sse_server.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"strings"
	"time"
)

var (
	datacounter = 0
	newline     = "\n"
)

func main() {
	http.HandleFunc("/events", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Connection", "keep-alive")
		w.Header().Set("Content-Type", "text/event-stream")
		w.Header().Set("Transfer-Encoding", "chunked")
		for e := range time.Tick(2 * time.Second) {
			datacounter += 1
			fmt.Fprint(w, formatData(datacounter, "time", e.String()))
			w.(http.Flusher).Flush()
		}
	})
	log.Fatal(http.ListenAndServe("127.0.0.1:8080", nil))
}

func formatData(id int, event, data string) string {
	var output []string

	if id > 0 {
		output = append(output, fmt.Sprintf("id: %d", id))
	}
	if event != "" {
		output = append(output, fmt.Sprintf("event: %s", event))
	}

	datas := strings.Split(data, newline)
	for i, data := range datas {
		datas[i] = fmt.Sprintf("data: %s", data)
	}
	output = append(output, strings.Join(datas, newline))
	return strings.Join(output, newline) + strings.Repeat(newline, 2)
}