📂 How to Guides

# Remix Example

Table of Contents

This project is a simple and quick introduction to API3's QRNG service. Simply follow the steps to see how a smart contract (known as a requester) can access an on-chain quantum random number. You will use the browser based Remix IDE and MetaMask. Some basic knowledge of these two tools is assumed.

Remix UI components to interact with are show as: UI name (brown) highlighted text.

# Step 1: Add the Sample Contract

Open the Remix online IDE (opens new window) using a browser that you have added Metamask support to. Not all browsers support MetaMask (opens new window).

Add a new file called RemixQrngExample.sol to a Remix workspace. You can use an existing workspace or create a new one. Copy and paste the code from the RemixQrngExample.sol contract into the file.

Add Contract

# Step 2: Compile the Contract

Switch to the SOLIDITY COMPILER tab. Select the 0.8.9 version of Solidity from the COMPILER pick list. Select the Compile RemixQrngExample.sol button to compile the RemixQrngExample.sol contract.

# Step 3: Deploy the Contract

Deploy to a testnet only.

Do not deploy the RemixQrngExample.sol contract to a production network. It lacks adequate security features.

Switch to the DEPLOY & RUN TRANSACTIONS tab. Use MetaMask and switch to the desired account and testnet for your deployment. Select the ENVIRONMENT pick list and switch to Injected Web3. Check that the testnet and account you selected in MetaMask are displayed in Remix as shown below.

Be sure RemixQrngExample - contracts/RemixQrngExample.sol is selected in the CONTRACT pick list. Add the Airnode _airnodeRrp address parameter value for the constructor into the field next to the Deploy button. See the list of addresses for the testnet you are using. Select the Deploy button and approve the transaction with MetaMask.

# Step 4: Setting the Parameters

Before making a request, parameters must be set. They determine which Airnode endpoint will be called and define the wallet used to pay the gas costs for the response.

Under Deployed Contracts expand and expose the functions and variables of the contract. Note the address of the contract that is displayed with its name. This is the requester's contract address which will be needed later. Next expand the setRequestParameters function. Add the following to the corresponding fields for the function.

  • _airnode: The airnode address (copy it here →

    ) of the desired QRNG service provider. See its value from the ANU Airnode.

  • _endpointIdUint256: The Airnode endpoint ID (copy it here →

    ) that will return a single random number. See its value from the ANU Airnode.

  • _sponsorWallet: A wallet derived from the requester's contract address, the Airnode address, and the Airnode xpub. The wallet is used to pay gas costs to acquire a random number. A sponsor wallet must be derived using the command derive-sponsor-wallet-address from the Admin CLI. Use the value of the sponsor wallet address that the command outputs.

    npx @api3/airnode-admin derive-sponsor-wallet-address \
      --airnode-xpub xpub6DXSDTZBd4aPVXnv6Q3SmnGUweFv6j24SK77W4qrSFuhGgi666awUiXakjXruUSCDQhhctVG7AQt67gMdaRAsDnDXv23bBRKsMWvRzo6kbf \
      --airnode-address 0x9d3C147cA16DB954873A498e0af5852AB39139f2 \
      --sponsor-address <use-the-address-of: RemixQrngExample.sol>
      # --airnode-xpub:    Pre-filled, see https://docs.api3.org/qrng/reference/providers.html.
      # --airnode-address: Pre-filled, see https://docs.api3.org/qrng/reference/providers.html.
      # --sponsor-address: Use the requester's contract address for
      #                    RemixQrngExample.sol as displayed in the Remix IDE.
      # The command outputs.
      Sponsor wallet address: 0x6394...5906757
      # Use the above address from your command execution as the value for _sponsorWallet.

    Be sure to fund the public address of the sponsor wallet that the command outputs. The funds are used to pay gas costs for the Airnode's response.

Lastly select the Transact button in Remix to send the parameters to the contract to be stored. Approve the transaction with MetaMask.

Designated Sponsor Wallets

Sponsors should not fund a sponsorWallet with more then they can trust the Airnode with, as the Airnode controls the private key to the sponsorWallet. The deployer of such Airnode undertakes no custody obligations, and the risk of loss or misuse of any excess funds sent to the sponsorWallet remains with the sponsor.

# Step 5: Make a Request

Be sure you have funded the sponsor wallet created in step #4. Its funds will be used to pay gas costs when Airnode returns a random number to the callback function fulfillUint256().

Each request made will use the parameters set in step 4. You can change the parameters at any time and subsequent requests will use the newer parameter set.

To make a request select the MakeRequest button in Remix. Approve the transaction with MetaMask.

As soon as the transaction completes in MetaMask, select the lastRequest button in Remix. You will see the requestId and a randomNumber which equals 0. This is because the random number has yet to be returned to the callback function. Copy and paste the requestId into the field for waitingFulfillment and select the button. You will see the value is true, meaning the callback has not been made.

# Step 6: View the Response

The request is gathered by the off-chain Airnode which in turn calls the API provider. Once the API provider returns data, Airnode will callback to the RemixQrngExample.sol contract function fulfillUint256(bytes32 requestId, bytes calldata data).

Select the the lastRequest button in Remix again. If the callback has been successfully completed the randomNumber will be present. The value of waitingFulfillment will be false.

Last Updated: 8/9/2022, 3:28:25 PM