Allow to have open & link tracking by SMTP headers

SMTP header "X-PM-TrackOpens" and "X-PM-TrackLinks" will mapped to
the correct payload name. This allows open and link tracking per swift
message.

src/Postmark/Transport.php

@@ -268,14 +268,24 @@ private function processHeaders(&$payload, $message) {
 
 				if ($value instanceof \Swift_Mime_Headers_UnstructuredHeader ||
 					$value instanceof \Swift_Mime_Headers_OpenDKIMHeader) {
-					if($fieldName != 'X-PM-Tag'){
-						array_push($headers, [
-							"Name" => $fieldName,
-							"Value" => $value->getValue(),
-						]);
-					}else{
-						$payload["Tag"] = $value->getValue();
+
+					$reservedFields = [
+						'X-PM-Tag' => 'Tag',
+						'X-PM-TrackOpens' => 'TrackOpens',
+						'X-PM-TrackLinks' => 'TrackLinks',
+					];
+
+					foreach ($reservedFields as $headerName => $payloadName) {
+						if($fieldName == $headerName){
+							$payload[$payloadName] = $value->getValue();
+							continue 2;
+						}
 					}
+
+					array_push($headers, [
+						"Name" => $fieldName,
+						"Value" => $value->getValue(),
+					]);
 				} else if ($value instanceof \Swift_Mime_Headers_DateHeader ||
 					$value instanceof \Swift_Mime_Headers_IdentificationHeader ||
 					$value instanceof \Swift_Mime_Headers_ParameterizedHeader ||

tests/TransportTest.php

@@ -34,6 +34,8 @@ public function testSend() {
 
 		$headers = $message->getHeaders();
 		$headers->addTextHeader('X-PM-Tag', 'movie-quotes');
+		$headers->addTextHeader('X-PM-TrackOpens', false);
+		$headers->addTextHeader('X-PM-TrackLinks', 'None');
 
 		$transport = new PostmarkTransportStub([new Response(200)]);
 
@@ -61,6 +63,8 @@ protected function assertExpectedMessageRequest($message, $request)
             'Tag' => 'movie-quotes',
             'TextBody' => 'Doo-wah-ditty.',
             'HtmlBody' => '<q>Help me Rhonda</q>',
+            'TrackOpens' => $message->getHeaders()->get('X-PM-TrackOpens')->getValue(),
+            'TrackLinks' => $message->getHeaders()->get('X-PM-TrackLinks')->getValue(),
             'Headers' => [
                 ['Name' => 'Message-ID', 'Value' => '<' . $message->getHeaders()->get('Message-ID')->getId() . '>'],
                 ['Name' => 'X-PM-KeepID', 'Value' => 'true'],