mercurial/parsers.c

parsers: avoid pointer aliasing

Newer versions of GCC have aggressive pointer alias optimizations that
might get fooled by our pointer manipulations. These issues shouldn't
be encountered in practice because distutils compiles extensions with
-fno-strict-alias but the code was not valid according to the standard.

/*
 parsers.c - efficient content parsing

 Copyright 2008 Matt Mackall <[e-mail]> and others

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

#include <Python.h>
#include <ctype.h>
#include <string.h>

#include "util.h"

static int hexdigit(char c)
{
	if (c >= '0' && c <= '9')
		return c - '0';
	if (c >= 'a' && c <= 'f')
		return c - 'a' + 10;
	if (c >= 'A' && c <= 'F')
		return c - 'A' + 10;

	PyErr_SetString(PyExc_ValueError, "input contains non-hex character");
	return 0;
}

/*
 * Turn a hex-encoded string into binary.
 */
static PyObject *unhexlify(const char *str, int len)
{
	PyObject *ret;
	const char *c;
	char *d;

	ret = PyBytes_FromStringAndSize(NULL, len / 2);

	if (!ret)
		return NULL;

	d = PyBytes_AsString(ret);

	for (c = str; c < str + len;) {
		int hi = hexdigit(*c++);
		int lo = hexdigit(*c++);
		*d++ = (hi << 4) | lo;
	}

	return ret;
}

/*
 * This code assumes that a manifest is stitched together with newline
 * ('\n') characters.
 */
static PyObject *parse_manifest(PyObject *self, PyObject *args)
{
	PyObject *mfdict, *fdict;
	char *str, *cur, *start, *zero;
	int len;

	if (!PyArg_ParseTuple(args, "O!O!s#:parse_manifest",
			      &PyDict_Type, &mfdict,
			      &PyDict_Type, &fdict,
			      &str, &len))
		goto quit;

	for (start = cur = str, zero = NULL; cur < str + len; cur++) {
		PyObject *file = NULL, *node = NULL;
		PyObject *flags = NULL;
		int nlen;

		if (!*cur) {
			zero = cur;
			continue;
		}
		else if (*cur != '\n')
			continue;

		if (!zero) {
			PyErr_SetString(PyExc_ValueError,
					"manifest entry has no separator");
			goto quit;
		}

		file = PyBytes_FromStringAndSize(start, zero - start);

		if (!file)
			goto bail;

		nlen = cur - zero - 1;

		node = unhexlify(zero + 1, nlen > 40 ? 40 : nlen);
		if (!node)
			goto bail;

		if (nlen > 40) {
			flags = PyBytes_FromStringAndSize(zero + 41,
							   nlen - 40);
			if (!flags)
				goto bail;

			if (PyDict_SetItem(fdict, file, flags) == -1)
				goto bail;
		}

		if (PyDict_SetItem(mfdict, file, node) == -1)
			goto bail;

		start = cur + 1;
		zero = NULL;

		Py_XDECREF(flags);
		Py_XDECREF(node);
		Py_XDECREF(file);
		continue;
	bail:
		Py_XDECREF(flags);
		Py_XDECREF(node);
		Py_XDECREF(file);
		goto quit;
	}

	if (len > 0 && *(cur - 1) != '\n') {
		PyErr_SetString(PyExc_ValueError,
				"manifest contains trailing garbage");
		goto quit;
	}

	Py_INCREF(Py_None);
	return Py_None;
quit:
	return NULL;
}

#ifdef _WIN32
#ifdef _MSC_VER
/* msvc 6.0 has problems */
#define inline __inline
typedef unsigned long uint32_t;
typedef unsigned __int64 uint64_t;
#else
#include <stdint.h>
#endif
static uint32_t ntohl(uint32_t x)
{
	return ((x & 0x000000ffUL) << 24) |
	       ((x & 0x0000ff00UL) <<  8) |
	       ((x & 0x00ff0000UL) >>  8) |
	       ((x & 0xff000000UL) >> 24);
}
#else
/* not windows */
#include <sys/types.h>
#if defined __BEOS__ && !defined __HAIKU__
#include <ByteOrder.h>
#else
#include <arpa/inet.h>
#endif
#include <inttypes.h>
#endif

static PyObject *parse_dirstate(PyObject *self, PyObject *args)
{
	PyObject *dmap, *cmap, *parents = NULL, *ret = NULL;
	PyObject *fname = NULL, *cname = NULL, *entry = NULL;
	char *str, *cur, *end, *cpos;
	int state, mode, size, mtime;
	unsigned int flen;
	int len;
	uint32_t decode[4]; /* for alignment */

	if (!PyArg_ParseTuple(args, "O!O!s#:parse_dirstate",
			      &PyDict_Type, &dmap,
			      &PyDict_Type, &cmap,
			      &str, &len))
		goto quit;

	/* read parents */
	if (len < 40)
		goto quit;

	parents = Py_BuildValue("s#s#", str, 20, str + 20, 20);
	if (!parents)
		goto quit;

	/* read filenames */
	cur = str + 40;
	end = str + len;

	while (cur < end - 17) {
		/* unpack header */
		state = *cur;
		memcpy(decode, cur + 1, 16);
		mode = ntohl(decode[0]);
		size = ntohl(decode[1]);
		mtime = ntohl(decode[2]);
		flen = ntohl(decode[3]);
		cur += 17;
		if (cur + flen > end || cur + flen < cur) {
			PyErr_SetString(PyExc_ValueError, "overflow in dirstate");
			goto quit;
		}

		entry = Py_BuildValue("ciii", state, mode, size, mtime);
		if (!entry)
			goto quit;
		PyObject_GC_UnTrack(entry); /* don't waste time with this */

		cpos = memchr(cur, 0, flen);
		if (cpos) {
			fname = PyBytes_FromStringAndSize(cur, cpos - cur);
			cname = PyBytes_FromStringAndSize(cpos + 1,
							   flen - (cpos - cur) - 1);
			if (!fname || !cname ||
			    PyDict_SetItem(cmap, fname, cname) == -1 ||
			    PyDict_SetItem(dmap, fname, entry) == -1)
				goto quit;
			Py_DECREF(cname);
		} else {
			fname = PyBytes_FromStringAndSize(cur, flen);
			if (!fname ||
			    PyDict_SetItem(dmap, fname, entry) == -1)
				goto quit;
		}
		cur += flen;
		Py_DECREF(fname);
		Py_DECREF(entry);
		fname = cname = entry = NULL;
	}

	ret = parents;
	Py_INCREF(ret);
quit:
	Py_XDECREF(fname);
	Py_XDECREF(cname);
	Py_XDECREF(entry);
	Py_XDECREF(parents);
	return ret;
}

const char nullid[20];
const int nullrev = -1;

/* RevlogNG format (all in big endian, data may be inlined):
 *    6 bytes: offset
 *    2 bytes: flags
 *    4 bytes: compressed length
 *    4 bytes: uncompressed length
 *    4 bytes: base revision
 *    4 bytes: link revision
 *    4 bytes: parent 1 revision
 *    4 bytes: parent 2 revision
 *   32 bytes: nodeid (only 20 bytes used)
 */
static int _parse_index_ng(const char *data, int size, int inlined,
			   PyObject *index)
{
	PyObject *entry;
	int n = 0, err;
	uint64_t offset_flags;
	int comp_len, uncomp_len, base_rev, link_rev, parent_1, parent_2;
	const char *c_node_id;
	const char *end = data + size;
	uint32_t decode[8]; /* to enforce alignment with inline data */

	while (data < end) {
		unsigned int step;

		memcpy(decode, data, 32);
		offset_flags = ntohl(decode[1]);
		if (n == 0) /* mask out version number for the first entry */
			offset_flags &= 0xFFFF;
		else {
			uint32_t offset_high =  ntohl(decode[0]);
			offset_flags |= ((uint64_t)offset_high) << 32;
		}

		comp_len = ntohl(decode[2]);
		uncomp_len = ntohl(decode[3]);
		base_rev = ntohl(decode[4]);
		link_rev = ntohl(decode[5]);
		parent_1 = ntohl(decode[6]);
		parent_2 = ntohl(decode[7]);
		c_node_id = data + 32;

		entry = Py_BuildValue("Liiiiiis#", offset_flags, comp_len,
			      uncomp_len, base_rev, link_rev,
			      parent_1, parent_2, c_node_id, 20);

		if (!entry)
			return 0;

		PyObject_GC_UnTrack(entry); /* don't waste time with this */

		if (inlined) {
			err = PyList_Append(index, entry);
			Py_DECREF(entry);
			if (err)
				return 0;
		} else
			PyList_SET_ITEM(index, n, entry); /* steals reference */

		n++;
		step = 64 + (inlined ? comp_len : 0);
		if (data + step > end || data + step < data)
			break;
		data += step;
	}
	if (data != end) {
		if (!PyErr_Occurred())
			PyErr_SetString(PyExc_ValueError, "corrupt index file");
		return 0;
	}

	/* create the magic nullid entry in the index at [-1] */
	entry = Py_BuildValue("Liiiiiis#", (uint64_t)0, 0, 0, -1, -1, -1, -1, nullid, 20);

	if (!entry)
		return 0;

	PyObject_GC_UnTrack(entry); /* don't waste time with this */

	if (inlined) {
		err = PyList_Append(index, entry);
		Py_DECREF(entry);
		if (err)
			return 0;
	} else
		PyList_SET_ITEM(index, n, entry); /* steals reference */

	return 1;
}

/* This function parses a index file and returns a Python tuple of the
 * following format: (index, cache)
 *
 * index: a list of tuples containing the RevlogNG records
 * cache: if data is inlined, a tuple (index_file_content, 0) else None
 */
static PyObject *parse_index2(PyObject *self, PyObject *args)
{
	const char *data;
	int size, inlined;
	PyObject *rval = NULL, *index = NULL, *cache = NULL;
	PyObject *data_obj = NULL, *inlined_obj;

	if (!PyArg_ParseTuple(args, "s#O", &data, &size, &inlined_obj))
		return NULL;
	inlined = inlined_obj && PyObject_IsTrue(inlined_obj);

	/* If no data is inlined, we know the size of the index list in
	 * advance: size divided by the size of one revlog record (64 bytes)
	 * plus one for nullid */
	index = inlined ? PyList_New(0) : PyList_New(size / 64 + 1);
	if (!index)
		goto quit;

	/* set up the cache return value */
	if (inlined) {
		/* Note that the reference to data_obj is only borrowed */
		data_obj = PyTuple_GET_ITEM(args, 0);
		cache = Py_BuildValue("iO", 0, data_obj);
		if (!cache)
			goto quit;
	} else {
		cache = Py_None;
		Py_INCREF(Py_None);
	}

	/* actually populate the index with data */
	if (!_parse_index_ng(data, size, inlined, index))
		goto quit;

	rval = Py_BuildValue("NN", index, cache);
	if (!rval)
		goto quit;
	return rval;

quit:
	Py_XDECREF(index);
	Py_XDECREF(cache);
	Py_XDECREF(rval);
	return NULL;
}


static char parsers_doc[] = "Efficient content parsing.";

static PyMethodDef methods[] = {
	{"parse_manifest", parse_manifest, METH_VARARGS, "parse a manifest\n"},
	{"parse_dirstate", parse_dirstate, METH_VARARGS, "parse a dirstate\n"},
	{"parse_index2", parse_index2, METH_VARARGS, "parse a revlog index\n"},
	{NULL, NULL}
};

#ifdef IS_PY3K
static struct PyModuleDef parsers_module = {
	PyModuleDef_HEAD_INIT,
	"parsers",
	parsers_doc,
	-1,
	methods
};

PyMODINIT_FUNC PyInit_parsers(void)
{
	return PyModule_Create(&parsers_module);
}
#else
PyMODINIT_FUNC initparsers(void)
{
	Py_InitModule3("parsers", methods, parsers_doc);
}
#endif