Add EventSource support (#11235)

If the browser supports EventSource switch to use this instead of
polling notifications.

Signed-off-by: Andrew Thornton art27@cantab.net

modules/eventsource/manager_run.go

@@ -0,0 +1,50 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package eventsource
+
+import (
+	"context"
+	"time"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/graceful"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/timeutil"
+)
+
+// Init starts this eventsource
+func (m *Manager) Init() {
+	go graceful.GetManager().RunWithShutdownContext(m.Run)
+}
+
+// Run runs the manager within a provided context
+func (m *Manager) Run(ctx context.Context) {
+	then := timeutil.TimeStampNow().Add(-2)
+	timer := time.NewTicker(setting.UI.Notification.EventSourceUpdateTime)
+loop:
+	for {
+		select {
+		case <-ctx.Done():
+			timer.Stop()
+			break loop
+		case <-timer.C:
+			now := timeutil.TimeStampNow().Add(-2)
+
+			uidCounts, err := models.GetUIDsAndNotificationCounts(then, now)
+			if err != nil {
+				log.Error("Unable to get UIDcounts: %v", err)
+			}
+			for _, uidCount := range uidCounts {
+				m.SendMessage(uidCount.UserID, &Event{
+					Name: "notification-count",
+					Data: uidCount,
+				})
+			}
+			then = now
+		}
+	}
+	m.UnregisterAll()
+}