Add nothing matcher

patterns.go

@@ -174,3 +174,26 @@ func (p Base) partialMatch(pcs []ma.Protocol) (bool, []ma.Protocol) {
 func (p Base) String() string {
 	return ma.ProtocolWithCode(int(p)).Name
 }
+
+// Nothing match an empty multiaddress, this let you write things like this:
+//
+//	mafmt.And(mafmt.TCP, mafmt.Or(mafmt.Nothing, mafmt.Base(ma.P_TLS)))
+//
+// For a matcher which accepts tcp maddrs with an optional TLS suffix.
+var Nothing empty
+
+var _ Pattern = empty{}
+
+type empty struct{}
+
+func (empty) Matches(a ma.Multiaddr) bool {
+	return len(a.Bytes()) == 0
+}
+
+func (empty) partialMatch(pcs []ma.Protocol) (bool, []ma.Protocol) {
+	return len(pcs) == 0, pcs
+}
+
+func (empty) String() string {
+	return ""
+}

patterns_test.go

@@ -109,6 +109,22 @@ func TestUnreliableGroup(t *testing.T) {
 	assertMismatches(t, Unreliable, TestVectors["IP"].Good, TestVectors["TCP"].Good, TestVectors["UTP"].Good, TestVectors["IPFS"].Good, TestVectors["QUIC"].Good)
 }
 
+func TestNothing(t *testing.T) {
+	matcher := And(TCP, Or(Nothing, Base(ma.P_TLS)))
+	good := TestVectors["TCP"].Good
+	good = good[:len(good):len(good)]
+	for _, v := range good {
+		good = append(good, v+"/tls")
+	}
+	bad := TestVectors["TCP"].Good
+	bad = bad[:len(bad):len(bad)]
+	for _, v := range bad {
+		bad = append(bad, v+"/tls")
+	}
+	assertMatches(t, matcher, good)
+	assertMismatches(t, Unreliable, bad)
+}
+
 func assertMatches(t *testing.T, p Pattern, args ...[]string) {
 	t.Helper()