Web Caches & Web Cookies

** Web Caches

Before we look at the web caches, let's first learn about the caches. The data stored in the caches is either a result of the previous operation or a copy of the data stored elsewhere. Computers can improve the performance of their systems by saving time to access actual data using cached data, or if it takes time to do so.

Web caching is the activity of storing data for reuse, such as a copy of a web page served by a web server. It is cached or stored the first time a user visits the page. The next time a user requests the same page, a cache will serve the copy, which helps keep the origin server from getting overloaded. Reduce the amount of information sent over the network and increase response speed by allowing a web browser or Web protocol server to store and reuse previous responses (web pages or images) from a web server. 

Web cache is also called a proxy server. The client browser establishes a TCP connection with the Web cache(=Proxy server) and sends an HTTP request message to request objects in the Web cache. The Web cache verifies that a copy of the object is stored. If stored, send the objects with HTTP response messages to the client browser. 

If a copy of the object is not saved, the web cache establishes a TCP connection to the original server. And the web cache sends an HTTP request message to the client on a TCP connection between the cache and the original server. The origin server that receives this request sends the HTTP response message to the Web cache and the object. When the Web cache receives this, it stores a copy of the object in the web cache and sends it to the client browser. Web cache can reduce response time to client requests and also reduce bottlenecks through traffic distribution to original servers.

** Web Cookies

Cookie files are used by the web server to restrict user access or to provide different content for different users. When a client connects to a Web server, the Web server generates an identification ID for each client. The cookies that are created are stored on the client. 

First, Client sends an HTTP request message to the Web server. Next, Server generates an ID value that identifies the client and sends it as part of an HTTP response message. Here, Set-cookie : part 1234 represents the ID value. Then, client save the ID value received from the web server in a cookie file. After a week, when a client attempts to access the same Web server, the HTTP request message contains the value (1234) it received from the server. The ID value contained in the HTTP request message allows the server to identify what the client previously requested and accessed to the web server. 

Cookies are often used for shopping cart functions or recommended functions in web shopping malls that we are familiar with. However, cookies also have a lot of security issues, as they contain personal information, which can lead to privacy and information leakage. Although encryption technology has reduced this problem a lot these days, we still need to be careful about leaking information from cookie files.