How to unsubscribe an iOS Device from an amazon SN

问题:

I'm developing an iOS application with Simple Notification Service (SNS) from Amazon Web Services. At this point the app registers the device to a Topic and can receive push notifications, which are published to the Topic. It is possible to subscribe a device to many Topics.

Now I'm trying to unsubscribe a device from a specific Topic, but the SNSUnsubscribeRequest needs a SubscriptionARN. I've tried to use the EndpointARN from the device, but it seems I've to use an extra SubscriptionARN for the combination of EndpointARN and TopicARN. How do I get this ARN?

In this post: How do you get the arn of a subscription? they ask for the whole list of subscribers and compare each EndpointARN with the EndpointARN of the device. This cant be the right way i think.

Subscribe to Topic

// Check if endpoint exist
if (endpointARN == nil) {
    dispatch_async(dispatch_get_main_queue(), ^{
        [[self universalAlertsWithTitle:@"endpointARN not found!" andMessage:@"Please create an endpoint for this device before subscribe to topic"] show];
    });
    return NO;
}

// Create topic if not exist
NSString *topicARN = [self findTopicARNFor:topic];
if (!topicARN) {
    [self createTopic:topic];
    topicARN = [self findTopicARNFor:topic];
}

// Subscribe to topic if exist
if (topicARN) {
    SNSSubscribeRequest *subscribeRequest = [[SNSSubscribeRequest alloc] initWithTopicArn:topicARN andProtocol:@"application" andEndpoint:endpointARN];
    SNSSubscribeResponse *subscribeResponse = [snsClient subscribe:subscribeRequest];
    if (subscribeResponse.error != nil) {
        NSLog(@"Error: %@", subscribeResponse.error);
        dispatch_async(dispatch_get_main_queue(), ^{
            [[self universalAlertsWithTitle:@"Subscription Error" andMessage:subscribeResponse.error.userInfo.description] show];
        });
        return NO;
    }
}
return YES;

The method findTopicARNForTopic already iterates over the list of Topics and compare the suffix with the topic name. I really don't know if this is the best practice.

Unsubscribe from Topic

NSString *topicARN = [self findTopicARNFor:topic];
if (topicARN) {
    SNSUnsubscribeRequest *unsubscribeRequest = [[SNSUnsubscribeRequest alloc] initWithSubscriptionArn:topicARN];
    SNSUnsubscribeResponse *unsubscribeResponse = [snsClient unsubscribe:unsubscribeRequest];
    if (unsubscribeResponse.error) {
        NSLog(@"Error: %@", unsubscribeResponse.error);
    }
}

回答1:

For now I ask for the whole subscriber list and compare the EndpointARN with the EndpointARN of the Device. With the following method i get the subscription arn:

- (NSString *)findSubscriptionARNForTopicARN:(NSString *)topicARN
{
    // Iterate over each subscription arn list for a topic arn
    NSString *nextToken = nil;
    do {
        SNSListSubscriptionsByTopicRequest *listSubscriptionRequest = [[SNSListSubscriptionsByTopicRequest alloc] initWithTopicArn:topicARN];
        SNSListSubscriptionsByTopicResponse *response = [snsClient listSubscriptionsByTopic:listSubscriptionRequest];
        if (response.error) {
            NSLog(@"Error: %@", response.error);
            return nil;
        }

        // Compare endpoint arn of subscription arn with endpoint arn of this device
        for (SNSSubscription *subscription in response.subscriptions) {
            if ([subscription.endpoint isEqualToString:endpointARN]) {
                return subscription.subscriptionArn;
            }
        }
        nextToken = response.nextToken;
    } while (nextToken != nil);
    return nil;
}

and with this method i remove the device from a topic:

- (void)unsubscribeDeviceFromTopic:(NSString *)topic
{
    NSString *subscriptionARN = [self findSubscriptionARNForTopic:topic];
    if (subscriptionARN) {
        SNSUnsubscribeRequest *unsubscribeRequest = [[SNSUnsubscribeRequest alloc] initWithSubscriptionArn:subscriptionARN];
        SNSUnsubscribeResponse *unsubscribeResponse = [snsClient unsubscribe:unsubscribeRequest];
        if (unsubscribeResponse.error) {
            NSLog(@"Error: %@", unsubscribeResponse.error);
        }
    }
}

回答2:

You could also store the SubscriptionArn in the SubscribeResponse and use this value in the UnSubscribeRequest.