Add DNS1123Label validation to IsFullyQualifiedDomainName func

This patch adds IsDNS1123Label validation to
IsFullyQualifiedDomainName func.

Even when one label is longer than 64 characters, the current
validation  does not validate it. Hence this patch adds the label
check and do not allow invalid domain.

Author: nak3

staging/src/k8s.io/apimachinery/pkg/util/validation/validation.go

@@ -106,6 +106,11 @@ func IsFullyQualifiedDomainName(fldPath *field.Path, name string) field.ErrorLis
 	if len(strings.Split(name, ".")) < 2 {
 		return append(allErrors, field.Invalid(fldPath, name, "should be a domain with at least two segments separated by dots"))
 	}
+	for _, label := range strings.Split(name, ".") {
+		if errs := IsDNS1123Label(label); len(errs) > 0 {
+			return append(allErrors, field.Invalid(fldPath, label, strings.Join(errs, ",")))
+		}
+	}
 	return allErrors
 }
 

staging/src/k8s.io/apimachinery/pkg/util/validation/validation_test.go

@@ -557,7 +557,8 @@ func TestIsFullyQualifiedDomainName(t *testing.T) {
 		"bbc.co.uk",
 		"10.0.0.1", // DNS labels can start with numbers and there is no requirement for letters.
 		"hyphens-are-good.k8s.io",
-		strings.Repeat("a", 246) + ".k8s.io",
+		strings.Repeat("a", 63) + ".k8s.io",
+		strings.Repeat("a", 63) + "." + strings.Repeat("b", 63) + "." + strings.Repeat("c", 63) + "." + strings.Repeat("d", 54) + ".k8s.io",
 	}
 	for _, val := range goodValues {
 		if err := IsFullyQualifiedDomainName(field.NewPath(""), val).ToAggregate(); err != nil {
@@ -579,7 +580,8 @@ func TestIsFullyQualifiedDomainName(t *testing.T) {
 		"underscores_are_bad.k8s.io",
 		"[email protected]",
 		"http://foo.example.com",
-		strings.Repeat("a", 247) + ".k8s.io",
+		strings.Repeat("a", 64) + ".k8s.io",
+		strings.Repeat("a", 63) + "." + strings.Repeat("b", 63) + "." + strings.Repeat("c", 63) + "." + strings.Repeat("d", 55) + ".k8s.io",
 	}
 	for _, val := range badValues {
 		if err := IsFullyQualifiedDomainName(field.NewPath(""), val).ToAggregate(); err == nil {