Introduction

So far, we have analyzed and learned about the PHP language itself – including data types, expressions, operators, and control statements – and how to use them in functions and classes. Before we jump into building a web application using what we have learned so far, it is crucial to understand client-server communication in a web application.

A web application (that is, a website) is designed to return a response for each request, which leads to a Request-Response cycle. In the web application world, this cycle is done through Hypertext Transfer Protocol (HTTP), which is a protocol that ensures both sides communicate with the same language or structure. HTTP requires data to be sent in two ways – from the client to the server (the request), and then the other way around; that is, from the server to the client (the response), closing the cycle. The Request-Response cycle doesn't necessarily mean a hit in application logic; it can be a request...