The basics of HTTP

HTTP (Hypertext Transfer Protocol) is a client-server protocol that enables a client and server to communicate over a network using request/response. It’s an application layer protocol that relies on TCP/IP for its services.

Note: TCP (Transmission Control Protocol) is a transport layer protocol that ensures messages get delivered in the order in which they are sent, either from client to server or server to client.

What is HTTPS?

HTTPS is an extension of the Hypertext Transfer Protocol. It is used for secure communication over a computer network. In HTTPS, the communication protocol is encrypted using a TLS-encrypted TCP connection.

The architecture of HTTP

Here is the basic block diagram of a web application architecture using HTTP.

In the diagram above,

Client: the client sends a request to the server via the HTTP protocol

Server: here, the server processes the request and sends the response for the requested information to the client

The basic aspects of HTTP

  • HTTP is connectionless: each client request is treated as a unique and independent connection.

  • HTTP is stateless but not sessionless. By stateless we mean that, HTTP does not keep any information about the client. Therefore, there is no relation between any requests that are being carried out consecutively on the same connection.

  • HTTP is extensible/customized. It can be integrated with any new functionality just by setting up or providing an agreement between a client and a server.

A sample HTTP request

Let’s make a simple HTTP request using the curl command and analyze the output.

curl -iX GET

Please click on the terminal to run this command and then see the response of the server.

Terminal 1

The server response has HTTP headers and a message body.

Response headers as key/value pairs

HTTP/2 200 
date: Fri, 27 Mar 2020 05:04:49 GMT
content-type: application/json; charset=utf-8
content-length: 370
set-cookie: __cfduid=da1cd20e010c26e64c1cabad561df2ba21585285489; 
  • The first line is the HTTP status code which is 200.

  • One of the keys is a content-type and has a corresponding value of application/json; charset=utf-8.

  • One of the keys is a set-cookie and has a corresponding value of da1cd20e010c26e64c1cabad561df2ba21585285489.

Note: Cookies are a unique identification number that help us keep track of our activity on different web pages. For example, Amazon keeps track of items in your cart using cookies. When you first visit the website, the server assigns the unique identification number to the client. After the cookie is set, the client will always request the server using the cookie. In this way, the server will know who is making the request so it can respond accordingly.

We will learn more about HTTP headers later in another section, HTTP headers.

Response message body

{"data":{"id":1,"email":"","first_name":"George","last_name":"Bluth","avatar":""},"ad":{"company":"StatusCode Weekly","url":"","text":"A weekly newsletter focusing on software development, infrastructure, the server, performance, and the stack end of things."}}

The second part of the HTTP response is the message body, which is in the JSON format. It is the information returned by the server for the requested resource and in this case, we have requested the details of user-1 (/api/users/1).

Now that you are familiar with the HTTP, in the next lesson, we will learn about various HTTP methods.