Interact with deployed smart contracts
You can get started with the Developer Quickstart to rapidly generate local blockchain networks.
This tutorial shows you how to interact with smart contracts that have been deployed to a network.
Prerequisites
- A network with a deployed smart contract as in the deploying smart contracts tutorial
Interact with public contracts
This tutorial uses the SimpleStorage.sol
contract:
pragma solidity ^0.7.0;
contract SimpleStorage {
uint public storedData;
constructor(uint initVal) public {
storedData = initVal;
}
function set(uint x) public {
storedData = x;
}
function get() view public returns (uint retVal) {
return storedData;
}
}
Once the contract is deployed, you can perform a read operation using the get
function call and a write operation using the set
function call. This tutorial uses the web3js library to interact with the contract. A full example of these calls can be found in the Developer Quickstart.
1. Perform a read operation
To perform a read operation, you need the address that the contract was deployed to and the contract's ABI. The contract's ABI can be obtained from compiling the contract; see the deploying smart contracts tutorial for an example.
Use the web3.eth.Contract
object to create a new instance of the smart contract, then make the get
function call from the contract's list of methods, which will return the value stored:
async function getValueAtAddress(
host,
deployedContractAbi,
deployedContractAddress,
) {
const web3 = new Web3(host);
const contractInstance = new web3.eth.Contract(
deployedContractAbi,
deployedContractAddress,
);
const res = await contractInstance.methods.get().call();
console.log("Obtained value at deployed contract is: " + res);
return res;
}
2. Perform a write operation
To perform a write operation, send a transaction to update the stored value. As with the get
call, you need to use the address that the contract was deployed to and the contract's ABI. The account address must correspond to an actual account with some ETH in it to perform the transaction. Because Besu doesn't manage accounts, this address is the address you use in EthSigner (or equivalent) to manage your accounts.
Make the set
call passing in your account address, value
as the updated value of the contract, and the amount of gas you are willing to spend for the transaction:
// You need to use the accountAddress details provided to Besu to send/interact with contracts
async function setValueAtAddress(
host,
accountAddress,
value,
deployedContractAbi,
deployedContractAddress,
) {
const web3 = new Web3(host);
const contractInstance = new web3.eth.Contract(
deployedContractAbi,
deployedContractAddress,
);
const res = await contractInstance.methods
.set(value)
.send({ from: accountAddress, gasPrice: "0xFF", gasLimit: "0x24A22" });
return res;
}
3. Verify an updated value
To verify that a value has been updated, perform a get
call after a set
update call.
Interact with private contracts
This private contracts example uses the same SimpleStorage.sol
contract as in the public contracts example, but it uses the web3js-quorum library and the generateAndSendRawTransaction
method to interact with the contract. Both read and write operations are performed using the generateAndSendRawTransaction
API call. A full example can be found in the Developer Quickstart.
1. Perform a read operation
As in the public contracts example, to perform a read operation, you need the address that the contract was deployed to and the contract's ABI. You also need your private and public keys and the recipient's public key.
Use the web3.eth.Contract
object to create a new instance of the smart contract, extract the signature of function's ABI for the get
method, and then use this value as the data
parameter for the generateAndSendRawTransaction
transaction.
The keys remain the same for the sender and recipient, and the to
field is the contract's address. Once you make the request, you receive a transactionHash
, which you can use to get a transactionReceipt
containing the value stored:
async function getValueAtAddress(
clientUrl,
address,
contractAbi,
fromPrivateKey,
fromPublicKey,
toPublicKey,
) {
const Web3 = require("web3");
const Web3Quorum = require("web3js-quorum");
const web3 = new Web3Quorum(new Web3("http://localhost:22000"));
// eslint-disable-next-line no-underscore-dangle
const functionAbi = contract._jsonInterface.find((e) => {
return e.name === "get";
});
const functionParams = {
to: address,
data: functionAbi.signature,
privateKey: fromPrivateKey,
privateFrom: fromPublicKey,
privateFor: [toPublicKey],
};
const transactionHash = await web3quorum.priv.generateAndSendRawTransaction(
functionParams,
);
// console.log(`Transaction hash: ${transactionHash}`);
const result = await web3quorum.priv.waitForTransactionReceipt(
transactionHash,
);
console.log(
"" + nodeName + " value from deployed contract is: " + result.output,
);
return result;
}
2. Perform a write operation
Performing a write operation is almost the same process as the read operation, except that you encode the new value to the set
function's ABI, and then append these arguments to the set
function's ABI and use this as the data
field:
async function setValueAtAddress(
clientUrl,
address,
value,
contractAbi,
fromPrivateKey,
fromPublicKey,
toPublicKey,
) {
const Web3 = require("web3");
const Web3Quorum = require("web3js-quorum");
const web3 = new Web3Quorum(new Web3("http://localhost:22000"));
// eslint-disable-next-line no-underscore-dangle
const functionAbi = contract._jsonInterface.find((e) => {
return e.name === "set";
});
const functionArgs = web3quorum.eth.abi
.encodeParameters(functionAbi.inputs, [value])
.slice(2);
const functionParams = {
to: address,
data: functionAbi.signature + functionArgs,
privateKey: fromPrivateKey,
privateFrom: fromPublicKey,
privateFor: [toPublicKey],
};
const transactionHash = await web3quorum.priv.generateAndSendRawTransaction(
functionParams,
);
console.log(`Transaction hash: ${transactionHash}`);
const result = await web3quorum.priv.waitForTransactionReceipt(
transactionHash,
);
return result;
}
3. Verify an updated value
To verify that a value has been updated, perform a get
call after a set
update call.