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

@@ -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

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)
+			}
+		})
+	}
+}