From 2cd60c7e775b481332703d9674f02c68ab3b3e91 Mon Sep 17 00:00:00 2001
From: Sergey Poznyakoff <gray@gnu.org.ua>
Date: Thu, 5 Mar 2020 09:10:32 +0200
Subject: Attempt better diagnosis of duplicate replies

* src/ping903.h (hostping): New member nreply - an array counting
replies for each echo request.
* src/pinger.c (hostping_create): Allocate nreply array.
(seqidx): Remove "replied", introduce "ping_num" instead.  Ping_num
is the ordinal number of the echo request that was assigned this
sequence number.  It is used to address the host->nreply array.
(seqno_alloc): Initialize ping_num to the number of transmitted
echos (i.e. next ordinal number).
(hostping_from_seqno): Diagnose all possible (and impossible)
variants of duplicate and unsolicited replies.
---
 src/ping903.h |  1 +
 src/pinger.c  | 34 ++++++++++++++++++++++++++--------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/src/ping903.h b/src/ping903.h
index ccf62b7..3e88c17 100644
--- a/src/ping903.h
+++ b/src/ping903.h
@@ -142,6 +142,7 @@ typedef struct hostping {
 	struct host_stat stat_last;
 
 	struct hostping *prev, *next;
+	int nreply[1];
 } HOSTPING;
 
 extern int verbose;
diff --git a/src/pinger.c b/src/pinger.c
index 2291a48..65e8e6a 100644
--- a/src/pinger.c
+++ b/src/pinger.c
@@ -114,10 +114,14 @@ hostping_free(HOSTPING *hp)
 static HOSTPING *
 hostping_create(char const *name, struct sockaddr *addr, socklen_t addrlen)
 {
-	HOSTPING *hp = malloc(sizeof(*hp));
+	HOSTPING *hp;
+	size_t hostsize = sizeof(*hp) +
+		           (ping_count - 1) * sizeof(hp->nreply[0]);
+
+	hp = malloc(hostsize);
 
 	if (hp) {
-		memset(hp, 0, sizeof(*hp));
+		memset(hp, 0, hostsize);
 		hp->tmin = HOSTPING_TMIN_INIT;
 		hp->name = strdup(name);
 		if (!hp)
@@ -306,6 +310,7 @@ hostping_reset(HOSTPING *host)
 	host->tmax = 0;
 	host->tsum = 0;
 	host->tsumsq = 0;
+	memset(host->nreply, 0, ping_count * sizeof(host->nreply[0]));
 	switch (host->stat_last.status) {
 	case HOST_STAT_INIT:
 		break;
@@ -942,7 +947,7 @@ enum {
 struct seqidx {
 	HOSTPING *host;
 	struct timeval tv;
-	int replied;
+	int ping_num;
 };
 
 static struct seqidx *seqidx;
@@ -958,7 +963,7 @@ seqno_alloc(HOSTPING *host, struct timeval *tv)
 		if (tv->tv_sec - seqidx[n].tv.tv_sec > MAX_PING_TIMEOUT) {
 			memcpy(&seqidx[n].tv, tv, sizeof(*tv));
 			seqidx[n].host = host;
-			seqidx[n].replied = 0;
+			seqidx[n].ping_num = host->xmit_count;
 			next_seqno = (n + 1) % MOD_SEQNO;
 			return n;
 		}
@@ -976,13 +981,26 @@ hostping_from_seqno(int seq)
 	pthread_mutex_lock(&seqno_mutex);
 	host = seqidx[seq].host;
 	if (host) {
+		int n;
+		
 		hostping_lock(host);
-		if (seqidx[seq].replied) {
-			host->dup_count++;
-			info("%s:%d: DUP!", host->name, seq);
+		n = seqidx[seq].ping_num;
+		if (n >= 0 && n < ping_count) {
+			if (++host->nreply[n] > 1) {
+				host->dup_count++;
+				info("%s: duplicate reply for echo #%d, seqno %d",
+				     host->name, n, seq);
+				host = NULL;
+			} else if (host->recv_count == host->xmit_count) {
+				error("%s: unexpected reply #%d, seqno %d",
+				      host->name, n, seq);
+				host = NULL;
+			}
+		} else {
+			error("%s: duplicate reply for unregistered echo #%d, seqno %d",
+			      host->name, n, seq);
 			host = NULL;
 		}
-		seqidx[seq].replied++;
 	} else
 		fatal("no host found for sequence number %d", seq);
 	pthread_mutex_unlock(&seqno_mutex);
-- 
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