# AddressValidity
> Check the validity of a Bitcoin, Dogecoin, or XRPL address.
> For the complete documentation index, see [llms.txt](/llms.txt). Markdown versions of documentation pages are available by appending `.md` to the page URL.
Source: https://dev.flare.network/fdc/guides/foundry/address-validity
The [AddressValidity](/fdc/attestation-types/address-validity) attestation type validates whether a string represents a valid address on supported blockchain networks (`BTC`, `DOGE`, and `XRP`). This validation ensures addresses meet chain-specific formatting and checksum requirements before they're used in transactions or smart contracts. The full specification is available on the official [specification repo](/fdc/attestation-types/address-validity).
The primary contract interface for this attestation type is [`IAddressValidity`](/fdc/reference/IFdcHub). Let's walk through validating a Bitcoin testnet address using the FDC protocol. We will use the address `mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs` as an example throughout this guide. You can swap this with any valid testnet address from the supported chains. You can follow this tutorial with any other valid address - just make sure it is a valid testnet address.
This validation process works identically for `BTC`, `DOGE`, and `XRP` addresses, with only minor chain-specific parameter adjustments which we'll highlight throughout the guide.
In this guide, we will follow the steps outlined in the [FDC overview](/fdc/overview).
Our implementation requires handling the FDC voting round finalization process. To manage this, we will create separate scripts in `script/fdcExample/AddressValidity.s.sol` that handle different stages of the validation process:
script/fdcExample/AddressValidity.s.sol
```
// SPDX-License-Identifier: MITpragma solidity ^0.8.25;import {Script} from "dependencies/forge-std-1.9.5/src/Script.sol";...// Configuration constantsstring constant attestationTypeName = "AddressValidity";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 overview](/fdc/overview).
To bridge the separate script executions, 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[](#prepare-request "Direct link to Prepare request")
A JSON request to the verifier follows the same structure for all attestation types, with field values varying per type.
### Required Fields[](#required-fields "Direct link to Required Fields")
- `attestationType`: UTF8 hex string encoding of the attestation type name, zero-padded to 32 bytes.
- `sourceId`: UTF8 hex string encoding of the data source identifier name, zero-padded to 32 bytes.
- `requestBody`: Specific to each attestation type.
For `AddressValidity`, `requestBody` contains a single field:
- `addressString`: The address to verify.
### Reference Documentation[](#reference-documentation "Direct link to Reference Documentation")
- [AddressValidity Specification](/fdc/attestation-types/address-validity)
- [Verifier Interactive Docs](https://fdc-verifiers-testnet.flare.network/verifier/btc_testnet4/api-doc#/AddressValidity/BTCAddressValidityVerifierController_prepareRequest)
- API available for [DOGE](https://fdc-verifiers-testnet.flare.network/verifier/doge/api-doc#/AddressValidity/BTCAddressValidityVerifierController_prepareRequest) and [XRP](https://fdc-verifiers-testnet.flare.network/verifier/xrp/api-doc#/AddressValidity/BTCAddressValidityVerifierController_prepareRequest).
### Example Values[](#example-values "Direct link to Example Values")
- `attestationType`: UTF8 hex encoding of `AddressValidity`, zero-padded to 32 bytes.
- `sourceId`: UTF8 hex encoding of `testBTC`, zero-padded to 32 bytes.
- `"test"` prefix denotes Bitcoin testnet.
- Supports deployment on Flare testchains (`Coston` or `Coston2`).
- Replace `testBTC` with `testDOGE` or `testXRP` for other chains.
- `addressString`: `mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs`.
### Encoding Functions[](#encoding-functions "Direct link to 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](https://github.com/flare-foundation/flare-foundry-starter/blob/master/script/fdcExample/Base.s.sol) within the [example repository](https://github.com/flare-foundation/flare-foundry-starter), but they can also be defined locally in your contract or script.
script/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);}
```
script/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.
script/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_TESTNET"); // 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](https://github.com/flare-foundation/flare-foundry-starter/blob/master/script/fdcExample/Base.s.sol) library file.
Thus, the part of the script that prepares the verifier request looks like:
script/fdcExample/AddressValidity.s.sol
```
// SPDX-License-Identifier: MITpragma 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 = "AddressValidity";string constant dirPath = "data/";contract PrepareAttestationRequest is Script { using Surl for *; // Setting request data string public addressStr = "mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs"; // Id of the Bitcoin address to be validated string public baseSourceName = "btc"; // Part of verifier URL string public sourceName = "testBTC"; // Bitcoin chain ID function prepareRequestBody( string memory addressStr ) private pure returns (string memory) { return string.concat('{"addressStr": "', addressStr, '"}'); } function run() external { // Preparing request data string memory attestationType = Base.toUtf8HexString( attestationTypeName ); string memory sourceId = Base.toUtf8HexString(sourceName); string memory requestBody = prepareRequestBody(addressStr); (string[] memory headers, string memory body) = Base .prepareAttestationRequest(attestationType, sourceId, requestBody); // TODO change key in .env // string memory baseUrl = "https://testnet-verifier-fdc-test.aflabs.org/"; string memory baseUrl = vm.envString("VERIFIER_URL_TESTNET"); string memory url = string.concat( baseUrl, "verifier/", baseSourceName, "/", attestationTypeName, "/prepareRequest" ); console.log("url: %s", url); (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 `xrp`.
The code above differs slightly from the [starter example](https://github.com/flare-foundation/flare-foundry-starter). 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](https://fdc-verifiers-testnet.flare.network/verifier/btc_testnet4/api-doc#/AddressValidity/BTCAddressValidityVerifierController_prepareRequest) to check what the response is.
We can run the script by calling the following commands in the console.
```
source .env
```
```
forge script script/fdcExample/AddressValidity.s.sol:PrepareAttestationRequest --private-key $PRIVATE_KEY --rpc-url $COSTON2_RPC_URL --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[](#post-request-to-verifier "Direct link to Post request to verifier")
Before submitting address validation requests to the FDC protocol, we first need to prepare and send them to a verifier server. This section walks through the request submission process using 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.
script/fdcExample/AddressValidity.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_testnet4/AddressValidity/prepareRequest`. We can do so dynamically with the following code.
script/fdcExample/AddressValidity.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.
script/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;}
```
Understanding the abiEncodedRequest.
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).
```
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
```
Let's break it down line by line:
- **First line:** `toUtf8HexString("AddressValidity")`
- **Second line:** `toUtf8HexString("testBTC")`
- **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 `AddressValidity.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/AddressValidity_abiEncodedRequest.txt`) to it in the next step.
script/fdcExample/AddressValidity.s.sol
```
Base.writeToFile( dirPath, string.concat(attestationTypeName, "_abiEncodedRequest"), StringsBase.toHexString(response.abiEncodedRequest), true);
```
## Submit request to FDC[](#submit-request-to-fdc "Direct link to Submit request to FDC")
This step transitions from offchain request preparation to onchain interaction with the FDC protocol. Now, we submit the validated request to the blockchain using deployed smart contracts.
### Submit request[](#submit-request "Direct link to Submit request")
The entire submission process requires only five key steps:
script/fdcExample/Base.s.sol
```
function submitAttestationRequest( bytes memory abiEncodedRequest) internal { uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY"); vm.startBroadcast(deployerPrivateKey); IFdcRequestFeeConfigurations fdcRequestFeeConfigurations = ContractRegistry .getFdcRequestFeeConfigurations(); uint256 requestFee = fdcRequestFeeConfigurations.getRequestFee( 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}(abiEncodedRequest); vm.stopBroadcast();}
```
### Step-by-Step Breakdown[](#step-by-step-breakdown "Direct link to Step-by-Step Breakdown")
1. Load Private Key The private key is read from the `.env` file using Foundry's `envUint` function:
```
uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
```
2. 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.
3. 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");
```
4. Submit the Attestation Request We send the attestation request with the required fee:
```
fdcHub.requestAttestation{value: requestFee}(response.abiEncodedRequest);
```
5. Calculate the 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).
Again, we write the `roundId` to a file (`data/AddressValidity_roundId.txt`).
## Wait for response[](#wait-for-response "Direct link to 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](https://coston2-systems-explorer.flare.rocks/attestation-request) page on the Flare Systems Explorer website. To check if the round has been finalized, go to [Finalizations](https://coston2-systems-explorer.flare.rocks/finalizations) page.
If you want to learn more about how the FDC protocol works, check [here](/fdc/overview).
## Prepare proof request[](#prepare-proof-request "Direct link to 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. note
script/fdcExample/AddressValidity.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.
```
string memory votingRoundId = vm.readLine(filePath);string memory requestBytes = vm.readLine(filePath);
```
The code is as follows.
script/fdcExample/AddressValidity.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 requestBytes = vm.readLine( string.concat( dirPath, attestationTypeName, "_abiEncodedRequest", ".txt" ) ); string memory votingRoundId = vm.readLine( string.concat( dirPath, attestationTypeName, "_votingRoundId", ".txt" ) ); console.log("votingRoundId: %s\n", votingRoundId); console.log("requestBytes: %s\n", requestBytes); string[] memory headers = Base.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[](#post-proof-request-to-da-layer "Direct link to 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.
script/fdcExample/AddressValidity.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) = postAttestationRequest(url, headers, body);
```
Parsing the returned data requires the definition of an auxiliary `struct`.
script/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 `IAddressValidity.Response` struct. We retrieve this data as follows.
script/fdcExample/AddressValidity.s.sol
```
bytes memory dataJson = Base.parseData(data);ParsableProof memory proof = abi.decode(dataJson, (ParsableProof));IAddressValidity.Response memory proofResponse = abi.decode( proof.responseHex, (IAddressValidity.Response));
```
An example complete proof response and decoded IAddressValidity.Response.
An example complete proof response and decoded `IAddressValidity.Response`.
An example DA Layer response for a request using the data provided in this example is:
```
{ response_hex: "0x 0000000000000000000000000000000000000000000000000000000000000020 4164647265737356616c69646974790000000000000000000000000000000000 7465737442544300000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000000000000e6bda 000000000000000000000000000000000000000000000000ffffffffffffffff 00000000000000000000000000000000000000000000000000000000000000c0 0000000000000000000000000000000000000000000000000000000000000140 0000000000000000000000000000000000000000000000000000000000000020 0000000000000000000000000000000000000000000000000000000000000022 6d6739503966347772397737633173674665695443356f4d4c59584363326337 6873000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000001 0000000000000000000000000000000000000000000000000000000000000060 6810e152510fe893f9cc8954c4dfaecd5c2be00e2732d6fe3e25922f30c5a3c5 0000000000000000000000000000000000000000000000000000000000000022 6d6739503966347772397737633173674665695443356f4d4c59584363326337 6873000000000000000000000000000000000000000000000000000000000000", attestation_type: "0x4164647265737356616c69646974790000000000000000000000000000000000", proof: [ "0x275dc338dd4e6a0a8749caa098c6749e0e77e22ba9db264f334b5dfb79aa6321", "0x084e002bbe12f4a163d82ddd17861d1d3131c816fe3b998d575d134043a6c8f1", "0xc30304c7d430e3d0f83d05017035f13ca19dec2799917745967f4c48685eab49", "0x4d622137c9e7c9a1fa3a5d2942a183a8e926ba8659fe606495ea994acbb6ec0f" ]}
```
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 `IAddressValidity.Response` struct is:
```
[ attestationType: "0x4164647265737356616c69646974790000000000000000000000000000000000", sourceId: "0x7465737442544300000000000000000000000000000000000000000000000000", votingRound: "945114", lowestUsedTimestamp: "18446744073709551615", requestBody: [ "mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs", addressStr: "mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs" ], responseBody: [ true, "mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs", "0x6810e152510fe893f9cc8954c4dfaecd5c2be00e2732d6fe3e25922f30c5a3c5", isValid: true, standardAddress: "mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs", standardAddressHash: "0x6810e152510fe893f9cc8954c4dfaecd5c2be00e2732d6fe3e25922f30c5a3c5" ]]
```
## Verify proof[](#verify-proof "Direct link to Verify proof")
FDC optimizes onchain storage costs by implementing a hybrid data verification system. Instead of storing complete datasets onchain, it stores only Merkle proofs, while maintaining the actual data through trusted offchain providers. This approach significantly reduces gas costs while preserving data integrity.
When requested, data providers supply the original data along with its corresponding Merkle proof. The protocol verifies data authenticity by comparing the provided Merkle proof against the onchain Merkle root. A successful match confirms the data's integrity and authenticity within the FDC system.
While data verification is optional if you trust your data provider, FDC ensures transparency by making verification possible at any time. This capability is crucial for maintaining system integrity and allowing users to independently verify data when needed, particularly in production environments.
FDC provides verification functionality through the `FdcVerification` contract. To verify address validity, we first format our data using the `IAddressValidity.Proof` struct, which contains both the Merkle proof and the response data.
script/fdcExample/AddressValidity.s.sol
```
IAddressValidity.Proof memory _proof = IAddressValidity.Proof( proof.proofs, proofResponse);
```
We then access the `FdcVerification` contract through the `ContractRegistry`, and feed it the proof. If we proof is valid, the function `verifyAddressValidity` 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.
script/fdcExample/AddressValidity.s.sol
```
uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");vm.startBroadcast(deployerPrivateKey);bool isValid = ContractRegistry .getFdcVerification() .verifyAddressValidity(proof);console.log("proof is valid: %s\n", StringsBase.toString(isValid));vm.stopBroadcast();
```
## Use the data[](#use-the-data "Direct link to Use the data")
We will now define a simple contract, that will demonstrate how the data can be used onchain. The contract will receive an address and proof, and decide if the address is valid. If the address is valid, the contract will add it to an array of valid addresses. Otherwise, it will raise an error.
The code for this contract is as follows.
src/fdcExample/AddressValidity.sol
```
// SPDX-License-Identifier: MITpragma solidity ^0.8.25;import {console} from "dependencies/forge-std-1.9.5/src/console.sol";import {Strings} from "@openzeppelin-contracts/utils/Strings.sol";import {ContractRegistry} from "flare-periphery/src/coston2/ContractRegistry.sol";import {IFdcHub} from "flare-periphery/src/coston2/IFdcHub.sol";import {IAddressValidity} from "flare-periphery/src/coston2/IAddressValidity.sol";import {IFdcVerification} from "flare-periphery/src/coston2/IFdcVerification.sol";import {FdcStrings} from "src/utils/fdcStrings/AddressValidity.sol";struct EventInfo { address sender; uint256 value; bytes data;}contract AddressValidity { string[] public verifiedAddresses; function isAddressValidityProofValid( IAddressValidity.Proof calldata transaction ) public view returns (bool) { // Use the library to get the verifier contract and verify that this transaction was proved by the FDC IFdcVerification fdc = ContractRegistry.getFdcVerification(); console.log("transaction: %s\n", FdcStrings.toJsonString(transaction)); // return true; return fdc.verifyAddressValidity(transaction); } function registerAddress( string calldata _addressStr, IAddressValidity.Proof calldata _transaction ) external { // 1. FDC Logic // Check that this AddressValidity has indeed been confirmed by the FDC require( isAddressValidityProofValid(_transaction), "Invalid transaction proof" ); // 2. Business logic string provedAddress = _transaction.data.requestBody.addressStr; require( Strings.equal(provedAddress, _addressStr), string.concat( "Invalid address.\n\tProvided: ", _addressStr, "\n\tProoved: ", provedAddress ) ); verifiedAddresses.push(provedAddress); }}
```
The function `registerAddress` takes as parameters a string representing an address, and a proof. If the proof is valid, and if the given address matches the one in the proof, the address is added to an array of verified addresses.
We deploy the contract through a simple script. The script creates a new `AddressRegistry` contract, and writes its address to a file (`data/Address_listenerAddress.txt`).
script/fdcExample/Address.s.sol
```
contract DeployContract is Script { function run() external { uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY"); vm.startBroadcast(deployerPrivateKey); AddressRegistry addressRegistry = new AddressRegistry(); address _address = address(addressRegistry); vm.stopBroadcast(); Base.writeToFile( dirPath, string.concat(attestationTypeName, "_address"), StringsBase.toHexString(abi.encodePacked(_address)), true ); }}
```
We run the above script with the following console command.
```
forge script script/fdcExample/AddressValidity.s.sol:Deploy --private-key $PRIVATE_KEY --rpc-url $COSTON2_RPC_URL --etherscan-api-key $FLARE_RPC_API_KEY --broadcast --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 `registerAddress` method of the contract.
script/fdcExample/AddressValidity.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); IAddressValidity.Proof memory proof = abi.decode( proofBytes, (IAddressValidity.Proof) ); uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY"); vm.startBroadcast(deployerPrivateKey); IAddressRegistry registry = IAddressRegistry(_address); registry.registerAddress("mg9P9f4wr9w7c1sgFeiTC5oMLYXCc2c7hs", proof); vm.stopBroadcast(); }}
```
We run this script with the console command:
```
forge script script/fdcExample/AddressValidity.s.sol:InteractWithContract --private-key $PRIVATE_KEY --rpc-url $COSTON2_RPC_URL --etherscan-api-key $FLARE_RPC_API_KEY --broadcast --ffi
```