fix(local): handle names under .localhost. (#8151)

plugin/local/setup_test.go

@@ -1,10 +1,14 @@
 package local
 
 import (
+	"context"
 	"testing"
 
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/miekg/dns"
 )
 
 func TestSetup(t *testing.T) {
@@ -32,3 +36,37 @@ func TestSetupRejectsBlockOptions(t *testing.T) {
 		t.Fatal("expected error for unexpected block option, got nil")
 	}
 }
+
+func TestSetupLocalhostPrefixOption(t *testing.T) {
+	c := caddy.NewTestController("dns", `local {
+		localhost_prefix off
+	}`)
+	if err := setup(c); err != nil {
+		t.Fatalf("expected no errors, but got: %v", err)
+	}
+
+	cfg := dnsserver.GetConfig(c)
+	if len(cfg.Plugin) != 1 {
+		t.Fatalf("expected 1 plugin, got %d", len(cfg.Plugin))
+	}
+
+	handler := cfg.Plugin[0](plugin.HandlerFunc(func(context.Context, dns.ResponseWriter, *dns.Msg) (int, error) {
+		return 0, nil
+	}))
+	l, ok := handler.(Local)
+	if !ok {
+		t.Fatalf("expected Local handler, got %T", handler)
+	}
+	if !l.disableLocalhostPrefix {
+		t.Fatal("expected localhost_prefix off to disable legacy localhost prefix handling")
+	}
+}
+
+func TestSetupRejectsInvalidLocalhostPrefixValue(t *testing.T) {
+	c := caddy.NewTestController("dns", `local {
+		localhost_prefix maybe
+	}`)
+	if err := setup(c); err == nil {
+		t.Fatal("expected error for invalid localhost_prefix value, got nil")
+	}
+}