PHP下载按钮不工作生成空文件

Question

我在表单中有两个按钮，一个是提交，第二个按钮是下载textarea中显示的输出。

提交工作正常但下载按钮创建空文件并且不写入输出文本区域的数据。

这是代码：

<?php    
error_reporting(0);
$mytext = "";

$txt = preg_replace('/\n+/', "\n", trim($_POST['inputtext']));
$text = explode("\n", $txt);
$output  = array();


if(isset($_POST["submit"]))
{
    for($i=0;$i<count($text);$i++)
    {
        $output[] .= trim($text[$i]) . ' Text added with output'.PHP_EOL;
    }
}


if(isset($_POST["download"]) ) {

    $handle = fopen("file.txt", "w");
    fwrite($handle, implode($output));
    fclose($handle);

    header('Content-type: application/octet-stream');
    header('Content-Disposition: attachment;filename='.basename('file.txt'));
    header('Expires: 0');
    ob_end_clean();
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize('file.txt'));
    readfile('file.txt');
    exit;
}   
?>


<form method="POST" action="test.php">
<textarea name="inputtext" rows="10" cols="100" placeholder="Enter Any Text!" required><?php if(!empty($_POST["inputtext"])) { echo $_POST["inputtext"]; } ?></textarea>
<br><br>
<input type="submit"  name="submit" value="Do it!">
<br><br>
<p>Output goes here. </p><textarea name="oputputtext" rows="10" cols="100" ><?php echo implode($output);?></textarea>
<input type="submit"   name="download" value="Download Output">
</form>