Payment

The Payment attestation type enables data collection about a transaction, classified as payment on the native chain. The currently supported chain are: BTC, DOGE, and XRP. You can learn more about it in the official specification repo.

We will now demonstrate how the FDC protocol can be used to collect the data of a given XRLP payment transaction. The transaction we will be observing has the id 2A3E7C7F6077B4D12207A9F063515EACE70FBBF3C55514CD8BD659D4AB721447; this is an arbitrary transaction that we acquired from the XRPL testnet explorer.

The same procedure works for all supported sources, BTC, DOGE, and XRP. The source then requires only a slight modification; we will remind you of that when it comes up in the guide.

In this guide, we will follow the steps outlined in the FDC overview.

Our implementation requires handling the FDC voting round finalization process. To manage this, we will create separate scripts in script/fdcExample/Payment.s.sol that handle different stages of the validation process:

scrip/fdcExample/Payment.s.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.25;

import {Script} from "dependencies/forge-std-1.9.5/src/Script.sol";
...

string constant attestationTypeName = "Payment";
string constant dirPath = "data/";

contract PrepareAttestationRequest is Script {
 ...
}

contract SubmitAttestationRequest is Script {
 ...
}

contract RetrieveDataAndProof is Script {
 ...
}

contract Deploy is Script {
 ...
}
...

The names of included contracts mostly mirror the steps described in the FDC guide.

To bridge the separate executions of the scripts, we will save the relevant data of each script to a file in the dirPath folder. Each succeeding script will then read that file to load the data.

Prepare request

The JSON request to the verifier is the same form for all attestation types, but the values of the fields differ between them. It contains the following fields.

Required Fields

attestationType is the UTF8 hex string encoding of the attestation type name, zero-padded to 32 bytes.
sourceId is the UTF8 hex string encoding of the data source identifier name, zero-padded to 32 bytes.
requestBody is different for each attestation type.

In the case of Payment, requestBody is a JSON containing the fields:

transactionId: id of the transaction; as bytes32
inUtxo: UTXO chains support multiple source addresses, so this is the index of the address considered, as uint256; for non-UTXO chains this should always be 0
utxo: UTXO chains support multiple receiving addresses, so this is the index of the address considered, as uint256; for non-UTXO chains this should always be 0

Reference Documentation

Example Values

transactionId: the above address 9421cbb7f195df66d16703442a408261fa973514a0bd9dfc680f10eb3942d11f
inUtxo: non-default 0
utxo: non-default 0

Encoding Functions

To encode values into UTF8 hex:

toUtf8HexString: Converts a string to UTF8 hex.
toHexString: Zero-right-pads the string to 32 bytes.

These functions are included in the Base library within the example repository, but they can also be defined locally in your contract or script.

scrip/fdcExample/Base.s.sol
function toHexString(
 bytes memory data
) public pure returns (string memory) {
 bytes memory alphabet = "0123456789abcdef";

 bytes memory str = new bytes(2 + data.length * 2);
 str[0] = "0";
 str[1] = "x";
 for (uint i = 0; i < data.length; i++) {
 str[2 + i * 2] = alphabet[uint(uint8(data[i] >> 4))];
 str[3 + i * 2] = alphabet[uint(uint8(data[i] & 0x0f))];
 }
 return string(str);
}

scrip/fdcExample/Base.s.sol
function toUtf8HexString(
 string memory _string
) internal pure returns (string memory) {
 string memory encodedString = toHexString(
 abi.encodePacked(_string)
 );
 uint256 stringLength = bytes(encodedString).length;
 require(stringLength <= 64, "String too long");
 uint256 paddingLength = 64 - stringLength + 2;
 for (uint256 i = 0; i < paddingLength; i++) {
 encodedString = string.concat(encodedString, "0");
 }
 return encodedString;
}

We also define a helper function for formatting data into a JSON string.

scrip/fdcExample/Base.s.sol
function prepareAttestationRequest(
 string memory attestationType,
 string memory sourceId,
 string memory requestBody
) internal view returns (string[] memory, string memory) {
 // We read the API key from the .env file
 string memory apiKey = vm.envString("VERIFIER_API_KEY");

 // Preparing headers
 string[] memory headers = prepareHeaders(apiKey);
 // Preparing body
 string memory body = prepareBody(
 attestationType,
 sourceId,
 requestBody
 );

 console.log(
 "headers: %s",
 string.concat("{", headers[0], ", ", headers[1]),
 "}\n"
 );
 console.log("body: %s\n", body);
 return (headers, body);
}

function prepareHeaders(
 string memory apiKey
) internal pure returns (string[] memory) {
 string[] memory headers = new string[](2);
 headers[0] = string.concat('"X-API-KEY": ', apiKey);
 headers[1] = '"Content-Type": "application/json"';
 return headers;
}

function prepareBody(
 string memory attestationType,
 string memory sourceId,
 string memory body
) internal pure returns (string memory) {
 return
 string.concat(
 '{"attestationType": ',
 '"',
 attestationType,
 '"',
 ', "sourceId": ',
 '"',
 sourceId,
 '"',
 ', "requestBody": ',
 body,
 "}"
 );
}

In the example repository, these are once again included within the Base library file.

Thus, the part of the script that prepares the verifier request looks like:

scrip/fdcExample/Payment.s.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.25;

import {console} from "dependencies/forge-std-1.9.5/src/console.sol";
import {Script} from "dependencies/forge-std-1.9.5/src/Script.sol";
import {Base} from "./Base.s.sol";
...

string constant attestationTypeName = "Payment";
string constant dirPath = "data/";

contract PrepareAttestationRequest is Script {
 using Surl for *;

 // Setting request data
 string public transactionId =
 "2A3E7C7F6077B4D12207A9F063515EACE70FBBF3C55514CD8BD659D4AB721447";
 string public inUtxo = "0";
 string public utxo = "0";
 string public baseSourceName = "xrp"; // Part of verifier URL
 string public sourceName = "testXRP"; // XRLP test chain ID

 function prepareRequestBody(
 string memory transactionId,
 string memory inUtxo,
 string memory utxo
 ) private pure returns (string memory) {
 return
 string.concat(
 '{"transactionId": "',
 transactionId,
 '", "inUtxo": "',
 inUtxo,
 '", "utxo": "',
 utxo,
 '"}'
 );
 }

 function run() external {
 // Preparing request data
 string memory attestationType = Base.toUtf8HexString(
 attestationTypeName
 );
 string memory sourceId = Base.toUtf8HexString(sourceName);
 string memory requestBody = prepareRequestBody(
 transactionId,
 inUtxo,
 utxo
 );

 (string[] memory headers, string memory body) =
 prepareAttestationRequest(attestationType, sourceId, requestBody);

 ...
 }
}

...

If you are accessing a different chain, replace the baseSourceName with an appropriate value, doge or btc.

The code above differs slightly from the starter example. But, if we remove the ellipses ... signifying missing code, we can still run the script.

Because of the console.log commands it will produce JSON strings that represent valid requests; we can then pass this to the interactive verifier to check what the response will be.

We can run the script by calling the following commands in the console.

source .env

forge script script/fdcExample/Payment.s.sol:PrepareAttestationRequest --private-key $PRIVATE_KEY --rpc-url $COSTON2_RPC_URL --etherscan-api-key $FLARE_API_KEY --broadcast  --ffi

The prerequisite for this is that the .env file is not missing the PRIVATE KEY and COSTON2_RPC_URL values. The script can also access other chains; that can be achieved by replacing the --rpc-url value with COSTON_RPC_URL, FLARE_RPC_URL, or SONGBIRD_RPC_URL.

Post request to verifier.

To post a request to a verifier server, we use the surl package. We place using Surl for *; at the start of our PostRequest contract, and then call its post method on the verifier URL.

scrip/fdcExample/Payment.s.sol
(, bytes memory data) = url.post(headers, body);

We construct the URL by appending to the verifier address https://fdc-verifiers-testnet.flare.network/ the path verifier/btc/Payment/prepareRequest. We can do so dynamically with the following code.

scrip/fdcExample/Payment.s.sol
string memory baseUrl = "https://fdc-verifiers-testnet.flare.network/";
string memory url = string.concat(
 baseUrl,
 "verifier/",
 baseSourceName,
 "/",
 attestationTypeName,
 "/prepareRequest"
);
console.log("url: %s", url);
string memory requestBody = string.concat(
 '{"addressStr": "',
 addressStr,
 '"}'
);

Lastly, we parse the return data from the verifier server. Using the Foundry parseJson shortcode, and a custom struct AttestationResponse, we decode the returned data and extract from it the ABI encoded request.

scrip/fdcExample/Base.s.sol
function parseAttestationRequest(
 bytes memory data
) internal pure returns (AttestationResponse memory) {
 string memory dataString = string(data);
 bytes memory dataJson = vm.parseJson(dataString);

 AttestationResponse memory response = abi.decode(
 dataJson,
 (AttestationResponse)
 );

 console.log("response status: %s\n", response.status);
 console.log("response abiEncodedRequest: ");
 console.logBytes(response.abiEncodedRequest);
 console.log("\n");

 return response;
}

Details

Understanding the abiEncodedRequest.

If everything went right, the abiEncodedRequest should look something like this (minus the line breaks - we split it after the 0x symbol and then after every 64 characters (32 bytes), for the sake of clarity).

0x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Let's break it down line by line:

First line: toUtf8HexString("Payment")
Second line: toUtf8HexString("testETH")
Third line: message integrity code (MIC), a hash of the whole response salted with a string "Flare", ensures the integrity of the attestation
Remaining lines: ABI encoded Payment.RequestBody Solidity struct

What this demonstrates is that, with some effort, the abiEncodedRequest can be constructed manually.

We write the abiEncodedRequest to a file (data/Payment_abiEncodedRequest.txt) to it in the next step.

scrip/fdcExample/Payment.s.sol
Base.writeToFile(
    dirPath,
    string.concat(attestationTypeName, "_abiEncodedRequest"),
    StringsBase.toHexString(response.abiEncodedRequest),
    true
);

Submit request to FDC

This step transitions from offchain request preparation to on-chain interaction with the FDC protocol. Now, we submit the validated request to the blockchain using deployed smart contracts.

Submit request

The entire submission process requires only five key steps:

scrip/fdcExample/Base.s.sol
function submitAttestationRequest(
 AttestationResponse memory response
) internal {
 uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
 vm.startBroadcast(deployerPrivateKey);
 IFdcRequestFeeConfigurations fdcRequestFeeConfigurations = ContractRegistry
 .getFdcRequestFeeConfigurations();
 uint256 requestFee = fdcRequestFeeConfigurations.getRequestFee(
 response.abiEncodedRequest
 );
 console.log("request fee: %s\n", requestFee);
 vm.stopBroadcast();

 vm.startBroadcast(deployerPrivateKey);

 IFdcHub fdcHub = ContractRegistry.getFdcHub();
 console.log("fcdHub address:");
 console.log(address(fdcHub));
 console.log("\n");
 fdcHub.requestAttestation{value: requestFee}(response.abiEncodedRequest);
 vm.stopBroadcast();
}

Step-by-Step Breakdown

Load Private Key The private key is read from the .env file using Foundry's envUint function:

       uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");

Obtain Request Fee We retrieve the required requestFee from the FdcRequestFeeConfigurations contract:

        IFdcRequestFeeConfigurations fdcRequestFeeConfigurations = ContractRegistry
            .getFdcRequestFeeConfigurations();
        uint256 requestFee = fdcRequestFeeConfigurations.getRequestFee(
            response.abiEncodedRequest
        );

This is done in a separate broadcast to ensure requestFee is available before submitting the request.

Access FdcHub Contract Using the ContractRegistry library (from flare-periphery), we fetch the FdcHub contract:

   IFdcHub fdcHub = ContractRegistry.getFdcHub();
   console.log("fcdHub address:");
   console.log(address(fdcHub));
   console.log("\n");

Submit the Attestation Request We send the attestation request with the required fee:

 fdcHub.requestAttestation{value: requestFee}(response.abiEncodedRequest);

Calculate Voting Round Number To determine the voting round in which the attestation request is processed, we query the FlareSystemsManager contract:

       // Calculating roundId
       IFlareSystemsManager flareSystemsManager = ContractRegistry
           .getFlareSystemsManager();

       uint32 roundId = flareSystemsManager.getCurrentVotingEpochId();
       console.log("roundId: %s\n", Strings.toString(roundId));

This can be done within the existing broadcast or in a new one (as done in the demo repository for better code organization).

Wait for response

We wait for the round to finalize. This takes no more than 180 seconds.

You can check if the request was submitted successfully on the AttestationRequests page on the Flare Systems Explorer website. To check if the round has been finalized, go to Finalizations page.

To learn more about how the FDC protocol works, check here.

Prepare proof request

We prepare the proof request in a similar manner as in the step Prepare the request, by string concatenation. We import two new variables from the .env file; the URL of a verifier server and the corresponding API key.

scrip/fdcExample/Payment.s.sol
string memory daLayerUrl = vm.envString("COSTON2_DA_LAYER_URL");
string memory apiKey = vm.envString("X_API_KEY");

Also, by repeatedly using the Foundry shortcode vm.readLine, we read the data, saved to a file in the previous step, to variables.

scrip/fdcExample/Payment.s.sol
string memory requestBytes = vm.readLine(
    string.concat(
        dirPath,
        attestationTypeName,
        "_abiEncodedRequest",
        ".txt"
    )
);
string memory votingRoundId = vm.readLine(
    string.concat(
        dirPath,
        attestationTypeName,
        "_votingRoundId",
        ".txt"
    )
);

The code is as follows.

scrip/fdcExample/Payment.s.sol
contract RetrieveDataAndProof is Script {
 using Surl for *;

 function run() external {
 string memory daLayerUrl = vm.envString("COSTON2_DA_LAYER_URL");
 string memory apiKey = vm.envString("X_API_KEY");
 string memory fileName = string.concat(attestationTypeName, ".txt");
 string memory filePath = string.concat(dirPath, fileName);

 // We import the roundId and abiEncodedRequest from the first file
 string memory votingRoundId = vm.readLine(filePath);
 string memory requestBytes = vm.readLine(filePath);
 console.log("votingRoundId: %s\n", votingRoundId);
 console.log("requestBytes: %s\n", requestBytes);

 // Preparing the proof request
 string[] memory headers = prepareHeaders(apiKey);
 string memory body = string.concat(
 '{"votingRoundId":',
 votingRoundId,
 ',"requestBytes":"',
 requestBytes,
 '"}'
 );
 console.log("body: %s\n", body);
 console.log(
 "headers: %s",
 string.concat("{", headers[0], ", ", headers[1]),
 "}\n"
 );

 ...
 }
}

Post proof request to DA Layer

We post the proof request to a chosen DA Layer provider server also with the same code as we did in the previous step.

scrip/fdcExample/Payment.s.sol
string memory url = string.concat(
 daLayerUrl,
 // "api/v0/fdc/get-proof-round-id-bytes"
 "api/v1/fdc/proof-by-request-round-raw"
);
console.log("url: %s\n", url);

(, bytes memory data) = Base.postAttestationRequest(url, headers, body);

Parsing the returned data requires the definition of an auxiliary struct.

scrip/fdcExample/Base.s.sol
struct ParsableProof {
 bytes32 attestationType;
 bytes32[] proofs;
 bytes responseHex;
}

The field attestationType holds the UTF8 encoded hex string of the attestation type name, padded to 32 bytes. Thus, it should match the value of the attestationType parameter in the Prepare the request step. In our case, that value is 0x4164647265737356616c69646974790000000000000000000000000000000000.

The array proofs holds the Merkle proofs of our attestation request.

Lastly, responseHex is the ABI encoding of the chosen attestation type response struct. In this case, it is the IPayment.Response struct. We retrieve this data as follows.

scrip/fdcExample/Payment.s.sol
bytes memory dataJson = parseData(data);
ParsableProof memory proof = abi.decode(dataJson, (ParsableProof));

IPayment.Response memory proofResponse = abi.decode(
 proof.responseHex,
 (IPayment.Response)
);

An example complete proof response and decoded IEVMTransaction.Response.

An example DA Layer response for a request using the data provided in this example is:

{
  response_hex: '0x
  5061796d656e7400000000000000000000000000000000000000000000000000
  7465737458525000000000000000000000000000000000000000000000000000
  00000000000000000000000000000000000000000000000000000000000e6c2d
  00000000000000000000000000000000000000000000000000000000a019d806
  2a3e7c7f6077b4d12207a9f063515eace70fbbf3c55514cd8bd659d4ab721447
  0000000000000000000000000000000000000000000000000000000000000000
  0000000000000000000000000000000000000000000000000000000000000000
  000000000000000000000000000000000000000000000000000000000048f822
  0000000000000000000000000000000000000000000000000000000067ac9486
  7f5b4967a9fbe9b447fed6d4e3699051516b6afe5f94db2e77ccf86470bfd74d
  a1475e9840d916c22f494c0dc25428d2affb5ae1f496efc82bbb59d46a336779
  cd582d251987f15ecb29b69c2e02051479e84c176e39cbbdf04a4d0ef89bcf82
  cd582d251987f15ecb29b69c2e02051479e84c176e39cbbdf04a4d0ef89bcf82
  0000000000000000000000000000000000000000000000000000000005f5e10c
  0000000000000000000000000000000000000000000000000000000005f5e10c
  0000000000000000000000000000000000000000000000000000000005f5e100
  0000000000000000000000000000000000000000000000000000000005f5e100
  0000000000000000000000000000000000000000000000000000000000000000
  0000000000000000000000000000000000000000000000000000000000000001
  0000000000000000000000000000000000000000000000000000000000000000',
  attestation_type: '0x5061796d656e7400000000000000000000000000000000000000000000000000',
  proof: [
    '0xe1f98d39167eab17b2157c06efb80530b161d5eb15c439fc476e3242e30b3ac1',
    '0x23a8ffdb2cbaf0e2f3653923a159150f8d4c3ad5160f9e127cc9797ba233e6c2',
    '0xd756b90367b336e127f0759a1457825b4c2bf9011b71b56e15d9fcb7ff735ec8',
    '0xc881d1566868a986aef2bda47e9ab6dafeb8241bde5f5d53235837595829a5ea'
  ]
}

The proof field is dependent on the round in which the attestation request was submitted; it contains proofs for all of the requests submitted in that round. In the case of a single attestation request it is an empty list [] (the proof is the merkle root itself).

The decoded IEVMTransaction.Response struct is:

[
  attestationType: '0x5061796d656e7400000000000000000000000000000000000000000000000000',
  sourceId: '0x7465737458525000000000000000000000000000000000000000000000000000',
  votingRound: '945197',
  lowestUsedTimestamp: '2686048262',
  requestBody: [
    '0x2a3e7c7f6077b4d12207a9f063515eace70fbbf3c55514cd8bd659d4ab721447',
    '0',
    '0',
    transactionId: '0x2a3e7c7f6077b4d12207a9f063515eace70fbbf3c55514cd8bd659d4ab721447',
    inUtxo: '0',
    utxo: '0'
  ],
  responseBody: [
    '4782114',
    '1739363462',
    '0x7f5b4967a9fbe9b447fed6d4e3699051516b6afe5f94db2e77ccf86470bfd74d',
    '0xa1475e9840d916c22f494c0dc25428d2affb5ae1f496efc82bbb59d46a336779',
    '0xcd582d251987f15ecb29b69c2e02051479e84c176e39cbbdf04a4d0ef89bcf82',
    '0xcd582d251987f15ecb29b69c2e02051479e84c176e39cbbdf04a4d0ef89bcf82',
    '100000012',
    '100000012',
    '100000000',
    '100000000',
    '0x0000000000000000000000000000000000000000000000000000000000000000',
    true,
    '0',
    blockNumber: '4782114',
    blockTimestamp: '1739363462',
    sourceAddressHash: '0x7f5b4967a9fbe9b447fed6d4e3699051516b6afe5f94db2e77ccf86470bfd74d',
    sourceAddressesRoot: '0xa1475e9840d916c22f494c0dc25428d2affb5ae1f496efc82bbb59d46a336779',
    receivingAddressHash: '0xcd582d251987f15ecb29b69c2e02051479e84c176e39cbbdf04a4d0ef89bcf82',
    intendedReceivingAddressHash: '0xcd582d251987f15ecb29b69c2e02051479e84c176e39cbbdf04a4d0ef89bcf82',
    spentAmount: '100000012',
    intendedSpentAmount: '100000012',
    receivedAmount: '100000000',
    intendedReceivedAmount: '100000000',
    standardPaymentReference: '0x0000000000000000000000000000000000000000000000000000000000000000',
    oneToOne: true,
    status: '0'
  ]
]

Verify proof

Because every node holds a copy of the whole chain, storing data on the blockchain is expensive. For the sake of efficiency, FDC keeps only the Merkle proof on-chain, while the data itself can be obtained from outside data providers. Per our request, they supply us with the specified data. That data then be encrypted, and its Merkle proof compared to the Merkle root stored on-chain. If they match, the data can be trusted.

This step is not strictly necessary; if we trust our data provider, we can skip this step. And in practice, we do just that. But it is crucial, that should we want to verify the data, we can do so.

One way to do it is using the FdcVerification contract. We first store our data as an appropriate Solidity struct, namely IPayment.Proof.

scrip/fdcExample/Payment.s.sol
IPayment.Proof memory _proof = IPayment.Proof(
 proof.proofs,
 proofResponse
);

We then access the FdcVerification contract through the ContractRegistry, and feed it the proof. If the proof is valid, the function verifyPayment will return true, otherwise false. As before, we wrap the whole thing into a broadcast environment, using the PRIVATE_KEY variable from our .env file.

scrip/fdcExample/Payment.s.sol
uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
vm.startBroadcast(deployerPrivateKey);

bool isValid = ContractRegistry
 .getFdcVerification()
 .verifyPayment(proof);
console.log("proof is valid: %s\n", StringsBase.toString(isValid));

vm.stopBroadcast();

In actuality, we will only verify the proof within a deployed contract, which we will define in the next step. What we will do here instead is, we will save the proof to a file so that it can be later loaded into a variable. The code that does this is as follows.

scrip/fdcExample/EVMTransaction.s.sol
Base.writeToFile(
    dirPath,
    string.concat(attestationTypeName, "_proof"),
    StringsBase.toHexString(abi.encode(_proof)),
    true
);

Use the data

We will now define a simple contract, that will demonstrate how the data can be used onchain. The contract will receive data and proof of a Payment transaction, and store it into an array of special Payment structs. It will do so only if the transaction is valid.

src/fdcExample/Payment.sol
struct Payment {
    uint64 blockNumber;
    uint64 blockTimestamp;
    bytes32 sourceAddressHash;
    bytes32 receivingAddressHash;
    int256 spentAmount;
    bytes32 standardPaymentReference;
    uint8 status;
}

First, we define an interface that the contract will inherit from. We do so, so that we may contact the contract later through a script.

src/fdcExample/Payment.sol
interface ITransferEventListener {
    function registerPayment(
        IPayment.Proof calldata _transaction
    ) external;
}

The interface exposes the only function the script will call, collectTransferEvents. We now define the contract as follows.

src/fdcExample/Payment.sol

contract PaymentRegistry is IPaymentRegistry {
    Payment[] public verifiedPayments;

    function isPaymentProofValid(
        IPayment.Proof calldata transaction
    ) public view returns (bool) {
        // Use the library to get the verifier contract and verify that this transaction was proved by state connector
        IFdcVerification fdc = ContractRegistry.getFdcVerification();
        console.log("transaction: %s\n", FdcStrings.toJsonString(transaction));
        // return true;
        return fdc.verifyPayment(transaction);
    }

    function registerPayment(IPayment.Proof calldata _transaction) external {
        // 1. FDC Logic
        // Check that this Payment has indeed been confirmed by the FDC
        require(isPaymentProofValid(_transaction), "Invalid transaction proof");

        // 2. Business logic
        Payment memory provedPayment = Payment(
            _transaction.data.responseBody.blockNumber,
            _transaction.data.responseBody.blockTimestamp,
            _transaction.data.responseBody.sourceAddressHash,
            _transaction.data.responseBody.receivingAddressHash,
            _transaction.data.responseBody.spentAmount,
            _transaction.data.responseBody.standardPaymentReference,
            _transaction.data.responseBody.status
        );

        verifiedPayments.push(provedPayment);
    }
}

We deploy the contract through a simple script. The script creates a new PaymentRegistry contract, and writes its address to a file (data/Payment_listenerAddress.txt).

scrip/fdcExample/DeployContract.s.sol
contract DeployContract is Script {
    function run() external {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        vm.startBroadcast(deployerPrivateKey);

        PaymentRegistry paymentRegistry = new PaymentRegistry();
        address _address = address(paymentRegistry);

        vm.stopBroadcast();

        Base.writeToFile(
            dirPath,
            string.concat(attestationTypeName, "_address"),
            StringsBase.toHexString(abi.encodePacked(_address)),
            true
        );
    }
}

We deploy the contract with the following console command.

forge script script/fdcExample/Payment.s.sol:DeployContract --private-key $PRIVATE_KEY --rpc-url $COSTON2_RPC_URL --etherscan-api-key $FLARE_API_KEY --broadcast --verify --ffi

Lastly, we define a script that interacts with the above contract. It first reads the ABI encoded proof data, and the contract address, from files. Then, it connects to the above contract at the saved address (this is why we require the interface). With that, it is able to call the registerPayment method of the contract.

script/fdcExample/Payment.s.sol
contract InteractWithContract is Script {
    function run() external {
        string memory addressString = vm.readLine(
            string.concat(dirPath, attestationTypeName, "_address", ".txt")
        );
        address _address = vm.parseAddress(addressString);
        string memory proofString = vm.readLine(
            string.concat(dirPath, attestationTypeName, "_proof", ".txt")
        );
        bytes memory proofBytes = vm.parseBytes(proofString);
        IPayment.Proof memory proof = abi.decode(proofBytes, (IPayment.Proof));
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        vm.startBroadcast(deployerPrivateKey);
        IPaymentRegistry registry = IPaymentRegistry(_address);
        registry.registerPayment(proof);
        vm.stopBroadcast();
    }
}

We run this script with the console command:

forge script script/fdcExample/Payment.s.sol:InteractWithContract --private-key $PRIVATE_KEY --rpc-url $COSTON2_RPC_URL --etherscan-api-key $FLARE_API_KEY --broadcast --ffi

Prepare request​

Required Fields​

Reference Documentation​

Example Values​

Encoding Functions​

Post request to verifier.​

Submit request to FDC​

Submit request​

Step-by-Step Breakdown​

Wait for response​

Prepare proof request​

Post proof request to DA Layer​

Verify proof​

Use the data​