we can resize and close the BytesIO
+        # again
         del buf
         support.gc_collect()
         memio.truncate()
+        memio.close()
+        self.assertRaises(ValueError, memio.getbuffer)
 
 
 class PyBytesIOTest(MemoryTestMixin, MemorySeekTestMixin,

Misc/NEWS

@@ -56,6 +56,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #23099: Closing io.BytesIO with exported buffer is rejected now to
+  prevent corrupting exported buffer.
+
 - Issue #23363: Fix possible overflow in itertools.permutations.
 
 - Issue #23364: Fix possible overflow in itertools.product.

Modules/_io/bytesio.c

@@ -657,6 +657,7 @@ PyDoc_STRVAR(close_doc,
 static PyObject *
 bytesio_close(bytesio *self)
 {
+    CHECK_EXPORTS(self);
     if (self->buf != NULL) {
         PyMem_Free(self->buf);
         self->buf = NULL;