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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 =
      "@(#)$Id: ascmagic.c,v 1.3.2.1 1996/12/20 22:28:54 joerg 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, has_escapes = 0;
      unsigned char *s;
      char nbuf[HOWMANY+1];   /* one extra for terminating '\0' */
      char *token;
      register struct names *p;

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

      /*
       * 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[1] == '"'))) {
                  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;
      }


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

      /* 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, nbytes);
      s[nbytes] = '\0';
      has_escapes = (memchr(s, '\033', nbytes) != 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;
                  }
            }
      }

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



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