Web sockets – Now Servers have freedom to talk too !

Introduction

Today we will cover what are web sockets and how they work.

Web sockets

Web sockets is a application layer protocol just like HTTP, HTTPS, etc. with the feature that it allows bi-directional communication (called Full Duplex) from client and server and vice-versa.

As we know, a simple system design has a client and a server. A client makes a request and the server returns a response. This happens over HTTP or HTTPS protocol. HTTP and HTTPS are application layer protocol connected over TCP. Confused ? Let me break it down.

In the OSI Model (Open Systems Interconnection), we have these 7 layers in the order

Now the above statement must be clear – HTTPS and HTTP are application layer protocols used by your browsers to communicate over TCP connection.

HTTP and HTTPs protocol are one-way connection protocol, i.e. only client can send requests and servers can send the response to those request. What if the server wants to communicate something to client?

Let’s understand with an example what Web-sockets are.

Imagine you tell your friend to tell you the score of a football match only when you ask him. However, the match is on and your friend wants to tell you that the scores are changing. Since you have established that your friend should only respond to you and not speak on its own, you will end up losing live match score commentary. – This is HTTP/HTTPS protocol messages where the server only responds when a client sends a request.

Now you are worried about the match and you decide that every minute you will call your friend and ask him to respond the current status of the match. You friend most of them time will end up saying “score is still the same“, that is, there is no latest update (or new response) to share with you. At the same time, your friend also gets frustrated by you pinging him constantly. – This is long polling when the client keeps polling for the new updates that the server has for the client. Most of the time server sends an empty response and the HTTP resources are wasted.

However if you just allow your friend to talk to you and tell you the score as well, your problem would be solved right away. You can just relax and expect your friend to tell you the score when it changes. – This is web-sockets. In web-sockets, servers can send messages too without client requesting them.

Web sockets in action

• First of all, there is an HTTP connection between the client and the server. HTTP communication is established over a TCP connection which is secure.
• Now if you want a web-socket connection instead of HTTP, the client will send a “protocol upgrade” request to the server. This is called the web-socket handshake. Key point to remember is that Web-Socket handshake happens with an HTTP request.
• The server then accepts the upgrade request and sends the response 101–switching protocol confirming that the connection is now web-socket connection.
• From now on, both the client and server can communicate with each other.

Applications

Web-sockets are useful in gaming applications, stock market websites, real-time chat applications etc.

See you in the next one !

Read and Learn more on Techshshila –

• Understand TCP in the way it is !
• SSL/TLS sounds scary but no more !

Resources

1. Web sockets in 100 seconds : https://www.youtube.com/watch?v=1BfCnjr_Vjg
2. How web sockets work: https://www.youtube.com/watch?v=pnj3Jbho5Ck