Mastering Blockchain Programming with Solidity

Subscription pattern

The subscription pattern is used when you need to provide a periodic subscription fee for any kind of service.

A contract can provide different kinds of features or a premium service. Any subscriber can subscribe for services that your contract provides. To enable this, you can charge a subscription fee for a period of time from the subscriber. To implement this service, you can create a Subscription contract, as we have developed in the following code example:

contract Subscription is Ownable {    using SafeMath for uint;    //subscriber address => expiry     mapping(address => uint) public subscribed;    address[] public subscriptions;    uint subscriptionFeePerDay = 1 ether;    modifier whenExpired() { require(isSubscriptionExpired(msg.sender)) ...