SSE response taking a long time - IE, what am I doing wrong?

[kmanc]

Summary

Hey folks, would appreciate an assist if someone spots what I'm doing wrong. I copied the example SSE handler from the docs and made a super small change to the return (below for completeness), and I have a React app frontend that makes a call to the backend to set up the stream (shown below the axum part). It is taking ~20 minutes for my SSE handler to respond and complete the original request, at which point I get the stream going. Am I doing something super wrong here? Eventually my goal is to have the handler return stuff from a database query, but I figure until I sort this part out I should keep it simple as possible.

Thank you in advance!!

axum handler

use axum::{
    Router,
    routing::get,
    response::sse::{Event, KeepAlive, Sse},
};
use std::{time::Duration, convert::Infallible};
use tokio_stream::StreamExt as _ ;
use futures_util::stream::{self, Stream};

let app = Router::new().route("/sse", get(sse_handler));

async fn sse_handler() -> impl IntoResponse {
    // A `Stream` that repeats an event every second
    let stream = stream::repeat_with(|| Event::default().data("hi!"))
        .map(Ok)
        .throttle(Duration::from_secs(1));

    Sse::new(stream).keep_alive(KeepAlive::default()).into_response()
}

react request

<stuff>
const eventSource = new EventSource("location_of_endpoint");

eventSource.onmessage = (event) => {
    console.log(event);
}

eventSource.onerror = (error) => {
    console.error("Uh oh: ", error);
}
<stuff>

axum version

0.7.5

[kmanc]

For any unfortunate soul in the same position as me, the problem wasn't really the code on either the Rust or React side...it was Nginx.

You can fix by changing the Sse handler into the following, see this link for details

async fn sse_handler() -> impl IntoResponse {
    // A `Stream` that repeats an event every second
    let stream = stream::repeat_with(|| Event::default().data("hi!"))
        .map(Ok)
        .throttle(Duration::from_secs(1));

    let mut resp = Sse::new(stream).keep_alive(KeepAlive::default()).into_response();
    resp.headers_mut().insert("X-Accel-Buffering", "no".parse().unwrap());
    resp
}