From 3a2c865ff6acf9a71cfd1ec127b6cbdf225498fb Mon Sep 17 00:00:00 2001
From: Wim <wim@42.be>
Date: Tue, 18 Feb 2020 17:09:11 +0100
Subject: [PATCH] Fix high cpu usage with IPv6 recursor address. Closes #6120
 (#6128)

---
 agent/dns.go      | 13 ++++++++++---
 agent/dns_test.go | 15 +++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/agent/dns.go b/agent/dns.go
index 73ae8e7c5d..e44a6fda96 100644
--- a/agent/dns.go
+++ b/agent/dns.go
@@ -274,9 +274,16 @@ func recursorAddr(recursor string) (string, error) {
 	// Add the port if none
 START:
 	_, _, err := net.SplitHostPort(recursor)
-	if ae, ok := err.(*net.AddrError); ok && ae.Err == "missing port in address" {
-		recursor = ipaddr.FormatAddressPort(recursor, 53)
-		goto START
+	if ae, ok := err.(*net.AddrError); ok {
+		if ae.Err == "missing port in address" {
+			recursor = ipaddr.FormatAddressPort(recursor, 53)
+			goto START
+		} else if ae.Err == "too many colons in address" {
+			if ip := net.ParseIP(recursor); ip != nil && ip.To4() == nil {
+				recursor = ipaddr.FormatAddressPort(recursor, 53)
+				goto START
+			}
+		}
 	}
 	if err != nil {
 		return "", err
diff --git a/agent/dns_test.go b/agent/dns_test.go
index c04e53fa23..57d420af2d 100644
--- a/agent/dns_test.go
+++ b/agent/dns_test.go
@@ -109,6 +109,21 @@ func TestRecursorAddr(t *testing.T) {
 	if addr != "8.8.8.8:53" {
 		t.Fatalf("bad: %v", addr)
 	}
+	addr, err = recursorAddr("2001:4860:4860::8888")
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if addr != "[2001:4860:4860::8888]:53" {
+		t.Fatalf("bad: %v", addr)
+	}
+	addr, err = recursorAddr("1.2.3.4::53")
+	if err == nil || !strings.Contains(err.Error(), "too many colons in address") {
+		t.Fatalf("err: %v", err)
+	}
+	addr, err = recursorAddr("2001:4860:4860::8888:::53")
+	if err == nil || !strings.Contains(err.Error(), "too many colons in address") {
+		t.Fatalf("err: %v", err)
+	}
 }
 
 func TestEncodeKVasRFC1464(t *testing.T) {