The 103 Early Hints status code is a part of the HTTP/2 protocol, specifically introduced in RFC 8297. This status code aims to improve the performance of web applications by allowing servers to send hints to clients about resources that are likely to be needed for rendering the requested page. In this article, we will dive into the details of 103 Early Hints, including its use cases, benefits, and examples of request and response.
Use Cases
The primary use case for 103 Early Hints is to optimize the loading of web pages by reducing the time spent waiting for the server to provide all the necessary resources. When a client requests a page, the server can send 103 Early Hints along with the HTTP headers of the resources that will be required to render the page. This allows the client to start fetching these resources even before the server has finished processing the request, potentially reducing the overall load time.
Benefits
The main benefit of 103 Early Hints is the potential to decrease the time it takes for a web page to load. By allowing clients to start fetching resources earlier, the server can reduce the amount of time the client spends waiting for resources to be sent. This is particularly useful for web applications that have many resources, such as stylesheets, scripts, and images, as it can help avoid the “waterfall” effect where clients must wait for each resource to be sent sequentially.
Example Request and Response
Let’s take a look at an example of a request and response using the 103 Early Hints status code. In this example, the client requests a web page from the server, and the server responds with 103 Early Hints along with the headers of the resources that will be needed to render the page.
Request
GET /example-page HTTP/2
Host: example.com
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8Response
HTTP/2 103 Early Hints
Link: </styles/app.css>; rel=preload; as=style
Link: </scripts/app.js>; rel=preload; as=script
Link: </images/logo.png>; rel=preload; as=image
HTTP/2 200 OK
Content-Type: text/html
Content-Length: 1234
...In this example, the server sends 103 Early Hints along with the Link headers for the resources that are likely to be needed for rendering the requested page. The client can then start fetching these resources while the server continues to process the request. Once the server has finished processing the request, it sends the 200 OK status code along with the requested page’s content.
It’s important to note that the 103 Early Hints status code does not guarantee that the resources listed in the Link headers will be required for rendering the page. The client should still be prepared to handle cases where the resources are not needed or where additional resources are required.
Summary
The 103 Early Hints status code is a valuable tool for optimizing the loading of web pages by allowing servers to send hints to clients about the resources that are likely to be needed for rendering the requested page. By enabling clients to start fetching these resources earlier, the server can potentially reduce the overall load time and improve the performance of web applications. This status code is especially useful for web applications with many resources, as it can help prevent the “waterfall” effect where clients must wait for each resource to be sent sequentially.
