Escrow Contract

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This example provides a simple implementation of an escrow contract, with a timeout callable function that concludes the transaction if the buyer has not provided approval within a given timeframe.

The code also includes an example of how contracts can pass data to each other through cross contract calls, and how the caller contract can handle the result.: ::info
This example does not have a frontend; ::

Starting with the Project

You have two options to start using the project:

The first and recommended is to open the project through Gitpod, which will open a web-based interactive environment with all dependencies installed.
The second option is to clone the repository locally, for which you will need to install all the Prerequisites.

Interacting With the Contract

Since this example does not have a frontend, we will interact with it using the NEAR CLI or writing tests using workspaces-js.

Check the project’s README.md. Briefly, you will need to:

1. Install Dependencies

To install dependencies, run:

npm i

1. Build the Contracts

You can build the contracts (creating the .wasm files that will be deployed to the network) by running:

npm run build

Once finished, check the build/ folder and you should see the escrow.wasm file. This is the file that will be deployed to the network alongside the assets.wasm file that is used to manage ownership for assets.

2. Deploy the Contracts

To deploy the escrow contract to testnet, run:

near deploy --wasmFile build/escrow.wasm --accountId <your-escrow-testnet-account-id>

To deploy the assets contract to testnet, run:

near deploy --wasmFile build/assets.wasm --accountId <your-assets-testnet-account-id>

3. Initialize the Assets Contract

To initialize the assets contract, run:

near call <your-assets-testnet-account-id> init '{"owner_id": "<your-asset-owner-account-id>", "total_supply": "1000", "escrow_contract_id": "<your-escrow-testnet-account-id>", "asset_price": "100000000000000000000000"}' --accountId <your-assets-testnet-account-id>

asset_price is the price of the asset in yoctoNEAR (10^-24 NEAR). In this example, the price is set to 0.1 NEAR.

3. Perform a Purchase on Escrow

To perform a purchase on the escrow contract, run:

near call <your-escrow-testnet-account-id> purchase_in_escrow '{"seller_account_id": "<your-asset-owner-account-id>", "asset_contract_id ": "<your-assets-testnet-account-id>"}' --accountId <your-account-id> --amount 0.11 --gas=300000000000000

Since we set the price of the asset to 0.1 NEAR, we need to send 0.11 NEAR to the escrow contract to cover the price of the asset and gas costs.

4. Check the Balance of the Buyer Account

To check the asset balance of the buyer account after the escrow purchase, run:

near view <your-assets-testnet-account-id> get_account_assets '{"account_id": "<your-account-id>"}'

You may also check the NEAR balance of the seller account, making sure they have not received the payment yet:

near state <your-asset-owner-account-id>

5. Approve the Purchase

To approve the purchase, run:

near call <your-escrow-testnet-account-id> approve_purchase '{}' --accountId <your-account-id>

Check the NEAR balance of the seller account again, and you should see that they have received the payment.

Contract

The contract exposes methods to purchase assets in escrow and approve or cancel the purchase by the buyer. Additionally, the contract exposes a method to check the creation time of the purchase, and if the purchase has been created a day or longer ago, the contract will approve the purchase without the buyer’s input.

Testing

When writing smart contracts it is critical to test all methods exhaustively. In this
project we test the contract methods using workspaces-js. Before digging into the tests,
go ahead and perform the tests present in the dApp through the command npm test. This will run the tests in tests/main.ava.js. Test names and outcomes are printed to the console.

Moving Forward

A nice way to learn is by trying to expand a contract. Modify the escrow-js example to use an NFT
contract!. In this way, you can try to make functionality where a user purchases an NFT in escrow! Remember to correctly handle the callback,
and to return the money to the user in case of errors.

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