From c7e5424e7cfb27c83630b402731b49761eba6e36 Mon Sep 17 00:00:00 2001
From: Michael Wolf <wolfmd@nullbrook.org>
Date: Wed, 5 Aug 2026 21:10:34 -0700
Subject: [PATCH] Support IPv6 service endpoints in trace plugin (#8410)

Use net.JoinHostPort rather than string concatenation to support
both ipv4, ipv6, and hostname service endpoints for the trace
plugin. Previously, ipv6 bind addresses in the coredns configuration
would fail to be parsed, as the ipv6 address was not surrounded in
brackets.

Signed-off-by: Michael Wolf <mwolf@cloudflare.com>

Closes #8409

Co-authored-by: Michael Wolf <mwolf@cloudflare.com>
---
 plugin/trace/setup.go      |  3 ++-
 plugin/trace/setup_test.go | 54 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/plugin/trace/setup.go b/plugin/trace/setup.go
index c5fb04aa5..c3b07ebb9 100644
--- a/plugin/trace/setup.go
+++ b/plugin/trace/setup.go
@@ -2,6 +2,7 @@ package trace
 
 import (
 	"fmt"
+	"net"
 	"strconv"
 	"strings"
 	"time"
@@ -38,7 +39,7 @@ func traceParse(c *caddy.Controller) (*trace, error) {
 
 	cfg := dnsserver.GetConfig(c)
 	if len(cfg.ListenHosts) > 0 && cfg.ListenHosts[0] != "" {
-		tr.serviceEndpoint = cfg.ListenHosts[0] + ":" + cfg.Port
+		tr.serviceEndpoint = net.JoinHostPort(cfg.ListenHosts[0], cfg.Port)
 	}
 
 	for c.Next() { // trace
diff --git a/plugin/trace/setup_test.go b/plugin/trace/setup_test.go
index 19f2d9acb..cfe444a4c 100644
--- a/plugin/trace/setup_test.go
+++ b/plugin/trace/setup_test.go
@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/coredns/caddy"
+	"github.com/coredns/coredns/core/dnsserver"
 )
 
 func TestTraceParse(t *testing.T) {
@@ -87,3 +88,56 @@ func TestTraceParse(t *testing.T) {
 		}
 	}
 }
+
+func TestParseServiceEndpoint(t *testing.T) {
+	tests := []struct {
+		name                    string
+		listenHosts             []string
+		port                    string
+		expectedServiceEndpoint string
+	}{
+		{
+			name:                    "IPv4 address",
+			listenHosts:             []string{"127.0.0.1"},
+			port:                    "8053",
+			expectedServiceEndpoint: "127.0.0.1:8053",
+		},
+		{
+			name:                    "IPv6 address",
+			listenHosts:             []string{"3d47:98c0:b113::3"},
+			port:                    "8853",
+			expectedServiceEndpoint: "[3d47:98c0:b113::3]:8853",
+		},
+		{
+			name:                    "Hostname",
+			listenHosts:             []string{"localhost"},
+			port:                    "8053",
+			expectedServiceEndpoint: "localhost:8053",
+		},
+		{
+			name:                    "Multiple addresses",
+			listenHosts:             []string{"3d47:98c0:b113::3", "127.0.0.1"},
+			port:                    "8853",
+			expectedServiceEndpoint: "[3d47:98c0:b113::3]:8853",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			c := caddy.NewTestController("dns", "trace")
+			cfg := dnsserver.GetConfig(c)
+			cfg.ListenHosts = tc.listenHosts
+			cfg.Port = tc.port
+
+			tr, err := traceParse(c)
+			if err != nil {
+				t.Errorf("Error parsing test input: %s", err)
+				return
+			}
+
+			if tr.serviceEndpoint != tc.expectedServiceEndpoint {
+				t.Errorf("Expected serviceEndpoint %s, got %s", tc.expectedServiceEndpoint, tr.serviceEndpoint)
+			}
+		})
+	}
+}