Use Solidity Development Tools

A DApp or Web3 game developer can also interact with the Adapter contract directly. While you can do this in many ways, such as via Remix, Etherscan, or programmatically, we recommend using Cast from the Foundry framework.

Prerequisites

• Smart Contract development experience in Solidity

• Experience with Foundry Solidity development toolkit

Installation

• Install Foundry

Steps

The instructions below outline the steps a user needs to take in order to request randomness from ARPA Randcast.

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Export your Environment Variables

You can export several environment variables to streamline the execution of the subsequent commands.

Note: the adapter contract address for the chain you are using can be found on the Supported Networks & Parameters.

export ADAPTER_CONTRACT=0xbd57b868bb3374faa88722d2ee7ba3023c744e05 # mainnet adapter contract
export RPC_URL= # Mainnet Alchemy / Infura RPC URL Here
export USER_PUBLIC_KEY= # Eth User You are using to deploy consumer / user contract
export USER_PRIVATE_KEY= # Corresponding Private Key

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Create a Subscription

In this step, a subscription is created on the ADAPTER_CONTRACT using the createSubscription method. Save this subscription ID as it will be used later on. The cast send command broadcasts a transaction to the Ethereum network.

(Reference: cast send)

cast block-number --rpc-url $RPC_URL # This will be useful for step 3
cast send $ADAPTER_CONTRACT "createSubscription()(uint64)" --private-key $USER_PRIVATE_KEY --rpc-url $RPC_URL  # returns subid

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Gather Subscription Details

The subscription id can be retrieved from the contract event logs for subsequent steps.

You can provide the block number from Step 2 to speed up the event search.

(Reference: cast logs)

cast logs --from-block 174270 --to-block latest 'SubscriptionCreated(uint64 indexed subId, address indexed owner)' "" $USER_PUBLIC_KEY --address $ADAPTER_CONTRACT --rpc-url $RPC_URL

#   topics: [ . # Sample response topics
#       0x464722b4166576d3dcbba877b999bc35cf911f4eaf434b7eba68fa113951d0bf # event sig
#       0x0000000000000000000000000000000000000000000000000000000000000001 # subId
#       0x00000000000000000000000070997970c51812dc3a010c7d01b50e0d17dc79c8 # user public key
#   ]
export SUB_ID= # export subid for your newly created subscription

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Fund the Subscription

Next, fund your subscription with Ethereum. These funds will be used to pay for your subsequent randomness requests.

Note: Recommended eth amounts:

• OP Goerli / Mainnet: 0.01 ETH

• Sepolia: 0.1 ETH

If needed, you can use the Randcast CLI dryrun to estimate how much ETH each randomness request will cost.

cast send $ADAPTER_CONTRACT "fundSubscription(uint64)" $SUB_ID --value 1ether --private-key $USER_PRIVATE_KEY --rpc-url $RPC_URL

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Deploy the Consumer Contract

The user needs to deploy a contract that will consume the randomness provided by Randcast. "forge create" is used to compile and deploy the contract.

(Reference: forge create)

git clone https://github.com/ARPA-Network/Randcast-User-Contract
cd Randcast-User-Contract
forge create --rpc-url $RPC_URL --private-key $USER_PRIVATE_KEY contracts/user/examples/GetRandomNumberExample.sol:GetRandomNumberExample --constructor-args $ADAPTER_CONTRACT

export USER_CONTRACT= # export address for your newly deployed user contract

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Add Consumer to Adapter

In this step, the created consumer contract is added to the adapter contract and linked to your existing subscription via the adapter's addConsumer method.

cast send $ADAPTER_CONTRACT "addConsumer(uint64, address)" $SUB_ID $USER_CONTRACT --private-key $USER_PRIVATE_KEY --rpc-url $RPC_URL

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Request Randomness

We can now request randomness via the user contract with the method getRandomNumber.

cast send $USER_CONTRACT "getRandomNumber()" --private-key $USER_PRIVATE_KEY --rpc-url $RPC_URL

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Check the Last Randomness

Finally, retrieve the last random number generated with the getLastRandomness method.

cast call $ADAPTER_CONTRACT "getLastRandomness()(uint256)" --rpc-url $RPC_URL

After completing the entire process, you should have a user contract capable of requesting randomness from the Randcast adapter contract.