🤗 [Question]: How to implement single connection close detection for Sever Sent Events (SSE) streams using Hijack

[Tibz-Dankan]

Question Description

I'm trying to implement single connection close detection for server-sent event streams using Hijack but am currently facing the following challenges:

• when HijackSetNoResponse is true, the connection close detection works fine but events are NOT sent to the client.
• when HijackSetNoResponse is false(default), the connection close detection DOESN'T work but events are successfully sent to the client.

So how can I get both single connection close detection and sending events to the client to work together simultaneously? any help is highly appreciated

I have provided minimal reproducible code below.

Code Snippet (optional)

package main

import (
	"log"

	"bufio"
	"context"
	"fmt"
	"net"
	"time"

	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/cors"
	"github.com/gofiber/fiber/v2/middleware/logger"
	"github.com/valyala/fasthttp"
)

var GetLive = func(c *fiber.Ctx) error {
	c.Set("Content-Type", "text/event-stream")
	c.Set("Cache-Control", "no-cache")
	c.Set("Connection", "keep-alive")
	c.Set("Transfer-Encoding", "chunked")

	keepAliveTicker := time.NewTicker(5 * time.Second)
	ctx, cancel := context.WithCancel(context.Background())

	c.Context().HijackSetNoResponse(true) //Currenly set to true

	c.Context().Hijack(func(conn net.Conn) {
		defer conn.Close()

		buf := make([]byte, 1)
		for {
			if _, err := conn.Read(buf); err != nil {
				cancel()
				log.Println("Connection closed")
				return
			}
		}
	})

	c.Context().SetBodyStreamWriter(fasthttp.StreamWriter(func(w *bufio.Writer) {
		for {
			select {
			case <-ctx.Done():
				log.Println("Stream stopped")
				keepAliveTicker.Stop()
				return

			case <-keepAliveTicker.C:
				msg := fmt.Sprintf("data: %v\n\n", "keepalive")

				if _, err := fmt.Fprintf(w, "%s", msg); err != nil {
					log.Printf("Error writing keep-alive message: %v\n", err)
					return
				}

				if err := w.Flush(); err != nil {
					log.Printf("Error flushing keep-alive message: %v\n", err)
					return
				}
				log.Println("Keep-alive sent")
				// case <-otherChannel:
			}
		}
	}))

	return nil
}

func main() {
	app := fiber.New()
	app.Use(cors.New(cors.Config{
		AllowOrigins:  "*",
		AllowHeaders:  "Origin, Content-Type, Accept, Authorization",
		ExposeHeaders: "Content-Length",
	}))
	app.Use(logger.New())

	app.Get("/live", GetLive)

	log.Fatal(app.Listen(":5000"))
}

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my questions prior to opening this one.
• I understand that improperly formatted questions may be closed without explanation.

[welcome]

Thanks for opening your first issue here! 🎉 Be sure to follow the issue template! If you need help or want to chat with us, join us on Discord https://gofiber.io/discord

[JIeJaitt]

@Tibz-Dankan The issue occurs because HijackSetNoResponse(true) prevents fasthttp from sending HTTP headers automatically while allowing connection close detection, but SSE requires proper HTTP headers to work. When it's set to false, headers are sent correctly but connection close detection doesn't work. This creates a conflict between these two requirements. A solution would be to manually send the HTTP headers after setting HijackSetNoResponse(true), thus achieving both connection close detection and proper SSE functionality. I'll try to submit a PR that provides a simple SSE helper function to handle this automatically. What do you think? @ReneWerner87 @efectn @gaby

[Tibz-Dankan]

ooh, okay now I understand why it is behaving that way

Thanks, @JIeJaitt, but how would manually sending the HTTP headers after setting HijackSetNoResponse(true) look like?