📝 Example Project

This example project will guide you through how to use Nodary Beacons in your own contract.

Project: Analyze

• We first start by creating our contract as described here in order to read data from Beacons.

// SPDX-License-Identifier: MIT
pragma solidity 0.8.9;

import "@api3/airnode-protocol-v1/contracts/dapis/DapiReader.sol";


contract BeaconReaderExample is DapiReader {
    constructor(address _dapiServer) DapiReader(_dapiServer) {} 

    function readBeaconWithId(bytes32 beaconId)
        external
        view
        returns (int224 value, uint256 timestamp)
    {
        (value, timestamp) = IDapiServer(dapiServer).readDataFeedWithId(
            beaconId
        );
    }

    function readBeaconValueWithId(bytes32 beaconId)
        external
        view
        returns (int224 value)
    {
        value = IDapiServer(dapiServer).readDataFeedValueWithId(beaconId);
    }

    function beaconIdToReaderToWhitelistStatus(
        bytes32 beaconId,
        address reader
    )
        external
        view
        returns (uint64 expirationTimestamp, uint192 indefiniteWhitelistCount)
    {
        return
            IDapiServer(dapiServer).dataFeedIdToReaderToWhitelistStatus(
                beaconId,
                reader 
            );
    }

    // Our functions go here

} 

• We write our functions. Our main function is Analyze(). It requires 2 Beacon addresses and enough token to "analyze".

...

    // Our functions go here

    function someAnalysis(bytes32 coin1BeaconId, bytes32 coin2BeaconId)
        public
        view
        returns (string memory)
    {
      int224 coin1Value = readBeaconValueWithId(coin1BeaconId);  
      int224 coin2Value = readBeaconValueWithId(coin2BeaconId);

      if (coin1Value > coin2Value) {
          return "coin1higher";
      } else if (coin1Value == coin2Value) {
          return "equal";
      } else {
          return "coin2higher";
      }
    } 

    event AnalysisEvent(string analysisResult);
    uint256 ANALYSIS_COST = 0.05 ether;

    function Analyze(bytes32 coin1BeaconId, bytes32 coin2BeaconId) external payable {

        // make sure this contract is whitelisted
        (uint64 expirationTs1, ) = beaconIdToReaderToWhitelistStatus(coin1BeaconId, address(this));
        (uint64 expirationTs2, ) = beaconIdToReaderToWhitelistStatus(coin2BeaconId, address(this));
        require(expirationTs1 > 0, "This contract is not whitelisted for coin1BeaconId!");
        require(expirationTs2 > 0, "This contract is not whitelisted for coin2BeaconId!");

        // make sure user send enough
        uint256 receivedAmount = msg.value;
        require(receivedAmount >= ANALYSIS_COST, "Need more than 0.05 ether!");

        // analyze and emit
        string memory analysisResult = someAnalysis(coin1BeaconId, coin2BeaconId); 
        emit AnalysisEvent(analysisResult);
        
        // return extra currency to sender (user)
        (bool success, ) = msg.sender.call{value: receivedAmount - ANALYSIS_COST}("");
        require(success, "Failed to call!");
    } 
}

Final code should look like this:

// SPDX-License-Identifier: MIT
pragma solidity 0.8.9;

import "@api3/airnode-protocol-v1/contracts/dapis/DapiReader.sol";


contract BeaconReaderExample is DapiReader {
    constructor(address _dapiServer) DapiReader(_dapiServer) {}

    function readBeaconWithId(bytes32 beaconId)
        private
        view
        returns (int224 value, uint256 timestamp)
    {
        (value, timestamp) = IDapiServer(dapiServer).readDataFeedWithId(
            beaconId
        );
    }

    function readBeaconValueWithId(bytes32 beaconId)
        private
        view
        returns (int224 value)
    {
        value = IDapiServer(dapiServer).readDataFeedValueWithId(beaconId);
    }

    function beaconIdToReaderToWhitelistStatus(
        bytes32 beaconId,
        address reader
    )
        private
        view
        returns (uint64 expirationTimestamp, uint192 indefiniteWhitelistCount)
    {
        return
            IDapiServer(dapiServer).dataFeedIdToReaderToWhitelistStatus(
                beaconId,
                reader
            );
    }

    

    // Our functions go here

    function someAnalysis(bytes32 coin1BeaconId, bytes32 coin2BeaconId)
        public
        view
        returns (string memory)
    {
      int224 coin1Value = readBeaconValueWithId(coin1BeaconId);  
      int224 coin2Value = readBeaconValueWithId(coin2BeaconId);

      if (coin1Value > coin2Value) {
          return "coin1higher";
      } else if (coin1Value == coin2Value) {
          return "equal";
      } else {
          return "coin2higher";
      }
    } 

    event AnalysisEvent(string analysisResult);
    uint256 ANALYSIS_COST = 0.05 ether;

    function Analyze(bytes32 coin1BeaconId, bytes32 coin2BeaconId) external payable {

        // make sure this contract is whitelisted
        (uint64 expirationTs1, ) = beaconIdToReaderToWhitelistStatus(coin1BeaconId, address(this));
        (uint64 expirationTs2, ) = beaconIdToReaderToWhitelistStatus(coin2BeaconId, address(this));
        require(expirationTs1 > 0, "This contract is not whitelisted for coin1BeaconId!");
        require(expirationTs2 > 0, "This contract is not whitelisted for coin2BeaconId!");

        // make sure user send enough 
        uint256 receivedAmount = msg.value;
        require(receivedAmount >= ANALYSIS_COST, "Need more than 0.05 ether!");

        // analyze and emit
        string memory analysisResult = someAnalysis(coin1BeaconId, coin2BeaconId); 
        emit AnalysisEvent(analysisResult);
        
        // return extra currency to sender (user)
        (bool success, ) = msg.sender.call{value: receivedAmount - ANALYSIS_COST}(""); 
        require(success, "Failed to call!");
    }  
}

• We want to deploy our contract on the Polygon testnet. We can obtain the address of DapiServer.sol on the Polygon testnet here. We also need 2 Beacon addresses. We can find the list of Beacons here.

• If everything is ready, we can use Remix to deploy our contract.

• Click the below button to go to Remix workspace and open MyContract.sol from Remix's file explorer.

• Once Remix workspace is loaded, go to the Solidity compiler section and compile the contract. Then, go to the Deploy & run transactions section. Connect your Metamask account on polygon-testnet (also called Mumbai Testnet). Finally select MyContract.sol, enter DapiServer.sol's address and deploy your contract.

• Now, we need to whitelist our freshly deployed contract. You can see this to find out how. Once the contract is whitelisted, the Analyze() function should give a similar log on the Remix console to the below.

...

logs    
[
    {
        "from": "0x071727416221e5c42DE91144a452Ee4D2d30A23c",
        "topic": "0x48e8b5bc2a9491a87c4f3123e474812d43c18d496bae119f97a9cdf178347a0a",
        "event": "AnalysisEvent",
        "args": {
            "0": "coin1higher",
            "analysisResult": "coin1higher"
        }
    }
]
...

info

Each value that is written to chain is multiplied by a number. It is required to handle floating number since floating numbers does not exist in solidity.

caution

It should be remembered that the corresponding sponsor wallet of a Beacon should have enough amount of currency for the Beacon to be updated.