archival/libunarchive/get_header_tar.c

/*
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Library General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "unarchive.h"
#include "libbb.h"

file_header_t *get_header_tar(FILE *tar_stream)
{
	union {
		unsigned char raw[512];
		struct {
			char name[100];		/*   0-99 */
			char mode[8];		/* 100-107 */
			char uid[8];		/* 108-115 */
			char gid[8];		/* 116-123 */
			char size[12];		/* 124-135 */
			char mtime[12];		/* 136-147 */
			char chksum[8];		/* 148-155 */
			char typeflag;		/* 156-156 */
			char linkname[100];	/* 157-256 */
			char magic[6];		/* 257-262 */
			char version[2];	/* 263-264 */
			char uname[32];		/* 265-296 */
			char gname[32];		/* 297-328 */
			char devmajor[8];	/* 329-336 */
			char devminor[8];	/* 337-344 */
			char prefix[155];	/* 345-499 */
			char padding[12];	/* 500-512 */
		} formated;
	} tar;
	file_header_t *tar_entry = NULL;
	long sum = 0;
	long i;

	if (archive_offset % 512 != 0) {
		seek_sub_file(tar_stream, 512 - (archive_offset % 512));
	}

	if (fread(tar.raw, 1, 512, tar_stream) != 512) {
		/* Unfortunatly its common for tar files to have all sorts of
		 * trailing garbage, fail silently */
//		error_msg("Couldnt read header");
		return(NULL);
	}
	archive_offset += 512;

	/* Check header has valid magic, unfortunately some tar files
	 * have empty (0'ed) tar entries at the end, which will
	 * cause this to fail, so fail silently for now
	 */
	if (strncmp(tar.formated.magic, "ustar", 5) != 0) {
		return(NULL);
	}

	/* Do checksum on headers */
	for (i =  0; i < 148 ; i++) {
		sum += tar.raw[i];
	}
	sum += ' ' * 8;
	for (i =  156; i < 512 ; i++) {
		sum += tar.raw[i];
	}
	if (sum != strtol(tar.formated.chksum, NULL, 8)) {
		error_msg("Invalid tar header checksum");
		return(NULL);
	}

	/* convert to type'ed variables */
	tar_entry = xcalloc(1, sizeof(file_header_t));
	tar_entry->name = xstrdup(tar.formated.name);

	parse_mode(tar.formated.mode, &tar_entry->mode);
	tar_entry->uid   = strtol(tar.formated.uid, NULL, 8);
	tar_entry->gid   = strtol(tar.formated.gid, NULL, 8);
	tar_entry->size  = strtol(tar.formated.size, NULL, 8);
	tar_entry->mtime = strtol(tar.formated.mtime, NULL, 8);
	tar_entry->link_name  = strlen(tar.formated.linkname) ? 
	    xstrdup(tar.formated.linkname) : NULL;
	tar_entry->device = (strtol(tar.formated.devmajor, NULL, 8) << 8) +
		strtol(tar.formated.devminor, NULL, 8);

	return(tar_entry);
}