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81 lines
1.8 KiB
Markdown
81 lines
1.8 KiB
Markdown
Publish & Subscribe Messaging Pattern
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============
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Publish-Subscribe is a messaging pattern used to communicate messages between
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different components without these components knowing anything about each other's identity.
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It is similar to the Observer behavioral design pattern.
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The fundamental design principals of both Observer and Publish-Subscribe is the decoupling of
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those interested in being informed about `Event Messages` from the informer (Observers or Publishers).
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Meaning that you don't have to program the messages to be sent directly to specific receivers.
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To accomplish this, an intermediary, called a "message broker" or "event bus",
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receives published messages, and then routes them on to subscribers.
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There are three components **messages**, **topics**, **users**.
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```go
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type Message struct {
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// Contents
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}
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type Subscription struct {
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ch chan<- Message
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Inbox chan Message
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}
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func (s *Subscription) Publish(msg Message) error {
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if _, ok := <-s.ch; !ok {
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return errors.New("Topic has been closed")
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}
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s.ch <- msg
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return nil
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}
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```
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```go
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type Topic struct {
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Subscribers []Session
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MessageHistory []Message
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}
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func (t *Topic) Subscribe(uid uint64) (Subscription, error) {
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// Get session and create one if it's the first
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// Add session to the Topic & MessageHistory
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// Create a subscription
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}
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func (t *Topic) Unsubscribe(Subscription) error {
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// Implementation
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}
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func (t *Topic) Delete() error {
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// Implementation
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}
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```
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```go
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type User struct {
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ID uint64
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Name string
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}
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type Session struct {
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User User
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Timestamp time.Time
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}
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```
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Improvements
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============
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Events can be published in a parallel fashion by utilizing stackless goroutines.
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Performance can be improved by dealing with straggler subscribers
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by using a buffered inbox and you stop sending events once the inbox is full.
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