NoContent Status Code for server-sent-events

[pjebs]

Server-Sent-Events basically stream responses to the client using (I think) chunked encoding.

The data looks like this:

event: userconnect
data: {"username": "bobby", "time": "02:33:48"}

<1 sec later>

event: usermessage
data: {"username": "bobby", "time": "02:34:11", "text": "Hi everyone."}

<1 sec later>

event: userdisconnect
data: {"username": "bobby", "time": "02:34:23"}

If the connection disconnects, the browser will automatically attempt to reconnect. That is part of the protocol.

For a server to close a connection, it must send a 204 No Content with empty body: https://javascript.info/server-sent-events
This signals to the browser to not attempt to reconnect.

Then the server must disconnect the client.

When we added the Early Hints:

func (ctx *RequestCtx) EarlyHints() error {
...
		c := acquireWriter(ctx)
		defer releaseWriter(ctx.s, c)
		_, err := c.Write(strEarlyHints) // []byte("HTTP/1.1 103 Early Hints\r\n")
		if err != nil {
			return err
		}
		
		_, err = c.Write(strCRLF)
		if err != nil {
			return err
		}
		err = c.Flush()
		if err != nil {
			return err
		}
	}
	return nil
}

Can we add the same functionality or a function to add a status code?

Also, is there way to disconnect?

When I try to send a Header: Connection: close it displays race condition warnings and then panics.
When I try to hijack,

fasthttpRequestCtx.Conn().Close()

it seems to panic on a nil pointer (perhaps due to streaming).

[erikdubbelboer]

Can you show some example code that gives that panic?
Doesn't it close the connection if you just return from the function where you write these responses?

[pjebs]

module stream

go 1.25.0

require (
	github.com/andybalholm/brotli v1.2.0 // indirect
	github.com/klauspost/compress v1.18.4 // indirect
	github.com/valyala/bytebufferpool v1.0.0 // indirect
	github.com/valyala/fasthttp v1.69.1-0.20260303234034-6fcfcb1ac0bc // indirect
)

package main

import (
	"bufio"
	"fmt"
	"time"

	"github.com/valyala/fasthttp"
)

func main() {
	fasthttp.ListenAndServe(":8081", serverSideEvent)
}

func serverSideEvent(ctx *fasthttp.RequestCtx) {
	ctx.Response.Header.Set("Content-Type", "text/event-stream")
	ctx.Response.Header.Set("Cache-Control", "no-cache")
	ctx.Response.Header.Set("Connection", "keep-alive")

	i := 0
	ctx.SetBodyStreamWriter(func(w *bufio.Writer) {
		for {

			w.Write([]byte("event: userconnect\n"))
			w.Write([]byte(fmt.Sprintf("data: {\"time\": \"%v\"}\n", time.Now())))
			w.Write([]byte("\n"))
			w.Flush()

			time.Sleep(2 * time.Second)

			if i == 5 {
				// Close connection
				w.Write([]byte("HTTP/1.1 204 No Content\r\n"))
				w.Write([]byte("Connection: close\n"))
				w.Flush()

				// THIS IS A CONTRIVED EXAMPLE. IN MY REAL USE CASE, I WON'T HAVE ACCESS TO ctx. 
				// PLUS I BELIEVE ctx WILL GET PUT BACK IN POOL ANYWAY!
				conn := ctx.Conn()

				// Flush Data
				bw := bufio.NewWriter(conn)
				err := ctx.Response.Write(bw)
				if err != nil {
					panic(err)
				}

				err = bw.Flush()
				if err != nil {
					panic(err)
				}

				conn.Close()
			}

			i++
		}
	})
}

You need to run:
go run -race . (race condition)

curl -v -k -X "GET" "http://localhost:8081"

[erikdubbelboer]

You're closing the connection but you don't terminate your write loop. It should be:

if i == 5 {
	// Close connection
	w.Write([]byte("HTTP/1.1 204 No Content\r\n"))
	w.Write([]byte("Connection: close\n"))
	w.Flush()
	return
}

Or this probably works just as well:

if i == 5 {
	return
}

[pjebs]

In my real code I am returning. Let me investigate further.

[pjebs]

Your saying I don't need to get ctx.Conn() to close connection? It's enough to send Connection: close header?

[pjebs]

When I send 204, the client thinks it is a payload. Is there any way to fix that, or is it not possible since we can't send Content Length?

[erikdubbelboer]

I don't see anything about needing to return a 204. The 204 is when the browser reconnects but you don't want to send events anymore. To stop sending initially you just close the connection (the return in your code). Then if the browser reconnects you return 204.