php 是否可以不设置 $_SERVER['HTTP_USER_AGENT'] ？
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Is it possible for $_SERVER['HTTP_USER_AGENT'] to not be set?
提问by Martin Bean
I've just been looking through a website's error_logand one of the error's that has been logged a few times is:
我刚刚浏览了一个网站error_log，多次记录的错误之一是：
[21-Jun-2011 12:24:03] PHP Notice: Undefined index: HTTP_USER_AGENT in /home/ukevents/public_html/lib/toro.php on line 130
[21-Jun-2011 12:24:03] PHP Notice: Undefined index: HTTP_USER_AGENT in /home/ukevents/public_html/lib/toro.php on line 130
The line this pertains to in toro.phpis:
与toro.php相关的行是：
private function ipad_request() {
return strstr($_SERVER['HTTP_USER_AGENT'], 'iPad');
}
Is it possible for $_SERVER['HTTP_USER_AGENT']to not be set by a HTTP request?
是否有可能$_SERVER['HTTP_USER_AGENT']不被 HTTP 请求设置？
回答by Maxim Krizhanovsky
Yes, it's possible, this a HTTP header sent (or not sent) by client, and you should not rely on it. From php manual:
是的，这是可能的，这是客户端发送（或不发送）的 HTTP 标头，您不应该依赖它。从 php 手册：
Contents of the User-Agent: header from the current request, if there is one
User-Agent 的内容：来自当前请求的标头，如果有
So the correct code would be:
所以正确的代码是：
private function ipad_request() {
return isset($_SERVER['HTTP_USER_AGENT']) && strstr($_SERVER['HTTP_USER_AGENT'], 'iPad');
}
回答by Andrew Moore
Yes. Any browser or user-agent can choose not to send the User-Agentheader. If they do not send that header, $_SERVER['HTTP_USER_AGENT']won't be set.
是的。任何浏览器或用户代理都可以选择不发送User-Agent标头。如果他们不发送该标头，$_SERVER['HTTP_USER_AGENT']则不会设置。
Use isset()to ensure that $_SERVER['HTTP_USER_AGENT']is set.
使用isset()以确保$_SERVER['HTTP_USER_AGENT']已设置。
private function ipad_request() {
if(!isset($_SERVER['HTTP_USER_AGENT'])) return false;
return strstr($_SERVER['HTTP_USER_AGENT'], 'iPad') !== false;
}
回答by Guffa
Yes, it's possible, but it never happens for a regular request.
是的，这是可能的，但它永远不会发生在常规请求中。
All browsers do send a browser string in the request, so any request that arrives without one comes from some other program. Even all well-behaving bots send a browser string, so you don't have to be concerned about not showing up in search engines either.
所有浏览器都会在请求中发送一个浏览器字符串，因此任何没有请求的请求都来自其他程序。即使所有行为良好的机器人都会发送浏览器字符串，因此您也不必担心不会出现在搜索引擎中。
回答by ChrisA
PHP docs says:
PHP 文档说：
'HTTP_USER_AGENT' Contents of the User-Agent: header from the current request, if there is one.
'HTTP_USER_AGENT' 用户代理的内容：来自当前请求的标头，如果有的话。
(relevant part italicised) so it would appear it might not always be set.
（相关部分斜体）所以看起来它可能并不总是被设置。
回答by Anono Mouser
An example where HTTP_USER_AGENT is undefined is if the request coming from GoDaddy's 404 page handler for your site where you have set the handler to be one of your pages.
未定义 HTTP_USER_AGENT 的一个示例是，如果请求来自您网站的 GoDaddy 404 页面处理程序，您已将处理程序设置为您的页面之一。
