Proposal: add sse extension

[li-jin-gou]

Is your feature request related to a problem? Please describe.

Currently Hertz does not support sse extension

Describe the solution you'd like

Add a sse extension or add a sse example

Additional context

• https://github.com/manucorporat/sse
• https://github.com/gofiber/recipes/tree/master/sse

[Haswf]

I would like to work on this.

[li-jin-gou]

I would like to work on this.

thanks,this is a feature that has real users who are looking forward to using it. @Haswf ❤️

[Haswf]

For anyone who are interested in this proposal, here is some update.

haswf/sse contains sse implementation for Hertz.

A few to-dos before pr:

1. add README
2. add a real-world example e.g. https://github.com/gin-gonic/examples/tree/master/server-sent-event
3. upstream license

[Haswf]

I ran into a problem that event.Render (which internally calls resp.AppendBody to write event) doesn't trigger a flush, which is required for server-sent event to work. For example, the following code only send response back to client after 10 seconds has elapled and the 2nd event has been rendered. The expected behaviour is http header is immediately returned with 1st event, then the 2nd event is sent after 10 seconds. Can someone know how Hertz response buffer work helps me out?

package main

import (
	"context"
	"time"

	"github.com/Haswf/sse"
	"github.com/cloudwego/hertz/pkg/app"
	"github.com/cloudwego/hertz/pkg/app/server"
	"github.com/cloudwego/hertz/pkg/common/hlog"
)

func main() {
	h := server.Default()

	h.GET("/sse", func(ctx context.Context, c *app.RequestContext) {
		// client can tell server last event it received with Last-Event-ID header
		lastEventID := sse.GetLastEventID(c)
		hlog.CtxInfof(ctx, "last event ID: %s", lastEventID)
		// you can call Render multiple times to send events to client
		c.Render(200, sse.Event{
			Event: "message",
			Data: map[string]string{
				"content": "hello world",
			},
		})
               // this doesn't work. long sigh
		c.Flush()
		time.Sleep(10 * time.Second)
		c.Render(200, sse.Event{
			Event: "timestamp",
			Data:  time.Now().Format(time.RFC3339),
		})
	})

	h.Spin()
}

[Haswf]

Postman privodes a reference server-sent event api, which returns immediately then event follows.

curl --location -N 'postman-echo.com/server-events/100'

[li-jin-gou]

refer to https://www.cloudwego.io/docs/hertz/tutorials/framework-exten/response_writer/

[Haswf]

refer to https://www.cloudwego.io/docs/hertz/tutorials/framework-exten/response_writer/

Thank you. This problem has been resolved by implementing a StreamBodyWriter according the document you referenced.