This repository contains the source code for Ispolink's payment infrastructure - an interoperable in-Dapp subscription system.
Users on the Ispolink platform are able to purchase subscriptions to unlock premium platform features in fully decentralized manner. The smart contract accepts payments in the native ERC-20 token of the Ispolink platform - ISP.
Transactions to the smart contract contain the unique subscription IDs which can be publicly verified on-chain.
The payment infrastructure is deployed on the following EVM chains:
- Ethereum
- BNB Smart Chain (BSC)
- Polygon
The following diagrams illustrate the user interaction with the payment system:
Supported features of the payments system:
- Blockchain transaction deadline - user must send the specified amount of ISP tokens before the payment expires
- SignTypedData V4 - it follows the EIP-712 standard to allow requesting the user sign a struct that can be verified on-chain
- The smart contract is covered with unit tests
This Hardhat project contains a Solidity smart contract PaymentContract which enables subscriptions using ERC20 tokens. The smart contract also includes a PaymentVerifier contract that verifies payment signatures.
- Install the required dependencies using the command:
npm install - Compile the smart contract using the command:
npx hardhat compile - Run the tests using the command:
npx hardhat test
The PaymentVerifier contract verifies payment signatures using the EIP712 standard. The contract inherits from the EIP712 and Ownable contracts from the OpenZeppelin library.
The contract constructor takes three parameters: name, version, and signer. The name and version parameters are used to create the EIP712 domain separator.
The signer parameter is the address of the signer used to verify the signature.
The contract includes a private constant _TYPEHASH which is the type hash of the payment struct used in the signature. The contract includes an internal view
function verifyPaymentSignature which verifies the payment signature using the EIP712 standard. The function takes four parameters: signature, subscriptionId, amount, and deadline.
If the signature is not valid, the function reverts with an error message.
The PaymentContract contract enables subscriptions using ERC20 tokens. The contract inherits from the PaymentVerifier contract. The contract constructor takes three parameters: token,
name and version. The token parameter is the address of the ERC20 token used for payments. The name and version parameters are used in the PaymentVerifier for domain separator.
The private mapping subscriptions stores subscription information which the following fields: buyer, timestamp, amount, and currency.
The function withdrawAll allows the contract owner to withdraw all tokens from the contract and transfer them to a specified address.
Also by setTokenAddress function is allowed the contract owner to change the address of the ERC20 token used for payments.
The contract includes a createSubscription function which creates a new subscription and stores the subscription information in the subscriptions mapping. The function takes four parameters: signature,
subscriptionId, amount, and deadline. The function verifies the payment signature using the verifyPaymentSignature function from the PaymentVerifier contract. If the signature is valid,
the function creates a new subscription and emits a SubscriptionPaid event.
By getSubscription function is possible to retrieve the subscription information for a specified subscription ID. The contract also includes getTokenAddress function which returns the
address of the ERC20 currency used for the subscription payment.
The smart contract can be deployed to a test network or mainnet using Hardhat. Please refer to the Hardhat documentation for more information on deployment.
The contract for the payment system - version v1.0.0, compiled with solc v0.8.9 is deployed here: