From 9a9f6e147cb5489faeb3ea220ab08cf81be7b72c Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Wed, 14 Sep 2022 16:16:08 +0100
Subject: [PATCH] Make fast-retry more configurable and do exponential backoff.

---
 man/dnsmasq.8 |  9 ++++++---
 src/config.h  |  1 +
 src/dnsmasq.h |  3 ++-
 src/forward.c | 15 +++++++++------
 src/option.c  | 30 ++++++++++++++++++++++--------
 5 files changed, 40 insertions(+), 18 deletions(-)

diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index 11640a7..3ae3000 100644
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -105,11 +105,14 @@ Dnsmasq limits the value of this option to one hour, unless recompiled.
 .B --auth-ttl=<time>
 Set the TTL value returned in answers from the authoritative server.
 .TP
-.B --fast-dns-retry=<time in ms>
+.B --fast-dns-retry=[<initial retry delay in ms>[,<time to continue retries in ms>]]
 Under normal circumstances, dnsmasq relies on DNS clients to do retries; it
 does not generate timeouts itself. Setting this option
-instructs dnsmasq to generate its own retries after the specified time, which
-must be greater than 500ms. Using this option increases memory usage and
+instructs dnsmasq to generate its own retries starting after a delay
+which defaults to 1000ms. If the second parameter is given this controls
+how long the retries will continue for
+otherwise this defaults to 10000ms. Retries are repeated with exponential
+backoff. Using this option increases memory usage and
 network bandwidth.
 .TP
 .B \-k, --keep-in-foreground
diff --git a/src/config.h b/src/config.h
index 5746c0b..df1d985 100644
--- a/src/config.h
+++ b/src/config.h
@@ -59,6 +59,7 @@
 #define SOA_EXPIRY 1209600 /* SOA expiry default */
 #define LOOP_TEST_DOMAIN "test" /* domain for loop testing, "test" is reserved by RFC 2606 and won't therefore clash */
 #define LOOP_TEST_TYPE T_TXT
+#define DEFAULT_FAST_RETRY 1000 /* ms, default delay before fast retry */
  
 /* compile-time options: uncomment below to enable or do eg.
    make COPTS=-DHAVE_BROKEN_RTC
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 6f02368..d86df10 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -758,6 +758,7 @@ struct frec {
   int forwardall, flags;
   time_t time;
   u32 forward_timestamp;
+  int forward_delay;
   unsigned char *hash[HASH_SIZE];
   struct blockdata *stash; /* Saved reply, whilst we validate */
   size_t stash_len;
@@ -1187,7 +1188,7 @@ extern struct daemon {
   int dump_mask;
   unsigned long soa_sn, soa_refresh, soa_retry, soa_expiry;
   u32 metrics[__METRIC_MAX];
-  int fast_retry_time;
+  int fast_retry_time, fast_retry_timeout;
 #ifdef HAVE_DNSSEC
   struct ds_config *ds;
   char *timestamp_file;
diff --git a/src/forward.c b/src/forward.c
index 7d85cf7..4e127ba 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -608,7 +608,7 @@ int fast_retry(time_t now)
       u32 millis = dnsmasq_milliseconds();
       
       for (f = daemon->frec_list; f; f = f->next)
-	if (f->sentto && f->stash && difftime(now, f->time) < TIMEOUT)
+	if (f->sentto && f->stash && difftime(now, f->time) < daemon->fast_retry_timeout)
 	  {
 #ifdef HAVE_DNSSEC
 	    if (f->blocking_query)
@@ -617,8 +617,8 @@ int fast_retry(time_t now)
 	    /* t is milliseconds since last query sent. */ 
 	    int to_run, t = (int)(millis - f->forward_timestamp);
 	    
-	    if (t < daemon->fast_retry_time)
-	      to_run = daemon->fast_retry_time - t;
+	    if (t < f->forward_delay)
+	      to_run = f->forward_delay - t;
 	    else
 	      {
 		unsigned char *udpsz;
@@ -639,7 +639,7 @@ int fast_retry(time_t now)
 		forward_query(-1, NULL, NULL, 0, header, f->stash_len, ((char *) header) + udp_size, now, f,
 			      f->flags & FREC_AD_QUESTION, f->flags & FREC_DO_QUESTION);
 
-		to_run = daemon->fast_retry_time;
+		to_run = f->forward_delay = 2 * f->forward_delay;
 	      }
 
 	    if (ret == -1 || ret > to_run)
@@ -2822,8 +2822,11 @@ static struct frec *get_new_frec(time_t now, struct server *master, int force)
     }
 
   if (target)
-    target->time = now;
-
+    {
+      target->time = now;
+      target->forward_delay = daemon->fast_retry_time;
+    }
+  
   return target;
 }
 
diff --git a/src/option.c b/src/option.c
index aaecebe..f2110cf 100644
--- a/src/option.c
+++ b/src/option.c
@@ -370,7 +370,7 @@ static const struct myoption opts[] =
     { "umbrella", 2, 0, LOPT_UMBRELLA },
     { "quiet-tftp", 0, 0, LOPT_QUIET_TFTP },
     { "port-limit", 1, 0, LOPT_RANDPORT_LIM },
-    { "fast-dns-retry", 1, 0, LOPT_FAST_RETRY },
+    { "fast-dns-retry", 2, 0, LOPT_FAST_RETRY },
     { "use-stale-cache", 0, 0 , LOPT_STALE_CACHE },
     { NULL, 0, 0, 0 }
   };
@@ -3230,14 +3230,28 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
       }
 
     case LOPT_FAST_RETRY:
-      {
-	int retry;
-      	if (!atoi_check(arg, &retry) || retry < 500)
-	  ret_err(gen_err);
-	daemon->fast_retry_time = retry;
-	break;
-      }
+      daemon->fast_retry_timeout = TIMEOUT;
       
+      if (!arg)
+	daemon->fast_retry_time = DEFAULT_FAST_RETRY;
+      else
+	{
+	  int retry;
+	  
+	  comma = split(arg);
+	  if (!atoi_check(arg, &retry) || retry < 50)
+	    ret_err(gen_err);
+	  daemon->fast_retry_time = retry;
+	  
+	  if (comma)
+	    {
+	      if (!atoi_check(comma, &retry))
+		ret_err(gen_err);
+	      daemon->fast_retry_timeout = retry/1000;
+	    }
+	}
+      break;
+            
 #ifdef HAVE_DHCP
     case 'X': /* --dhcp-lease-max */
       if (!atoi_check(arg, &daemon->dhcp_max))