Mobile Purchases

IOS receipt validation and purchase persistence

Structure of the project

• The scala part of the project is considered "legacy". It's only kept for very old iOS devices and should be decommissioned once there's only a tiny amount of traffic reaching the service.
• The Typescript part of the project contains the more modern approach to validating and storing mobile purchases.

Local Setup

Node

Make sure that you are using the right Node version, we recommend fnm as the Node version manager.

1. Install yarn: npm install -g yarn
2. Run yarn to install dependencies
3. Run local tests: yarn test

Architecture

This service is a set of cloud functions (AWS lambdas), triggered either by an API Gateway or by SQS queues. This allow us to scale very efficiently and very cheaply as well as getting retries for free when querying Apple and Google's services.

Diagram source

Data

There are three dynamo DB tables:

• Events (mobile-purchases-<stage>-subscription-events-v2): This table records all events as they are received by Google and Apple.
• Subscriptions (mobile-purchases-CODE-subscriptions): This table records all the subscriptions held by our users. It contains information such as start date, expiration date, type of subscription and whether it will automatically renew at the end of its validity.
• UserSubscriptions (mobile-purchases-CODE-user-subscriptions): This table records the link between a User (as defined by the Guardian), and a subscription.

These three tables are exported daily to the datalake.

Cloud Functions

• Pubsub: This is triggered by Apple and Google when any event happen on a subscription, such as a subscription has been purchased, renewed, cancelled etc. The data received by this function is stored in the Event table and forwarded to the Update Subs function.
• Link: This is triggered by the Apps if a users is logged-in and has a subscription. The function will store that link in the UserSubscriptions table (after ensuring the user is logged in), and forward the subscription to the Update Subs function.
• Subscription Status: This is triggered by an API call from the app to check if a Google purchase token or an Apple receipt is a proof to a valid subscription.
• Update Subs: This function checks the status of a subscription and updates it in the Subscriptions table.
• Subscription Status: This function checks the status of a subscription on behalf of the App.
• Delete Link: This function deletes rows from the UserSubscriptions table if their corresponding subscription has been deleted. It relies on dynamo streams.

Running typescript lambdas locally

We're using TypeScript to develop this project and it's useful to be able to test these locally, without having to resubmit a build and deploy to the cloud.

To avoid committing test data locally a test-launcher is provided to run a lambda locally, that will only read a file in a directory that's configured to not commit anything.

This can be run locally, and assumes a module with a function handler which takes some kind of a payload as a parameter.

Test a lambda locally by creating a payload json file under the mobile-purchases-payload directory and invoke the test-launcher with the name of your lambda module relative to the test-launcher along with the name of a payload file.

For example, to test the lambda that updates google subscriptions (typescript/update-subs/google.ts). This reads from an SQS queue, so create a a file sqs.json like this and put it in mobile-purchases-payload.

{
  "Records": [
    {
      "messageId": "19dd0b57-b21e-4ac1-bd88-01bbb068cb78",
      "receiptHandle": "MessageReceiptHandle",
      "body": "{\"packageName\":\"not-saying\",\"purchaseToken\":\"idontwanttopushthistogithub",\"subscriptionId\":\"keeo-under-wraps\"}",
      "attributes": {
        "ApproximateReceiveCount": "1",
        "SentTimestamp": "1523232000000",
        "SenderId": "123456789012",
        "ApproximateFirstReceiveTimestamp": "1523232000001"
      },
      "messageAttributes": {},
      "md5OfBody": "7b270e59b47ff90a553787216d55d91d",
      "eventSource": "aws:sqs",
      "eventSourceARN": "arn:aws:sqs:eu-west-1:123456789012:MyQueue",
      "awsRegion": "eu-west-1"
    }
  ]
}

This directory has its own .gitignore which means that any json files here remain local.

Invoke your function locally via the launcher script thus

yarn test-lambda update-subs/google sqs.json