Deploy a Contract in Qtum

Deploy a simple Smart Contract in Qtum’s Regtest mode. To deploy a contract, you will need the contract's bytecode and ABI, generated using solc. Finally, you’ll invoke its methods in JavaScript using qweb3.js.

Requirements

Solidity v0.6.4 (solc)
Qtum v0.19.0.1
QWeb3 v1.2.2
NodeJS v13.5.0
NPM v6.13.4

Generate Bytecode and ABI

Create a folder on your preferred location. From this point onwards, we will refer to this as your workspace.
Implement a simple storage contract.

Install solc if you don’t have it, yet. Don’t forget to run the command as an administrator.

$ npm install -g solc@0.6.4

Compile the contract. This will generate the bytecode and ABI files on your workspace.

$ solcjs SimpleStorage.sol --bin --abi

You will need the bytecode later to deploy the contract and the ABI to interact with it.

Run Qtum regtest

Download Qtum 0.19.0.1 from their GitHub repository. It’s more convenient to download the zip file for your platform.
Extract the archive on your workspace and open up a new terminal on that location.

For MacOS users, run the following command to extract the archive:

$ tar xvzf qtum-0.19.0.1-osx64.tar.gz

Go to the bin folder and run the qtum daemon on regtest mode with username, password and port. If you want, you can set your data directory to point at your desired location.

NOTE: Remember not to close this terminal for the rest of the activity.

$ ./qtumd --regtest --datadir=. --rpcuser=username --rpcpassword=password --rpcport=13889

The Qtum regtest mode provides the option to generate blocks in order to speed up the process using PoW during testing. To generate an account, launch a new terminal on the same location and interact with the daemon using qtum-cli with the following command:

$ ./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 getnewaddress

Get test QTUMs. The command is: generatetoaddress 600 your_generated_address
This will mine 600 blocks and the block reward will go to the specified address.

NOTE: This command may take some time as qtum-core mines new blocks. If you examine the qtumd.exe terminal, you’ll see the mining process happening.

$ ./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 generatetoaddress 600 qN1ipWSFoEhKbigPUcirHxpTbehkpWiiM6

To check the wallet's address and current balance, type getwalletinfo.

./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 getwalletinfo

Deploy Contract

To deploy the contract, call createcontract with the bytecode found in your workspace folder named: SimpleStorage_sol_SimpleStorage.bin

$ ./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 createcontract 6080604052348015610011576000600...

The result of this command is a JSON, storing the transaction hash, sender address, hash160 and the address of the contract.

At this point, save the following as we will use them later:

tx_id - The transaction ID
sender - The contract creator
address - The contract address

Mine one block:

$ ./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 generatetoaddress 1 qN1ipWSFoEhKbigPUcirHxpTbehkpWiiM6

Check whether the transaction is confirmed using gettransaction:

$ ./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 gettransaction INSERT_TRANSACTION_ID

Check what is behind the address of the contract using getaccountinfo:

$ ./qtum-cli --regtest --rpcuser=username --rpcpassword=password --rpcport=13889 getaccountinfo INSERT_CONTRACT_ADDRESS

Interact with the Contract

On your workspace, initialize a new NPM project. Then, install qweb3.js:

$ npm init –y
$ npm install qweb3@1.2.2

Create a file named client.js and start implementing the client. First, import the necessary dependencies.
Create the contract instance using the contract address, abi and rpc. Copy the ABI generated from solc.
Set the variables in the transaction object and send it.
Run the client. Open a terminal on the workspace and run:

$ node client.js

This returns a transaction receipt of the transaction.

Get the value of the contract. Let’s reuse client.js but comment out the set implementation.
Run client.js.

$ node client.js

The result is successfully retrieved. If the result is still not reflected, you have to mine a new block which can be accomplished by the generatetoaddress qtum-cli command earlier.

Module

MI4: Module 6: E1