Comparing Client-Server Communication Methods: Short Polling, Long Polling, SSE, and WebSocket |

Comparing Client-Server Communication Methods: Short Polling, Long Polling, SSE, and WebSocket

Posted on May 15, 2023

Short Polling

Short polling is a client-server communication method where the client periodically sends requests to the server to check if there is any new data available. This is like constantly asking “Is there any new data?” at regular intervals. If there is new data, the server responds with it; if not, it responds saying there’s nothing new.

Long Polling

Long polling is a variation of the traditional polling technique and allows emulation of an information push from a server to a client. With long polling, the client requests information from the server in a similar way to short polling, but with the expectation that the server may not respond immediately. If the server has no new information for the client when the poll is received, instead of sending an empty response, the server holds the request and waits for some information to be available. Once the information becomes available, a complete response is sent to the client. The client then immediately re-requests information.

Server-Sent Events (SSE)

Server-Sent Events (SSE) is a standard that allows a web server to push updates to the client whenever it wants. Unlike short and long polling, where the client must request updates, SSE allows the server to send updates whenever new data is available. The client opens a connection to the server and waits for data to arrive. This is more efficient than polling as it reduces the number of requests a client has to make.

WebSocket

WebSocket is a communication protocol that provides full-duplex communication between the client and the server over a single, long-lived connection. This means that both the client and the server can send data to each other at any time. WebSocket is more efficient than both polling and SSE because it doesn’t require multiple HTTP requests to send and receive data.

Here is a diagram illustrating the concepts of Short Polling, Long Polling, Server-Sent Events (SSE), and WebSocket:

Diagram

In this diagram:

  • Short Polling: The client sends regular requests to the server. The server responds when data is available.
  • Long Polling: The client sends a request and waits. The server responds when data is available.
  • Server-Sent Events (SSE): The client opens a connection and waits. The server pushes updates to the client.
  • WebSocket: The client opens a connection with the server. Both the client and the server can send data to each other at any time, enabling full-duplex communication.

What is the best option?

  1. Short Polling: This is the simplest method, but also the least efficient. It’s easy to implement, but it generates a lot of network traffic, and it may have a noticeable delay (equal to the polling interval) in delivering updates. You might use this if your updates are infrequent and not time-sensitive.

  2. Long Polling: This method reduces network traffic and delivers updates with no delay. It’s more complex to implement than short polling, and it may require more resources on the server to maintain open requests. This might be a good choice if you need real-time updates but can’t use WebSockets or SSE due to browser compatibility issues.

  3. Server-Sent Events (SSE): This is a good choice for one-way real-time updates (from server to client) that need to be delivered with no delay. It’s more efficient than long polling, but not as efficient as WebSockets. It’s easier to implement than WebSockets, but it doesn’t support IE and older browsers.

  4. WebSockets: This is the most efficient method for real-time, two-way communication. It supports any kind of message content (not just text), and it doesn’t use HTTP, so it can bypass some network restrictions. However, it’s also the most complex to implement and debug, and it may not be supported in all environments.

In conclusion, if you need the most efficient, real-time, two-way communication and can handle the complexity, then WebSockets is the best choice. If you only need one-way updates and want something easier to implement, consider SSE. If you’re dealing with older browsers or network environments that don’t support WebSockets or SSE, consider long polling. If your updates are infrequent and not time-sensitive, and you want the simplest possible solution, consider short polling.

You can use a combination of WebSockets and long polling to ensure real-time communication even when the client does not support WebSockets. This approach is commonly used in libraries and frameworks that provide real-time communication.

Here’s how it works:

  1. Try WebSockets first: When a client attempts to connect, your application first tries to establish a WebSocket connection.

  2. Fallback to long polling: If the WebSocket connection fails (either because the client doesn’t support WebSockets, or because a network firewall blocks the connection), your application falls back to long polling.

This way, you can still get the benefits of WebSockets for clients that support it, while also providing a robust solution for clients that don’t.

One popular library that uses this approach is Socket.IO. It provides real-time communication between web clients and servers, and it automatically handles the transition between WebSockets and long polling depending on what the client supports.