Add FQDN validation checker and tests to v2. (#135)

# Describe Request

Add FQDN validation checker and tests to v2.

# Change Type

New code.

v2/fqdn.go

@@ -0,0 +1,43 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2
+
+import (
+    "reflect"
+    "regexp"
+)
+
+const (
+    // nameFQDN is the name of the FQDN check.
+    nameFQDN = "fqdn"
+)
+
+var (
+    // ErrNotFQDN indicates that the given value is not a valid FQDN.
+    ErrNotFQDN = NewCheckError("FQDN")
+
+    // fqdnRegex is the regular expression for validating FQDN.
+    fqdnRegex = regexp.MustCompile(`^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}$`)
+)
+
+// IsFQDN checks if the value is a valid fully qualified domain name (FQDN).
+func IsFQDN(value string) (string, error) {
+    if !fqdnRegex.MatchString(value) {
+        return value, ErrNotFQDN
+    }
+    return value, nil
+}
+
+// checkFQDN checks if the value is a valid fully qualified domain name (FQDN).
+func checkFQDN(value reflect.Value) (reflect.Value, error) {
+    _, err := IsFQDN(value.Interface().(string))
+    return value, err
+}
+
+// makeFQDN makes a checker function for the FQDN checker.
+func makeFQDN(_ string) CheckFunc[reflect.Value] {
+    return checkFQDN
+}

v2/fqdn_test.go

@@ -0,0 +1,76 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2_test
+
+import (
+	"fmt"
+	"testing"
+
+	v2 "github.com/cinar/checker/v2"
+)
+
+func ExampleIsFQDN() {
+	_, err := v2.IsFQDN("example.com")
+	if err != nil {
+		fmt.Println(err)
+	}
+}
+
+func TestIsFQDNInvalid(t *testing.T) {
+	_, err := v2.IsFQDN("invalid_fqdn")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+}
+
+func TestIsFQDNValid(t *testing.T) {
+	_, err := v2.IsFQDN("example.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestCheckFQDNNonString(t *testing.T) {
+	defer FailIfNoPanic(t, "expected panic")
+
+	type Domain struct {
+		Name int `checkers:"fqdn"`
+	}
+
+	domain := &Domain{}
+
+	v2.CheckStruct(domain)
+}
+
+func TestCheckFQDNInvalid(t *testing.T) {
+	type Domain struct {
+		Name string `checkers:"fqdn"`
+	}
+
+	domain := &Domain{
+		Name: "invalid_fqdn",
+	}
+
+	_, ok := v2.CheckStruct(domain)
+	if ok {
+		t.Fatal("expected error")
+	}
+}
+
+func TestCheckFQDNValid(t *testing.T) {
+	type Domain struct {
+		Name string `checkers:"fqdn"`
+	}
+
+	domain := &Domain{
+		Name: "example.com",
+	}
+
+	_, ok := v2.CheckStruct(domain)
+	if !ok {
+		t.Fatal("expected valid")
+	}
+}

v2/maker.go

@@ -21,6 +21,7 @@ var makers = map[string]MakeCheckFunc{
 	nameCIDR:         makeCIDR,
 	nameDigits:       makeDigits,
 	nameEmail:        makeEmail,
+	nameFQDN:         makeFQDN,
 	nameMaxLen:       makeMaxLen,
 	nameMinLen:       makeMinLen,
 	nameRequired:     makeRequired,