Edit File: is_tar.c
/* * Copyright (c) Ian F. Darwin 1986-1995. * Software written by Ian F. Darwin and others; * maintained 1995-present by Christos Zoulas and others. * * 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 immediately at the beginning of the file, without modification, * 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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. */ /* * is_tar() -- figure out whether file is a tar archive. * * Stolen (by the author!) from the public domain tar program: * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu). * * @(#)list.c 1.18 9/23/86 Public Domain - gnu * * Comments changed and some code/comments reformatted * for file command by Ian Darwin. */ #include "file.h" #ifndef lint FILE_RCSID("@(#)$File: is_tar.c,v 1.44 2019/02/20 02:35:27 christos Exp $") #endif #include "magic.h" #include <string.h> #include <ctype.h> #include "tar.h" #define isodigit(c) ( ((c) >= '0') && ((c) <= '7') ) private int is_tar(const unsigned char *, size_t); private int from_oct(const char *, size_t); /* Decode octal number */ static const char tartype[][32] = { /* should be equal to messages */ "tar archive", /* found in ../magic/Magdir/archive */ "POSIX tar archive", "POSIX tar archive (GNU)", /* */ }; protected int file_is_tar(struct magic_set *ms, const struct buffer *b) { const unsigned char *buf = CAST(const unsigned char *, b->fbuf); size_t nbytes = b->flen; /* * Do the tar test first, because if the first file in the tar * archive starts with a dot, we can confuse it with an nroff file. */ int tar; int mime = ms->flags & MAGIC_MIME; if ((ms->flags & (MAGIC_APPLE|MAGIC_EXTENSION)) != 0) return 0; tar = is_tar(buf, nbytes); if (tar < 1 || tar > 3) return 0; if (mime == MAGIC_MIME_ENCODING) return 1; if (file_printf(ms, "%s", mime ? "application/x-tar" : tartype[tar - 1]) == -1) return -1; return 1; } /* * Return * 0 if the checksum is bad (i.e., probably not a tar archive), * 1 for old UNIX tar file, * 2 for Unix Std (POSIX) tar file, * 3 for GNU tar file. */ private int is_tar(const unsigned char *buf, size_t nbytes) { const union record *header = RCAST(const union record *, RCAST(const void *, buf)); size_t i; int sum, recsum; const unsigned char *p, *ep; if (nbytes < sizeof(*header)) return 0; recsum = from_oct(header->header.chksum, sizeof(header->header.chksum)); sum = 0; p = header->charptr; ep = header->charptr + sizeof(*header); while (p < ep) sum += *p++; /* Adjust checksum to count the "chksum" field as blanks. */ for (i = 0; i < sizeof(header->header.chksum); i++) sum -= header->header.chksum[i]; sum += ' ' * sizeof(header->header.chksum); if (sum != recsum) return 0; /* Not a tar archive */ if (strncmp(header->header.magic, GNUTMAGIC, sizeof(header->header.magic)) == 0) return 3; /* GNU Unix Standard tar archive */ if (strncmp(header->header.magic, TMAGIC, sizeof(header->header.magic)) == 0) return 2; /* Unix Standard tar archive */ return 1; /* Old fashioned tar archive */ } /* * Quick and dirty octal conversion. * * Result is -1 if the field is invalid (all blank, or non-octal). */ private int from_oct(const char *where, size_t digs) { int value; if (digs == 0) return -1; while (isspace(CAST(unsigned char, *where))) { /* Skip spaces */ where++; if (digs-- == 0) return -1; /* All blank field */ } value = 0; while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */ value = (value << 3) | (*where++ - '0'); digs--; } if (digs > 0 && *where && !isspace(CAST(unsigned char, *where))) return -1; /* Ended on non-(space/NUL) */ return value; }