[Mailer] Throw TransportException when unable to read from socket

Author: xdanik

src/Symfony/Component/Mailer/Transport/Smtp/Stream/AbstractStream.php

@@ -74,7 +74,7 @@ public function readLine(): string
             return '';
         }
 
-        $line = fgets($this->out);
+        $line = @fgets($this->out);
         if ('' === $line || false === $line) {
             $metas = stream_get_meta_data($this->out);
             if ($metas['timed_out']) {
@@ -83,6 +83,9 @@ public function readLine(): string
             if ($metas['eof']) {
                 throw new TransportException(sprintf('Connection to "%s" has been closed unexpectedly.', $this->getReadConnectionDescription()));
             }
+            if (false === $line) {
+                throw new TransportException(sprintf('Unable to read from connection to "%s": ', $this->getReadConnectionDescription()).error_get_last()['message']);
+            }
         }
 
         $this->debug .= sprintf('< %s', $line);