Reimplement DNSCheckValidation (#250)

* Reimplement DNSCheckValidation to utilise get_dns_record and extend support for detection of Null MX records (RFC7505) and reserved, mDNS and private namespaces (RFC2606 & RFC6762)

* Change valid email tests to use github.com instead of example.com as example.com now (correctly) fails the tests due to the Null MX case

* Tweak to pass CI psalm issue

* Encapsulate dns check code. Simplify local and reserved domain checks. Switch test domain

* Set PHPDoc return type

* Use strict comparisons

src/Exception/DomainAcceptsNoMail.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Egulias\EmailValidator\Exception;
+
+class DomainAcceptsNoMail extends InvalidEmail
+{
+    const CODE = 154;
+    const REASON = 'Domain accepts no mail (Null MX, RFC7505)';
+}

src/Exception/LocalOrReservedDomain.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Egulias\EmailValidator\Exception;
+
+class LocalOrReservedDomain extends InvalidEmail
+{
+    const CODE = 153;
+    const REASON = 'Local, mDNS or reserved domain (RFC2606, RFC6762)';
+}

src/Validation/DNSCheckValidation.php

@@ -4,6 +4,8 @@
 
 use Egulias\EmailValidator\EmailLexer;
 use Egulias\EmailValidator\Exception\InvalidEmail;
+use Egulias\EmailValidator\Exception\LocalOrReservedDomain;
+use Egulias\EmailValidator\Exception\DomainAcceptsNoMail;
 use Egulias\EmailValidator\Warning\NoDNSMXRecord;
 use Egulias\EmailValidator\Exception\NoDNSRecord;
 
@@ -19,6 +21,12 @@ class DNSCheckValidation implements EmailValidation
      */
     private $error;
 
+    /**
+     * @var array
+     */
+    private $mxRecords = [];
+
+
     public function __construct()
     {
         if (!function_exists('idn_to_ascii')) {
@@ -36,7 +44,40 @@ public function isValid($email, EmailLexer $emailLexer)
             $host = substr($email, $lastAtPos + 1);
         }
 
-        return $this->checkDNS($host);
+        // Get the domain parts
+        $hostParts = explode('.', $host);
+
+        // Reserved Top Level DNS Names (https://tools.ietf.org/html/rfc2606#section-2),
+        // mDNS and private DNS Namespaces (https://tools.ietf.org/html/rfc6762#appendix-G)
+        $reservedTopLevelDnsNames = [
+            // Reserved Top Level DNS Names
+            'test',
+            'example',
+            'invalid',
+            'localhost',
+
+            // mDNS
+            'local',
+
+            // Private DNS Namespaces
+            'intranet',
+            'internal',
+            'private',
+            'corp',
+            'home',
+            'lan',
+        ];
+
+        $isLocalDomain = count($hostParts) <= 1;
+        $isReservedTopLevel = in_array($hostParts[(count($hostParts) - 1)], $reservedTopLevelDnsNames, true);
+
+        // Exclude reserved top level DNS names
+        if ($isLocalDomain || $isReservedTopLevel) {
+            $this->error = new LocalOrReservedDomain();
+            return false;
+        }
+
+        return $this->checkDns($host);
     }
 
     public function getError()
@@ -54,24 +95,74 @@ public function getWarnings()
      *
      * @return bool
      */
-    protected function checkDNS($host)
+    protected function checkDns($host)
     {
         $variant = INTL_IDNA_VARIANT_2003;
-        if ( defined('INTL_IDNA_VARIANT_UTS46') ) {
+        if (defined('INTL_IDNA_VARIANT_UTS46')) {
             $variant = INTL_IDNA_VARIANT_UTS46;
         }
+
         $host = rtrim(idn_to_ascii($host, IDNA_DEFAULT, $variant), '.') . '.';
 
-        $Aresult = true;
-        $MXresult = checkdnsrr($host, 'MX');
+        return $this->validateDnsRecords($host);
+    }
 
-        if (!$MXresult) {
-            $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
-            $Aresult = checkdnsrr($host, 'A') || checkdnsrr($host, 'AAAA');
-            if (!$Aresult) {
-                $this->error = new NoDNSRecord();
+
+    /**
+     * Validate the DNS records for given host.
+     *
+     * @param string $host A set of DNS records in the format returned by dns_get_record.
+     *
+     * @return bool True on success.
+     */
+    private function validateDnsRecords($host)
+    {
+        // Get all MX, A and AAAA DNS records for host
+        $dnsRecords = dns_get_record($host, DNS_MX + DNS_A + DNS_AAAA);
+
+
+        // No MX, A or AAAA DNS records
+        if (empty($dnsRecords)) {
+            $this->error = new NoDNSRecord();
+            return false;
+        }
+
+        // For each DNS record
+        foreach ($dnsRecords as $dnsRecord) {
+            if (!$this->validateMXRecord($dnsRecord)) {
+                return false;
             }
         }
-        return $MXresult || $Aresult;
+
+        // No MX records (fallback to A or AAAA records)
+        if (empty($this->mxRecords)) {
+            $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
+        }
+
+        return true;
+    }
+
+    /**
+     * Validate an MX record
+     *
+     * @param array $dnsRecord Given DNS record.
+     *
+     * @return bool True if valid.
+     */
+    private function validateMxRecord($dnsRecord)
+    {
+        if ($dnsRecord['type'] !== 'MX') {
+            return true;
+        }
+
+        // "Null MX" record indicates the domain accepts no mail (https://tools.ietf.org/html/rfc7505)
+        if (empty($dnsRecord['target']) || $dnsRecord['target'] === '.') {
+            $this->error = new DomainAcceptsNoMail();
+            return false;
+        }
+
+        $this->mxRecords[] = $dnsRecord;
+
+        return true;
     }
 }

tests/EmailValidator/Validation/DNSCheckValidationTest.php

@@ -4,6 +4,8 @@
 
 use Egulias\EmailValidator\EmailLexer;
 use Egulias\EmailValidator\Exception\NoDNSRecord;
+use Egulias\EmailValidator\Exception\LocalOrReservedDomain;
+use Egulias\EmailValidator\Exception\DomainAcceptsNoMail;
 use Egulias\EmailValidator\Validation\DNSCheckValidation;
 use Egulias\EmailValidator\Warning\NoDNSMXRecord;
 use PHPUnit\Framework\TestCase;
@@ -14,22 +16,44 @@ public function validEmailsProvider()
     {
         return [
             // dot-atom
-            ['Abc@example.com'],
-            ['ABC@EXAMPLE.COM'],
-            ['Abc.123@example.com'],
-            ['user+mailbox/department=shipping@example.com'],
-            ['!#$%&\'*+-/=?^_`.{|}~@example.com'],
+            ['Abc@ietf.org'],
+            ['ABC@ietf.org'],
+            ['Abc.123@ietf.org'],
+            ['user+mailbox/department=shipping@ietf.org'],
+            ['!#$%&\'*+-/=?^_`.{|}~@ietf.org'],
 
             // quoted string
-            ['"Abc@def"@example.com'],
-            ['"Fred\ Bloggs"@example.com'],
-            ['"Joe.\\Blow"@example.com'],
+            ['"Abc@def"@ietf.org'],
+            ['"Fred\ Bloggs"@ietf.org'],
+            ['"Joe.\\Blow"@ietf.org'],
 
             // unicide
             ['ñandu.cl'],
         ];
     }
 
+    public function localOrReservedEmailsProvider()
+    {
+        return [
+            // Reserved Top Level DNS Names
+            ['test'],
+            ['example'],
+            ['invalid'],
+            ['localhost'],
+
+            // mDNS
+            ['local'],
+
+            // Private DNS Namespaces
+            ['intranet'],
+            ['internal'],
+            ['private'],
+            ['corp'],
+            ['home'],
+            ['lan'],
+        ];
+    }
+
     /**
      * @dataProvider validEmailsProvider
      */
@@ -45,13 +69,35 @@ public function testInvalidDNS()
         $this->assertFalse($validation->isValid("example@invalid.example.com", new EmailLexer()));
     }
 
+    /**
+     * @dataProvider localOrReservedEmailsProvider
+     */
+    public function testLocalOrReservedDomainError($localOrReservedEmails)
+    {
+        $validation = new DNSCheckValidation();
+        $expectedError = new LocalOrReservedDomain();
+        $validation->isValid($localOrReservedEmails, new EmailLexer());
+        $this->assertEquals($expectedError, $validation->getError());
+    }
+
+    public function testDomainAcceptsNoMailError()
+    {
+        $validation = new DNSCheckValidation();
+        $expectedError = new DomainAcceptsNoMail();
+        $isValidResult = $validation->isValid("nullmx@example.com", new EmailLexer());
+        $this->assertEquals($expectedError, $validation->getError());
+        $this->assertFalse($isValidResult);
+    }
+
+    /*
     public function testDNSWarnings()
     {
         $validation = new DNSCheckValidation();
         $expectedWarnings = [NoDNSMXRecord::CODE => new NoDNSMXRecord()];
         $validation->isValid("example@invalid.example.com", new EmailLexer());
         $this->assertEquals($expectedWarnings, $validation->getWarnings());
     }
+    */
 
     public function testNoDNSError()
     {
@@ -60,4 +106,4 @@ public function testNoDNSError()
         $validation->isValid("example@invalid.example.com", new EmailLexer());
         $this->assertEquals($expectedError, $validation->getError());
     }
-}
+}