Merge pull request #6 from PDOK/slack-ratelimit

feat(slack) add rate limiting

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/slack-go/slack v0.13.0
 	github.com/stretchr/testify v1.9.0
 	github.com/traefik/traefik/v2 v2.11.5
+	golang.org/x/time v0.5.0
 	golang.org/x/tools v0.22.0
 	k8s.io/apimachinery v0.30.2
 	k8s.io/client-go v0.30.2
@@ -72,7 +73,6 @@ require (
 	golang.org/x/sys v0.21.0 // indirect
 	golang.org/x/term v0.21.0 // indirect
 	golang.org/x/text v0.16.0 // indirect
-	golang.org/x/time v0.5.0 // indirect
 	gomodules.xyz/jsonpatch/v2 v2.4.0 // indirect
 	google.golang.org/protobuf v1.34.2 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect

internal/service/slack.go

@@ -5,23 +5,38 @@ import (
 
 	"github.com/PDOK/uptime-operator/internal/model"
 	"github.com/slack-go/slack"
+	"golang.org/x/time/rate"
 	"sigs.k8s.io/controller-runtime/pkg/log"
 )
 
+const (
+	nrOfMessagesPerSec   = 1
+	nrOfMessagesPerBurst = 10
+)
+
 type Slack struct {
 	webhookURL string
 	channelID  string
+
+	rateLimit *rate.Limiter
 }
 
 func NewSlack(webhookURL, channelID string) *Slack {
 	return &Slack{
 		webhookURL: webhookURL,
 		channelID:  channelID,
+
+		// see https://api.slack.com/apis/rate-limits
+		rateLimit: rate.NewLimiter(nrOfMessagesPerSec, nrOfMessagesPerBurst),
 	}
 }
 
 func (s *Slack) Send(ctx context.Context, message string) {
-	err := slack.PostWebhook(s.webhookURL, &slack.WebhookMessage{
+	err := s.rateLimit.Wait(ctx)
+	if err != nil {
+		log.FromContext(ctx).Error(err, "failed waiting for slack rate limit")
+	}
+	err = slack.PostWebhook(s.webhookURL, &slack.WebhookMessage{
 		Channel:   s.channelID,
 		Text:      message,
 		Username:  model.OperatorName,