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.go

@@ -0,0 +1,84 @@
+// 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 (
+	"sync"
+)
+
+// Manager manages the eventsource Messengers
+type Manager struct {
+	mutex sync.Mutex
+
+	messengers map[int64]*Messenger
+}
+
+var manager *Manager
+
+func init() {
+	manager = &Manager{
+		messengers: make(map[int64]*Messenger),
+	}
+}
+
+// GetManager returns a Manager and initializes one as singleton if there's none yet
+func GetManager() *Manager {
+	return manager
+}
+
+// Register message channel
+func (m *Manager) Register(uid int64) <-chan *Event {
+	m.mutex.Lock()
+	messenger, ok := m.messengers[uid]
+	if !ok {
+		messenger = NewMessenger(uid)
+		m.messengers[uid] = messenger
+	}
+	m.mutex.Unlock()
+	return messenger.Register()
+}
+
+// Unregister message channel
+func (m *Manager) Unregister(uid int64, channel <-chan *Event) {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+	messenger, ok := m.messengers[uid]
+	if !ok {
+		return
+	}
+	if messenger.Unregister(channel) {
+		delete(m.messengers, uid)
+	}
+}
+
+// UnregisterAll message channels
+func (m *Manager) UnregisterAll() {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+	for _, messenger := range m.messengers {
+		messenger.UnregisterAll()
+	}
+	m.messengers = map[int64]*Messenger{}
+}
+
+// SendMessage sends a message to a particular user
+func (m *Manager) SendMessage(uid int64, message *Event) {
+	m.mutex.Lock()
+	messenger, ok := m.messengers[uid]
+	m.mutex.Unlock()
+	if ok {
+		messenger.SendMessage(message)
+	}
+}
+
+// SendMessageBlocking sends a message to a particular user
+func (m *Manager) SendMessageBlocking(uid int64, message *Event) {
+	m.mutex.Lock()
+	messenger, ok := m.messengers[uid]
+	m.mutex.Unlock()
+	if ok {
+		messenger.SendMessageBlocking(message)
+	}
+}