## Establish Connection

Before you can publish/subscribe to a topic, you need to establish a connection. You can do that using one of the following methods provided by the SDK.

### Certificate based mutual authentication

To connect with the AWS IoT Core service on the standard MQTT port 8883, you can use the `connect` API as shown below.

```swift
func mqttEventCallback(_ status: AWSIoTMQTTStatus ) {
    print("connection status = \(status.rawValue)")
}

iotDataManager.connect(withClientId: "<YOUR_CLIENT_ID>",
                       cleanSession: true,
                       certificateId: "<YOUR_CERTIFICATE_ID>",
                       statusCallback: mqttEventCallback)
```

The AWS IoT Core service also allows you to connect devices using MQTT with certificate based mutual authentication on port 443. You can do this using the `connectUsingALPN` API as shown below. See [MQTT with TLS client authentication on port 443](https://aws.amazon.com/blogs/iot/mqtt-with-tls-client-authentication-on-port-443-why-it-is-useful-and-how-it-works/) for more information.

```swift
func mqttEventCallback(_ status: AWSIoTMQTTStatus ) {
    print("connection status = \(status.rawValue)")
}

iotDataManager.connectUsingALPN(withClientId: "<YOUR_CLIENT_ID>",
                       cleanSession: true,
                       certificateId: "<YOUR_CERTIFICATE_ID>",
                       statusCallback: mqttEventCallback)
```

You can take a look at the [API Reference](https://aws-amplify.github.io/aws-sdk-ios/docs/reference/AWSIoT/Classes/AWSIoTDataManager.html#/c:objc(cs)AWSIoTDataManager(im)connectUsingALPNWithClientId:cleanSession:certificateId:statusCallback:) to get more information.

### AWS Credentials based Authentication

This method uses AWS Signature Version 4 Credentials to sign the request to connect to the AWS IoT endpoint.

```swift
func mqttEventCallback(_ status: AWSIoTMQTTStatus ) {
    print("connection status = \(status.rawValue)")
}

iotDataManager.connectUsingWebSocket(withClientId: "<YOUR_CLIENT_ID>",
                                     cleanSession: true,
                                     statusCallback: mqttEventCallback)
```

You can take a look at the [API Reference](https://aws-amplify.github.io/aws-sdk-ios/docs/reference/AWSIoT/Classes/AWSIoTDataManager.html#/c:objc(cs)AWSIoTDataManager(im)connectUsingWebSocketWithClientId:cleanSession:statusCallback:) to know more information.

### Custom Authentication

AWS IoT allows you to define custom authorizers that allow you to manage your own authentication and authorization strategy using a custom authentication service and a Lambda function. Custom authorizers allow AWS IoT to authenticate your devices and authorize operations using bearer token authentication and authorization strategies. See [AWS IoT Custom Authentication](https://docs.aws.amazon.com/iot/latest/developerguide/iot-custom-authentication.html) for more details.

Please follow the steps outlined in [Setting up Custom Authentication](https://aws.amazon.com/blogs/security/how-to-use-your-own-identity-and-access-management-systems-to-control-access-to-aws-iot-resources/) to create the custom authorizer and configure the workflow with AWS IoT.

Once the custom authorizer workflow is configured, you can establish a connection as follows:

```swift
func mqttEventCallback(_ status: AWSIoTMQTTStatus ) {
    print("connection status = \(status.rawValue)")
}

iotDataManager.connectUsingWebSocket(withClientId: uuid,
                                     cleanSession: true,
                                     customAuthorizerName: "<name-of-the-custom-authorizer>",
                                     tokenKeyName: "<key-name-for-the-token>",
                                     tokenValue: "<token>",
                                     tokenSignature: "<signature-of-the-token>",
                                     statusCallback: mqttEventCallback)
```

You can take a look at the [API Reference](https://aws-amplify.github.io/aws-sdk-ios/docs/reference/AWSIoT/Classes/AWSIoTDataManager.html#/c:objc(cs)AWSIoTDataManager(im)connectUsingWebSocketWithClientId:cleanSession:customAuthorizerName:tokenKeyName:tokenValue:tokenSignature:statusCallback:) to know more information. This feature is available in the AWS SDK for iOS starting from `2.8.4` version. See [AWSIoT - 2.8.4](https://github.com/aws-amplify/aws-sdk-ios/blob/main/CHANGELOG.md#284) for more details.

## Subscribe to a topic

In order to start receiving messages from your provider, you need to subscribe to a topic as follows;

```swift
iotDataManager.subscribe(
    toTopic: "myTopic",
    qoS: .messageDeliveryAttemptedAtMostOnce, /* Quality of Service */
    messageCallback: {
        (payload) ->Void in
        let stringValue = NSString(data: payload, encoding: String.Encoding.utf8.rawValue)!

        print("Message received: \(stringValue)")
} )
```

## Subscribe to multiple topics

To subscribe for multiple topics, just call `subscribe()` for each topic you wish to subscribe. 

## Publish to a topic

To send a message to a topic, use `publishString()` method with your topic name and the message:

```swift
iotDataManager.publishString(
    "Hello to all subscribers!",
    onTopic: "myTopic", 
    qoS:.messageDeliveryAttemptedAtMostOnce)
```

## Unsubscribe from a topic

To stop receiving messages from a topic, you can use `unsubscribeTopic()` method:

```swift
iotDataManager.unsubscribeTopic("myTopic")

// You will no longer get messages for "myTopic"
```

## Close Connection

In order to disconnect, you need to close the connection as follows:

```swift
iotDataManager.disconnect()
```

## API Reference

For the complete API documentation for AWS IoT, visit our [API reference](https://aws-amplify.github.io/aws-sdk-ios/docs/reference/AWSIoT/Classes/AWSIoTDataManager.html).