usr.bin/file/softmagic.c

/*
 * softmagic - interpret variable magic from /etc/magic
 *
 * Copyright (c) Ian F. Darwin, 1987.
 * Written by Ian F. Darwin.
 *
 * This software is not subject to any license of the American Telephone
 * and Telegraph Company or of the Regents of the University of California.
 *
 * Permission is granted to anyone to use this software for any purpose on
 * any computer system, and to alter it and redistribute it freely, subject
 * to the following restrictions:
 *
 * 1. The author is not responsible for the consequences of use of this
 *    software, no matter how awful, even if they arise from flaws in it.
 *
 * 2. The origin of this software must not be misrepresented, either by
 *    explicit claim or by omission.  Since few users ever read sources,
 *    credits must appear in the documentation.
 *
 * 3. Altered versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.  Since few users
 *    ever read sources, credits must appear in the documentation.
 *
 * 4. This notice may not be removed or altered.
 */

#include <stdio.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>

#include "file.h"

#ifndef lint
static char *moduleid =
        "@(#)softmagic.c,v 1.2 1993/06/10 00:38:18 jtc Exp";
#endif  /* lint */

static int match        __P((unsigned char *));
static int mcheck       __P((unsigned char      *, struct magic *));
static void mprint      __P((struct magic *, unsigned char *));

/*
 * softmagic - lookup one file in database
 * (already read from /etc/magic by apprentice.c).
 * Passed the name and FILE * of one file to be typed.
 */
/*ARGSUSED1*/           /* nbytes passed for regularity, maybe need later */
int
softmagic(buf, nbytes)
unsigned char *buf;
int nbytes;
{
        if (match(buf))
                return 1;

        return 0;
}

/*
 * Go through the whole list, stopping if you find a match.  Process all
 * the continuations of that match before returning.
 *
 * We support multi-level continuations:
 *
 *      At any time when processing a successful top-level match, there is a
 *      current continuation level; it represents the level of the last
 *      successfully matched continuation.
 *
 *      Continuations above that level are skipped as, if we see one, it
 *      means that the continuation that controls them - i.e, the
 *      lower-level continuation preceding them - failed to match.
 *
 *      Continuations below that level are processed as, if we see one,
 *      it means we've finished processing or skipping higher-level
 *      continuations under the control of a successful or unsuccessful
 *      lower-level continuation, and are now seeing the next lower-level
 *      continuation and should process it.  The current continuation
 *      level reverts to the level of the one we're seeing.
 *
 *      Continuations at the current level are processed as, if we see
 *      one, there's no lower-level continuation that may have failed.
 *
 *      If a continuation matches, we bump the current continuation level
 *      so that higher-level continuations are processed.
 */
static int
match(s)
unsigned char   *s;
{
        int magindex = 0;
        int cont_level = 0;
        int need_separator = 0;

        while (magindex < nmagic) {
                /* if main entry matches, print it... */
                if (mcheck(s, &magic[magindex])) {
                        mprint(&magic[magindex],s);
                        /*
                         * If we printed something, we'll need to print
                         * a blank before we print something else.
                         */
                        if (magic[magindex].desc[0])
                                need_separator = 1;
                        /* and any continuations that match */
                        cont_level++;
                        while (magic[magindex+1].cont_level != 0 &&
                                magindex < nmagic) {
                                ++magindex;
                                if (cont_level >=
                                    magic[magindex].cont_level) {
                                        if (cont_level >
                                            magic[magindex].cont_level) {
                                                /*
                                                 * We're at the end of the
                                                 * level-"cont_level"
                                                 * continuations.
                                                 */
                                                cont_level =
                                                  magic[magindex].cont_level;
                                        }
                                        if (mcheck(s, &magic[magindex])) {
                                                /*
                                                 * This continuation matched.
                                                 * Print its message, with
                                                 * a blank before it if
                                                 * the previous item printed
                                                 * and this item isn't empty.
                                                 */
                                                /* space if previous printed */
                                                if (need_separator
                                                   && (magic[magindex].nospflag == 0)
                                                   && (magic[magindex].desc[0] != '\0')
                                                   ) {
                                                        (void) putchar(' ');
                                                        need_separator = 0;
                                                }
                                                mprint(&magic[magindex],s);
                                                if (magic[magindex].desc[0])
                                                        need_separator = 1;

                                                /*
                                                 * If we see any continuations
                                                 * at a higher level,
                                                 * process them.
                                                 */
                                                cont_level++;
                                        }
                                }
                        }
                        return 1;               /* all through */
                } else {
                        /* main entry didn't match, flush its continuation */
                        while (magic[magindex+1].cont_level != 0 &&
                                magindex < nmagic) {
                                ++magindex;
                        }
                }
                ++magindex;                     /* on to the next */
        }
        return 0;                               /* no match at all */
}

static void
mprint(m, s)
struct magic *m;
unsigned char *s;
{
        register union VALUETYPE *p = (union VALUETYPE *)(s+m->offset);
        char *pp, *rt;

        /* correct byte order dependancies */
        switch (m->type) {
        case BESHORT:
                p->h = (short)((p->hs[0]<<8)|(p->hs[1]));
                break;
        case BELONG:
        case BEDATE:
                p->l = (long)
                    ((p->hl[0]<<24)|(p->hl[1]<<16)|(p->hl[2]<<8)|(p->hl[3]));
                break;
        case LESHORT:
                p->h = (short)((p->hs[1]<<8)|(p->hs[0]));
                break;
        case LELONG:
        case LEDATE:
                p->l = (long)
                    ((p->hl[3]<<24)|(p->hl[2]<<16)|(p->hl[1]<<8)|(p->hl[0]));
                break;
        }

        switch (m->type) {
        case BYTE:
                (void) printf(m->desc,
                              (m->reln & MASK) ? p->b & m->mask : p->b);
                break;
        case SHORT:
        case BESHORT:
        case LESHORT:
                (void) printf(m->desc,
                              (m->reln & MASK) ? p->h & m->mask : p->h);
                break;
        case LONG:
        case BELONG:
        case LELONG:
                (void) printf(m->desc,
                              (m->reln & MASK) ? p->l & m->mask : p->l);
                break;
        case STRING:
                if ((rt=strchr(p->s, '\n')) != NULL)
                        *rt = '\0';
                (void) printf(m->desc, p->s);
                if (rt)
                        *rt = '\n';
                break;
        case DATE:
        case BEDATE:
        case LEDATE:
                pp = ctime((time_t*) &p->l);
                if ((rt = strchr(pp, '\n')) != NULL)
                        *rt = '\0';
                (void) printf(m->desc, pp);
                if (rt)
                        *rt = '\n';
                break;
        default:
                error("invalid m->type (%d) in mprint().\n", m->type);
                /*NOTREACHED*/
        }
}

static int
mcheck(s, m)
unsigned char   *s;
struct magic *m;
{
        register union VALUETYPE *p = (union VALUETYPE *)(s+m->offset);
        register long l = m->value.l;
        register long mask = m->mask;
        register long v;

        if (debug) {
                (void) printf("mcheck: %10.10s ", s);
                mdump(m);
        }

        if ( (m->value.s[0] == 'x') && (m->value.s[1] == '\0') ) {
                printf("BOINK");
                return 1;
        }

        switch (m->type) {
        case BYTE:
                v = p->b; break;
        case SHORT:
                v = p->h; break;
        case LONG:
        case DATE:
                v = p->l; break;
        case STRING:
                l = 0;
                /* What we want here is:
                 * v = strncmp(m->value.s, p->s, m->vallen);
                 * but ignoring any nulls.  bcmp doesn't give -/+/0
                 * and isn't universally available anyway.
                 */
                v = 0;
                {
                        register unsigned char *a = (unsigned char*)m->value.s;
                        register unsigned char *b = (unsigned char*)p->s;
                        register int len = m->vallen;

                        while (--len >= 0)
                                if ((v = *b++ - *a++) != 0)
                                        break;
                }
                break;
        case BESHORT:
                v = (short)((p->hs[0]<<8)|(p->hs[1]));
                break;
        case BELONG:
        case BEDATE:
                v = (long)
                    ((p->hl[0]<<24)|(p->hl[1]<<16)|(p->hl[2]<<8)|(p->hl[3]));
                break;
        case LESHORT:
                v = (short)((p->hs[1]<<8)|(p->hs[0]));
                break;
        case LELONG:
        case LEDATE:
                v = (long)
                    ((p->hl[3]<<24)|(p->hl[2]<<16)|(p->hl[1]<<8)|(p->hl[0]));
                break;
        default:
                error("invalid type %d in mcheck().\n", m->type);
                return -1;/*NOTREACHED*/
        }

        if (m->mask != 0L)
                v &= m->mask;

        switch (m->reln) {
        case 'x':
                return 1;
        case '!':
                return v != l;
        case '=':
                return v == l;
        case '>':
                return v > l;
        case '<':
                return v < l;
        case '&':
                return (v & l) == l;
        case '^':
                return (v & l) != l;
        case MASK | '=':
                return (v & mask) == l;
        case MASK | '>':
                return (v & mask) > l;
        case MASK | '<':
                return (v & mask) < l;
        default:
                error("mcheck: can't happen: invalid relation %d.\n", m->reln);
                return -1;/*NOTREACHED*/
        }
}