unfold before calling iconv_mime_decode

src/Header/HeaderWrap.php

@@ -103,6 +103,13 @@ public static function mimeEncodeValue($value, $encoding, $lineLength = 998)
      */
     public static function mimeDecodeValue($value)
     {
+        // unfold first, because iconv_mime_decode is discarding "\n" with no apparent reason
+        // making the resulting value no longer valid.
+
+        // see https://tools.ietf.org/html/rfc2822#section-2.2.3 about unfolding
+        $parts = explode(Headers::FOLDING, $value);
+        $value = implode(' ', $parts);
+
         $decodedValue = iconv_mime_decode($value, ICONV_MIME_DECODE_CONTINUE_ON_ERROR, 'UTF-8');
 
         return $decodedValue;

test/Header/HeaderWrapTest.php

@@ -12,6 +12,7 @@
 use PHPUnit\Framework\TestCase;
 use Zend\Mail\Header\GenericHeader;
 use Zend\Mail\Header\HeaderWrap;
+use Zend\Mail\Storage;
 
 /**
  * @group      Zend_Mail
@@ -74,6 +75,26 @@ public function testMimeDecoding()
         $this->assertEquals($expected, $decoded);
     }
 
+    /**
+     * Test that header lazy-loading doesn't break later header access
+     * because undocumented behavior in iconv_mime_decode()
+     * @see https://github.com/zendframework/zend-mail/pull/187
+     */
+    public function testMimeDecodeBreakageBug()
+    {
+        $headerValue = "v=1; a=rsa-sha25; c=relaxed/simple; d=example.org; h=\r\n\tcontent-language:content-type:content-type:in-reply-to";
+        $headers = "DKIM-Signature: {$headerValue}";
+
+        $message = new Storage\Message(['headers' => $headers, 'content' => 'irrelevant']);
+        $headers = $message->getHeaders();
+        // calling toString will lazy load all headers
+        // and would break DKIM-Signature header access
+        $headers->toString();
+
+        $header = $headers->get('DKIM-Signature');
+        $this->assertEquals('v=1; a=rsa-sha25; c=relaxed/simple; d=example.org; h= content-language:content-type:content-type:in-reply-to', $header->getFieldValue());
+    }
+
     /**
      * Test that fails with HeaderWrap::canBeEncoded at lowest level:
      *   iconv_mime_encode(): Unknown error (7)