Add empty check on host in other methods + add unit tests

Add empty on host in other methods where checkdnsrr is called and add unit tests to prevent future regressions

src/Symfony/Component/Validator/Constraints/EmailValidator.php

@@ -138,7 +138,7 @@ class EmailValidator extends ConstraintValidator
      */
     private function checkMX($host)
     {
-        if (null === $host || '' === $host) {
+        if ('' === $host) {
             return false;
         }
 
@@ -154,6 +154,10 @@ class EmailValidator extends ConstraintValidator
      */
     private function checkHost($host)
     {
+        if ('' === $host) {
+            return false;
+        }
+        
         return $this->checkMX($host) || (checkdnsrr($host, 'A') || checkdnsrr($host, 'AAAA'));
     }
 }

src/Symfony/Component/Validator/Constraints/UrlValidator.php

@@ -80,7 +80,7 @@ class UrlValidator extends ConstraintValidator
         if ($constraint->checkDNS) {
             $host = parse_url($value, PHP_URL_HOST);
 
-            if (!checkdnsrr($host, 'ANY')) {
+            if ('' === $host || !checkdnsrr($host, 'ANY')) {
                 if ($this->context instanceof ExecutionContextInterface) {
                     $this->context->buildViolation($constraint->dnsMessage)
                        ->setParameter('{{ value }}', $this->formatValue($host))

src/Symfony/Component/Validator/Tests/Constraints/EmailValidatorTest.php

@@ -159,4 +159,10 @@ class EmailValidatorTest extends AbstractConstraintValidatorTest
 
         $this->assertNoViolation();
     }
+
+    public function testEmptyHostReturnsFalse()
+    {
+        $this->assertFalse($this->validator->checkMX(''));
+        $this->assertFalse($this->validator->checkHost(''));
+    }
 }

src/Symfony/Component/Validator/Tests/Constraints/UrlValidatorTest.php

@@ -171,6 +171,7 @@ class UrlValidatorTest extends AbstractConstraintValidatorTest
             array('http://example.com/exploit.html?<script>alert(1);</script>'),
             array('http://example.com/exploit.html?hel lo'),
             array('http://example.com/exploit.html?not_a%hex'),
+            array('http:/.com'),
         );
     }