tarsnap/libarchive/archive_write_disk_set_standard_lookup.c

/*-
 * Copyright (c) 2003-2007 Tim Kientzle
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "archive_platform.h"
__FBSDID("$FreeBSD: src/lib/libarchive/archive_write_disk_set_standard_lookup.c,v 1.4 2007/05/29 01:00:19 kientzle Exp $");

#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#ifdef HAVE_GRP_H
#include <grp.h>
#endif
#ifdef HAVE_PWD_H
#include <pwd.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif

#include "archive.h"
#include "archive_private.h"
#include "archive_read_private.h"
#include "archive_write_disk_private.h"

struct bucket {
	char	*name;
	int	 hash;
	id_t	 id;
};

static const size_t cache_size = 127;
static unsigned int	hash(const char *);
static gid_t	lookup_gid(void *, const char *uname, gid_t);
static uid_t	lookup_uid(void *, const char *uname, uid_t);
static void	cleanup(void *);

/*
 * Installs functions that use getpwnam()/getgrnam()---along with
 * a simple cache to accelerate such lookups---into the archive_write_disk
 * object.  This is in a separate file because getpwnam()/getgrnam()
 * can pull in a LOT of library code (including NIS/LDAP functions, which
 * pull in DNS resolvers, etc).  This can easily top 500kB, which makes
 * it inappropriate for some space-constrained applications.
 *
 * Applications that are size-sensitive may want to just use the
 * real default functions (defined in archive_write_disk.c) that just
 * use the uid/gid without the lookup.  Or define your own custom functions
 * if you prefer.
 *
 * TODO: Replace these hash tables with simpler move-to-front LRU
 * lists with a bounded size (128 items?).  The hash is a bit faster,
 * but has a bad pathology in which it thrashes a single bucket.  Even
 * walking a list of 128 items is a lot faster than calling
 * getpwnam()!
 */
int
archive_write_disk_set_standard_lookup(struct archive *a)
{
	struct bucket *ucache = malloc(cache_size * sizeof(struct bucket));
	struct bucket *gcache = malloc(cache_size * sizeof(struct bucket));
	if (ucache == NULL || gcache == NULL) {
		free(ucache);
		free(gcache);
		return (ARCHIVE_FATAL);
	}
	memset(ucache, 0, cache_size * sizeof(struct bucket));
	memset(gcache, 0, cache_size * sizeof(struct bucket));
	archive_write_disk_set_group_lookup(a, gcache, lookup_gid, cleanup);
	archive_write_disk_set_user_lookup(a, ucache, lookup_uid, cleanup);
	return (ARCHIVE_OK);
}

static gid_t
lookup_gid(void *private_data, const char *gname, gid_t gid)
{
	int h;
	struct bucket *b;
	struct bucket *gcache = (struct bucket *)private_data;

	/* If no gname, just use the gid provided. */
	if (gname == NULL || *gname == '\0')
		return (gid);

	/* Try to find gname in the cache. */
	h = hash(gname);
	b = &gcache[h % cache_size ];
	if (b->name != NULL && b->hash == h && strcmp(gname, b->name) == 0)
		return ((gid_t)b->id);

	/* Free the cache slot for a new entry. */
	if (b->name != NULL)
		free(b->name);
	b->name = strdup(gname);
	/* Note: If strdup fails, that's okay; we just won't cache. */
	b->hash = h;
#if HAVE_GRP_H
	{
		char _buffer[128];
		size_t bufsize = 128;
		char *buffer = _buffer;
		struct group	grent, *result;
		int r;

		for (;;) {
			r = getgrnam_r(gname, &grent, buffer, bufsize, &result);
			if (r == 0)
				break;
			if (r != ERANGE)
				break;
			bufsize *= 2;
			if (buffer != _buffer)
				free(buffer);
			buffer = malloc(bufsize);
			if (buffer == NULL)
				break;
		}
		if (result != NULL)
			gid = result->gr_gid;
		if (buffer != _buffer)
			free(buffer);
	}
#elif defined(_WIN32) && !defined(__CYGWIN__)
	/* TODO: do a gname->gid lookup for Windows. */
#else
	#error No way to perform gid lookups on this platform
#endif
	b->id = gid;

	return (gid);
}

static uid_t
lookup_uid(void *private_data, const char *uname, uid_t uid)
{
	int h;
	struct bucket *b;
	struct bucket *ucache = (struct bucket *)private_data;

	/* If no uname, just use the uid provided. */
	if (uname == NULL || *uname == '\0')
		return (uid);

	/* Try to find uname in the cache. */
	h = hash(uname);
	b = &ucache[h % cache_size ];
	if (b->name != NULL && b->hash == h && strcmp(uname, b->name) == 0)
		return ((uid_t)b->id);

	/* Free the cache slot for a new entry. */
	if (b->name != NULL)
		free(b->name);
	b->name = strdup(uname);
	/* Note: If strdup fails, that's okay; we just won't cache. */
	b->hash = h;
#if HAVE_PWD_H
	{
		char _buffer[128];
		size_t bufsize = 128;
		char *buffer = _buffer;
		struct passwd	pwent, *result;
		int r;

		for (;;) {
			r = getpwnam_r(uname, &pwent, buffer, bufsize, &result);
			if (r == 0)
				break;
			if (r != ERANGE)
				break;
			bufsize *= 2;
			if (buffer != _buffer)
				free(buffer);
			buffer = malloc(bufsize);
			if (buffer == NULL)
				break;
		}
		if (result != NULL)
			uid = result->pw_uid;
		if (buffer != _buffer)
			free(buffer);
	}
#elif defined(_WIN32) && !defined(__CYGWIN__)
	/* TODO: do a uname->uid lookup for Windows. */
#else
	#error No way to look up uids on this platform
#endif
	b->id = uid;

	return (uid);
}

static void
cleanup(void *private)
{
	size_t i;
	struct bucket *cache = (struct bucket *)private;

	for (i = 0; i < cache_size; i++)
		free(cache[i].name);
	free(cache);
}


static unsigned int
hash(const char *p)
{
	/* A 32-bit version of Peter Weinberger's (PJW) hash algorithm,
	   as used by ELF for hashing function names. */
	unsigned g, h = 0;
	while (*p != '\0') {
		h = ( h << 4 ) + *p++;
		if (( g = h & 0xF0000000 )) {
			h ^= g >> 24;
			h &= 0x0FFFFFFF;
		}
	}
	return h;
}