Compressed Batching w/Restricted uux

[Brian Yost]

Recently, I ported the USENET software to my system, an Altos 586
running XENIX 3.0.  One of the problems I ran into was with
compressed batching.  The problem is that my particular version
of ``uux'' will allow the following commands to be executed, and
no others:

		rnews	rmail	uusend	uucp

I get the impression that many other sites may have a similarly
restricted version of ``uux,'' so I am posting my solution.

As distributed, compressed batching requires that ``uux'' run
``cunbatch'' to decompress the batched files.  One solution would be
to bypass ``cunbatch'' and replace ``rnews'' with a shell script to
decompress and then call the real ``rnews.''  However, in order to be
capable of receiving unbatched news, batched news, and compressed batched
news, I decided to go into the source for ``rnews'' and have it take
care of decompression.

The idea is straightforward.  First, ``rnews'' must check for the magic
number used by the ``compress'' program (version 4.0).  If this magic
number is seen, then fork/exec ``compress'' with a temp file as its
standard output.  Once this child process has terminated, reopen the
temp file as the standard input to ``rnews,'' and continue as usual.

The routine ``checkbatch'' in the source file ifuncs.c reads the first
character of its input, to see if it is a '#' which indicates batching.
The test for the magic number must be inserted just before the test for
'#'.  If the magic number is seen, the new function ``uncompress'' is
called, which takes care of fork/exec'ing ``compress'' and redirecting
the i/o.

Please note that I have made an effort to limit my modifications to a
single source file.

The first group of additional lines comes right before the test
	if (c == '#')
in the function checkbatch() of ifuncs.c:

743a744,757
> 	/* Brian Yost	11/17/85	infopro!bty!yost
> 	 * Check for the compress(1) program's magic number,
> 	 * 037 235.  If found, uncompress the data before checking
> 	 * for batching.
> 	 */
> 	if (c == '\037') {	/* magic number for compress(1) */
> 		reset_stdin();
> 		uncompress();
> 		c = getc(stdin);
> 		if (c != EOF)
> 			ungetc(c, stdin);
> 		clearerr(stdin);
> 	}
> 	/* no else-if here! */

Note that I've only checked for the first byte of the magic number.
The second addition is the function uncompress(), which I chose to
place right after checkbatch() to keep the modifications localized
as much as possible:

751a766,794
> }
> 
> /* Brian Yost	11/17/85	infopro!bty!yost
>  * pipe stdin through compress(1) into a temporary file, and
>  * then redirect the standard input of rnews from this file.
>  */
> uncompress()
> {
> 	int wait_pid, child_pid, exit_status;
> 	char *tmp_file;
> 
> 	tmp_file = "/tmp/inewsXXXXXX";
> 	mktemp(tmp_file);
> 	if ((child_pid = fork()) == 0) {
> 		char uncompress[BUFLEN];
> 
> 		sprintf(uncompress, "%s/compress", BIN);
> 		/* redirect standard output to tmp_file */
> 		(void) freopen(tmp_file, "w", stdout);
> 		execl(uncompress, "compress", "-d", (char *)0);
> 		xerror("Unable to exec shell to uncompress news.");
> 	}
> 	while ((wait_pid = wait(&exit_status)) != child_pid)
> 		if (wait_pid == -1)
> 			break;
> 
> 	/* now redirect standard input from tmp_file */
> 	(void) freopen(tmp_file, "r", stdin);
> 	(void) unlink(tmp_file);	/* will disappear once closed */

I hope these changes will be of some help to sites with picky ``uux''
programs.  If any errors or omissions are found in the above code, kindly
forward the fixes to me.  Thanks in advance.

Brian Yost
infopro!bty!yost