WebSocket vs HTTP: A Detailed Comparison

The internet as we know it today runs on HTTP (Hypertext Transfer Protocol). But with the rise of real-time web applications, HTTP‘s limitations have become more apparent. This led to the development of WebSocket, a new communication protocol that aims to overcome these limitations.

In this post, we‘ll take an in-depth look at how WebSocket and HTTP work, their key differences, and when to use each protocol.

Overview of HTTP

HTTP is an application-layer protocol for transmitting hypermedia documents like HTML. It follows a client-server model where the client initiates requests and the server sends responses.

Some key points about HTTP:

• HTTP is a request-response protocol. The client makes requests and the server provides resources in response.

• HTTP connections are short-lived. A new connection is established for each request-response cycle.

• HTTP connections are unidirectional. Requests go client -> server and responses go server -> client.

• HTTP uses TCP as the transport layer protocol. TCP ensures reliable delivery of data.

• HTTP is a stateless protocol. No data is retained between connections.

• HTTP supports caching for improved performance. Frequently accessed resources can be cached to avoid re-fetching.

The typical flow of HTTP communication looks like this:

1. The client initiates a TCP connection to the server
2. The client sends an HTTP request message specifying the resource it needs
3. The server sends back an HTTP response message containing the resource
4. The TCP connection is closed

If the client wants additional resources, new TCP connections must be opened.

Limitations of HTTP

HTTP works well for simple request-response scenarios like document transfer. But it has some limitations when building real-time applications:

1. HTTP doesn‘t support full-duplex communication

HTTP only allows requests to be sent from client to server. For bidirectional communication, the client would have to poll the server continuously to get updates.

2. Creating new connections has overhead

For every request, a new TCP connection must be established and TLS handshake performed. This wastes resources.

3. Messages have high latency

Each request can only be sent after the response to the previous one is received. This head-of-line blocking delays messages.

4. No support for unsolicited messages

The server can‘t push data to clients until they request it. HTTP streaming helps but doesn‘t fully address this.

5. HTTP headers add overhead

Headers must be sent even for small amounts of data, adding overhead.

These limitations motivated the creation of a new protocol optimized for real-time data exchange – WebSocket.

Introducing WebSocket

WebSocket was designed to overcome HTTP‘s limitations and enable real-time communication between clients and servers.

Here are some key aspects of WebSocket:

• WebSocket enables full-duplex communication over a single TCP connection. Both client and server can send data at any time.

• The initial handshake uses HTTP for backwards compatibility, but data transfer uses a separate WebSocket protocol.

• Messages have very low latency since there is no handshake overhead per message.

• No headers are required for sending data after the initial handshake. Binary data can be sent as-is.

• WebSockets allow unsolicited messages. Servers can send real-time updates to clients without waiting for requests.

• The connection stays open until explicitly closed by either party. This reduces network overhead.

The WebSocket communication flow looks like:

1. Client sends HTTP request to initiate WebSocket handshake

2. Server replies with response completing the handshake

3. WebSocket connection is established over the same underlying TCP socket

4. Client and server exchange WebSocket data frames containing messages

5. Either client or server closes connection when done

This enables much more flexible real-time communication compared to HTTP.

Key Differences Between WebSocket and HTTP

Let‘s summarize some of the major differences between the two protocols:

WebSocket	HTTP
Bidirectional	Unidirectional
Persistent connection	Short-lived connections
Low overhead	High overhead per request/response
Unsolicited messages supported	Requires client to poll for updates
Primarily used for real-time apps	Optimized for document transfer
Efficient small message transfer	Header overhead even for small messages
Binary frame-based protocol	Text-based with metadata

In a nutshell:

• HTTP is good for retrieving documents and resources when low-latency real-time communication is not required.

• WebSocket is optimized for low-latency real-time communication and pushing updates from server to clients.

When to Use HTTP vs WebSocket

Based on their strengths, here are some general guidelines on when to use HTTP vs WebSocket:

Use HTTP for:

• Retrieving static resources like documents, images, files
• Making infrequent requests for data
• API calls to get or update data
• Delivery of complete resources/documents
• Page navigation and form submissions
• Caching of resources

Use WebSocket for:

• Real-time dashboards and monitoring
• Chat applications and instant messaging
• Real-time location tracking
• Multiplayer games
• Pushing updates from server to client
• Rapid exchange of small messages
• Collaborative applications with live cursors
• Financial/stock trading platforms

There are also hybrid use cases where both HTTP and WebSocket are used:

• Single-page web apps use HTTP for initial document transfer then use WebSocket for real-time updates
• REST APIs use HTTP requests for CRUD operations but use WebSocket for pushing notifications

So in summary:

• Use HTTP for traditional request-response interactions
• Use WebSockets when you need fast real-time communication and server push capabilities

WebSocket Frames vs HTTP Messages

WebSocket and HTTP also differ in their approach to formatting data:

HTTP

• HTTP messages contain headers with metadata and the payload body.

• Even small amounts of data require headers which add overhead.

• The body can contain text or binary data.

• Extra work is needed to parse metadata headers.

WebSocket

• WebSocket uses framed messages with a small header and the data payload.

• Frame header contains just enough metadata to reassemble message.

• No headers for metadata that isn‘t needed for framing.

• Frames are sent as binary data by default.

• Easier to parse since header has fixed size.

So WebSockets use a frame-based approach optimized for efficient real-time transmission, unlike HTTP‘s text-based headers.

Fallback Options When WebSocket Not Available

While most modern browsers support WebSocket, sometimes fallback options are needed for compatibility:

• Long-polling – The client makes an HTTP request and keeps the connection open until the server sends a response. Useful but can be resource-intensive.

• HTTP streaming – The server sends multiple responses to one HTTP request. Provides some bi-directionality but still has overhead.

• SockJS – A JavaScript library that provides a WebSocket-like object. Falls back to other options like long-polling if needed.

• WebSocket emulation – Simulate WebSocket API over HTTP requests. Increased latency but compatible.

So while native WebSocket is preferred, these fallbacks help support more environments when needed.

Summary: Choosing Between WebSocket and HTTP

To summarize the WebSocket vs HTTP decision:

• Use WebSocket when you need real-time, low-latency, bidirectional communication.

• Stick to HTTP for typical request-response scenarios like document transfer.

• Know the fallback options if you need to support clients that don‘t have WebSocket.

• Both protocols can co-exist in the same application. Use each one where it makes the most sense.

• WebSocket doesn‘t fully replace HTTP – they solve different problems.

WebSocket represents the future of real-time web communication while HTTP continues to evolve incrementally. Knowing when to use each technology and how they complement each other enables building robust, scalable applications.