plugin/secondary: parse catalog zones after transfer (#8209)

plugin/secondary/secondary.go

@@ -1,13 +1,22 @@
 // Package secondary implements a secondary plugin.
 package secondary
 
-import "github.com/coredns/coredns/plugin/file"
+import (
+	"sync"
+
+	"github.com/coredns/coredns/plugin/file"
+	"github.com/coredns/coredns/plugin/pkg/catalog"
+)
 
 // Secondary implements a secondary plugin that allows CoreDNS to retrieve (via AXFR)
 // zone information from a primary server.
 type Secondary struct {
 	file.File
+
+	catalogMu    sync.RWMutex
+	catalogs     map[string]*catalog.Catalog
+	catalogZones map[string]struct{}
 }
 
 // Name implements the Handler interface.
-func (s Secondary) Name() string { return "secondary" }
+func (s *Secondary) Name() string { return "secondary" }