SSE close event is not being forwarded to the server when using Vite as Reverse Proxy

[MajedMuhammad]

Describe the bug

This is a duplicate of #12157. I am opening this bug due to it is closed and can't proceed with it.
As the title: SSE close event is not being forwarded to the server when using Vite as Reverse Proxy.
In the dev server and in the preview server, both are not forwarding the close event to the server.
After many hours of debugging, and traffic inspection, after calling sse.close(), the connection is closed between the client and the proxy, but still open between the proxy and the server!

Reproduction

#12157

Steps to reproduce

No response

System Info

Ubuntu.

Used Package Manager

pnpm

Logs

No response

Validations

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• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
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• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

I found this workaround.
https://github.com/chimurai/http-proxy-middleware/blob/cd58f962aec22c925b7df5140502978da8f87d5f/src/plugins/default/debug-proxy-errors-plugin.ts#L25-L37
If you try this out by configure option of server.proxy and works for you, I think we can include this by default.

[MajedMuhammad]

res.on('close', () => { console.log(”closed”); })

I have tried this to listen to close events from the client using both res and req (i.e., proxyReq and proxyRes events). It is not listening to close events from the client when using EventSource, but it works when the connection is closed by the server. I will double-check for you and confirm.

[MajedMuhammad]

I confirm that Vite proxy is not listening to close events when emitted from EventSource.

[MajedMuhammad]

Important Update:
The solution provided is working fine.
I mistakenly confirmed because I was using it like:

proxy.on("proxyReq", (req) => {
    req.on("close", () => {
        proxy.destroy();
    });
});

It will never work due to the first parameter is just the Client Request, not the actual streaming request.
It works if three parameters are passed:

proxy.on("proxyReq", (proxyReq, req, res) => {
    res.on("close", () => {
        if (!res.writableEnded) { # This if statement to check if the server still writing
            proxyReq.destroy();
        }
    });
});

I think it will be better as you mentioned if it is enabled by default. Whenever the proxy gets a close event, then the related proxy should be destroyed.