The Hypertext Transfer Protocol (HTTP) has served as the backbone of web communication for over two decades. However, with the evolution of real-time web capabilities, HTTP started to show its limitations. This led to the development of WebSocket, a new communication protocol designed for low-latency bidirectional communication.
In this comprehensive technical guide, we will do a deep dive into WebSocket and HTTP protocols, analyze their differences, pros and cons, performance characteristics, and suitable use cases for each.
A Brief History of HTTP
To understand WebSocket, we first need to understand the history and origins of HTTP.
HTTP was created by Tim Berners-Lee at CERN in 1989. It was originally designed as a protocol to facilitate hypertext document sharing between researchers.
In the early 1990s, first web browsers like Mosaic and Netscape emerged. As the web started to grow rapidly, HTTP/0.9 and HTTP/1.0 were introduced. HTTP/1.1, which is still most widely used today, was standardized in 1997.
Over the decades, HTTP proved remarkably successful at serving static documents and HTML pages. However, with the evolution of real-time capabilities, HTTP started to show limitations in supporting low-latency bidirectional communication.
Limitations of HTTP
Here are some key limitations of HTTP that necessitated the development of a new communication protocol like WebSocket:
Unidirectional – HTTP only allows client to server requests. For server to push updates to client, client must poll server with frequent requests.
Request-Response model – Each HTTP request can only have one response from server. Cannot reuse connection for multiple messaging.
New TCP connection – Requires opening new TCP socket for each request-response adding networking overhead.
Text based – HTTP message formats like headers not optimal for binary data exchange.
Stateless – No client session context retained between requests by default.
Caching – Responses are often cached preventing real-time data transfer.
The Need for Bidirectional Full Duplex Communication
While HTTP request-response pattern performs well for document transfer and navigation, it starts to strain as more real-time capabilities are expected from the web.
Frequent long polling using HTTP incurs unnecessary overhead due to new TCP connections being opened. This triggered the need for a bidirectional full duplex communication protocol.
To address the limitations of HTTP, the WebSocket protocol was standardized in 2011 as part of the HTML5 specification.
WebSocket provides full-duplex communication over a single TCP connection. This makes it ideal for real-time web applications.
How WebSocket Works
WebSocket connection is initiated by client requesting a websocket handshake. This request is made over HTTP so that it can leverage existing HTTP ports 80 and 443.
If server supports websocket, it returns status 101 switching protocols response. This upgrades TCP socket from HTTP to WebSocket protocol.
Once handshake is complete, client and server can exchange messages in both directions independently. The WebSocket connection can remain open for as long as needed.
WebSocket Frame Format
WebSocket communication involves exchanging framed messages between client and server.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-------+-+-------------+-------------------------------+ |F|R|R|R| opcode|M| Payload len | Extended payload length | |I|S|S|S| (4) |A| (7) | (16/64) | |N|V|V|V| |S| | (if payload len==126/127) | | |1|2|3| |K| | | +-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - + | Extended payload length continued, if payload len == 127 | + - - - - - - - - - - - - - - - +-------------------------------+ | Payload Data continued ... | +---------------------------------------------------------------+
HTTP uses text-based headers and verbs like GET and POST whereas WebSocket frame format is better optimized for efficient binary data transfer.
Key Differences Between WebSocket and HTTP
Now that we have looked at both protocols in detail, let‘s analyze some of the fundamental differences between WebSocket and HTTP:
- HTTP is unidirectional – client sends request, server provides response.
- WebSocket is bidirectional – both client and server can send messages independently.
- HTTP opens a new TCP connection for each request-response.
- WebSocket starts with HTTP handshake then upgrades to persistent socket connection.
- HTTP uses headers with verbs like GET, POST and status codes.
- WebSocket uses custom frame-based binary messaging format.
- HTTP better suited for traditional document transfer and navigation.
- WebSocket excels at real-time communication like instant messaging, push notifications.
- HTTP has extra latency of TCP handshake per request.
- WebSocket has lower latency as only one handshake required.
WebSocket vs HTTP Latency and Overhead Comparison
To demonstrate the performance differences, here is a latency and overhead comparison between HTTP and WebSocket:
As we can see, WebSocket has significantly lower connection overhead compared to HTTP when multiple messages need to be sent.
When to use WebSocket vs HTTP?
Based on their technical characteristics and performance profile, here are some general guidelines on when to use WebSocket vs HTTP:
Use WebSocket for:
- Real-time applications – chat, live updates, multiplayer games etc.
- Push notifications from server to client
- Frequent messages where low latency is critical
- Continuous data streaming use cases
- Binary data transfer for efficiency
Use HTTP for:
- Traditional request-response scenarios
- REST API communication
- Fetching static or cacheable assets
- Server rendered pages and form submissions
- Cases where connection overhead is not critical
Fallback Options for Unsupported Browsers
One key aspect to consider is that WebSocket browser support is not as wide as HTTP. Older browsers do not implement required WebSocket APIs.
For supporting legacy browsers, we can fallback to HTTP long-polling or other polling techniques to simulate bidirectional communication.
There are also polyfill libraries like SockJS that add missing WebSocket objects and behavior in older browsers.
Best Practices for Using WebSocket Effectively
Here are some tips for working effectively with WebSocket when building real-time web applications:
- Properly handle connection open, close and error events.
- Make sure to encode/decode WebSocket binary frames correctly.
- Avoid sending unnecessary small messages to reduce overhead.
- Distinguish between user messages vs. control frames.
- Implement reconnection and heartbeat checks if needed.
- Secure WebSocket connection using WSS protocol.
- Handle unreliable delivery properly with acknowledgements.
HTTP and WebSocket are two fundamentally different communication protocols with their own strengths and use cases.
HTTP request-response model excels for traditional scenarios like document transfer, navigation and caching.
WebSocket full duplex messaging enables low latency real-time communication for capabilities like instant messaging, push notifications and real-time data streaming.
Understanding the key differences in communication model, connection management, framing, performance and use cases provides clarity on when to use which protocol.
By leveraging both protocols properly in web applications, we can build rich user experiences that combine the best of static content delivery with real-time messaging.