Hosting a Testnet and Deploying a Contract

Using Foundry to start a local testnet and deploy a Solidity contract.

Foundry

We use Foundry for this.

Developing a Contract

$ forge init

in the desired folder.

Starting a Testnet

anvil

This will give you an RPC URL, plus 10 accounts and their private keys.

Deploying a Contract

forge create --rpc-url 127.0.0.1:8545 src/Counter.sol:Counter --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 --broadcast

• The RPC URL should be the one provided by anvil

• src/Counter.sol is the file path to the smart contract's Solidity source code

• Counter is the name of the smart contract

• --private-key is one of the private keys displayed by anvil

• --broadcast broadcasts the deployment of the transaction

Deployer: 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266
Deployed to: 0x5FbDB2315678afecb367f032d93F642f64180aa3
Transaction hash: 0x9c43e48790455815acecf9e5ae2a835daac756fe3f8164eb1a294bf7a768e00e

Without the --broadcast, foundry will do a "dry run" - simulate the contract's execution without actually deploying it. Broadcasting it will return an address!

Interacting with the Contract

We can increment the counter as follows:

$ cast send 0x5FbDB2315678afecb367f032d93F642f64180aa3 "increment()" --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 --rpc-url 127.0.0.1:8545

blockHash            0x85443db3aa3b5761016586e3cb720b28fda0819f179a9ed4f7b45b12fe849695
blockNumber          2
contractAddress      
cumulativeGasUsed    43517
effectiveGasPrice    876013326
from                 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266
gasUsed              43517
logs                 []
logsBloom            0x00[...]
root                 
status               1 (success)
transactionHash      0x35d8a6b48a3cef67a9301b6c4d818b294e6ad1eac7e219870d9afd49e3984265
transactionIndex     0
type                 2
blobGasPrice         1
blobGasUsed          
authorizationList    
to                   0x5FbDB2315678afecb367f032d93F642f64180aa3

cast send is used for transactions that write to the blockchain, and therefore require signing.

getCounter() is a view function, so does not require a transaction to call. We use cast call instead, which does not requires a private key:

$ cast call 0x5FbDB2315678afecb367f032d93F642f64180aa3 "getCounter()" --rpc-url 127.0.0.1:8545
0x0000000000000000000000000000000000000000000000000000000000000001

And we see it returns the value 1! If we cast send another increment call and then cast call to read the counter again, we see it's incremented again:

$ cast call 0x5FbDB2315678afecb367f032d93F642f64180aa3 "getCounter()" --rpc-url 127.0.0.1:8545 
0x0000000000000000000000000000000000000000000000000000000000000002