add a messaging pattern

gomore/messaging/README.md

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+# 发布订阅模式
+
+发布-订阅是一种消息传递模式，基本设计原则是将消息发布者和提供者分开，常常用于在不同组件之间传递消息。
+
+它有点类似于观察者行为设计模式,但是发布订阅模式往往要依赖一个中介<通常是各类的消息中间件，消息队列>
+
+有三个关键组是：消息本身、消息主题、订阅用户。

gomore/messaging/messaging.go

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+package gomore
+
+import (
+	"errors"
+	"time"
+)
+
+//Message for msg in bus
+type Message struct {
+	Alarm    int
+	priority int
+}
+
+//User for user
+type User struct {
+	ID   uint64
+	Name string
+}
+
+//Session of user
+type Session struct {
+	User      User
+	Timestamp time.Time
+}
+
+//Subscription for user
+type Subscription struct {
+	ch    chan Message
+	Inbox chan Message
+}
+
+//Publish a message to subscription queue
+func (s *Subscription) Publish(msg Message) error {
+	if _, ok := <-s.ch; !ok {
+		return errors.New("Topic has been closed")
+	}
+
+	s.ch <- msg
+
+	return nil
+}
+
+//Topic that user is interested in
+type Topic struct {
+	Subscribers    []Session
+	MessageHistory []Message
+}
+
+//Subscribe a topic
+func (t *Topic) Subscribe(uid uint64) (Subscription, error) {
+	// Get session and create one if it's the first
+
+	// Add session to the Topic & MessageHistory
+
+	// Create a subscription
+
+	return Subscription{}, nil
+}
+
+//Unsubscribe remove Subscription
+func (t *Topic) Unsubscribe(Subscription) error {
+
+	return nil
+}
+
+//Delete message
+func (t *Topic) Delete() error {
+
+	return nil
+}

gomore/messaging/messaging_test.go

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+package gomore