Backport from py3k: Implement the new buffer interface from pep3118

for ctypes instances.  Closes issue #2404.

Lib/ctypes/test/test_pep3118.py

+import unittest
+from ctypes import *
+import re, struct, sys
+
+if sys.byteorder == "little":
+    THIS_ENDIAN = "<"
+    OTHER_ENDIAN = ">"
+else:
+    THIS_ENDIAN = ">"
+    OTHER_ENDIAN = "<"
+
+class memoryview(object):
+    # This class creates a memoryview - like object from data returned
+    # by the private _ctypes._buffer_info() function, just enough for
+    # these tests.
+    #
+    # It can be removed when the py3k memoryview object is backported.
+    def __init__(self, ob):
+        from _ctypes import _buffer_info
+        self.format, self.ndim, self.shape = _buffer_info(ob)
+        if self.shape == ():
+            self.shape = None
+            self.itemsize = sizeof(ob)
+        else:
+            size = sizeof(ob)
+            for dim in self.shape:
+                size /= dim
+            self.itemsize = size
+        self.strides = None
+        self.readonly = False
+        self.size = sizeof(ob)
+
+def normalize(format):
+    # Remove current endian specifier and white space from a format
+    # string
+    format = format.replace(OTHER_ENDIAN, THIS_ENDIAN)
+    return re.sub(r"\s", "", format)
+
+class Test(unittest.TestCase):
+
+    def test_native_types(self):
+        for tp, fmt, shape, itemtp in native_types:
+            ob = tp()
+            v = memoryview(ob)
+            try:
+                self.failUnlessEqual(normalize(v.format), normalize(fmt))
+                self.failUnlessEqual(v.size, sizeof(ob))
+                self.failUnlessEqual(v.itemsize, sizeof(itemtp))
+                self.failUnlessEqual(v.shape, shape)
+                # ctypes object always have a non-strided memory block
+                self.failUnlessEqual(v.strides, None)
+                # they are always read/write
+                self.failIf(v.readonly)
+
+                if v.shape:
+                    n = 1
+                    for dim in v.shape:
+                        n = n * dim
+                    self.failUnlessEqual(v.itemsize * n, v.size)
+            except:
+                # so that we can see the failing type
+                print(tp)
+                raise
+
+    def test_endian_types(self):
+        for tp, fmt, shape, itemtp in endian_types:
+            ob = tp()
+            v = memoryview(ob)
+            try:
+                self.failUnlessEqual(v.format, fmt)
+                self.failUnlessEqual(v.size, sizeof(ob))
+                self.failUnlessEqual(v.itemsize, sizeof(itemtp))
+                self.failUnlessEqual(v.shape, shape)
+                # ctypes object always have a non-strided memory block
+                self.failUnlessEqual(v.strides, None)
+                # they are always read/write
+                self.failIf(v.readonly)
+
+                if v.shape:
+                    n = 1
+                    for dim in v.shape:
+                        n = n * dim
+                    self.failUnlessEqual(v.itemsize * n, v.size)
+            except:
+                # so that we can see the failing type
+                print(tp)
+                raise
+
+# define some structure classes
+
+class Point(Structure):
+    _fields_ = [("x", c_long), ("y", c_long)]
+
+class PackedPoint(Structure):
+    _pack_ = 2
+    _fields_ = [("x", c_long), ("y", c_long)]
+
+class Point2(Structure):
+    pass
+Point2._fields_ = [("x", c_long), ("y", c_long)]
+
+class EmptyStruct(Structure):
+    _fields_ = []
+
+class aUnion(Union):
+    _fields_ = [("a", c_int)]
+
+################################################################
+#
+# This table contains format strings as they look on little endian
+# machines.  The test replaces '<' with '>' on big endian machines.
+#
+native_types = [
+    # type                      format                  shape           calc itemsize
+
+    ## simple types
+
+    (c_char,                    "<c",                   None,           c_char),
+    (c_byte,                    "<b",                   None,           c_byte),
+    (c_ubyte,                   "<B",                   None,           c_ubyte),
+    (c_short,                   "<h",                   None,           c_short),
+    (c_ushort,                  "<H",                   None,           c_ushort),
+
+    # c_int and c_uint may be aliases to c_long
+    #(c_int,                     "<i",                   None,           c_int),
+    #(c_uint,                    "<I",                   None,           c_uint),
+
+    (c_long,                    "<l",                   None,           c_long),
+    (c_ulong,                   "<L",                   None,           c_ulong),
+
+    # c_longlong and c_ulonglong are aliases on 64-bit platforms
+    #(c_longlong,                "<q",                   None,           c_longlong),
+    #(c_ulonglong,               "<Q",                   None,           c_ulonglong),
+
+    (c_float,                   "<f",                   None,           c_float),
+    (c_double,                  "<d",                   None,           c_double),
+    # c_longdouble may be an alias to c_double
+
+    (c_bool,                    "<?",                   None,           c_bool),
+    (py_object,                 "<O",                   None,           py_object),
+
+    ## pointers
+
+    (POINTER(c_byte),           "&<b",                  None,           POINTER(c_byte)),
+    (POINTER(POINTER(c_long)),  "&&<l",                 None,           POINTER(POINTER(c_long))),
+
+    ## arrays and pointers
+
+    (c_double * 4,              "(4)<d",                (4,),           c_double),
+    (c_float * 4 * 3 * 2,       "(2,3,4)<f",            (2,3,4),        c_float),
+    (POINTER(c_short) * 2,      "(2)&<h",               (2,),           POINTER(c_short)),
+    (POINTER(c_short) * 2 * 3,  "(3,2)&<h",             (3,2,),         POINTER(c_short)),
+    (POINTER(c_short * 2),      "&(2)<h",               None,           POINTER(c_short)),
+
+    ## structures and unions
+
+    (Point,                     "T{<l:x:<l:y:}",        None,           Point),
+    # packed structures do not implement the pep
+    (PackedPoint,               "B",                    None,           PackedPoint),
+    (Point2,                    "T{<l:x:<l:y:}",        None,           Point2),
+    (EmptyStruct,               "T{}",                  None,           EmptyStruct),
+    # the pep does't support unions
+    (aUnion,                    "B",                    None,           aUnion),
+
+    ## other
+
+    # function signatures are not implemented
+    (CFUNCTYPE(None),           "X{}",                  None,           CFUNCTYPE(None)),
+
+    ]
+
+class BEPoint(BigEndianStructure):
+    _fields_ = [("x", c_long), ("y", c_long)]
+
+class LEPoint(LittleEndianStructure):
+    _fields_ = [("x", c_long), ("y", c_long)]
+
+################################################################
+#
+# This table contains format strings as they really look, on both big
+# and little endian machines.
+#
+endian_types = [
+    (BEPoint,                   "T{>l:x:>l:y:}",        None,           BEPoint),
+    (LEPoint,                   "T{<l:x:<l:y:}",        None,           LEPoint),
+    (POINTER(BEPoint),          "&T{>l:x:>l:y:}",       None,           POINTER(BEPoint)),
+    (POINTER(LEPoint),          "&T{<l:x:<l:y:}",       None,           POINTER(LEPoint)),
+    ]
+
+if __name__ == "__main__":
+    unittest.main()

Modules/_ctypes/callproc.c

@@ -1666,10 +1666,37 @@ pointer(PyObject *self, PyObject *arg)
 	return result;
 }
 
+static PyObject *
+buffer_info(PyObject *self, PyObject *arg)
+{
+	StgDictObject *dict = PyType_stgdict(arg);
+	PyObject *shape;
+	Py_ssize_t i;
+
+	if (dict == NULL)
+		dict = PyObject_stgdict(arg);
+	if (dict == NULL) {
+		PyErr_SetString(PyExc_TypeError,
+				"not a ctypes type or object");
+		return NULL;
+	}
+	shape = PyTuple_New(dict->ndim);
+	for (i = 0; i < (int)dict->ndim; ++i)
+		PyTuple_SET_ITEM(shape, i, PyLong_FromSsize_t(dict->shape[i]));
+
+	if (PyErr_Occurred()) {
+		Py_DECREF(shape);
+		return NULL;
+	}
+	return Py_BuildValue("siN", dict->format, dict->ndim, shape);
+}
+
 PyMethodDef module_methods[] = {
 	{"POINTER", POINTER, METH_O },
 	{"pointer", pointer, METH_O },
 	{"_unpickle", unpickle, METH_VARARGS },
+	{"_buffer_info", buffer_info, METH_O,
+	 "Return buffer interface information (for testing only)"},
 	{"resize", resize, METH_VARARGS, "Resize the memory buffer of a ctypes instance"},
 #ifdef CTYPES_UNICODE
 	{"set_conversion_mode", set_conversion_mode, METH_VARARGS, set_conversion_mode_doc},

Modules/_ctypes/ctypes.h

@@ -235,6 +235,14 @@ typedef struct {
 	PyObject *restype;	/* CDataObject or NULL */
 	PyObject *checker;
 	int flags;		/* calling convention and such */
+
+	/* pep3118 fields, pointers neeed PyMem_Free */
+	char *format;
+	int ndim;
+	Py_ssize_t *shape;
+/*	Py_ssize_t *strides;	*/ /* unused in ctypes */
+/*	Py_ssize_t *suboffsets;	*/ /* unused in ctypes */
+
 } StgDictObject;
 
 /****************************************************************
@@ -415,6 +423,7 @@ extern void *MallocClosure(void);
 extern void _AddTraceback(char *, char *, int);
 
 extern PyObject *CData_FromBaseObj(PyObject *type, PyObject *base, Py_ssize_t index, char *adr);
+extern char *alloc_format_string(const char *prefix, const char *suffix);
 
 /* XXX better name needed! */
 extern int IsSimpleSubType(PyObject *obj);

Modules/_ctypes/stgdict.c

@@ -6,6 +6,7 @@
 #include <ffi.h>
 #ifdef MS_WIN32
 #include <windows.h>
+#include <malloc.h>
 #endif
 #include "ctypes.h"
 
@@ -24,6 +25,9 @@ StgDict_init(StgDictObject *self, PyObject *args, PyObject *kwds)
 {
 	if (PyDict_Type.tp_init((PyObject *)self, args, kwds) < 0)
 		return -1;
+	self->format = NULL;
+	self->ndim = 0;
+	self->shape = NULL;
 	return 0;
 }
 
@@ -42,6 +46,8 @@ static void
 StgDict_dealloc(StgDictObject *self)
 {
 	StgDict_clear(self);
+	PyMem_Free(self->format);
+	PyMem_Free(self->shape);
 	PyMem_Free(self->ffi_type_pointer.elements);
 	PyDict_Type.tp_dealloc((PyObject *)self);
 }
@@ -54,6 +60,10 @@ StgDict_clone(StgDictObject *dst, StgDictObject *src)
 
 	StgDict_clear(dst);
 	PyMem_Free(dst->ffi_type_pointer.elements);
+	PyMem_Free(dst->format);
+	dst->format = NULL;
+	PyMem_Free(dst->shape);
+	dst->shape = NULL;
 	dst->ffi_type_pointer.elements = NULL;
 
 	d = (char *)dst;
@@ -68,6 +78,20 @@ StgDict_clone(StgDictObject *dst, StgDictObject *src)
 	Py_XINCREF(dst->restype);
 	Py_XINCREF(dst->checker);
 
+	if (src->format) {
+		dst->format = PyMem_Malloc(strlen(src->format) + 1);
+		if (dst->format == NULL)
+			return -1;
+		strcpy(dst->format, src->format);
+	}
+	if (src->shape) {
+		dst->shape = PyMem_Malloc(sizeof(Py_ssize_t) * src->ndim);
+		if (dst->shape == NULL)
+			return -1;
+		memcpy(dst->shape, src->shape,
+		       sizeof(Py_ssize_t) * src->ndim);
+	}
+
 	if (src->ffi_type_pointer.elements == NULL)
 		return 0;
 	size = sizeof(ffi_type *) * (src->length + 1);
@@ -349,6 +373,11 @@ StructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct)
 		return -1;
 	}
 
+	if (stgdict->format) {
+		PyMem_Free(stgdict->format);
+		stgdict->format = NULL;
+	}
+
 	if (stgdict->ffi_type_pointer.elements)
 		PyMem_Free(stgdict->ffi_type_pointer.elements);
 
@@ -387,6 +416,15 @@ StructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct)
 		ffi_ofs = 0;
 	}
 
+	if (isStruct && !isPacked) {
+		stgdict->format = alloc_format_string(NULL, "T{");
+	} else {
+		/* PEP3118 doesn't support union, or packed structures (well,
+		   only standard packing, but we dont support the pep for
+		   that). Use 'B' for bytes. */
+		stgdict->format = alloc_format_string(NULL, "B");
+	}
+
 #define realdict ((PyObject *)&stgdict->dict)
 	for (i = 0; i < len; ++i) {
 		PyObject *name = NULL, *desc = NULL;
@@ -451,6 +489,24 @@ StructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct)
 			}
 		} else
 			bitsize = 0;
+		if (isStruct && !isPacked) {
+			char *fieldfmt = dict->format ? dict->format : "B";
+			char *fieldname = PyString_AsString(name);
+			char *ptr;
+			Py_ssize_t len = strlen(fieldname) + strlen(fieldfmt);
+			char *buf = alloca(len + 2 + 1);
+
+			sprintf(buf, "%s:%s:", fieldfmt, fieldname);
+
+			ptr = stgdict->format;
+			stgdict->format = alloc_format_string(stgdict->format, buf);
+			PyMem_Free(ptr);
+
+			if (stgdict->format == NULL) {
+				Py_DECREF(pair);
+				return -1;
+			}
+		}
 		if (isStruct) {
 			prop = CField_FromDesc(desc, i,
 					       &field_size, bitsize, &bitofs,
@@ -481,6 +537,13 @@ StructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct)
 		Py_DECREF(prop);
 	}
 #undef realdict
+
+	if (isStruct && !isPacked) {
+		stgdict->format = alloc_format_string(stgdict->format, "}");
+		if (stgdict->format == NULL)
+			return -1;
+	}
+
 	if (!isStruct)
 		size = union_size;