cpython/Objects/bufferobject.c

/* Buffer object implementation */

#include "Python.h"


typedef struct {
	PyObject_HEAD
	PyObject *b_base;
	void *b_ptr;
	int b_size;
	int b_offset;
	int b_readonly;
	long b_hash;
} PyBufferObject;


static int
get_buf(PyBufferObject *self, void **ptr, int *size)
{
	if (self->b_base == NULL) {
		assert (ptr != NULL);
		*ptr = self->b_ptr;
		*size = self->b_size;
	}
	else {
		int count, offset;
		getreadbufferproc proc;
		PyBufferProcs *bp = self->b_base->ob_type->tp_as_buffer;
		if ((*bp->bf_getsegcount)(self->b_base, NULL) != 1) {
			PyErr_SetString(PyExc_TypeError,
				"single-segment buffer object expected");
			return 0;
		}
		if (self->b_readonly)
			proc = bp->bf_getreadbuffer;
		else
			proc = (getreadbufferproc)bp->bf_getwritebuffer;
		if ((count = (*proc)(self->b_base, 0, ptr)) < 0)
			return 0;
		/* apply constraints to the start/end */
		if (self->b_offset > count)
			offset = count;
		else
			offset = self->b_offset;
		(char *)*ptr = (char *)*ptr + offset;
		if (self->b_size == Py_END_OF_BUFFER)
			*size = count;
		else
			*size = self->b_size;
		if (offset + *size > count)
			*size = count - offset;
	}
	return 1;
}


static PyObject *
buffer_from_memory(PyObject *base, int size, int offset, void *ptr,
		   int readonly)
{
	PyBufferObject * b;

	if (size < 0 && size != Py_END_OF_BUFFER) {
		PyErr_SetString(PyExc_ValueError,
				"size must be zero or positive");
		return NULL;
	}

	b = PyObject_NEW(PyBufferObject, &PyBuffer_Type);
	if ( b == NULL )
		return NULL;

	Py_XINCREF(base);
	b->b_base = base;
	b->b_ptr = ptr;
	b->b_size = size;
	b->b_offset = offset;
	b->b_readonly = readonly;
	b->b_hash = -1;

	return (PyObject *) b;
}

static PyObject *
buffer_from_object(PyObject *base, int size, int offset, int readonly)
{
	if ( offset < 0 ) {
		PyErr_SetString(PyExc_ValueError,
				"offset must be zero or positive");
		return NULL;
	}

	/* if the base object is another buffer, then try to refer to the
	 * base object.
	 */
	if ( PyBuffer_Check(base) && (((PyBufferObject *)base)->b_base) ) {
		base = ((PyBufferObject *)base)->b_base;
		offset = ((PyBufferObject *)base)->b_offset + offset;
	}
	
	return buffer_from_memory(base, size, offset, NULL, readonly);
}


PyObject *
PyBuffer_FromObject(PyObject *base, int offset, int size)
{
	PyBufferProcs *pb = base->ob_type->tp_as_buffer;

	if ( pb == NULL ||
	     pb->bf_getreadbuffer == NULL ||
	     pb->bf_getsegcount == NULL )
	{
		PyErr_SetString(PyExc_TypeError, "buffer object expected");
		return NULL;
	}

	return buffer_from_object(base, size, offset, 1);
}

PyObject *
PyBuffer_FromReadWriteObject(PyObject *base, int offset, int size)
{
	PyBufferProcs *pb = base->ob_type->tp_as_buffer;

	if ( pb == NULL ||
	     pb->bf_getwritebuffer == NULL ||
	     pb->bf_getsegcount == NULL )
	{
		PyErr_SetString(PyExc_TypeError, "buffer object expected");
		return NULL;
	}

	return buffer_from_object(base, size,  offset, 0);
}

PyObject *
PyBuffer_FromMemory(void *ptr, int size)
{
	return buffer_from_memory(NULL, size, 0, ptr, 1);
}

PyObject *
PyBuffer_FromReadWriteMemory(void *ptr, int size)
{
	return buffer_from_memory(NULL, size, 0, ptr, 0);
}

PyObject *
PyBuffer_New(int size)
{
	PyObject *o;
	PyBufferObject * b;

	if (size < 0) {
		PyErr_SetString(PyExc_ValueError,
				"size must be zero or positive");
		return NULL;
	}
	/* Inline PyObject_New */
	o = PyObject_MALLOC(sizeof(*b) + size);
	if ( o == NULL )
		return PyErr_NoMemory();
	b = (PyBufferObject *) PyObject_INIT(o, &PyBuffer_Type);

	b->b_base = NULL;
	b->b_ptr = (void *)(b + 1);
	b->b_size = size;
	b->b_offset = 0;
	b->b_readonly = 0;
	b->b_hash = -1;

	return o;
}

/* Methods */

static PyObject *
buffer_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
	PyObject *ob;
	int offset = 0;
	int size = Py_END_OF_BUFFER;

	if ( !PyArg_ParseTuple(args, "O|ii:buffer", &ob, &offset, &size) )
	    return NULL;
	return PyBuffer_FromObject(ob, offset, size);
}

PyDoc_STRVAR(buffer_doc,
"buffer(object [, offset[, size]])\n\
\n\
Create a new buffer object which references the given object.\n\
The buffer will reference a slice of the target object from the\n\
start of the object (or at the specified offset). The slice will\n\
extend to the end of the target object (or with the specified size).");


static void
buffer_dealloc(PyBufferObject *self)
{
	Py_XDECREF(self->b_base);
	PyObject_DEL(self);
}

static int
buffer_compare(PyBufferObject *self, PyBufferObject *other)
{
	void *p1, *p2;
	int len_self, len_other, min_len, cmp;

	if (!get_buf(self, &p1, &len_self))
		return -1;
	if (!get_buf(other, &p2, &len_other))
		return -1;
	min_len = (len_self < len_other) ? len_self : len_other;
	if (min_len > 0) {
		cmp = memcmp(p1, p2, min_len);
		if (cmp != 0)
			return cmp;
	}
	return (len_self < len_other) ? -1 : (len_self > len_other) ? 1 : 0;
}

static PyObject *
buffer_repr(PyBufferObject *self)
{
	char *status = self->b_readonly ? "read-only" : "read-write";

	if ( self->b_base == NULL )
		return PyString_FromFormat("<%s buffer ptr %p, size %d at %p>",
					   status,
					   self->b_ptr,
					   self->b_size,
					   self);
	else
		return PyString_FromFormat(
			"<%s buffer for %p, size %d, offset %d at %p>",
			status,
			self->b_base,
			self->b_size,
			self->b_offset,
			self);
}

static long
buffer_hash(PyBufferObject *self)
{
	void *ptr;
	int size;
	register int len;
	register unsigned char *p;
	register long x;

	if ( self->b_hash != -1 )
		return self->b_hash;

	/* XXX potential bugs here, a readonly buffer does not imply that the
	 * underlying memory is immutable.  b_readonly is a necessary but not
	 * sufficient condition for a buffer to be hashable.  Perhaps it would
	 * be better to only allow hashing if the underlying object is known to
	 * be immutable (e.g. PyString_Check() is true).  Another idea would
	 * be to call tp_hash on the underlying object and see if it raises
	 * an error. */
	if ( !self->b_readonly )
	{
		PyErr_SetString(PyExc_TypeError,
				"writable buffers are not hashable");
		return -1;
	}

	if (!get_buf(self, &ptr, &size))
		return -1;
	p = (unsigned char *) ptr;
	len = size;
	x = *p << 7;
	while (--len >= 0)
		x = (1000003*x) ^ *p++;
	x ^= size;
	if (x == -1)
		x = -2;
	self->b_hash = x;
	return x;
}

static PyObject *
buffer_str(PyBufferObject *self)
{
	void *ptr;
	int size;
	if (!get_buf(self, &ptr, &size))
		return NULL;
	return PyString_FromStringAndSize(ptr, size);
}

/* Sequence methods */

static int
buffer_length(PyBufferObject *self)
{
	void *ptr;
	int size;
	if (!get_buf(self, &ptr, &size))
		return -1;
	return size;
}

static PyObject *
buffer_concat(PyBufferObject *self, PyObject *other)
{
	PyBufferProcs *pb = other->ob_type->tp_as_buffer;
	void *ptr1, *ptr2;
	char *p;
	PyObject *ob;
	int size, count;

	if ( pb == NULL ||
	     pb->bf_getreadbuffer == NULL ||
	     pb->bf_getsegcount == NULL )
	{
		PyErr_BadArgument();
		return NULL;
	}
	if ( (*pb->bf_getsegcount)(other, NULL) != 1 )
	{
		/* ### use a different exception type/message? */
		PyErr_SetString(PyExc_TypeError,
				"single-segment buffer object expected");
		return NULL;
	}

 	if (!get_buf(self, &ptr1, &size))
 		return NULL;
 
	/* optimize special case */
	if ( size == 0 )
	{
	    Py_INCREF(other);
	    return other;
	}

	if ( (count = (*pb->bf_getreadbuffer)(other, 0, &ptr2)) < 0 )
		return NULL;

 	ob = PyString_FromStringAndSize(NULL, size + count);
 	p = PyString_AS_STRING(ob);
 	memcpy(p, ptr1, size);
 	memcpy(p + size, ptr2, count);

	/* there is an extra byte in the string object, so this is safe */
	p[size + count] = '\0';

	return ob;
}

static PyObject *
buffer_repeat(PyBufferObject *self, int count)
{
	PyObject *ob;
	register char *p;
	void *ptr;
	int size;

	if ( count < 0 )
		count = 0;
	if (!get_buf(self, &ptr, &size))
		return NULL;
	ob = PyString_FromStringAndSize(NULL, size * count);
	if ( ob == NULL )
		return NULL;

	p = PyString_AS_STRING(ob);
	while ( count-- )
	{
	    memcpy(p, ptr, size);
	    p += size;
	}

	/* there is an extra byte in the string object, so this is safe */
	*p = '\0';

	return ob;
}

static PyObject *
buffer_item(PyBufferObject *self, int idx)
{
	void *ptr;
	int size;
	if (!get_buf(self, &ptr, &size))
		return NULL;
	if ( idx < 0 || idx >= size ) {
		PyErr_SetString(PyExc_IndexError, "buffer index out of range");
		return NULL;
	}
	return PyString_FromStringAndSize((char *)ptr + idx, 1);
}

static PyObject *
buffer_slice(PyBufferObject *self, int left, int right)
{
	void *ptr;
	int size;
	if (!get_buf(self, &ptr, &size))
		return NULL;
	if ( left < 0 )
		left = 0;
	if ( right < 0 )
		right = 0;
	if ( right > size )
		right = size;
	if ( right < left )
		right = left;
	return PyString_FromStringAndSize((char *)ptr + left,
					  right - left);
}

static int
buffer_ass_item(PyBufferObject *self, int idx, PyObject *other)
{
	PyBufferProcs *pb;
	void *ptr1, *ptr2;
	int size;
	int count;

	if ( self->b_readonly ) {
		PyErr_SetString(PyExc_TypeError,
				"buffer is read-only");
		return -1;
	}

	if (!get_buf(self, &ptr1, &size))
		return -1;

	if (idx < 0 || idx >= size) {
		PyErr_SetString(PyExc_IndexError,
				"buffer assignment index out of range");
		return -1;
	}

	pb = other ? other->ob_type->tp_as_buffer : NULL;
	if ( pb == NULL ||
	     pb->bf_getreadbuffer == NULL ||
	     pb->bf_getsegcount == NULL )
	{
		PyErr_BadArgument();
		return -1;
	}
	if ( (*pb->bf_getsegcount)(other, NULL) != 1 )
	{
		/* ### use a different exception type/message? */
		PyErr_SetString(PyExc_TypeError,
				"single-segment buffer object expected");
		return -1;
	}

	if ( (count = (*pb->bf_getreadbuffer)(other, 0, &ptr2)) < 0 )
		return -1;
	if ( count != 1 ) {
		PyErr_SetString(PyExc_TypeError,
				"right operand must be a single byte");
		return -1;
	}

	((char *)ptr1)[idx] = *(char *)ptr2;
	return 0;
}

static int
buffer_ass_slice(PyBufferObject *self, int left, int right, PyObject *other)
{
	PyBufferProcs *pb;
	void *ptr1, *ptr2;
	int size;
	int slice_len;
	int count;

	if ( self->b_readonly ) {
		PyErr_SetString(PyExc_TypeError,
				"buffer is read-only");
		return -1;
	}

	pb = other ? other->ob_type->tp_as_buffer : NULL;
	if ( pb == NULL ||
	     pb->bf_getreadbuffer == NULL ||
	     pb->bf_getsegcount == NULL )
	{
		PyErr_BadArgument();
		return -1;
	}
	if ( (*pb->bf_getsegcount)(other, NULL) != 1 )
	{
		/* ### use a different exception type/message? */
		PyErr_SetString(PyExc_TypeError,
				"single-segment buffer object expected");
		return -1;
	}
	if (!get_buf(self, &ptr1, &size))
		return -1;
	if ( (count = (*pb->bf_getreadbuffer)(other, 0, &ptr2)) < 0 )
		return -1;

	if ( left < 0 )
		left = 0;
	else if ( left > size )
		left = size;
	if ( right < left )
		right = left;
	else if ( right > size )
		right = size;
	slice_len = right - left;

	if ( count != slice_len ) {
		PyErr_SetString(
			PyExc_TypeError,
			"right operand length must match slice length");
		return -1;
	}

	if ( slice_len )
	    memcpy((char *)ptr1 + left, ptr2, slice_len);

	return 0;
}

/* Buffer methods */

static int
buffer_getreadbuf(PyBufferObject *self, int idx, void **pp)
{
	int size;
	if ( idx != 0 ) {
		PyErr_SetString(PyExc_SystemError,
				"accessing non-existent buffer segment");
		return -1;
	}
	if (!get_buf(self, pp, &size))
		return -1;
	return size;
}

static int
buffer_getwritebuf(PyBufferObject *self, int idx, void **pp)
{
	if ( self->b_readonly )
	{
		PyErr_SetString(PyExc_TypeError, "buffer is read-only");
		return -1;
	}
	return buffer_getreadbuf(self, idx, pp);
}

static int
buffer_getsegcount(PyBufferObject *self, int *lenp)
{
	void *ptr;
	int size;
	if (!get_buf(self, &ptr, &size))
		return -1;
	if (lenp)
		*lenp = size;
	return 1;
}

static int
buffer_getcharbuf(PyBufferObject *self, int idx, const char **pp)
{
	void *ptr;
	int size;
	if ( idx != 0 ) {
		PyErr_SetString(PyExc_SystemError,
				"accessing non-existent buffer segment");
		return -1;
	}
	if (!get_buf(self, &ptr, &size))
		return -1;
	*pp = (const char *)ptr;
	return size;
}


static PySequenceMethods buffer_as_sequence = {
	(inquiry)buffer_length, /*sq_length*/
	(binaryfunc)buffer_concat, /*sq_concat*/
	(intargfunc)buffer_repeat, /*sq_repeat*/
	(intargfunc)buffer_item, /*sq_item*/
	(intintargfunc)buffer_slice, /*sq_slice*/
	(intobjargproc)buffer_ass_item, /*sq_ass_item*/
	(intintobjargproc)buffer_ass_slice, /*sq_ass_slice*/
};

static PyBufferProcs buffer_as_buffer = {
	(getreadbufferproc)buffer_getreadbuf,
	(getwritebufferproc)buffer_getwritebuf,
	(getsegcountproc)buffer_getsegcount,
	(getcharbufferproc)buffer_getcharbuf,
};

PyTypeObject PyBuffer_Type = {
	PyObject_HEAD_INIT(&PyType_Type)
	0,
	"buffer",
	sizeof(PyBufferObject),
	0,
	(destructor)buffer_dealloc, 		/* tp_dealloc */
	0,					/* tp_print */
	0,					/* tp_getattr */
	0,					/* tp_setattr */
	(cmpfunc)buffer_compare,		/* tp_compare */
	(reprfunc)buffer_repr,			/* tp_repr */
	0,					/* tp_as_number */
	&buffer_as_sequence,			/* tp_as_sequence */
	0,					/* tp_as_mapping */
	(hashfunc)buffer_hash,			/* tp_hash */
	0,					/* tp_call */
	(reprfunc)buffer_str,			/* tp_str */
	PyObject_GenericGetAttr,		/* tp_getattro */
	0,					/* tp_setattro */
	&buffer_as_buffer,			/* tp_as_buffer */
	Py_TPFLAGS_DEFAULT,			/* tp_flags */
	buffer_doc,				/* tp_doc */
	0,					/* tp_traverse */
	0,					/* tp_clear */
	0,					/* tp_richcompare */
	0,					/* tp_weaklistoffset */
	0,					/* tp_iter */
	0,					/* tp_iternext */
	0,					/* tp_methods */	
	0,					/* tp_members */
	0,					/* tp_getset */
	0,					/* tp_base */
	0,					/* tp_dict */
	0,					/* tp_descr_get */
	0,					/* tp_descr_set */
	0,					/* tp_dictoffset */
	0,					/* tp_init */
	0,					/* tp_alloc */
	buffer_new,				/* tp_new */
};