usr.bin/file/ascmagic.c

/*
 * Ascii magic -- file types that we know based on keywords
 * that can appear anywhere in the file.
 *
 * 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 <ctype.h>
#include <stdlib.h>
#include <unistd.h>
#include "file.h"
#include "names.h"

#ifndef lint
static char *moduleid =
        "@(#)ascmagic.c,v 1.2 1993/06/10 00:38:04 jtc Exp";
#endif  /* lint */

                        /* an optimisation over plain strcmp() */
#define STREQ(a, b)     (*(a) == *(b) && strcmp((a), (b)) == 0)

int
ascmagic(buf, nbytes)
unsigned char *buf;
int nbytes;     /* size actually read */
{
        int i, isblock, has_escapes = 0;
        unsigned char *s;
        char nbuf[HOWMANY+1];   /* one extra for terminating '\0' */
        char *token;
        register struct names *p;

        /* these are easy, do them first */

        /*
         * for troff, look for . + letter + letter or .\";
         * this must be done to disambiguate tar archives' ./file
         * and other trash from real troff input.
         */
        if (*buf == '.') {
                unsigned char *tp = buf + 1;

                while (isascii(*tp) && isspace(*tp))
                        ++tp;   /* skip leading whitespace */
                if ((isascii(*tp) && (isalnum(*tp) || *tp=='\\') &&
                    isascii(*(tp+1)) && (isalnum(*(tp+1)) || *tp=='"'))) {
                        ckfputs("troff or preprocessor input text", stdout);
                        return 1;
                }
        }
        if ((*buf == 'c' || *buf == 'C') &&
            isascii(*(buf + 1)) && isspace(*(buf + 1))) {
                ckfputs("fortran program text", stdout);
                return 1;
        }

        /* look for tokens from names.h - this is expensive! */
        /* make a copy of the buffer here because strtok() will destroy it */
        s = (unsigned char*) memcpy(nbuf, buf, HOWMANY);
        has_escapes = (memchr(s, '\033', HOWMANY) != NULL);
        while ((token = strtok((char*)s, " \t\n\r\f")) != NULL) {
                s = NULL;       /* make strtok() keep on tokin' */
                for (p = names; p < names + NNAMES; p++) {
                        if (STREQ(p->name, token)) {
                                ckfputs(types[p->type], stdout);
                                if (has_escapes)
                                        ckfputs(" (with escape sequences)",
                                                stdout);
                                return 1;
                        }
                }
        }

        switch (is_tar(buf)) {
        case 1:
                ckfputs("tar archive", stdout);
                return 1;
        case 2:
                ckfputs("POSIX tar archive", stdout);
                return 1;
        }

        if (i = is_compress(buf, &isblock)) {
                if (zflag) {
                        unsigned char *newbuf;
                        int newsize;

                        if (newsize = uncompress(buf, &newbuf, nbytes)) {
                            tryit(newbuf, newsize);
                            free(newbuf);
                        }
                        printf(" (%scompressed data - %d bits)",
                                isblock ? "block " : "", i);
                }
                else printf("%scompressed data - %d bits",
                        isblock ? "block " : "", i);
                return 1;
        }

        for (i = 0; i < nbytes; i++) {
                if (!isascii(*(buf+i)))
                        return 0;       /* not all ascii */
        }

        /* all else fails, but it is ascii... */
        ckfputs("ascii text", stdout);
        if (has_escapes) {
                ckfputs(" (with escape sequences)", stdout);
        }
        return 1;
}