tailcfg, controlclient: add DisplayName field to tailcfg.Node and populate it from controlclient (#1191)

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

util/dnsname/dnsname.go

@@ -17,3 +17,11 @@ func HasSuffix(name, suffix string) bool {
 	nameBase := strings.TrimSuffix(name, suffix)
 	return len(nameBase) < len(name) && strings.HasSuffix(nameBase, ".")
 }
+
+// ToBaseName removes the domain ending from a DNS name of a node.
+func ToBaseName(name string) string {
+	if i := strings.Index(name, "."); i != -1 {
+		return name[:i]
+	}
+	return name
+}

util/dnsname/dnsname_test.go

@@ -26,3 +26,21 @@ func TestHasSuffix(t *testing.T) {
 		}
 	}
 }
+
+func TestToBaseName(t *testing.T) {
+	tests := []struct {
+		name string
+		want string
+	}{
+		{"foo", "foo"},
+		{"foo.com", "foo"},
+		{"foo.example.com.beta.tailscale.net", "foo"},
+		{"computer-a.test.gmail.com.beta.tailscale.net", "computer-a"},
+	}
+	for _, tt := range tests {
+		got := ToBaseName(tt.name)
+		if got != tt.want {
+			t.Errorf("ToBaseName(%q) = %q; want %q", tt.name, got, tt.want)
+		}
+	}
+}