view mercurial/cext/dirs.c @ 50662:12f13b13f414 stable

revlog: avoid possible collision between directory and temporary index

Since 6.4, we create a temporary index file to write the split data without
overwriting the inline version too early. However, the store encoding does not
prevent these new `.i.s` file to collide with a directory with the same name.
While the odds for such a collision to happens are fairly low, the collision
would prevent Mercurial from working.

The store encoding have a mitigation solution in place to prevent such
collisions from happening for `.i` and `.d` files, but not for other extensions.
We cannot update this encoding scheme to solve the issue since it would diverge
from older version of Mercurial.

Instead, we create an alternative directory tree dedicated to such files.
The use of the `.i` extension combined with store encoding will prevent
collisions there.

/*
 dirs.c - dynamic directory diddling for dirstates

 Copyright 2013 Facebook

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

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

#include "util.h"

#if PY_VERSION_HEX >= 0x030C00A5
#define PYLONG_VALUE(o) ((PyLongObject *)o)->long_value.ob_digit[0]
#else
#define PYLONG_VALUE(o) ((PyLongObject *)o)->ob_digit[0]
#endif

/*
 * This is a multiset of directory names, built from the files that
 * appear in a dirstate or manifest.
 *
 * A few implementation notes:
 *
 * We modify Python integers for refcounting, but those integers are
 * never visible to Python code.
 */
/* clang-format off */
typedef struct {
	PyObject_HEAD
	PyObject *dict;
} dirsObject;
/* clang-format on */

static inline Py_ssize_t _finddir(const char *path, Py_ssize_t pos)
{
	while (pos != -1) {
		if (path[pos] == '/')
			break;
		pos -= 1;
	}
	if (pos == -1) {
		return 0;
	}

	return pos;
}

/* Mercurial will fail to run on directory hierarchies deeper than
 * this constant, so we should try and keep this constant as big as
 * possible.
 */
#define MAX_DIRS_DEPTH 2048

static int _addpath(PyObject *dirs, PyObject *path)
{
	const char *cpath = PyBytes_AS_STRING(path);
	Py_ssize_t pos = PyBytes_GET_SIZE(path);
	PyObject *key = NULL;
	int ret = -1;
	size_t num_slashes = 0;

	/* This loop is super critical for performance. That's why we inline
	 * access to Python structs instead of going through a supported API.
	 * The implementation, therefore, is heavily dependent on CPython
	 * implementation details. We also commit violations of the Python
	 * "protocol" such as mutating immutable objects. But since we only
	 * mutate objects created in this function or in other well-defined
	 * locations, the references are known so these violations should go
	 * unnoticed. */
	while ((pos = _finddir(cpath, pos - 1)) != -1) {
		PyObject *val;
		++num_slashes;
		if (num_slashes > MAX_DIRS_DEPTH) {
			PyErr_SetString(PyExc_ValueError,
			                "Directory hierarchy too deep.");
			goto bail;
		}

		/* Sniff for trailing slashes, a marker of an invalid input. */
		if (pos > 0 && cpath[pos - 1] == '/') {
			PyErr_SetString(
			    PyExc_ValueError,
			    "found invalid consecutive slashes in path");
			goto bail;
		}

		key = PyBytes_FromStringAndSize(cpath, pos);
		if (key == NULL)
			goto bail;

		val = PyDict_GetItem(dirs, key);
		if (val != NULL) {
			PYLONG_VALUE(val) += 1;
			Py_CLEAR(key);
			break;
		}

		/* Force Python to not reuse a small shared int. */
		val = PyLong_FromLong(0x1eadbeef);

		if (val == NULL)
			goto bail;

		PYLONG_VALUE(val) = 1;
		ret = PyDict_SetItem(dirs, key, val);
		Py_DECREF(val);
		if (ret == -1)
			goto bail;
		Py_CLEAR(key);
	}
	ret = 0;

bail:
	Py_XDECREF(key);

	return ret;
}

static int _delpath(PyObject *dirs, PyObject *path)
{
	char *cpath = PyBytes_AS_STRING(path);
	Py_ssize_t pos = PyBytes_GET_SIZE(path);
	PyObject *key = NULL;
	int ret = -1;

	while ((pos = _finddir(cpath, pos - 1)) != -1) {
		PyObject *val;

		key = PyBytes_FromStringAndSize(cpath, pos);

		if (key == NULL)
			goto bail;

		val = PyDict_GetItem(dirs, key);
		if (val == NULL) {
			PyErr_SetString(PyExc_ValueError,
			                "expected a value, found none");
			goto bail;
		}

		if (--PYLONG_VALUE(val) <= 0) {
			if (PyDict_DelItem(dirs, key) == -1)
				goto bail;
		} else
			break;
		Py_CLEAR(key);
	}
	ret = 0;

bail:
	Py_XDECREF(key);

	return ret;
}

static int dirs_fromdict(PyObject *dirs, PyObject *source, bool only_tracked)
{
	PyObject *key, *value;
	Py_ssize_t pos = 0;

	while (PyDict_Next(source, &pos, &key, &value)) {
		if (!PyBytes_Check(key)) {
			PyErr_SetString(PyExc_TypeError, "expected string key");
			return -1;
		}
		if (only_tracked) {
			if (!dirstate_tuple_check(value)) {
				PyErr_SetString(PyExc_TypeError,
				                "expected a dirstate tuple");
				return -1;
			}
			if (!(((dirstateItemObject *)value)->flags &
			      dirstate_flag_wc_tracked))
				continue;
		}

		if (_addpath(dirs, key) == -1)
			return -1;
	}

	return 0;
}

static int dirs_fromiter(PyObject *dirs, PyObject *source)
{
	PyObject *iter, *item = NULL;
	int ret;

	iter = PyObject_GetIter(source);
	if (iter == NULL)
		return -1;

	while ((item = PyIter_Next(iter)) != NULL) {
		if (!PyBytes_Check(item)) {
			PyErr_SetString(PyExc_TypeError, "expected string");
			break;
		}

		if (_addpath(dirs, item) == -1)
			break;
		Py_CLEAR(item);
	}

	ret = PyErr_Occurred() ? -1 : 0;
	Py_DECREF(iter);
	Py_XDECREF(item);
	return ret;
}

/*
 * Calculate a refcounted set of directory names for the files in a
 * dirstate.
 */
static int dirs_init(dirsObject *self, PyObject *args, PyObject *kwargs)
{
	PyObject *dirs = NULL, *source = NULL;
	int only_tracked = 0;
	int ret = -1;
	static char *keywords_name[] = {"map", "only_tracked", NULL};

	self->dict = NULL;

	if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|Oi:__init__",
	                                 keywords_name, &source, &only_tracked))
		return -1;

	dirs = PyDict_New();

	if (dirs == NULL)
		return -1;

	if (source == NULL)
		ret = 0;
	else if (PyDict_Check(source))
		ret = dirs_fromdict(dirs, source, (bool)only_tracked);
	else if (only_tracked)
		PyErr_SetString(PyExc_ValueError,
		                "`only_tracked` is only supported "
		                "with a dict source");
	else
		ret = dirs_fromiter(dirs, source);

	if (ret == -1)
		Py_XDECREF(dirs);
	else
		self->dict = dirs;

	return ret;
}

PyObject *dirs_addpath(dirsObject *self, PyObject *args)
{
	PyObject *path;

	if (!PyArg_ParseTuple(args, "O!:addpath", &PyBytes_Type, &path))
		return NULL;

	if (_addpath(self->dict, path) == -1)
		return NULL;

	Py_RETURN_NONE;
}

static PyObject *dirs_delpath(dirsObject *self, PyObject *args)
{
	PyObject *path;

	if (!PyArg_ParseTuple(args, "O!:delpath", &PyBytes_Type, &path))
		return NULL;

	if (_delpath(self->dict, path) == -1)
		return NULL;

	Py_RETURN_NONE;
}

static int dirs_contains(dirsObject *self, PyObject *value)
{
	return PyBytes_Check(value) ? PyDict_Contains(self->dict, value) : 0;
}

static void dirs_dealloc(dirsObject *self)
{
	Py_XDECREF(self->dict);
	PyObject_Del(self);
}

static PyObject *dirs_iter(dirsObject *self)
{
	return PyObject_GetIter(self->dict);
}

static PySequenceMethods dirs_sequence_methods;

static PyMethodDef dirs_methods[] = {
    {"addpath", (PyCFunction)dirs_addpath, METH_VARARGS, "add a path"},
    {"delpath", (PyCFunction)dirs_delpath, METH_VARARGS, "remove a path"},
    {NULL} /* Sentinel */
};

static PyTypeObject dirsType = {PyVarObject_HEAD_INIT(NULL, 0)};

void dirs_module_init(PyObject *mod)
{
	dirs_sequence_methods.sq_contains = (objobjproc)dirs_contains;
	dirsType.tp_name = "parsers.dirs";
	dirsType.tp_new = PyType_GenericNew;
	dirsType.tp_basicsize = sizeof(dirsObject);
	dirsType.tp_dealloc = (destructor)dirs_dealloc;
	dirsType.tp_as_sequence = &dirs_sequence_methods;
	dirsType.tp_flags = Py_TPFLAGS_DEFAULT;
	dirsType.tp_doc = "dirs";
	dirsType.tp_iter = (getiterfunc)dirs_iter;
	dirsType.tp_methods = dirs_methods;
	dirsType.tp_init = (initproc)dirs_init;

	if (PyType_Ready(&dirsType) < 0)
		return;
	Py_INCREF(&dirsType);

	PyModule_AddObject(mod, "dirs", (PyObject *)&dirsType);
}