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Subscribe & Receive Message

After we have connected to broker, we can subscribe to any topic that we want and receive emitted message from that particular topic when the broker pushes the message.

Subscribe to topics from Broker​

To subscribe to a topic from the broker. we can invoke CourierSession/subscribe(_:) and pass a tuple containing the topic string and QoS enum.

courierClient.subscribe(("chat/user1", QoS.zero))

You can also subscribe to multiple topics, invoking CourierSession/subscribe(_:) and pass an array containing tuples of topic string and QoS enum

courierClient.subscribe([
    ("chat/user1", QoS.zero),
    ("order/1234", QoS.one),
    ("order/123456", QoS.two),
])

Receive Message from Subscribed Topic​

After you have subscribed to the topic, you need to subscribe to a message publisher passing the associated topic using CourierSession/messagePublisher(topic:). This method uses Generic for serializing the binary data to a type. Make sure you have provided the associated MessageAdapter that can decode the data to the type. 

courierClient.messagePublisher(topic: topic)
    .sink { [weak self] (note: Note) in
        self?.messages.insert(Message(id: UUID().uuidString, name: "Protobuf: \(note.title)", timestamp: Date()), at: 0)
    }.store(in: &cancellables)

This method returns AnyPublisher which you can chain with operators such as AnyPublisher/filter(predicate:) or AnyPublisher/map(transform:).

The observable API that Courier provide is very similar to Apple Combine although it is implemented internally using RxSwift so we can support iOS 12, only the filter and map operators are supported.

Unsubscribe from topics​

To unsubscribe from a topic. we can invoke CourierSession/unsubscribe(_:) and pass a topic string.

courierClient.unsubscribe("chat/user1")

You can also subscribe to multiple topics, invoking CourierSession/unsubscribe(_:) and pass an array containing tuples of topic string and QoS enum

courierClient.unsubscribe([
    "chat/user1",
    "order/"
])