go-sse data-race condition example

Fail with a race detection.

$ go test -race
2021/07/02 16:58:04 server started.
2021/07/02 16:58:04 channel 'siner' created.
2021/07/02 16:58:04 new client connected to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
==================
WARNING: DATA RACE
Write at 0x00c00021a018 by goroutine 10:
  github.com/alexandrevicenzi/go-sse.(*Channel).SendMessage()
      /Users/iscander/go/pkg/mod/github.com/alexandrevicenzi/go-sse@v1.6.0/channel.go:26 +0x8c
  github.com/alexandrevicenzi/go-sse.(*Server).SendMessage()
      /Users/iscander/go/pkg/mod/github.com/alexandrevicenzi/go-sse@v1.6.0/sse.go:116 +0x21b
  example.com/m.(*servSSE).handle.func2()
      /Users/iscander/go-sse/sse_test.go:49 +0x13c

Previous write at 0x00c00021a018 by goroutine 12:
  github.com/alexandrevicenzi/go-sse.(*Channel).SendMessage()
      /Users/iscander/go/pkg/mod/github.com/alexandrevicenzi/go-sse@v1.6.0/channel.go:26 +0x8c
  github.com/alexandrevicenzi/go-sse.(*Server).SendMessage()
      /Users/iscander/go/pkg/mod/github.com/alexandrevicenzi/go-sse@v1.6.0/sse.go:116 +0x21b
  example.com/m.(*servSSE).handle.func2()
      /Users/iscander/go-sse/sse_test.go:49 +0x13c

Goroutine 10 (running) created at:
  example.com/m.(*servSSE).handle()
      /Users/iscander/go-sse/sse_test.go:30 +0x1f3
  example.com/m.TestSimultaneouslyDelivery()
      /Users/iscander/go-sse/sse_test.go:80 +0x54c
  testing.tRunner()
      /usr/local/Cellar/go/1.16.3/libexec/src/testing/testing.go:1193 +0x202

Goroutine 12 (running) created at:
  example.com/m.(*servSSE).handle()
      /Users/iscander/go-sse/sse_test.go:30 +0x1f3
  example.com/m.TestSimultaneouslyDelivery()
      /Users/iscander/go-sse/sse_test.go:80 +0x54c
  testing.tRunner()
      /usr/local/Cellar/go/1.16.3/libexec/src/testing/testing.go:1193 +0x202
==================
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:04 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 message sent to channel 'siner'.
2021/07/02 16:58:05 client disconnected from channel 'siner'.
2021/07/02 16:58:05 channel 'siner' has no clients.
2021/07/02 16:58:05 channel 'siner' closed.
2021/07/02 16:58:05 handler complete
--- FAIL: TestSimultaneouslyDelivery (1.01s)
    testing.go:1092: race detected during execution of test
FAIL
exit status 1
FAIL	example.com/m	1.040s

sse_test.go

package test

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"net/http/httptest"
	"testing"
	"time"

	"github.com/alexandrevicenzi/go-sse"
	"github.com/stretchr/testify/assert"
)

type servSSE struct {
	sse *sse.Server
}

func (s *servSSE) handle(w http.ResponseWriter, r *http.Request) {
	done := make(chan struct{})

  // start an HTTP handler
	go func() {
		defer close(done)
		s.sse.ServeHTTP(w, r)
	}()

  // start a number of Goroutines to send to the same channel
	for _, sin := range []string{"pride", "greed", "lust", "envy", "gluttony", "wrath", "sloth"} {
		go func(name string) {
			event := fmt.Sprintf("commit:%s", name)
			var (
				sin = struct {
					Count int    `json:"number"`
					Sin   string `json:"sin"`
				}{0, name}
			)
			for {
				select {
				case <-done:
					log.Printf("complete %s", name)
					return
				default:
				}
				sin.Count++
				js, _ := json.Marshal(sin)
				data := string(js)

				s.sse.SendMessage("siner", sse.NewMessage(id(), data, event))
				time.Sleep(300 * time.Millisecond)
			}
		}(sin)
	}

	<-done
	log.Println("handler complete")
}

func channelName(r *http.Request) string {
	return "siner"
}

func id() string {
	return fmt.Sprintf("%d", time.Now().UTC().Unix()*1000)
}

// Test example to rise a data race
func TestSimultaneouslyDelivery(t *testing.T) {
	s := servSSE{
		sse: sse.NewServer(
			&sse.Options{
				ChannelNameFunc: channelName,
				Logger:          log.Default(),
			}),
	}
	r, _ := http.NewRequest("GET", "/", nil)
	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(1*time.Second))
	r = r.WithContext(ctx)
	w := httptest.NewRecorder()

	s.handle(w, r)
	<-ctx.Done()
	cancel()

	result := w.Result()
	//body, _ := ioutil.ReadAll(result.Body)
	defer result.Body.Close()

	//fmt.Printf("\n==\n%s\n=\n", string(body))
	assert.Equal(t, http.StatusOK, result.StatusCode)
}

Successfully passed without a race detection

$ go test
2021/07/02 16:56:17 server started.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:17 channel 'siner' created.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:17 new client connected to channel 'siner'.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:17 message not sent because channel 'siner' has no clients.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 message sent to channel 'siner'.
2021/07/02 16:56:18 client disconnected from channel 'siner'.
2021/07/02 16:56:18 channel 'siner' has no clients.
2021/07/02 16:56:18 handler complete
2021/07/02 16:56:18 channel 'siner' closed.
PASS
ok  	example.com/m	1.016s