Domain Name and cookie problems (domain name suffix)

Domain Name and cookie
By accident, I think that www.g.cn can set the cookie to .g.cn. Can www.com.cn set the cookie to .com.cn?

Test results: No. Because the browser knows that the suffix of www.com.cn is .com.cn rather than. cn, it is prohibited to set cookies.
Because the browser has a built-in domain name suffix list. Todo: if a new suffix appears in the future, but the old browser cannot update the list, wouldn't it allow cookie settings?

	Extension suffix	Primary Domain Name	Second-level domain name
Www.g.cn	. Cn	G.cn	* .G.cn
Www.com.cn	.Com.cn	Www.com.cn	* .Www.com.cn
Www.google.com.cn	.Com.cn	Google.com.cn	* .Google.com.cn

Can www.example.com read the .example.com cookie?
Yes.
Can www.example.com read example.com cookies?
No. Todo: Use www.example.com and example.com as SSO to prevent the cookie from being sent to static.example.com.
Can example.com read the cookie of www.example.com?
A: No.
Setcookie ('A', 'A', time () + 1234, '/', 'example. com '); is the cookie set to .example.com or example.com?
A: It is .example.com.
If you want to set example.com cookies, you need to use setcookie ('default', 'default', time () + 1234 ,'/');.
Cookie setting and reading range:

HTTP request Domain Name	Primary Domain Name	Cookie configurable (and readable) Range	Cookie cannot be set	The cookie cannot be read.
Example.com	Example.com	Example.com, .example.com	Www.example.com	Www.example.com
Www.example.com	Example.com	Www.example.com, .www.example.com, .example.com	Example.com	Example.com
G.com.cn	G.com.cn	G.com.cn, .g.com.cn	.Com.cn
Www.com.cn	Www.com.cn	Www.com.cn, .www.com.cn	.Com.cn

Set cookie code:
Copy codeThe Code is as follows:
<? Php
Setcookie ('default', 'default', time () + 1234 ,'/');
Setcookie ('A', 'A', time () + 1234, '/', 'example. com ');
Setcookie ('B', 'bb ', time () + 1234,'/',' .example.com ');
?>

Read cookie code:
Copy codeThe Code is as follows:
<? Php
Var_dump ($ _ COOKIE );
?>

Result: