fxfactorial / payspec-contract Goto Github PK

An Invoice System for ERC20 Tokens that helps merchants accept payment from users with a simple API.

Imagine a situation where one party, the 'seller', wants to sell an asset 'X' for a predetermined amount of ERC20 tokens Y. First, the seller constructs a JSON object offchain like this:

let newInvoiceData = {
  description: 'assetXname', //can be anything
  nonce: 2, //randomly generated number 
  token: 0xb6...,  //contract address of token for payment 
  amountDue: 100,   //raw amount of token to pay this invoice 
  payTo: 0x...., //sellerAddress   
  feeAddresses: [ 0x... ],  //addresses of any third parties that should take a % fee for this transaction, like a website this invoice flows through  (optional) 
  feePercents: [ 2 ], //fee amounts of feeAddresses
  expiresAt: 0    //block number that this invoice will expire on (0 for never expire) 
}

Now, the seller will run this through the static method

  getInvoiceUUID(  string memory description, uint256 nonce, address token, uint256 amountDue, address payTo, address[] memory feeAddresses, uint[] memory feePercents, uint expiresAt  ) public view returns (bytes32 uuid) 

This will give the seller the universally unique ID (UUID) corresponding to this invoice. No other invoice will ever have this particular UUID and the seller will use this UUID in order to track and trace whether or not this invoice is paid.

Now, the seller gives this invoice data to potential buyers along with the UUID (or the buyer can compute the UUID.)

The buyer will approve tokens to the Payspec contract and then call this method:

  createAndPayInvoice(  string memory description, uint256 nonce, address token, uint256 amountDue, address payTo, address[] memory feeAddresses, uint[] memory feePercents, uint256 ethBlockExpiresAt, bytes32 expecteduuid  ) public returns (bool)  

This method will make the pre-approved ERC20 tokens in quantity 'AmountDue' flow from the buyer's account and into the sellers account and it will permanently mark this invoice as being 'paid'. Now, the seller (or a bot) can check the 'paid' status of the corresponding UUID and deliver the sold asset to the buyer. This does require that the buyer trust the seller to actually deliver the item.

Considerations:

• If the buyer tries to change any of the data, the UUID will be different and so the order will not be considered paid by the seller. The UUID is the SHA3 hash of all of the invoice data, including the contract address.
• An invoice can only be paid once
• Invoices automatically expire based on block number (if expiration is not 0)
• Invoices can be cancelled by the seller with an onchain tx
• Invoices are created by sellers offchain
• Without this type of system, ERC20 payments are non-atomic and hard to verify

npm install -g ganache-cli (https://github.com/trufflesuite/ganache-cli)

npm run ganache

npm run test