HTTP Status Code: 101 Switching Protocols.

When interacting with the web, we often come across common HTTP status codes like 200 OK, 404 Not Found, or 500 Internal Server Error. But there are many lesser-known yet important codes, such as HTTP Status Code 101 – Switching Protocols. In this article, we’ll explore what this status code means, when it's used, and why it's important in modern web applications.

What is the 101 HTTP Status Code?

The HTTP status code 101 Switching Protocols is part of the 1xx series, indicating an informational response from the server. It is utilized when the server agrees to upgrade its protocol and is ready to switch to a different protocol specified in the client's request. This status code is commonly associated with the WebSocket protocol, which allows for full-duplex communication channels over a single TCP connection.

Conditions for Receiving 101 Switching Protocols.

The HTTP status code 101 Switching Protocols is received under specific conditions when a client sends a request with the intention of switching to a different protocol. Here are the conditions for receiving the 101 Switching Protocols status:

Upgrade Request Header: The client sends a request with an Upgrade header, indicating the desire to switch protocols. This header specifies the protocol the client wants to switch to.
Server Agreement: The server supports the requested protocol and is willing to switch. The server includes the Upgrade header in its response to acknowledge the protocol switch.

How to Handle 101 Switching Protocols?

Client's Upgrade Request: The client sends an initial request to the server, specifying the desired protocol in the Upgrade header.

GET /example HTTP/1.1
Host: example.com
Upgrade: websocket
Connection: Upgrade

Server Acknowledgment (101 Switching Protocols): If the server supports the requested protocol, it responds with a 101 Switching Protocols status.

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade

Switching Protocols: Both the client and server switch to the agreed-upon protocol. Subsequent communication follows the rules and specifications of the newly established protocol.

In this example, the client requests to upgrade the protocol to WebSocket by including the Upgrade: websocket and Connection: Upgrade headers. The server, supporting WebSocket, responds with a 101 Switching Protocols status, acknowledging the switch. Subsequently, both the client and server switch to the WebSocket protocol for further communication.

Use Cases:

The most common use case for 101 Switching Protocols is during the establishment of WebSocket connections.
It can be employed for other scenarios where the client and server agree to switch to a different protocol for enhanced communication.

When You Don't See It

You won’t typically see 101 Switching Protocols in a browser or developer console unless you’re specifically working with protocol upgrades like WebSockets.

It’s a behind-the-scenes part of setting up persistent, real-time connections.

Conclusion.

HTTP status code 101 Switching Protocols serves as an indicator that the server agrees to upgrade its protocol based on the client's request. This is particularly significant in scenarios like WebSocket communication, providing a seamless transition to a different protocol for enhanced and real-time interaction between clients and servers.