From 213e724e1b202f113b8cbc07a3b0323ed0740043 Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Sat, 22 Jun 2019 20:03:17 +0200
Subject: [PATCH] Add retries to all DNS calls

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 iana.go    | 13 ++++++++++---
 opennic.go | 34 +++++++++++++++++++++++++---------
 retry.go   | 26 ++++++++++++++++++++++++++
 3 files changed, 61 insertions(+), 12 deletions(-)
 create mode 100644 retry.go

diff --git a/iana.go b/iana.go
index ddad1de..b0b0cf1 100644
--- a/iana.go
+++ b/iana.go
@@ -42,9 +42,16 @@ func getIANAZoneMasters(tld string) ([]string, error) {
 	m := new(dns.Msg)
 	m.SetQuestion(tld, dns.TypeNS)
 
-	r, _, err := c.Exchange(m, getRandomInternicRoot())
-	if err != nil {
-		return nil, errors.Wrap(err, "Could not query nameservers")
+	var (
+		err error
+		r   *dns.Msg
+	)
+
+	if err = retry(func() error {
+		r, _, err = c.Exchange(m, getRandomInternicRoot())
+		return errors.Wrap(err, "Could not query nameservers")
+	}); err != nil {
+		return nil, err
 	}
 
 	if r.Rcode != dns.RcodeSuccess {
diff --git a/opennic.go b/opennic.go
index eccccb0..11b3766 100644
--- a/opennic.go
+++ b/opennic.go
@@ -13,9 +13,16 @@ func getOpenNICTLDs() ([]string, error) {
 	m := new(dns.Msg)
 	m.SetQuestion("tlds.opennic.glue.", dns.TypeTXT)
 
-	r, _, err := c.Exchange(m, cfg.OpenNICRoot+":53")
-	if err != nil {
-		return nil, errors.Wrap(err, "Could not query nameservers")
+	var (
+		err error
+		r   *dns.Msg
+	)
+
+	if err = retry(func() error {
+		r, _, err = c.Exchange(m, cfg.OpenNICRoot+":53")
+		return errors.Wrap(err, "Could not query nameservers")
+	}); err != nil {
+		return nil, err
 	}
 
 	if r.Rcode != dns.RcodeSuccess {
@@ -42,9 +49,16 @@ func getOpenNICZoneMasters(tld string) ([]string, error) {
 	m := new(dns.Msg)
 	m.SetQuestion(tld+"opennic.glue.", dns.TypeCNAME)
 
-	r, _, err := c.Exchange(m, cfg.OpenNICRoot+":53")
-	if err != nil {
-		return nil, errors.Wrap(err, "Could not query nameservers")
+	var (
+		err error
+		r   *dns.Msg
+	)
+
+	if err = retry(func() error {
+		r, _, err = c.Exchange(m, cfg.OpenNICRoot+":53")
+		return errors.Wrap(err, "Could not query nameservers")
+	}); err != nil {
+		return nil, err
 	}
 
 	if r.Rcode != dns.RcodeSuccess {
@@ -65,9 +79,11 @@ func getOpenNICZoneMasters(tld string) ([]string, error) {
 		m = new(dns.Msg)
 		m.SetQuestion(master, dns.TypeA)
 
-		r, _, err := c.Exchange(m, cfg.OpenNICRoot+":53")
-		if err != nil {
-			return nil, errors.Wrap(err, "Could not query nameservers")
+		if err = retry(func() error {
+			r, _, err = c.Exchange(m, cfg.OpenNICRoot+":53")
+			return errors.Wrap(err, "Could not query nameservers")
+		}); err != nil {
+			return nil, err
 		}
 
 		if r.Rcode != dns.RcodeSuccess {
diff --git a/retry.go b/retry.go
new file mode 100644
index 0000000..384f2a9
--- /dev/null
+++ b/retry.go
@@ -0,0 +1,26 @@
+package main
+
+import (
+	"math"
+	"time"
+)
+
+const (
+	maxRetries = 5
+	retryDelay = 1.2
+)
+
+func retry(f func() error) error {
+	var err error
+
+	for i := 1; i <= maxRetries; i++ {
+		if err = f(); err == nil {
+			return nil
+		}
+
+		sleep := time.Duration(math.Pow(retryDelay, float64(i)) * float64(time.Second))
+		time.Sleep(sleep)
+	}
+
+	return err
+}