Revealed: Where cookies are stored on your computer

With the popularity of the Internet, every time we open a web page, the browser will automatically save some data, such as user name, password, and some website settings and other information. This data is a cookie that is encoded and stored on your computer. So how are cookies saved? Below we will reveal where cookies are saved on your computer and related code examples.

When visiting a website for the first time, the server will add a Set-Cookie directive to the http response header, which contains a cookie identifier stored on the local computer and the value corresponding to the cookie. In each subsequent request, the browser will add a Cookie field to the http request header to carry the previously saved cookie information.

So how are cookies stored in the local computer? The answer is saved in a text file under the browser's cache folder. For example, when using the Chrome browser, we can find the Cookies folder under the local disk path "C:UsersyourusernameAppDataLocalGoogleChromeUser DataDefault", which stores all cookie information related to the website.

The following is a simple code example, taking JavaScript as an example, let us understand how to use code to read and write cookie information.

Write Cookie information:

function setCookie(name, value, days) {
  var date = new Date();
  date.setTime(date.getTime() + days * 24 * 3600 * 1000); //设置cookie过期时间
  var expires = "; expires=" + date.toGMTString(); 
  document.cookie = name + "=" + value + expires + "; path=/"; //设置cookie
}

This function has three parameters, namely the name, value and expiration time of the cookie. Among them, name and value respectively represent the key-value pair corresponding to the cookie; days is the expiration time of the cookie, in days.

Read Cookie information:

function getCookie(name) {
  var prefix = name + "=";
  var cookies = document.cookie.split(';');
  for(var i=0; i<cookies.length;i++) {
    var cookie = cookies[i];
    while (cookie.charAt(0) == ' ') cookie = cookie.substring(1,cookie.length); //去掉cookie中多余的空格
    if (cookie.indexOf(prefix) == 0) return cookie.substring(prefix.length,cookie.length); //找到cookie并返回值
  }
  return null; //找不到则返回null
}

This function has one parameter, which is the name of the cookie. The function first obtains all cookie information through the document.cookie attribute, then traverses each cookie and compares its name one by one to see if it is the same as the given name. If the corresponding cookie is found, its value is returned, otherwise null is returned.

When using cookies, you also need to pay attention to the following issues:

1. Cookie size limit: Different browsers have different restrictions on the size of cookies, generally 4KB to 20KB between. If the cookie value is greater than this limit, the server will not be able to recognize the cookie information.
2. Cookie security issues: Cookie data is passed in clear text. If the cookie is intercepted or maliciously tampered with, the security of the system data will be threatened. Therefore, when storing sensitive information, encryption or other more secure technologies need to be used.
3. Cookie expiration time: When the cookie expires, it will be automatically cleared, but before expiration, if the same site writes to the same cookie multiple times, subsequent writes will overwrite the previous value. Therefore, you need to pay attention to its expiration time and domain name range when writing cookies.

To sum up, cookie is a technology that interacts between the client and the server through the HTTP protocol. As part of the HTTP transmission protocol, it can save some website setting information to the client. , thus having a certain impact on the performance and user experience of the website. When doing web development, understanding the relevant knowledge of cookies can effectively improve our development efficiency and user experience.

The above is the detailed content of Revealed: Where cookies are stored on your computer. For more information, please follow other related articles on the PHP Chinese website!