Terminal association from the server side to Amazon SNS (python + boto3)

Task

If you want to link a terminal to topic to SNS, there is an example of directly accessing SNS from a smartphone terminal using sdk, but considering the future (such as managing tokens on the dynamoDB side as well), the server When I tried to do it on the side side, there were surprisingly few cases, so I summarized it.

This time, the push notification target is a smartphone, so that is the premise. Also, I'm implementing it in Lambda, but I don't think it depends on Lambda.

Overview

handler.py

import boto3

def lambda_handler(event, context):

    application_arn = 'arn:aws:sns:us-east-1:999999999999:notify_sample'
    topic_arn       = 'arn:aws:sns:us-east-1:999999999999:notify_sample'

    endpoint = add_endpoint(application_arn, token)
    subscribe_token(topic_arn, endpoint['EndpointArn'], is_subscribe)

The rough procedure is

1. Register endpoint in Application
2. Subscribe endpoint to Topic

It will be. Please register and acquire the ARN of Application and Topic appearing here using the dashboard on the AWS side in advance.

Register endpoint in Application

handler.py

def add_endpoint(application_arn, token):
    # token(boto3 doc excerpt) :
    # For example, when using APNS as the notification service, you need the device token.
    # Alternatively, when using GCM or ADM, the device token equivalent is called the registration ID.

    client = boto3.client('sns')
    endpoint = client.create_platform_endpoint(
        PlatformApplicationArn=application_arn,
        Token=token
    )

    return endpoint

Call it even if it has already been added. token is a token obtained from APNS or FCM (GCM). create_platform_endpoint () returns the information of the existing endpoint without adding a new one if the endpoint has already been added. In any case, endpoint information can be obtained, so subscribe based on this information.

The CreatePlatformEndpoint action is idempotent, so if the requester already owns an endpoint with the same device token and attributes, that endpoint's ARN is returned without creating a new endpoint.

Subscribe endpoint to Topic

This is a bit of a hassle.

You can simply execute subscribe () to subscribe, but in the case of unsubscribe, SubscriptionArn of the target terminal is required. This time, I execute subscribe () once to get SubscriptionArn, and then use it to execute unsubscribe ().

handler.py

def subscribe_token(topic_arn, endpoint_arn, is_subscribe):

    client = boto3.client('sns')
    subscription = client.subscribe(
        TopicArn=topic_arn,
        Protocol='application',
        Endpoint=endpoint_arn
    )
    if not is_subscribe:
        client.unsubscribe(
            SubscriptionArn=subscription['SubscriptionArn']
        )

Question

This is the last method to get Subscription Arn, but even if you look at the manual, you can only find such a good method. Please point out if there is an appropriate method.

Retest

I got a slightly unclear error at runtime, so I reviewed the boto3 manual and reviewed the code, but I think that it is more straightforward to write as follows. However, rewriting did not improve the error, so I think the client is a low-level client.

handler.py

def add_endpoint(dry_run, application_arn, token):

    sns = boto3.resource('sns')
    platform_application = sns.PlatformApplication(application_arn)
    endpoint = platform_application.create_platform_endpoint(
        Token=token
    )
    return endpoint.arn


def subscribe_token(dry_run, topic_arn, endpoint_arn, is_subscribe):

    sns = boto3.resource('sns')
    topic = sns.Topic(topic_arn)
    subscription = topic.subscribe(
        TopicArn=topic_arn,
        Protocol='application',
        Endpoint=endpoint_arn
    )
    if not is_subscribe:
        subscription.delete()