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compress.c

/*
 * compress routines:
 *    zmagic() - returns 0 if not recognized, uncompresses and prints
 *             information if recognized
 *    uncompress(method, old, n, newch) - uncompress old into new,
 *                                using method, return sizeof new
 * $Id: compress.c,v 1.3 1996/01/23 12:40:08 mpp Exp $
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>

#include "file.h"

static struct {
   char *magic;
   int   maglen;
   char *argv[3];
   int       silent;
} compr[] = {
    { "\037\235", 2, { "uncompress", "-c", NULL }, 0 },     /* compressed */
    { "\037\213", 2, { "gzip", "-cdq", NULL }, 1 },   /* gzipped */
    { "\037\236", 2, { "gzip", "-cdq", NULL }, 1 },   /* frozen */
    { "\037\240", 2, { "gzip", "-cdq", NULL }, 1 },   /* SCO LZH */
    /* the standard pack utilities do not accept standard input */
    { "\037\036", 2, { "gzip", "-cdq", NULL }, 0 },   /* packed */
};

static int ncompr = sizeof(compr) / sizeof(compr[0]);


static int uncompress __P((int, const unsigned char *, unsigned char **, int));

int
zmagic(buf, nbytes)
unsigned char *buf;
int nbytes;
{
      unsigned char *newbuf;
      int newsize;
      int i;

      for (i = 0; i < ncompr; i++) {
            if (nbytes < compr[i].maglen)
                  continue;
            if (memcmp(buf, compr[i].magic,  compr[i].maglen) == 0)
                  break;
      }

      if (i == ncompr)
            return 0;

      if ((newsize = uncompress(i, buf, &newbuf, nbytes)) != 0) {
            tryit(newbuf, newsize, 1);
            free(newbuf);
            printf(" (");
            tryit(buf, nbytes, 0);
            printf(")");
      }
      return 1;
}


static int
uncompress(method, old, newch, n)
int method;
const unsigned char *old;
unsigned char **newch;
int n;
{
      int fdin[2], fdout[2];

      if (pipe(fdin) == -1 || pipe(fdout) == -1) {
            error("cannot create pipe (%s).\n", strerror(errno));
            /*NOTREACHED*/
      }
      switch (fork()) {
      case 0:     /* child */
            (void) close(0);
            (void) dup(fdin[0]);
            (void) close(fdin[0]);
            (void) close(fdin[1]);

            (void) close(1);
            (void) dup(fdout[1]);
            (void) close(fdout[0]);
            (void) close(fdout[1]);
            if (compr[method].silent)
                (void) close(2);

            execvp(compr[method].argv[0], compr[method].argv);
            error("could not execute `%s' (%s).\n",
                  compr[method].argv[0], strerror(errno));
            /*NOTREACHED*/
      case -1:
            error("could not fork (%s).\n", strerror(errno));
            /*NOTREACHED*/

      default: /* parent */
            (void) close(fdin[0]);
            (void) close(fdout[1]);
            if (write(fdin[1], old, n) != n) {
                  error("write failed (%s).\n", strerror(errno));
                  /*NOTREACHED*/
            }
            (void) close(fdin[1]);
            if ((*newch = (unsigned char *) malloc(n)) == NULL) {
                  error("out of memory.\n");
                  /*NOTREACHED*/
            }
            if ((n = read(fdout[0], *newch, n)) <= 0) {
                  free(*newch);
                  error("read failed (%s).\n", strerror(errno));
                  /*NOTREACHED*/
            }
            (void) close(fdout[0]);
            (void) wait(NULL);
            return n;
      }
}

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