make sse keepalive interval configurable

Signed-off-by: Jörn Friedrich Dreyer <jfd@butonic.de>

changelog/unreleased/sse-keepalive.md

@@ -0,0 +1,5 @@
+Bugfix: make SSE keepalive interval configurable
+
+To prevent intermediate proxies from closing the SSE connection admins can now configure a `SSE_KEEPALIVE_INTERVAL`.
+
+https://github.com/owncloud/ocis/pull/10411

services/sse/pkg/config/config.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"context"
+	"time"
 
 	"github.com/owncloud/ocis/v2/ocis-pkg/shared"
 )
@@ -14,7 +15,8 @@ type Config struct {
 	Debug   Debug    `mask:"struct" yaml:"debug"`
 	Tracing *Tracing `yaml:"tracing"`
 
-	Service Service `yaml:"-"`
+	Service           Service       `yaml:"-"`
+	KeepAliveInterval time.Duration `yaml:"keepalive_interval" env:"SSE_KEEPALIVE_INTERVAL" desc:"To prevent intermediate proxies from closing the SSE connection send periodic SSE comments." introductionVersion:"6.7"`
 
 	Events       Events
 	HTTP         HTTP          `yaml:"http"`

services/sse/pkg/service/service.go

@@ -2,6 +2,7 @@ package service
 
 import (
 	"net/http"
+	"time"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/r3labs/sse/v2"
@@ -81,6 +82,18 @@ func (s SSE) HandleSSE(w http.ResponseWriter, r *http.Request) {
 	stream := s.sse.CreateStream(uid)
 	stream.AutoReplay = false
 
+	if s.c.KeepAliveInterval != 0 {
+		ticker := time.NewTicker(s.c.KeepAliveInterval)
+		defer ticker.Stop()
+		go func() {
+			for range ticker.C {
+				s.sse.Publish(uid, &sse.Event{
+					Comment: []byte("keepalive"),
+				})
+			}
+		}()
+	}
+
 	// add stream to URL
 	q := r.URL.Query()
 	q.Set("stream", uid)