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API3

API3 is a collaborative project to deliver traditional API services to smart contract platforms in a decentralized and trust-minimized way. API3 provides the technology for Airnodes to push off-chain data to on-chain contracts. This data can then be queried directly through the Airnode (initiating a “pull-type” request) or through dAPIs (data-feeds sourced directly from multiple first-party oracles owned and operated by API providers).

Querying the price of $ARB through API3​

Here’s an example of how to use an API3 data feed to query the current price of $ARB on-chain. The API3 market provides a list of all the dAPIs available across multiple chains including testnets. You can go forward and activate the dAPI you want to use.

API3 provides an npm package with the contracts needed to access their feeds. We first install that package in our project:

yarn add @api3/contracts

To use a data feed, we retrieve the information through the specific proxy address for that feed. We’ll use the IProxy interface to do so.

import "@api3/contracts/api3-server-v1/proxies/interfaces/IProxy.sol";

In this case, we want to obtain the current price of $ARB in $USD in Arbitrum One, so we need to know the proxy address that will provide that information. We will search the feed on the API3 Market and connect our wallet. We would then want to see if the feed is active, and if it is, we can check its configuration parameters, deploy the proxy contract and click on Integrate. You can find the proxy address of ARB/USD here.

info

If a dAPI is already active, you can use the proxy address directly. If it is not active, you can activate it by clicking on Activate and following the instructions to deploy a proxy contract.

We can now build the function to get the latest price of $ARB. We’ll use this example contract:

contract ARBPriceConsumer {
    /**
     * Network: Arbitrum One
     * Aggregator: ARB/USD
     * Proxy: 0x0cB281EC7DFB8497d07196Dc0f86D2eFD21066A5
     */
    address constant PROXY = 0x0cB281EC7DFB8497d07196Dc0f86D2eFD21066A5;

    /**
     * Returns the latest price.
     */
    function getLatestPrice()
        external
        view
        returns (int224 value, uint256 timestamp)
    {
        (value, timestamp) = IProxy(PROXY).read();
        // If you have any assumptions about `value` and `timestamp`, make sure
        // to validate them right after reading from the proxy.
    }
}

You can adapt this contract to your needs. Just remember to use the address of the asset you want to request the price for in the appropriate network and to deploy your contract to the same network. Remember we have a Quickstart available that goes through the process of compiling and deploying a contract.

Querying a random number through API3​

API3 QRNG is a public utility provided with the courtesy of Australian National University (ANU). It is served as a public good, it is free of charge (apart from the gas costs), and it provides quantum randomness when requiring RNG on-chain.

To request randomness on-chain, the requester submits a request for a random number to AirnodeRrpV0. The ANU Airnode gathers the request from the AirnodeRrpV0 protocol contract, retrieves the random number off-chain, and sends it back to AirnodeRrpV0. Once received, it performs a callback to the requester with the random number.

Here’s an example of a basic QrngRequester that requests a random number.

API3 provides an npm package with the contracts needed to access the ANU QRNG airnode. We first install that package in our project:

yarn add @api3/airnode-protocol

We’ll need several pieces of data to request a random number:

  • address airnodeRrp: Address of the protocol contract. See the Chains page for a list of addresses on different chains. For Arbitrum, we’ll use 0xb015ACeEdD478fc497A798Ab45fcED8BdEd08924.
  • address airnode: The address that belongs to the Airnode that will be called to get the QRNG data via its endpoints. See the Providers page for a list of addresses on different chains. For Arbitrum we’ll use 0x9d3C147cA16DB954873A498e0af5852AB39139f2.
  • bytes32 endpointId: Endpoint ID known by the Airnode that will map to an API provider call (allowed to be bytes32(0)). You can also find that information in the Providers page. For Arbitrum we’ll use 0xfb6d017bb87991b7495f563db3c8cf59ff87b09781947bb1e417006ad7f55a78.
  • address sponsorWallet: The address of the wallet that will pay for the gas costs for the callback request to get the random number on-chain. You need to fund this wallet with enough ETH to cover the gas costs.

To derive your sponsorWallet address, you can use the following command:

yarn @api3/airnode-admin derive-sponsor-wallet-address \
  --airnode-address 0x9d3C147cA16DB954873A498e0af5852AB39139f2 \
  --airnode-xpub xpub6DXSDTZBd4aPVXnv6Q3SmnGUweFv6j24SK77W4qrSFuhGgi666awUiXakjXruUSCDQhhctVG7AQt67gMdaRAsDnDXv23bBRKsMWvRzo6kbf \
  --sponsor-address <use-the-address-of-your-requester-contract>

  # The command outputs.
  Sponsor wallet address: 0x6394...5906757
  # Use this address as the value for _sponsorWallet.

We can now build the function to get a random number. We’ll use this example contract:

import "@api3/airnode-protocol/contracts/rrp/requesters/RrpRequesterV0.sol";

contract QrngRequester is RrpRequesterV0 {
    event RequestedUint256(bytes32 indexed requestId);
    event ReceivedUint256(bytes32 indexed requestId, uint256 response);

    /**
     * Network: Arbitrum One
     * AirnodeRrpV0 Address: 0xb015ACeEdD478fc497A798Ab45fcED8BdEd08924
     * Airnode: 0x9d3C147cA16DB954873A498e0af5852AB39139f2
     * Endpoint ID: 0xfb6d017bb87991b7495f563db3c8cf59ff87b09781947bb1e417006ad7f55a78
     */
    address constant _airnodeRrp = 0xb015ACeEdD478fc497A798Ab45fcED8BdEd08924;
    address constant airnode = 0x9d3C147cA16DB954873A498e0af5852AB39139f2;
    bytes32 constant endpointIdUint256 = 0xfb6d017bb87991b7495f563db3c8cf59ff87b09781947bb1e417006ad7f55a78;
    mapping(bytes32 => bool) public waitingFulfillment;
    address sponsorWallet;

    constructor() RrpRequesterV0(_airnodeRrp) {}

    // Set the sponsor wallet address that you just derived.
    function setSponsorWallet(address _sponsorWallet) external {
        sponsorWallet = _sponsorWallet;
    }

    function makeRequestUint256() external {
        bytes32 requestId = airnodeRrp.makeFullRequest(
            airnode,
            endpointIdUint256,
            address(this),
            sponsorWallet,
            address(this),
            this.fulfillUint256.selector,
            ""
        );
        waitingFulfillment[requestId] = true;
        emit RequestedUint256(requestId);
    }

    function fulfillUint256(bytes32 requestId, bytes calldata data)
        external
        onlyAirnodeRrp
    {
        require(
            waitingFulfillment[requestId],
            "Request ID not known"
        );
        waitingFulfillment[requestId] = false;
        uint256 qrngUint256 = abi.decode(data, (uint256));

        // Use `qrngUint256` here...

        emit ReceivedUint256(requestId, qrngUint256);
    }
}

You can adapt this contract to your needs. Just remember to set the sponsorWallet address before making the request to use the appropriate network's addresses, and to deploy your contract to the same network. Remember, we have a Quickstart available that goes through the process of compiling and deploying a contract.

More examples​

Refer to API3’s documentation for more examples of querying other data feeds and Airnodes.

You can also check out some other detailed guides: