bpo-41103: Resurrect the old buffer protocol. (GH-27437)

Revert "bpo-41103: Remove old buffer protocol support (#21117)"

This reverts commit 6f8a6ee59c.

Doc/c-api/abstract.rst

@@ -24,3 +24,4 @@ but whose items have not been set to some non-\ ``NULL`` value yet.
    mapping.rst
    iter.rst
    buffer.rst
+   objbuffer.rst

Doc/c-api/objbuffer.rst

@@ -0,0 +1,55 @@
+.. highlight:: c
+
+Old Buffer Protocol
+-------------------
+
+.. deprecated:: 3.0
+
+These functions were part of the "old buffer protocol" API in Python 2.
+In Python 3, this protocol doesn't exist anymore but the functions are still
+exposed to ease porting 2.x code.  They act as a compatibility wrapper
+around the :ref:`new buffer protocol <bufferobjects>`, but they don't give
+you control over the lifetime of the resources acquired when a buffer is
+exported.
+
+Therefore, it is recommended that you call :c:func:`PyObject_GetBuffer`
+(or the ``y*`` or ``w*`` :ref:`format codes <arg-parsing>` with the
+:c:func:`PyArg_ParseTuple` family of functions) to get a buffer view over
+an object, and :c:func:`PyBuffer_Release` when the buffer view can be released.
+
+
+.. c:function:: int PyObject_AsCharBuffer(PyObject *obj, const char **buffer, Py_ssize_t *buffer_len)
+
+   Returns a pointer to a read-only memory location usable as character-based
+   input.  The *obj* argument must support the single-segment character buffer
+   interface.  On success, returns ``0``, sets *buffer* to the memory location
+   and *buffer_len* to the buffer length.  Returns ``-1`` and sets a
+   :exc:`TypeError` on error.
+
+
+.. c:function:: int PyObject_AsReadBuffer(PyObject *obj, const void **buffer, Py_ssize_t *buffer_len)
+
+   Returns a pointer to a read-only memory location containing arbitrary data.
+   The *obj* argument must support the single-segment readable buffer
+   interface.  On success, returns ``0``, sets *buffer* to the memory location
+   and *buffer_len* to the buffer length.  Returns ``-1`` and sets a
+   :exc:`TypeError` on error.
+
+
+.. c:function:: int PyObject_CheckReadBuffer(PyObject *o)
+
+   Returns ``1`` if *o* supports the single-segment readable buffer interface.
+   Otherwise returns ``0``.  This function always succeeds.
+
+   Note that this function tries to get and release a buffer, and exceptions
+   which occur while calling corresponding functions will get suppressed.
+   To get error reporting use :c:func:`PyObject_GetBuffer()` instead.
+
+
+.. c:function:: int PyObject_AsWriteBuffer(PyObject *obj, void **buffer, Py_ssize_t *buffer_len)
+
+   Returns a pointer to a writable memory location.  The *obj* argument must
+   support the single-segment, character buffer interface.  On success,
+   returns ``0``, sets *buffer* to the memory location and *buffer_len* to the
+   buffer length.  Returns ``-1`` and sets a :exc:`TypeError` on error.
+

Doc/data/refcounts.dat

@@ -1571,6 +1571,21 @@ PyOS_FSPath:PyObject*:path:0:
 PyObject_ASCII:PyObject*::+1:
 PyObject_ASCII:PyObject*:o:0:
 
+PyObject_AsCharBuffer:int:::
+PyObject_AsCharBuffer:PyObject*:obj:0:
+PyObject_AsCharBuffer:const char**:buffer::
+PyObject_AsCharBuffer:Py_ssize_t*:buffer_len::
+
+PyObject_AsReadBuffer:int:::
+PyObject_AsReadBuffer:PyObject*:obj:0:
+PyObject_AsReadBuffer:const void**:buffer::
+PyObject_AsReadBuffer:Py_ssize_t*:buffer_len::
+
+PyObject_AsWriteBuffer:int:::
+PyObject_AsWriteBuffer:PyObject*:obj:0:
+PyObject_AsWriteBuffer:void**:buffer::
+PyObject_AsWriteBuffer:Py_ssize_t*:buffer_len::
+
 PyObject_Bytes:PyObject*::+1:
 PyObject_Bytes:PyObject*:o:0:
 
@@ -1606,6 +1621,9 @@ PyObject_CallObject:PyObject*:args:0:
 PyObject_CheckBuffer:int:::
 PyObject_CheckBuffer:PyObject*:obj:0:
 
+PyObject_CheckReadBuffer:int:::
+PyObject_CheckReadBuffer:PyObject*:o:0:
+
 PyObject_DelAttr:int:::
 PyObject_DelAttr:PyObject*:o:0:
 PyObject_DelAttr:PyObject*:attr_name:0:

Doc/data/stable_abi.dat

@@ -462,7 +462,10 @@ function,PyOS_strtoul,3.2,
 function,PyOS_vsnprintf,3.2,
 type,PyObject,3.2,
 function,PyObject_ASCII,3.2,
+function,PyObject_AsCharBuffer,3.2,
 function,PyObject_AsFileDescriptor,3.2,
+function,PyObject_AsReadBuffer,3.2,
+function,PyObject_AsWriteBuffer,3.2,
 function,PyObject_Bytes,3.2,
 function,PyObject_Call,3.2,
 function,PyObject_CallFunction,3.2,
@@ -472,6 +475,7 @@ function,PyObject_CallMethodObjArgs,3.2,
 function,PyObject_CallNoArgs,3.10,
 function,PyObject_CallObject,3.2,
 function,PyObject_Calloc,3.7,
+function,PyObject_CheckReadBuffer,3.2,
 function,PyObject_ClearWeakRefs,3.2,
 function,PyObject_DelItem,3.2,
 function,PyObject_DelItemString,3.2,

Doc/whatsnew/3.10.rst

@@ -2113,11 +2113,6 @@ Deprecated
 Removed
 -------
 
-* ``PyObject_AsCharBuffer()``, ``PyObject_AsReadBuffer()``, ``PyObject_CheckReadBuffer()``,
-  and ``PyObject_AsWriteBuffer()`` are removed. Please migrate to new buffer protocol;
-  :c:func:`PyObject_GetBuffer` and :c:func:`PyBuffer_Release`.
-  (Contributed by Inada Naoki in :issue:`41103`.)
-
 * Removed ``Py_UNICODE_str*`` functions manipulating ``Py_UNICODE*`` strings.
   (Contributed by Inada Naoki in :issue:`41123`.)
 

Include/abstract.h

@@ -309,6 +309,53 @@ PyAPI_FUNC(int) PyObject_DelItemString(PyObject *o, const char *key);
 PyAPI_FUNC(int) PyObject_DelItem(PyObject *o, PyObject *key);
 
 
+/* === Old Buffer API ============================================ */
+
+/* FIXME:  usage of these should all be replaced in Python itself
+   but for backwards compatibility we will implement them.
+   Their usage without a corresponding "unlock" mechanism
+   may create issues (but they would already be there). */
+
+/* Takes an arbitrary object which must support the (character, single segment)
+   buffer interface and returns a pointer to a read-only memory location
+   useable as character based input for subsequent processing.
+
+   Return 0 on success.  buffer and buffer_len are only set in case no error
+   occurs. Otherwise, -1 is returned and an exception set. */
+Py_DEPRECATED(3.0)
+PyAPI_FUNC(int) PyObject_AsCharBuffer(PyObject *obj,
+                                      const char **buffer,
+                                      Py_ssize_t *buffer_len);
+
+/* Checks whether an arbitrary object supports the (character, single segment)
+   buffer interface.
+
+   Returns 1 on success, 0 on failure. */
+Py_DEPRECATED(3.0) PyAPI_FUNC(int) PyObject_CheckReadBuffer(PyObject *obj);
+
+/* Same as PyObject_AsCharBuffer() except that this API expects (readable,
+   single segment) buffer interface and returns a pointer to a read-only memory
+   location which can contain arbitrary data.
+
+   0 is returned on success.  buffer and buffer_len are only set in case no
+   error occurs.  Otherwise, -1 is returned and an exception set. */
+Py_DEPRECATED(3.0)
+PyAPI_FUNC(int) PyObject_AsReadBuffer(PyObject *obj,
+                                      const void **buffer,
+                                      Py_ssize_t *buffer_len);
+
+/* Takes an arbitrary object which must support the (writable, single segment)
+   buffer interface and returns a pointer to a writable memory location in
+   buffer of size 'buffer_len'.
+
+   Return 0 on success.  buffer and buffer_len are only set in case no error
+   occurs. Otherwise, -1 is returned and an exception set. */
+Py_DEPRECATED(3.0)
+PyAPI_FUNC(int) PyObject_AsWriteBuffer(PyObject *obj,
+                                       void **buffer,
+                                       Py_ssize_t *buffer_len);
+
+
 /* === New Buffer API ============================================ */
 
 /* Takes an arbitrary object and returns the result of calling

Misc/NEWS.d/next/C API/2021-07-29-16-04-28.bpo-41103.hiKKcF.rst

@@ -0,0 +1,2 @@
+Reverts removal of the old buffer protocol because they are part of stable
+ABI.

Misc/stable_abi.txt

@@ -1642,6 +1642,17 @@ function _Py_VaBuildValue_SizeT
     added 3.2
     abi_only
 
+# Old buffer protocol support (deprecated)
+
+function PyObject_AsCharBuffer
+    added 3.2
+function PyObject_AsReadBuffer
+    added 3.2
+function PyObject_AsWriteBuffer
+    added 3.2
+function PyObject_CheckReadBuffer
+    added 3.2
+
 # Flags are implicitly part of the ABI:
 
 const Py_TPFLAGS_DEFAULT

Objects/abstract.c

@@ -293,6 +293,85 @@ PyObject_CheckBuffer(PyObject *obj)
 }
 
 
+/* We release the buffer right after use of this function which could
+   cause issues later on.  Don't use these functions in new code.
+ */
+int
+PyObject_CheckReadBuffer(PyObject *obj)
+{
+    PyBufferProcs *pb = Py_TYPE(obj)->tp_as_buffer;
+    Py_buffer view;
+
+    if (pb == NULL ||
+        pb->bf_getbuffer == NULL)
+        return 0;
+    if ((*pb->bf_getbuffer)(obj, &view, PyBUF_SIMPLE) == -1) {
+        PyErr_Clear();
+        return 0;
+    }
+    PyBuffer_Release(&view);
+    return 1;
+}
+
+static int
+as_read_buffer(PyObject *obj, const void **buffer, Py_ssize_t *buffer_len)
+{
+    Py_buffer view;
+
+    if (obj == NULL || buffer == NULL || buffer_len == NULL) {
+        null_error();
+        return -1;
+    }
+    if (PyObject_GetBuffer(obj, &view, PyBUF_SIMPLE) != 0)
+        return -1;
+
+    *buffer = view.buf;
+    *buffer_len = view.len;
+    PyBuffer_Release(&view);
+    return 0;
+}
+
+int
+PyObject_AsCharBuffer(PyObject *obj,
+                      const char **buffer,
+                      Py_ssize_t *buffer_len)
+{
+    return as_read_buffer(obj, (const void **)buffer, buffer_len);
+}
+
+int PyObject_AsReadBuffer(PyObject *obj,
+                          const void **buffer,
+                          Py_ssize_t *buffer_len)
+{
+    return as_read_buffer(obj, buffer, buffer_len);
+}
+
+int PyObject_AsWriteBuffer(PyObject *obj,
+                           void **buffer,
+                           Py_ssize_t *buffer_len)
+{
+    PyBufferProcs *pb;
+    Py_buffer view;
+
+    if (obj == NULL || buffer == NULL || buffer_len == NULL) {
+        null_error();
+        return -1;
+    }
+    pb = Py_TYPE(obj)->tp_as_buffer;
+    if (pb == NULL ||
+        pb->bf_getbuffer == NULL ||
+        ((*pb->bf_getbuffer)(obj, &view, PyBUF_WRITABLE) != 0)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "expected a writable bytes-like object");
+        return -1;
+    }
+
+    *buffer = view.buf;
+    *buffer_len = view.len;
+    PyBuffer_Release(&view);
+    return 0;
+}
+
 /* Buffer C-API for Python 3.0 */
 
 int

PC/python3dll.c

@@ -413,8 +413,11 @@ EXPORT_FUNC(PyNumber_Subtract)
 EXPORT_FUNC(PyNumber_ToBase)
 EXPORT_FUNC(PyNumber_TrueDivide)
 EXPORT_FUNC(PyNumber_Xor)
+EXPORT_FUNC(PyObject_AsCharBuffer)
 EXPORT_FUNC(PyObject_ASCII)
 EXPORT_FUNC(PyObject_AsFileDescriptor)
+EXPORT_FUNC(PyObject_AsReadBuffer)
+EXPORT_FUNC(PyObject_AsWriteBuffer)
 EXPORT_FUNC(PyObject_Bytes)
 EXPORT_FUNC(PyObject_Call)
 EXPORT_FUNC(PyObject_CallFunction)
@@ -424,6 +427,7 @@ EXPORT_FUNC(PyObject_CallMethodObjArgs)
 EXPORT_FUNC(PyObject_CallNoArgs)
 EXPORT_FUNC(PyObject_CallObject)
 EXPORT_FUNC(PyObject_Calloc)
+EXPORT_FUNC(PyObject_CheckReadBuffer)
 EXPORT_FUNC(PyObject_ClearWeakRefs)
 EXPORT_FUNC(PyObject_DelItem)
 EXPORT_FUNC(PyObject_DelItemString)