What Is WebSocket and How Does It Work?

Key Takeaways

WebSocket is a communication protocol that allows simultaneous, bidirectional communication over a single connection.
It offers two main approaches for data handling: multiplexed streams (multiple data feeds over one connection) and multi-connections (using several WebSocket connections for different tasks).
Binance offers two types of WebSocket connections, each differing in the connection data required, the information provided, and their respective limitations.

Introduction

Software systems are indispensable for seamless and efficient communication across platforms and environments. To facilitate this, numerous interfaces and protocols have been developed, each tailored to specific use cases. Among these solutions, APIs are one of the most widely adopted and standardized solutions.

WebSocket is a particularly notable protocol among APIs, valued for its ability to maintain real-time communication between clients and servers. Its efficiency in delivering data swiftly makes it an essential tool for modern applications.

In this article, we delve into the mechanics of WebSocket, explore its working principles, highlight different ways to use it effectively, explain why it is often preferred over HTTP for real-time data transmission, and present the differences between WebSocket API and WebSocket Streams.

What Is WebSocket?

WebSocket is a computer communications protocol that enables simultaneous, bidirectional communication over a single Transmission Control Protocol (TCP) connection. Unlike traditional protocols, WebSocket is stateful, meaning the connection between the client and server remains active until explicitly terminated by either party. Once the connection is closed, it is permanently severed on both ends.

When establishing a WebSocket connection with Binance servers, clients can subscribe to multiple streams. These streams act as logical channels within the connection, delivering specific types of data. For instance, in a financial application, one stream might provide live price updates while another delivers trade data. Streams remain active for the duration of the connection and are closed automatically when the connection is terminated.

How the WebSocket Protocol Works

To establish a WebSocket connection, the client initiates a process called the handshake. This begins with the client sending an HTTP Upgrade request, which signals the desire to transition the connection from HTTP to WebSocket. The request includes details such as how the specific events will be handled during the WebSocket session.

On the server side, a TCP socket listens for incoming connection requests. Upon receiving a handshake request, the server responds with a confirmation, upgrading the connection to the WebSocket protocol. At this point, both parties can exchange data freely.

Essential WebSocket events

WebSocket connections rely on predefined events that manage various stages of the protocol's lifecycle. These events allow applications to respond to change and maintain stability during communication. There are four standard WebSocket events:

On open: Triggered when the WebSocket connection is successfully established. It signals that communication between the client and server can begin.
On message: Fires whenever a message is received from the server. This event carries the data transmitted by the server.
On close: Occurs when the WebSocket connection is intentionally or unintentionally closed. This may result from a user action, network issue, or server problem.
On error: Signals an error in the WebSocket connection, such as protocol violations or unexpected network failures.

These events ensure the application reacts appropriately, whether processing incoming messages, attempting to reconnect after an error, or cleaning up resources when a session ends.

The Differences Between WebSocket API and WebSocket Streams

Binance provides two types of WebSocket connections: WebSocket API and WebSocket Streams. Both utilize the WebSocket protocol to establish bidirectional communication with a server. However, they differ in terms of the connection data required, the information they provide, and their respective limitations.

The two WebSocket types have distinct base endpoints:

wss://ws-api.binance.com for the WebSocket API.
wss://stream.binance.com for WebSocket Streams.

The naming conventions for subscribing to a new stream also vary:

WebSocket Streams include an @ symbol before the stream name, and the parameter is directly written with the stream name.
WebSocket API separates the stream name from the parameters, and the stream name does not include the @ character.

In addition, WebSocket Streams are limited to market data endpoints, while the WebSocket API also supports user data endpoints.

Finally, Binance imposes rate limits on the number of requests or orders a user can make. Rate limits are applied exclusively to the WebSocket API, while WebSocket Streams have specific error messages that are not returned by the WebSocket API (e.g., Unknown Property, Invalid Value Type, etc.).

For additional information regarding protocol limitations, refer to the article: "What Are Binance WebSocket Limits?"

In summary, users can choose either the WebSocket Stream, which is simple to set up, has no rate limits, but offers limited retrievable data, or the WebSocket API, which provides access to a wider variety of streams and a more diverse range of information.

Exploring WebSocket Streams: Multiplexing vs. Multi-Connections

Clients often need access to various data streams simultaneously. This can be achieved through two primary methods: multiplexed streams or multi-connections.

What is Multiplexing in WebSocket?

Multiplexing allows multiple independent streams of data to be handled over a single WebSocket connection. By consolidating streams, this approach optimizes resource usage and enhances efficiency. Key benefits include:

Efficient resource usage: Using one connection for multiple streams minimizes network load, reduces latency, and decreases server overhead.
Dynamic subscription: Clients can subscribe to or unsubscribe from specific streams on-the-fly without disrupting the connection.

However, a single Binance’s WebSocket connection is limited to 1024 streams.

For example, using APIs such as Binance's WebSocket API, a user can subscribe to multiple streams over a single connection (e.g., price updates for BTC/USDT and ETH/USDT).

Python Snippet:

import logging
import time
from binance.websocket.spot.websocket_stream import SpotWebsocketStreamClient


def message_handler(_, message):
   logging.info(message)


my_client = SpotWebsocketStreamClient(on_message=message_handler, is_combined=True)
my_client.subscribe(
   stream=["bnbusdt@bookTicker", "ethusdt@kline_1m"],
)
time.sleep(10)
my_client.stop()

What are WebSocket Multi-Connections?

Multi-connection refers to establishing multiple WebSocket connections to handle distinct tasks or data streams. This approach is beneficial when the capacity of a single WebSocket connection is exceeded or when segregation of streams improves organization and reliability. Multi-connection setups also ensure continued data flow if one connection encounters an error.

When employing multi-connections, consider the following:

Resource management: Additional connections consume more CPU, memory, and bandwidth on both the client and server.
Connection limits: Some APIs impose limits on connection attempts. For example, Binance's WebSocket API restricts users to 300 connections per five minutes per IP. Exceeding this limit may result in temporary bans.

Why Choose WebSocket Over HTTP for Real-Time Applications

Unlike the HTTP protocol, which operates on a request-response model requiring the client to poll for updates, WebSocket enables real-time data exchange. Either the client or server can send data at any time without a prior request, making it highly suitable for applications requiring instant updates. Examples include chat applications, trading platforms, and online multiplayer games.

Moreover, the simplicity of WebSocket message formatting—compared to the more complex HTTP structure—streamlines communication, reduces latency, and enhances performance in real-time scenarios.

Closing Thoughts

WebSocket is a useful protocol for users seeking real-time data, offering fast and efficient communication with lower latency compared to traditional methods like HTTP. Whether for live financial tracking, real-time gaming updates, or other applications requiring immediate information, WebSocket enables smooth and continuous connectivity.

As real-time applications gain importance, understanding how WebSocket improves communication can help users make the most of its speed and reliability.