/**
  * @return array|bool
  * @visible for testing
  */
 private function process()
 {
     $this->transformToUploadUrl();
     $postBody = '';
     $contentType = false;
     $meta = (string) $this->request->getBody();
     $meta = is_string($meta) ? json_decode($meta, true) : $meta;
     $uploadType = $this->getUploadType($meta);
     $this->request->getQuery()->set('uploadType', $uploadType);
     $mimeType = $this->mimeType ? $this->mimeType : $this->request->getHeader('content-type');
     if (self::UPLOAD_RESUMABLE_TYPE == $uploadType) {
         $contentType = $mimeType;
         $postBody = is_string($meta) ? $meta : json_encode($meta);
     } else {
         if (self::UPLOAD_MEDIA_TYPE == $uploadType) {
             $contentType = $mimeType;
             $postBody = $this->data;
         } else {
             if (self::UPLOAD_MULTIPART_TYPE == $uploadType) {
                 // This is a multipart/related upload.
                 $boundary = $this->boundary ? $this->boundary : mt_rand();
                 $boundary = str_replace('"', '', $boundary);
                 $contentType = 'multipart/related; boundary=' . $boundary;
                 $related = "--{$boundary}\r\n";
                 $related .= "Content-Type: application/json; charset=UTF-8\r\n";
                 $related .= "\r\n" . json_encode($meta) . "\r\n";
                 $related .= "--{$boundary}\r\n";
                 $related .= "Content-Type: {$mimeType}\r\n";
                 $related .= "Content-Transfer-Encoding: base64\r\n";
                 $related .= "\r\n" . base64_encode($this->data) . "\r\n";
                 $related .= "--{$boundary}--";
                 $postBody = $related;
             }
         }
     }
     $this->request->setBody(Stream::factory($postBody));
     if (isset($contentType) && $contentType) {
         $this->request->setHeader('content-type', $contentType);
     }
     return $this->request;
 }