use adaptive reconnect_interval

Start reconnect attempts in 10s interval and enlarge
the interval by 10s each time until it reaches 100s.

This makes reasonable retry density for both small/large reconnect timeouts.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

cstp.c

@@ -324,15 +324,24 @@ int make_cstp_connection(struct openconnect_info *vpninfo)
 
 static int cstp_reconnect(struct openconnect_info *vpninfo)
 {
-	int retries, nr_retries, ret;
+	int ret;
+	int timeout;
+	int interval;
 
-	nr_retries = vpninfo->reconnect_timeout / vpninfo->reconnect_interval;
+	timeout = vpninfo->reconnect_timeout;
+	interval = vpninfo->reconnect_interval;
 
 	while ((ret = make_cstp_connection(vpninfo))) {
-		retries++;
-		if (retries >= nr_retries)
+		if (timeout <= 0)
 			return ret;
-		sleep(vpninfo->reconnect_interval);
+		vpninfo->progress(vpninfo, PRG_INFO,
+				  "sleep %ds, remain timeout %ds\n",
+				  interval, timeout);
+		sleep(interval);
+		timeout -= interval;
+		interval += vpninfo->reconnect_interval;
+		if (interval > RECONNECT_INTERVAL_MAX)
+			interval = RECONNECT_INTERVAL_MAX;
 	}
 	return 0;
 }

main.c

@@ -157,7 +157,7 @@ int main(int argc, char **argv)
 	vpninfo->deflate = 1;
 	vpninfo->dtls_attempt_period = 60;
 	vpninfo->max_qlen = 10;
-	vpninfo->reconnect_interval = 20;
+	vpninfo->reconnect_interval = RECONNECT_INTERVAL_MIN;
 	vpninfo->reconnect_timeout = 300;
 
 	if (RAND_bytes(vpninfo->dtls_secret, sizeof(vpninfo->dtls_secret)) != 1) {

openconnect.h

@@ -69,6 +69,9 @@ struct split_include {
 	struct split_include *next;
 };
 
+#define RECONNECT_INTERVAL_MIN	10
+#define RECONNECT_INTERVAL_MAX	100
+
 struct openconnect_info {
 	char *redirect_url;