1 files changed, 44 insertions, 0 deletions
diff --git a/plugin/file/tree/glue.go b/plugin/file/tree/glue.go
new file mode 100644
index 000000000..937ae5482
--- /dev/null
+++ b/plugin/file/tree/glue.go
@@ -0,0 +1,44 @@
+package tree
+
+import (
+	"github.com/coredns/coredns/plugin/file/rrutil"
+
+	"github.com/miekg/dns"
+)
+
+// Glue returns any potential glue records for nsrrs.
+func (t *Tree) Glue(nsrrs []dns.RR, do bool) []dns.RR {
+	glue := []dns.RR{}
+	for _, rr := range nsrrs {
+		if ns, ok := rr.(*dns.NS); ok && dns.IsSubDomain(ns.Header().Name, ns.Ns) {
+			glue = append(glue, t.searchGlue(ns.Ns, do)...)
+		}
+	}
+	return glue
+}
+
+// searchGlue looks up A and AAAA for name.
+func (t *Tree) searchGlue(name string, do bool) []dns.RR {
+	glue := []dns.RR{}
+
+	// A
+	if elem, found := t.Search(name); found {
+		glue = append(glue, elem.Type(dns.TypeA)...)
+		if do {
+			sigs := elem.Type(dns.TypeRRSIG)
+			sigs = rrutil.SubTypeSignature(sigs, dns.TypeA)
+			glue = append(glue, sigs...)
+		}
+	}
+
+	// AAAA
+	if elem, found := t.Search(name); found {
+		glue = append(glue, elem.Type(dns.TypeAAAA)...)
+		if do {
+			sigs := elem.Type(dns.TypeRRSIG)
+			sigs = rrutil.SubTypeSignature(sigs, dns.TypeAAAA)
+			glue = append(glue, sigs...)
+		}
+	}
+	return glue
+}