feat: add validator for IPv4 bind address / host:port

supporting older Golang versions by using net.ParseIP, not netip.ParseAddr

baked_in.go

@@ -186,6 +186,7 @@ var (
 		"ipv4":                          isIPv4,
 		"ipv6":                          isIPv6,
 		"ip":                            isIP,
+		"ipv4_port":                     isIPv4Port,
 		"cidrv4":                        isCIDRv4,
 		"cidrv6":                        isCIDRv6,
 		"cidr":                          isCIDR,
@@ -2704,6 +2705,29 @@ func isHostnamePort(fl FieldLevel) bool {
 	return true
 }
 
+// isIPv4Port validates a <ipv4>:<port> combination for fields typically used for socket address.
+func isIPv4Port(fl FieldLevel) bool {
+	val := fl.Field().String()
+	ip, port, err := net.SplitHostPort(val)
+	if err != nil {
+		return false
+	}
+	// Port must be a iny <= 65535.
+	if portNum, err := strconv.ParseInt(
+		port, 10, 32,
+	); err != nil || portNum > 65535 || portNum < 1 {
+		return false
+	}
+
+	// If IP address is specified, it should match a valid IPv4 address
+	if ip != "" {
+		// we need to support older Golang versions, so we can not use netip.ParseAddr
+		parsedIp := net.ParseIP(ip)
+		return parsedIp != nil && parsedIp.To4() != nil
+	}
+	return true
+}
+
 // isLowercase is the validation function for validating if the current field's value is a lowercase string.
 func isLowercase(fl FieldLevel) bool {
 	field := fl.Field()

validator_test.go

@@ -12377,6 +12377,38 @@ func Test_hostnameport_validator(t *testing.T) {
 	}
 }
 
+func Test_ipv4_port_validator(t *testing.T) {
+	type IPv4Port struct {
+		BindAddr string `validate:"ipv4_port"`
+	}
+
+	type testInput struct {
+		data     string
+		expected bool
+	}
+	testData := []testInput{
+		{"192.168.1.1:1234", true},
+		{":1234", true},
+		{"localhost:1234", false},
+		{"aaa.bbb.ccc.ddd:234", false},
+		{":alpha", false},
+		{"1.2.3.4", false},
+		{"2001:db8::1:0.0.0.0:234", false},
+		{"2001:db8::1:0.0.0.0", false},
+		{"2001:db8::1:0.0.0.0:", false},
+		{"2001:db8::1:0.0.0.0:123456", false},
+		{"2001:db8::1:0.0.0.0:123456:", false},
+	}
+	for _, td := range testData {
+		h := IPv4Port{BindAddr: td.data}
+		v := New()
+		err := v.Struct(h)
+		if td.expected != (err == nil) {
+			t.Fatalf("Test failed for data: %v Error: %v", td.data, err)
+		}
+	}
+}
+
 func TestLowercaseValidation(t *testing.T) {
 	tests := []struct {
 		param    string