渲染从Web服务流式传输的PDF

Question

流式传输PDF文件的Web服务：

header('Pragma: public');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Cache-Control: public');
header("Content-length: " . $filesize); 
header('Content-Description: File Transfer');
header('Content-type: application/pdf');
header("Content-Disposition: attachment; filename={$name}");
header('Content-Transfer-Encoding: binary');
header('Cache-Control: max-age=0');  
ob_start();
fpassthru($fp);
$response = ob_get_contents();
ob_end_clean();
return $response;

启动请求并使用响应的jQuery代码：

$.ajax({
      url: "/xxx/xxx/1/xxx/5",
      type: "GET",
      async:   true,
      dataType: 'binary',
      headers:{'Content-Type':'application/pdf',
                'X-Requested-With':'XMLHttpRequest',
      },
      processData: false,
      success: function(data,status,xhr) {
        var file = new Blob([data], {type: 'application/pdf'});
        var fileURL = URL.createObjectURL(file);
        var a = document.createElement("a");
        a.href = fileURL;
        a.download = "Testing.pdf";
        document.body.appendChild(a);
        a.click();
        $(window).on('focus', function(e) {
          $('a').remove();
        });
      },
        error: function(XMLHttpRequest, textStatus, errorThrown) { 
           console.log("fail");
      }  

PDF文件生成完美，并自动打开。这里唯一的问题是，当应该有文本时，PDF内容会变空！

有人知道为什么会这样吗？