mercurial/cext/bdiff.c

cext: accept arguments as Py_buffer

The s*/y* value formatters receive a Py_buffer instead of a char *.
This value format is more flexible in the types that it allows.

We change bdiff() to accept any object that conforms to the buffer
protocol. We validate the buffers are contiguous and have a single
dimension.

This allows memoryview instances to be handled by the function, so
we revert a recent change to cast arguments to bytes before calling
this function.

Differential Revision: https://phab.mercurial-scm.org/D2587

/*
 bdiff.c - efficient binary diff extension for Mercurial

 Copyright 2005, 2006 Matt Mackall <[e-mail]>

 This software may be used and distributed according to the terms of
 the GNU General Public License, incorporated herein by reference.

 Based roughly on Python difflib
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include "bdiff.h"
#include "bitmanipulation.h"
#include "util.h"

static PyObject *blocks(PyObject *self, PyObject *args)
{
	PyObject *sa, *sb, *rl = NULL, *m;
	struct bdiff_line *a, *b;
	struct bdiff_hunk l, *h;
	int an, bn, count, pos = 0;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))
		return NULL;

	an = bdiff_splitlines(PyBytes_AsString(sa), PyBytes_Size(sa), &a);
	bn = bdiff_splitlines(PyBytes_AsString(sb), PyBytes_Size(sb), &b);

	if (!a || !b)
		goto nomem;

	count = bdiff_diff(a, an, b, bn, &l);
	if (count < 0)
		goto nomem;

	rl = PyList_New(count);
	if (!rl)
		goto nomem;

	for (h = l.next; h; h = h->next) {
		m = Py_BuildValue("iiii", h->a1, h->a2, h->b1, h->b2);
		PyList_SetItem(rl, pos, m);
		pos++;
	}

nomem:
	free(a);
	free(b);
	bdiff_freehunks(l.next);
	return rl ? rl : PyErr_NoMemory();
}

static PyObject *bdiff(PyObject *self, PyObject *args)
{
	Py_buffer ba, bb;
	char *rb, *ia, *ib;
	PyObject *result = NULL;
	struct bdiff_line *al = NULL, *bl = NULL;
	struct bdiff_hunk l, *h;
	int an, bn, count;
	Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lmax;
	PyThreadState *_save = NULL;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, PY23("s*s*:bdiff", "y*y*:bdiff"), &ba, &bb))
		return NULL;

	if (!PyBuffer_IsContiguous(&ba, 'C') || ba.ndim > 1) {
		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
		goto cleanup;
	}

	if (!PyBuffer_IsContiguous(&bb, 'C') || bb.ndim > 1) {
		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
		goto cleanup;
	}

	la = ba.len;
	lb = bb.len;

	if (la > UINT_MAX || lb > UINT_MAX) {
		PyErr_SetString(PyExc_ValueError, "bdiff inputs too large");
		goto cleanup;
	}

	_save = PyEval_SaveThread();

	lmax = la > lb ? lb : la;
	for (ia = ba.buf, ib = bb.buf; li < lmax && *ia == *ib;
	     ++li, ++ia, ++ib) {
		if (*ia == '\n')
			lcommon = li + 1;
	}
	/* we can almost add: if (li == lmax) lcommon = li; */

	an = bdiff_splitlines(ba.buf + lcommon, la - lcommon, &al);
	bn = bdiff_splitlines(bb.buf + lcommon, lb - lcommon, &bl);
	if (!al || !bl) {
		PyErr_NoMemory();
		goto cleanup;
	}

	count = bdiff_diff(al, an, bl, bn, &l);
	if (count < 0) {
		PyErr_NoMemory();
		goto cleanup;
	}

	/* calculate length of output */
	la = lb = 0;
	for (h = l.next; h; h = h->next) {
		if (h->a1 != la || h->b1 != lb)
			len += 12 + bl[h->b1].l - bl[lb].l;
		la = h->a2;
		lb = h->b2;
	}
	PyEval_RestoreThread(_save);
	_save = NULL;

	result = PyBytes_FromStringAndSize(NULL, len);

	if (!result)
		goto cleanup;

	/* build binary patch */
	rb = PyBytes_AsString(result);
	la = lb = 0;

	for (h = l.next; h; h = h->next) {
		if (h->a1 != la || h->b1 != lb) {
			len = bl[h->b1].l - bl[lb].l;
			putbe32((uint32_t)(al[la].l + lcommon - al->l), rb);
			putbe32((uint32_t)(al[h->a1].l + lcommon - al->l),
			        rb + 4);
			putbe32((uint32_t)len, rb + 8);
			memcpy(rb + 12, bl[lb].l, len);
			rb += 12 + len;
		}
		la = h->a2;
		lb = h->b2;
	}

cleanup:
	if (_save)
		PyEval_RestoreThread(_save);
	PyBuffer_Release(&ba);
	PyBuffer_Release(&bb);
	if (al) {
		free(al);
	}
	if (bl) {
		free(bl);
	}
	if (l.next) {
		bdiff_freehunks(l.next);
	}
	return result;
}

/*
 * If allws != 0, remove all whitespace (' ', \t and \r). Otherwise,
 * reduce whitespace sequences to a single space and trim remaining whitespace
 * from end of lines.
 */
static PyObject *fixws(PyObject *self, PyObject *args)
{
	PyObject *s, *result = NULL;
	char allws, c;
	const char *r;
	Py_ssize_t i, rlen, wlen = 0;
	char *w;

	if (!PyArg_ParseTuple(args, "Sb:fixws", &s, &allws))
		return NULL;
	r = PyBytes_AsString(s);
	rlen = PyBytes_Size(s);

	w = (char *)PyMem_Malloc(rlen ? rlen : 1);
	if (!w)
		goto nomem;

	for (i = 0; i != rlen; i++) {
		c = r[i];
		if (c == ' ' || c == '\t' || c == '\r') {
			if (!allws && (wlen == 0 || w[wlen - 1] != ' '))
				w[wlen++] = ' ';
		} else if (c == '\n' && !allws && wlen > 0 &&
		           w[wlen - 1] == ' ') {
			w[wlen - 1] = '\n';
		} else {
			w[wlen++] = c;
		}
	}

	result = PyBytes_FromStringAndSize(w, wlen);

nomem:
	PyMem_Free(w);
	return result ? result : PyErr_NoMemory();
}

static bool sliceintolist(PyObject *list, Py_ssize_t destidx,
                          const char *source, Py_ssize_t len)
{
	PyObject *sliced = PyBytes_FromStringAndSize(source, len);
	if (sliced == NULL)
		return false;
	PyList_SET_ITEM(list, destidx, sliced);
	return true;
}

static PyObject *splitnewlines(PyObject *self, PyObject *args)
{
	const char *text;
	Py_ssize_t nelts = 0, size, i, start = 0;
	PyObject *result = NULL;

	if (!PyArg_ParseTuple(args, PY23("s#", "y#"), &text, &size)) {
		goto abort;
	}
	if (!size) {
		return PyList_New(0);
	}
	/* This loops to size-1 because if the last byte is a newline,
	 * we don't want to perform a split there. */
	for (i = 0; i < size - 1; ++i) {
		if (text[i] == '\n') {
			++nelts;
		}
	}
	if ((result = PyList_New(nelts + 1)) == NULL)
		goto abort;
	nelts = 0;
	for (i = 0; i < size - 1; ++i) {
		if (text[i] == '\n') {
			if (!sliceintolist(result, nelts++, text + start,
			                   i - start + 1))
				goto abort;
			start = i + 1;
		}
	}
	if (!sliceintolist(result, nelts++, text + start, size - start))
		goto abort;
	return result;
abort:
	Py_XDECREF(result);
	return NULL;
}

static char mdiff_doc[] = "Efficient binary diff.";

static PyMethodDef methods[] = {
    {"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},
    {"blocks", blocks, METH_VARARGS, "find a list of matching lines\n"},
    {"fixws", fixws, METH_VARARGS, "normalize diff whitespaces\n"},
    {"splitnewlines", splitnewlines, METH_VARARGS,
     "like str.splitlines, but only split on newlines\n"},
    {NULL, NULL},
};

static const int version = 2;

#ifdef IS_PY3K
static struct PyModuleDef bdiff_module = {
    PyModuleDef_HEAD_INIT, "bdiff", mdiff_doc, -1, methods,
};

PyMODINIT_FUNC PyInit_bdiff(void)
{
	PyObject *m;
	m = PyModule_Create(&bdiff_module);
	PyModule_AddIntConstant(m, "version", version);
	return m;
}
#else
PyMODINIT_FUNC initbdiff(void)
{
	PyObject *m;
	m = Py_InitModule3("bdiff", methods, mdiff_doc);
	PyModule_AddIntConstant(m, "version", version);
}
#endif