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From: rsalz@bbn.com (Rich Salz)
Newsgroups: news.software.b
Subject: Re: Ideas for Message-ID's
Message-ID: <3434@litchi.bbn.com>
Date: 22 Mar 91 13:35:43 GMT
References: <3427@litchi.bbn.com>
Organization: BBN Systems and Technology, Inc.
Lines: 129

I got email pointing out that if the PID wraps around in less than 24
hours, and the new process posts within the same second, there will be a
conflict.  Hmm...  I don't think this is likely unless the machine crashes
a lot.  (Maybe it *IS* that likely. :-)

At any rate, here's what I'm going to do now:
	<ddd.sss.ppp@fqdn>
where
	ddd	The day of the year, in radix 64 (not fixed width)
	sss	The second within the day, in radix 64 (not fixed width)
	ppp	The process ID, in radix 64 (not fixed width)
	fqdn	The fully-qualified domain name

Here's some sample code:

/*
**  Test program to generate Message-ID's.
**  The ID includes the day number, the second within the day, and the current
**  process ID.  To conserver space, they are decoded into radix-64 strings,
**  using [0-9a-zA-Z.+] to represent 0..63.  Assumes 32-bit longs.
**
**  Rich $alz <rsalz@bbn.com>, 22-March-1991.
*/
#include <stdio.h>
#include <sys/types.h>
#include <time.h>


static char	ALPHABET[] =
    "+.ZYXWVUTSRQPONMLKJIHGFEDCBAzyxwvutsrqponmlkjihgfedcba9876543210";

extern char	*strchr();


/*
**  Turn a number into a Radix-64 string.
*/
void
Radix64(l, buff)
    register unsigned long	l;
    register char		*buff;
{
    register char		*p;
    register int		i;
    char			temp[20];

    /* Simple sanity checks. */
    l &= 0xFFFFFFFF;
    if (l == 0) {
	*buff++ = '0';
	*buff = '\0';
	return;
    }

    /* Format the string, in reverse. */
    for (p = temp; l; l >>= 6)
	*p++ = ALPHABET[(int)(l & 077)];

    /* Reverse it. */
    for (i = p - temp; --i >= 0; )
	*buff++ = *--p;
    *buff = '\0';
}


/*
**  Decode and print a radix-64 string as a number.
*/
Decode64(what, l, p)
    char	*what;
    long	l;
    char	*p;
{
    long	l2;
    char	*cp;

    printf("%s:  %ld = %s = ", what, l, p);
    for (l2 = 0; *p; p++) {
	if ((cp = strchr(ALPHABET, *p)) == NULL) {
	    printf("-->Invalid char %c\n", *p);
	    return;
	}
	l2 = (l2 << 6) + cp - ALPHABET;
    }
    printf("%ld\n", l2);
}


/*
**  Stub routine to get the fully-qualified domain name of this host.
*/
char *
GetFQDN()
{
    static char buff[256];

    gethostname(buff, sizeof buff);
    return buff;
}


main()
{
    struct tm		*gmt;
    time_t		now;
    char		day64[20];
    char		pid64[20];
    char		sec64[20];
    unsigned long	day;
    unsigned long	sec;
    unsigned long	pid;

    (void)time(&now);
    gmt = gmtime(&now);
    day = gmt->tm_year * 1000L + gmt->tm_yday;
    sec = gmt->tm_hour * 3600L + gmt->tm_min * 60L + gmt->tm_sec;
    pid = getpid();
    Radix64(day, day64);
    Radix64(sec, sec64);
    Radix64(pid, pid64);
    printf("<%s.%s.%s@%s>\n", day64, sec64, pid64, GetFQDN());

    Decode64("day", day, day64);
    Decode64("sec", sec, sec64);
    Decode64("pid", pid, pid64);
}
-- 
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