WebSocket and HTTP are computer communications protocols that enable client-server communication. While both protocols operate over establishing the TCP connection with a server, they carry distinct differences that determine their capabilities and application modes.
This article will help in sorting out the key features of the HTTP and WebSocket protocols. The principles of their operation, main limitations, and major differences will be discussed. Also, you will learn about specific use cases when either HTTP or WebSocket is a better match.
What is HTTP?
HTTP (The Hypertext Transfer Protocol) is a request-response protocol used in the communication between a client, such as a web browser, and a server. The HTTP protocol is unidirectional, which means that the connection between the client and the server is established on the client’s initiative and maintained for the instant request only.
This type of connection involves the client sending an HTTP or HTTPS request and the server responding to this request. The client here is always the first to begin the communication process and request data from the server. After the HTTP request is completed, the connection is terminated. For a new request, a new connection to the server has to be established. That is, if the client sends 5 HTTP requests, 5 separate connections have to be made.
HTTP can operate based on any well-grounded connection protocol such as TCP (Transmission Control Protocol), for example. TCP uses a three-way handshake method to create a connection between the client and the server. As its name suggests, the three-way handshake method involves sending three messages by the TCP protocol before the session ends.
The main steps of an HTTP session can be described as follows:
- The client sends the first message to the server. This action aims at establishing the connection with the server by sending it a SYN (Synchronize Sequence Number) data packet. Accomplishing this step reveals if the server is open for communication.
- The server sends the second message to the client. The main goal of this message is to confirm that the server has received the client’s packet and acknowledged it (ACK packet).
- The client sends the third message to the server. When the client receives the SYN/ACK packet from the server, now it is the client’s turn to respond with an ACK packet to confirm the receipt of the message.
After this message, the connection closes.
Each HTTP protocol request message sent to the server contains the following information:
- A request line that includes HTTP methods (GET/POST etc.), the HTTP protocol version (HTTP/1.1, HTTP/2), etc.
- HTTP headers (content type and length)
- An optional message body that is being transmitted to the server
From HTTP to WebSocket
Despite the improvements in the latest HTTP versions, the HTTP protocol remained limited in many respects. One of the main disadvantages of the HTTP communication protocol is that it is a strictly unidirectional model, where all the data from the server has to be requested by the client in the first place. After the request is completed, the connection shuts down. This can be a severe obstacle when, for example, a client needs constant updates from the server in real-time mode.
The advent and development of the HTTP long-polling helped bypass this limitation to a certain degree. Long-polling is a method that servers use to maintain the client-server connection for a longer period, giving more time for the new information to become available and sending back a response once the updates arrive. The long-polling method works, however, it can be resource inefficient for the server, especially when there’s no data to send.
Another limitation of the HTTP protocol is that only one HTTP request can be sent over a single HTTP connection. To circumvent this restriction, the HTTP streaming method was developed. It allows the server to send a response of an unspecified length per one HTTP connection. Even with this upgrade, the problem is that the connection can be still interrupted at any time by an intermediary. It means that it is still not suitable enough for maintaining the connection and communication in real-time.
Due to these restraints and the inability to deal with them using other methods, a need for a different communication technology came.
What is WebSocket?
Just as HTTP, the WebSocket protocol operates on the top of the TCP connection. However, while the HTTP protocol is strictly unidirectional, which causes critical limitations to the communication process, WebSocket is a bidirectional protocol that enables full-duplex communication.
Being a full-duplex bidirectional protocol means that both the client and the server can push messages in both directions independently and without any linking to a previous request. Once the connection is established, the client and the server can communicate via the same TCP connection throughout the entire communication cycle.
The WebSocket protocol uses HTTP transmitting mechanisms and starts as standard HTTP requests and responses. Inside of this communication chain, the client requests to open a WebSocket connection. If the request is successful, the client and the server start using the TCP connection as a WebSocket connection. From now on, data can run over this connection until it is shut down by either the client or the server.
WebSocket vs HTTP: Use cases
Most of the WebSocket use cases involve real-time web applications. Real-time web applications are web apps capable of interacting with clients in a mode close to real-time. For this type of web application, it is essential to maintain constant communication with the clients to make sure they are updated on all the recent changes.
The WebSocket protocol enables continuous connection where clients and the server can send requests and responses back and forth. The WebSocket protocol creates a better user experience and uses fewer resources to update data. The HTTP protocol would be less efficient since it requires more connections and additional data.
To be more specific, there are three main categories of real-time web applications that are most likely to use WebSocket:
- Social media platforms and messaging services. These platforms rely on real-time web technologies and use the WebSocket protocol to establish connections between multiple users to exchange and broadcast messages in real-time.
- Gaming applications. In real-time multiplayer games, the client and the server have to send information packets at the same time. It can only be reached by using WebSocket since the HTTP protocol implies that the client is the one who has to send the request first.
- Other real-time applications where quick updates take place. Some other examples of real-time applications are the stock market, cryptocurrency, and sport betting web pages. If you see any scoreboards and price tables, most probably, the webpage is using WebSocket.
While WebSocket is the best solution when it comes to real-time updates and constant data flows, there are several cases when using HTTP would be a better option. Using HTTP is more suitable when you need to:
- Retrieve static data. Static data that needs to be fetched only once can be obtained with an HTTP request.
- Cache a resource. Caching makes sense when the appearance and content of a resource don’t change much over time and when multiple clients visit the resource, e.g. a high-traffic website. In this case, WebSocket can’t be employed since they don’t allow caching in contrast to HTTP.
- Address error scenarios. The HTTP protocol is based on the request-response model, which means it can support error scenarios.
Summing up the differences between WebSocket and HTTP
Now let’s briefly summarize the key differences between the HTTP and WebSocket protocols. The main differences are shown in the table below:
|Bidirectional protocol. Either the client or the server can send a message to one another without any previous requests needed.||Unidirectional protocol. The client initiates the connection for the instant request only.|
|Single TCP connection, meaning that the client and the server can communicate until the WebSocket connection is maintained and not terminated by either party.||Separate connections have to be established for separate requests. After the request is completed, the connection is terminated.|
|Mostly used by real-time web applications where immediate updates take place, and constant communication with the client is required.||Most suitable for cacheable resources, when static data needs to be fetched or to address error scenarios.|
HTTP and WebSocket are communication protocols used between the client and the server. The HTTP protocol is a forerunner of the WebSocket protocol, and they both operate over a TCP connection. With this in mind, they offer different functionality and are applicable in different use cases.
While the HTTP protocol is a suitable fit when it comes to caching resources and retrieving considerable amounts of static data, this communication protocol has limitations. HTTP is a unidirectional protocol that needs to establish separate connections for separate requests. It makes it inefficient for real-time web applications, where instant updates and constant communication with the client are of great importance.
WebSocket is a better option for this situation since it operates over the principles of bidirectional full-duplex communication and allows unlimited messaging per single TCP connection. These features make it indispensable for real-time web applications, such as messaging services, online multiplayer games, stock market websites, and many more.