PHP cannot obtain Referer troubleshooting

Test results:

The same page is opened twice. The Referer can be obtained the first time but not the second time. I am very curious about the reason. The code of

test1.php is:

<?php echo <span>'测试来源：直接载入页面<br>';

echo <span>'<a href="test_cookie.php">进入页面</a><br>'</span>;

echo <span>'测试来源：新窗口打开<br>'</span>;

echo <span>'<a target="_blank" href="test_cookie.php">进入页面</a><br>'</span>;

the code of test_cookie.php is:

<?php date_default_timezone_set(<span>'Asia/Shanghai');<span>//设置默认时区</span>header(<span>'content-type:text/html; charset=utf8'</span>);<span>//设置返回头信息</span>
echo date(<span>'Y-m-d H:i:s'</span>);
echo <span>"<br>\r\n"</span>;

echo <span>'PHP获取Refer是：'</span>;
$refer=isset($_SERVER[<span>'HTTP_REFERER'</span>])?$_SERVER[<span>'HTTP_REFERER'</span>]:<span>'No refer found'</span>;
echo $refer;
echo <span>"<br>\r\n"</span>;

echo <span>'JS获取Refer是：'</span>;
    echo <span>"<script>document.writeln(document.referrer);</script>"</span>;
echo <span>"<br>\r\n"</span>;

  

I am extremely curious as to why I can get it the first time but not the second time.

The environment is LNMPA, the official one is http://lnmp.org/lnmpa.html

Use charles to capture packets under Mac

The header of test1.php requested twice is consistent.

The header of the two requests to test_cookie.php is consistent.

Then the question arises, what is the reason why PHP cannot get the referral due to two identical requests? Kneel down and ask for answers.

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The above introduces the troubleshooting of the problem that PHP cannot obtain the Referer, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.