[Mailer] Do not ping the SMTP server before sending every message

src/Symfony/Component/Mailer/Tests/Transport/Smtp/SmtpTransportTest.php

@@ -12,8 +12,12 @@
 namespace Symfony\Component\Mailer\Tests\Transport\Smtp;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\Mailer\Envelope;
 use Symfony\Component\Mailer\Transport\Smtp\SmtpTransport;
+use Symfony\Component\Mailer\Transport\Smtp\Stream\AbstractStream;
 use Symfony\Component\Mailer\Transport\Smtp\Stream\SocketStream;
+use Symfony\Component\Mime\Address;
+use Symfony\Component\Mime\RawMessage;
 
 class SmtpTransportTest extends TestCase
 {
@@ -25,4 +29,95 @@ class SmtpTransportTest extends TestCase
         $t = new SmtpTransport((new SocketStream())->setHost('127.0.0.1')->setPort(2525)->disableTls());
         $this->assertEquals('smtp://127.0.0.1:2525', (string) $t);
     }
+
+    public function testSendDoesNotPingBelowThreshold(): void
+    {
+        $stream = new DummyStream();
+        $envelope = new Envelope(new Address('sender@example.org'), [new Address('recipient@example.org')]);
+
+        $transport = new SmtpTransport($stream);
+        $transport->send(new RawMessage('Message 1'), $envelope);
+        $transport->send(new RawMessage('Message 2'), $envelope);
+        $transport->send(new RawMessage('Message 3'), $envelope);
+
+        $this->assertNotContains("NOOP\r\n", $stream->getCommands());
+    }
+
+    public function testSendDoesPingAboveThreshold(): void
+    {
+        $stream = new DummyStream();
+        $envelope = new Envelope(new Address('sender@example.org'), [new Address('recipient@example.org')]);
+
+        $transport = new SmtpTransport($stream);
+        $transport->setPingThreshold(1);
+
+        $transport->send(new RawMessage('Message 1'), $envelope);
+        $transport->send(new RawMessage('Message 2'), $envelope);
+
+        $this->assertNotContains("NOOP\r\n", $stream->getCommands());
+
+        $stream->clearCommands();
+        sleep(1);
+
+        $transport->send(new RawMessage('Message 3'), $envelope);
+        $this->assertContains("NOOP\r\n", $stream->getCommands());
+    }
+}
+
+class DummyStream extends AbstractStream
+{
+    /**
+     * @var string
+     */
+    private $nextResponse;
+
+    /**
+     * @var string[]
+     */
+    private $commands;
+
+    public function initialize(): void
+    {
+        $this->nextResponse = '220 localhost';
+    }
+
+    public function write(string $bytes, $debug = true): void
+    {
+        $this->commands[] = $bytes;
+
+        if (0 === strpos($bytes, 'DATA')) {
+            $this->nextResponse = '354 Enter message, ending with "." on a line by itself';
+        } elseif (0 === strpos($bytes, 'QUIT')) {
+            $this->nextResponse = '221 Goodbye';
+        } else {
+            $this->nextResponse = '250 OK';
+        }
+    }
+
+    public function readLine(): string
+    {
+        return $this->nextResponse;
+    }
+
+    public function flush(): void
+    {
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getCommands(): array
+    {
+        return $this->commands;
+    }
+
+    public function clearCommands(): void
+    {
+        $this->commands = [];
+    }
+
+    protected function getReadConnectionDescription(): string
+    {
+        return 'null';
+    }
 }

src/Symfony/Component/Mailer/Transport/Smtp/SmtpTransport.php

@@ -35,6 +35,8 @@ class SmtpTransport extends AbstractTransport
     private $restartThreshold = 100;
     private $restartThresholdSleep = 0;
     private $restartCounter;
+    private $pingThreshold = 100;
+    private $lastMessageTime = 0;
     private $stream;
     private $domain = '[127.0.0.1]';
 
@@ -66,6 +68,28 @@ class SmtpTransport extends AbstractTransport
         return $this;
     }
 
+    /**
+     * Sets the minimum number of seconds required between two messages, before the server is pinged.
+     * If the transport wants to send a message and the time since the last message exceeds the specified threshold,
+     * the transport will ping the server first (NOOP command) to check if the connection is still alive.
+     * Otherwise the message will be sent without pinging the server first.
+     *
+     * Do not set the threshold too low, as the SMTP server may drop the connection if there are too many
+     * non-mail commands (like pinging the server with NOOP).
+     *
+     * By default, the threshold is set to 100 seconds.
+     *
+     * @param int $seconds The minimum number of seconds between two messages required to ping the server
+     *
+     * @return $this
+     */
+    public function setPingThreshold(int $seconds): self
+    {
+        $this->pingThreshold = $seconds;
+
+        return $this;
+    }
+
     /**
      * Sets the name of the local domain that will be used in HELO.
      *
@@ -160,7 +184,10 @@ class SmtpTransport extends AbstractTransport
 
     protected function doSend(SentMessage $message): void
     {
-        $this->ping();
+        if (microtime(true) - $this->lastMessageTime > $this->pingThreshold) {
+            $this->ping();
+        }
+
         if (!$this->started) {
             $this->start();
         }
@@ -183,6 +210,8 @@ class SmtpTransport extends AbstractTransport
             $e->appendDebug($this->stream->getDebug());
 
             throw $e;
+        } finally {
+            $this->lastMessageTime = microtime(true);
         }
     }
 
@@ -213,6 +242,7 @@ class SmtpTransport extends AbstractTransport
         $this->assertResponseCode($this->getFullResponse(), [220]);
         $this->doHeloCommand();
         $this->started = true;
+        $this->lastMessageTime = 0;
 
         $this->getLogger()->debug(sprintf('Email transport "%s" started', __CLASS__));
     }