vertx-web
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vert-x3
Implement 103 Early Hints (RFC 8297)
Describe the feature
Currently it's not possible to send an early-hints response (103 Early Hints (RFC 8297)) using the RoutingContext.
Use cases
Early hints is useful to instruct the browser to preload some webpage resources and reduce the loading time
Contribution
I never contributed to vert.x before, I don't know to implement it correctly. I found that vert.x implemented an HTTP response that can be sent before the final response, almost like 103 Early Hints: HTTP 100 Continue. Using RountingContext.writeContinue() I can send a HTTP 100 Continue before the final response. To implement early hints, vert.x-web could implement a method called RountingContext.writeEarlyHints(...) that works in the same way.
I've to be honest, this is the 1st time I've heard about this header. From what I understood from the RFC this is similar to what H2 does and we actually have some support (for H2) in the static handler:
https://github.com/vert-x3/vertx-web/blob/master/vertx-web/src/main/java/io/vertx/ext/web/handler/impl/StaticHandlerImpl.java#L524-L540
However in order to write the correct response, we may need to also implement some support for it on vertx-core as this special 103 mode requires writing the HTTP response headers, but not complete the request
This is also an experimental RFC and currently only supported by Google Chrome:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/103
We are using Vert.x since few years to implement our micro-frontend aggregator. It is currently used on leroymerlin.fr, leroymerlin.it, leroymerlin.es and leroymerlin.pt (2.3 billions hits/month). Until today we use server push to push critical css and js to the browser, we discover that Chrome removed the support of server push (https://developer.chrome.com/blog/removing-push/) in Chrome 106 (august 2022). This results in a 100ms increase in our "largest contentful paint".
Early Hint is replacing Server Push and should become a great feature to improve web performance. Browsers that are not able to handle early hints just ignore it.
There are many experimentation on early hints today and it should become a standard for all the browsers in few months https://www.fastly.com/blog/beyond-server-push-experimenting-with-the-103-early-hints-status-code https://blog.cloudflare.com/early-hints/ https://developer.chrome.com/blog/early-hints/
@Ludo-LM we are trying first to get https://github.com/eclipse-vertx/vert.x/pull/4508 there and then we can implement this like we did for push
@Ludo-LM @cavallium I can imagine this feature as a new handler that takes the functionality out of the static handler. You can imagine it like:
router.get("/static/*")
.handler(EarlyHintsHandler.create()
.link(Link.create("style.css").as("style").rel("preload"))
.link(Link.create("script.js").as("script").rel("preload"))
...
Which should then at the wire level write:
103 Early Hint
Link: </styles.css>; rel=preload; as=style
200 OK
Content-Type: text/html
<!DOCTYPE html>
...
<link rel=”stylesheet” type=”text/css” href=”style.css”>
...
According to the spec we can do multiple 103 responses, so we don't need to keep any state at the server processing side, as the HTML spec states that only the 1st will be processed.
https://html.spec.whatwg.org/multipage/semantics.html#early-hints
We need to define this Link @DataObject to allow customization of the resource.
I scoped it to 4.4.0 to be on the radar, not sure it makes the deadline though.