Compute the local clock offset from the server's response.

ok henning@

src/usr.sbin/ntpd/Makefile

@@ -1,10 +1,10 @@
-#	$OpenBSD: Makefile,v 1.6 2004/06/18 04:48:12 henning Exp $
+#	$OpenBSD: Makefile,v 1.7 2004/07/04 11:01:49 alexander Exp $
 
 .PATH:		${.CURDIR}/..
 
 PROG=	ntpd
 SRCS=	ntpd.c buffer.c log.c imsg.c ntp.c ntp_msg.c parse.y config.c \
-	server.c client.c
+	server.c client.c util.c
 CFLAGS+= -Wall -I${.CURDIR}
 CFLAGS+= -Wstrict-prototypes -Wmissing-prototypes
 CFLAGS+= -Wmissing-declarations

src/usr.sbin/ntpd/client.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: client.c,v 1.2 2004/07/03 21:11:29 alexander Exp $ */
+/*	$OpenBSD: client.c,v 1.3 2004/07/04 11:01:49 alexander Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -80,7 +80,7 @@ client_query(struct ntp_peer *p)
 
 	p->query->msg.xmttime.int_part = arc4random();
 	p->query->msg.xmttime.fraction = arc4random();
-	get_ts(&p->query->xmttime);
+	p->query->xmttime = gettime();
 
 	ntp_sendmsg(p->query->fd, (struct sockaddr *)&p->ss, &p->query->msg,
 	    NTP_MSGSIZE_NOAUTH, 0);
@@ -99,13 +99,16 @@ client_dispatch(struct ntp_peer *p)
 	char			 buf[NTP_MSGSIZE];
 	ssize_t			 size;
 	struct ntp_msg		 msg;
-	struct l_fixedpt	 rtt, t;
+	double			 T1, T2, T3, T4;
+	double			 offset, error;
 
 	fsa_len = sizeof(fsa);
 	if ((size = recvfrom(p->query->fd, &buf, sizeof(buf), 0,
 	    (struct sockaddr *)&fsa, &fsa_len)) == -1)
 		fatal("recvfrom");
 
+	T4 = gettime();
+
 	ntp_getmsg(buf, size, &msg);
 
 	if (msg.orgtime.int_part != p->query->msg.xmttime.int_part ||
@@ -114,16 +117,35 @@ client_dispatch(struct ntp_peer *p)
 		return (0);
 	}
 
-log_debug("reply received");
+	/* 
+	 * From RFC 2030:
+	 *
+	 *      Timestamp Name          ID   When Generated
+	 *     ------------------------------------------------------------
+	 *     Originate Timestamp     T1   time request sent by client
+	 *     Receive Timestamp       T2   time request received by server
+	 *     Transmit Timestamp      T3   time reply sent by server
+	 *     Destination Timestamp   T4   time reply received by client
+	 *
+	 *  The roundtrip delay d and local clock offset t are defined as
+	 *
+	 *    d = (T4 - T1) - (T2 - T3)     t = ((T2 - T1) + (T3 - T4)) / 2.
+	 */
+
+	T1 = p->query->xmttime;
+	T2 = lfp_to_d(msg.rectime);
+	T3 = lfp_to_d(msg.xmttime);
 
-	/* XXX parse */
-	get_ts(&t);
-	rtt.int_part = (t.int_part - p->query->xmttime.int_part) -
-	    (msg.rectime.int_part - msg.xmttime.int_part);
+	offset = ((T2 - T1) + (T3 - T4)) / 2;
+	error = (T2 - T1) - (T3 - T4);
 
 	p->state = STATE_REPLY_RECEIVED;
 	p->next = time(NULL) + QUERY_INTERVAL;
 	p->deadline = 0;
+	p->offset = offset;
+	p->error = error;
+
+	log_debug("reply received: offset %f error %f", offset, error);
 
 	return (0);
 }

src/usr.sbin/ntpd/ntp.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntp.h,v 1.5 2004/06/17 19:17:48 henning Exp $ */
+/*	$OpenBSD: ntp.h,v 1.6 2004/07/04 11:01:49 alexander Exp $ */
 
 /*
  * Copyright (c) 2004 Henning Brauer <henning@openbsd.org>
@@ -112,7 +112,7 @@ struct ntp_msg {
 struct ntp_query {
 	int			fd;
 	struct ntp_msg		msg;
-	struct l_fixedpt	xmttime;
+	double			xmttime;
 };
 
 /*

src/usr.sbin/ntpd/ntpd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntpd.h,v 1.7 2004/06/18 04:51:31 henning Exp $ */
+/*	$OpenBSD: ntpd.h,v 1.8 2004/07/04 11:01:49 alexander Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -55,6 +55,8 @@ struct ntp_peer {
 	enum client_state		 state;
 	time_t				 next;
 	time_t				 deadline;
+	double				 offset;
+	double				 error;
 };
 
 struct ntpd_conf {
@@ -168,3 +170,8 @@ int	ntp_reply(int, struct sockaddr *, struct ntp_msg *, int);
 int	client_peer_init(struct ntp_peer *);
 int	client_query(struct ntp_peer *);
 int	client_dispatch(struct ntp_peer *);
+
+/* util.c */
+double	gettime(void);
+double	lfp_to_d(struct l_fixedpt);
+struct	l_fixedpt d_to_lfp(double);

src/usr.sbin/ntpd/util.c

@@ -0,0 +1,59 @@
+/*	$OpenBSD: util.c,v 1.1 2004/07/04 11:01:49 alexander Exp $ */
+
+/*
+ * Copyright (c) 2004 Alexander Guy <alexander.guy@andern.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/time.h>
+
+#include "ntpd.h"
+
+double
+gettime(void)
+{
+	struct timeval tv;
+	double ret;
+
+	if (gettimeofday(&tv, NULL) == -1)
+		fatal("gettimeofday");
+
+	ret = tv.tv_sec + JAN_1970 + 1.0e-6 * tv.tv_usec;
+
+	return (ret);
+}
+
+double
+lfp_to_d(struct l_fixedpt lfp)
+{
+	double ret;
+
+	lfp.int_part = ntohl(lfp.int_part);
+	lfp.fraction = ntohl(lfp.fraction);
+
+	ret = (double)(lfp.int_part) + ((double)lfp.fraction / UINT_MAX);
+
+	return (ret);
+}
+
+struct l_fixedpt
+d_to_lfp(double d)
+{
+	struct l_fixedpt lfp;
+	
+	lfp.int_part = htonl(d);
+	lfp.fraction = htonl((d - lfp.int_part) * UINT_MAX);
+
+	return (lfp);
+}