base64_decode may return false in PHP < 7.1 (#324)

Closes #284

Author: Slamdunk

src/Message/AbstractPart.php

@@ -336,6 +336,10 @@ final public function getDecodedContent(): string
                 $content = \quoted_printable_decode($content);
             }
 
+            if (false === $content) {
+                throw new UnexpectedEncodingException('Cannot decode content');
+            }
+
             // If this part is a text part, convert its charset to UTF-8.
             // We don't want to decode an attachment's charset.
             if (!$this instanceof Attachment && null !== $this->getCharset() && self::TYPE_TEXT === $this->getType()) {

tests/MessageTest.php

@@ -903,6 +903,23 @@ public function test_imap_mime_header_decode_returns_false()
         $this->assertSame('=?UTF-8?B?nnDusSNdG92w6Fuw61fMjAxOF8wMy0xMzMyNTMzMTkzLnBkZg==?=', $message->getSubject());
     }
 
+    public function testBooleanDecodedContent()
+    {
+        if (PHP_VERSION_ID >= 70100) {
+            $this->markTestSkipped('Requires PHP < 7.1');
+        }
+
+        $this->mailbox->addMessage($this->getFixture('boolean_decoded_content'));
+
+        $message = $this->mailbox->getMessage(1);
+        $attachments = $message->getAttachments();
+        $attachment = \current($attachments);
+
+        $this->expectException(UnexpectedEncodingException::class);
+
+        $attachment->getDecodedContent();
+    }
+
     private function resetAttachmentCharset(MessageInterface $message)
     {
         // Mimic GMAIL behaviour that correctly doesn't report charset

tests/fixtures/boolean_decoded_content.eml

@@ -0,0 +1,31 @@
+From: [email protected]
+To: [email protected]
+Subject: Nuu
+Date: Wed, 13 Sep 2017 13:05:45 +0200
+Content-Type: multipart/mixed; boundary="=-vyqYb0SSRwuGFKv/Trdf"
+
+--=-vyqYb0SSRwuGFKv/Trdf
+Content-Type: multipart/alternative; boundary="=-ewUvwipK68Y6itClYNpy"
+
+--=-ewUvwipK68Y6itClYNpy
+Content-Type: text/plain; charset="us-ascii"
+
+Here is the problem mail
+ 
+Body text
+--=-ewUvwipK68Y6itClYNpy
+Content-Type: text/html; charset="us-ascii"
+
+Here is the problem mail
+ 
+Body text
+--=-ewUvwipK68Y6itClYNpy--
+
+--=-vyqYb0SSRwuGFKv/Trdf
+Content-Type: application/pdf; name="Example Domain.pdf"
+Content-Disposition: attachment; filename="Example Domain.pdf"
+Content-Transfer-Encoding: base64
+
+nnDusSNdG92w6Fuw61fMjAxOF8wMy0xMzMyNTMzMTkzLnBkZg==?=
+
+--=-vyqYb0SSRwuGFKv/Trdf--