This blog post compares Socket.IO and WebSocket, two of the most popular options available for building realtime functionality such as chat, multiplayer games, or multi-user document collaboration. We will look at the following:
WebSocket is a realtime technology that enables bi-directional, full-duplex communication between client and server over a persistent, single-socket connection.
A WebSocket connection starts as an HTTP request/response handshake. If this initial handshake is successful, the client and server have agreed to use the existing TCP connection that was established for the HTTP request as a WebSocket connection. This connection is kept alive for as long as needed (in theory, it can last forever), allowing the server and the client to independently send data at will.
The WebSocket technology includes two core building blocks:
The WebSocket protocol. Standardized in December 2011 through RFC 6455, the WebSocket protocol enables real time communication between a WebSocket client and a WebSocket server over the web. It supports transmission of binary data and text strings.
The WebSocket API. Allows you to perform necessary actions, like managing the WebSocket connection, sending and receiving messages, and listening for events triggered by the WebSocket server. Almost all modern browsers support the WebSocket API.
Socket.IO is a realtime library that enables low-latency, bi-directional communication between web clients and servers. Socket.IO is built on top of the WebSocket protocol and provides additional capabilities such as automatic reconnections, broadcast support, or falling back to HTTP long polling.
Note that Socket.IO uses Engine.IO under the hood to establish the low-level connection and exchange data between client and server.
Beyond the officially-supported implementations, there are multiple other Socket.IO client and server implementations, maintained by the community, covering programming languages and platforms such as Python, Golang, or .NET.
Before WebSocket, HTTP techniques like AJAX long polling and Comet were the standard for building realtime apps. Compared to HTTP, WebSocket eliminates the need for a new connection with every request, drastically reducing the size of each message (no HTTP headers). This helps save bandwidth, improves latency, and makes WebSockets less taxing on the server side compared to HTTP.
Flexibility is ingrained into the design of the WebSocket technology, which allows for the implementation of application-level protocols and extensions for additional functionality (such as pub/sub messaging).
As an event-driven technology, WebSocket allows data to be transferred without the client requesting it. This characteristic is desirable in scenarios where the client needs to react quickly to an event (especially ones it cannot predict, such as a fraud alert).
Unlike HTTP, WebSocket is stateful. This can be tricky to handle, especially at scale, because it requires the server layer to keep track of each individual WebSocket connection and maintain state information.
WebSockets don’t automatically recover when connections are terminated – this is something you need to implement yourself, and is part of the reason why there are many WebSocket client-side libraries in existence.
Certain environments (such as corporate networks with proxy servers) will block WebSocket connections, while some browsers still don't support WebSockets.
Socket.io supports multiplexing through namespaces. Making use of namespaces enables you to minimize the number of TCP connections used, and save socket ports on the server.
Socket.IO allows the server side to flexibly broadcast events to all the connected clients. You can also broadcast events to a subset of clients via the rooms feature.
Socket.IO offers HTTP long-polling as a fallback option, which is useful in environments that don't support WebSockets.
Socket.IO provides a configurable Ping/Pong heartbeat mechanism, allowing you to detect if a connection is alive or not. Additionally, if and when a client gets disconnected, it automatically reconnects.
Socket.IO does not guarantee exactly-once messaging semantics. By default, an at-most-once guarantee is provided. Socket.IO can also be configured to provide at-least-once guarantees, although this brings additional engineering complexity - you have to use acknowledgments, timeouts, assign a unique ID to each event, and persist events in the database.
Socket.IO comes with limited native security features. For example, it doesn't provide end-to-end encryption, and it doesn't offer a mechanism to generate and renew tokens for authentication.
Socket.IO is not compatible with any other WebSocket implementation. For example, you can't use a plain WebSocket client with a Socket.IO server; a Socket.IO client will not be able to connect to a plain WebSocket server either.
Socket.IO is designed to work in a single region, rather than a multi-region architecture. This can lead to issues such as increased latency (if your users are in different regions), and even system downtime - what happens if the datacenter where you have your Socket.IO servers goes through an outage?
As similar technologies, Socket.IO and WebSocket can both be used to deliver realtime features for end-users. We can broadly group WebSocket and Socket.IO use cases into two categories:
Realtime updates, where the communication is unidirectional, and the server is streaming low-latency (and often frequent) updates to the client. Think of live sports updates, alerts, realtime dashboards, or live location tracking.
Bidirectional communication, where both the client and the server send and receive messages. Examples include chat applications, virtual events, and virtual classrooms (the last two usually involve features like polls, quizzes, and Q&As). WebSocket and Socket.IO can also be used to underpin multi-user synchronized collaboration functionality, such as multiple people editing the same document simultaneously.
WebSocket is a technology that enables two-way realtime communication between client and server. In contrast, Socket.IO is a library that provides an abstraction layer on top of WebSockets, making it easier to create realtime applications.
It seems that WebSockets have an edge in terms of performance over Socket.IO; for example, WebSockets have a much lower memory requirement compared to Socket.IO. However, some differences are to be expected. After all, Socket.IO is a more complex (and demanding) solution than raw WebSockets.
Socket.IO provides features such as auto-reconnect, rooms, and fallback to long polling. With vanilla WebSockets, you don’t benefit from such features out of the box; you have to build all these capabilities yourself if they're relevant for your use case.
Whether you should use Socket.IO or WebSocket depends on a couple of factors. Firstly, the specifics of your use case. For example, raw WebSocket is suitable for simplistic use cases, such as sending data to (most) browsers. On the other hand, for more complex use cases, such as a chat app, Socket.IO is a superior alternative, as it allows you to move faster than plain WebSockets.
Another aspect to bear in mind is the degree of flexibility you need for your use case. Raw WebSockets provide more flexibility - you can design your own architecture and your own protocol on top (although this is incredibly difficult and time-consuming). In contrast, Socket.IO comes with a pre-designed architecture and protocol, which may become restrictive at some point.
Irrespective of your choice (WebSocket or Socket.IO), building dependable realtime functionality and delivering it at scale to end-users is far from trivial.
We hope this article has helped you gain a good understanding of the advantages, disadvantages, and differences between Socket.IO and WebSockets. It's worth noting that Socket.IO and WebSocket are not the only technologies you can use to build realtime features. Here are some:
If you want to avoid the headache and high costs of managing WebSocket infrastructure in-house, you might want to consider using a fully-managed WebSocket solution.
Ably is a serverless WebSocket platform operating at the edge. We make it easy for developers to build live and collaborative experiences for millions of users in a few lines of code, without the hassle of managing and scaling WebSocket infrastructure. Our platform is underpinned by a globally-distributed, autoscaling network of datacenters and edge acceleration points of presence.
We provide robust capabilities and guarantees, including 25+ client SDKs targeting every major platform and programming language, feature-rich pub/sub APIs, and guaranteed message ordering and delivery.
To find out more about what Ably can do for you, get started with a free account.
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