CryptoZombies, lesson 5

Overview

This is from the tutorial at https://share.cryptozombies.io/en/lesson/5/share/AlexT?id=Z2l0aHVifDE2MjQ1MjI=

ERC721 Token has been implemented in this lesson.

In addition, unit tests and testnet-based tests have been added.

Build

To build and test, dapp is required, similar to this repository https://github.com/alext234/dapp-tutorial.

• Install dapp.tools:

curl https://nixos.org/nix/install > nix-install.sh
nix-env -iA dapphub.master.{dapp,seth,hevm,solc}

• Build

make all

Tests

Unit test

make test

Testnet tests

On another terminal launch testnet with 2 accounts

dapp testnet --accounts=2

Now run the test script

./testnet_script.sh

Deploy

A contract has been deployed on the Kovan testnet at https://kovan.etherscan.io/address/0xc4e157d452fbaa20767cfd051099a4ccb7a9a911

Below are the steps used:

Create wallet on Kovan network

• Go to https://www.myetherwallet.com/ and follow the steps to generate a wallet (make sure to select Network Kovan (infura.io)).

• Download the wallet key as a keystore file into a directory such as ~/keystore-directory.

• Have some Kovan ETH sent to the wallet address (one way is to request through https://gitter.im/kovan-testnet/faucet). This is used to pay for the transaction cost.

Deploy with dapp

Set environment variables to be used by dapp:

export ETH_KEYSTORE=~/keystore-directory/
export ETH_FROM=<wallet-address>
export ETH_RPC_URL=https://kovan.infura.io
export ETH_GAS=4500000

Run dapp deploy command

dapp create ZombieOwnership

+ seth send --create out/ZombieOwnership.bin 'ZombieOwnership()'
Ethereum account passphrase (not echoed): seth-send: Published transaction with 8692 bytes of calldata.
seth-send: 0x56f0eeed31b83cb65db19b8e88d11ba53f2ff1349b22cfc6072be783224a7f7c
seth-send: Waiting for transaction receipt.....
seth-send: Transaction included in block 6172760.
0xc4e157d452fbaa20767cfd051099a4ccb7a9a911

The deployed contract can be viewed on etherscan at https://kovan.etherscan.io/address/

Have the source code verified

Etherscan does not allow uploading multiple source files. Therefore the first step is to have a flattened version of the contract, which means the contract itself and all dependencies in one single file.

• solidity_flattener can be used to flatten the contract

Python3 is required.

(activate python3 virtualenv)
pip install solidity_flattener
solidity_flattener  src/ZombieOwnership.sol --output flattened.sol

• Upload the file flattened.sol to etherscan.io and it should be verified successfully.

Interact with the deployed contract

Following are some examples of interaction with the contract 0xc4e157d452fbaa20767cfd051099a4ccb7a9a911 deployed on Kovan testnet.

With seth

Having 2 accounts will be helpful try out the transfer of zombies based on the ERC721 interface.

Some environment variables have to be set:

export SETH_CHAIN=kovan
export ETH_GAS=450000
export ETH_KEYSTORE=~/keystore-directory/

export CONTRACT=0xc4e157D452FBaA20767cFD051099a4ccb7a9A911

Use seth from account1 to create a zombie:

export ETH_FROM=<account1-address>
seth send $CONTRACT 'createRandomZombie(string)' 'a1'

Use seth from account2 to create a zombie:

export ETH_FROM=<account2-address>
seth send $CONTRACT 'createRandomZombie(string)' 'a2'

Verify the owners of the 2 zombies:

seth call $CONTRACT 'ownerOf(uint256)' 0
seth call $CONTRACT 'ownerOf(uint256)' 1

From account2, call approve() to transfer the ownership of its zombie to account1:

export ETH_FROM=<account2-address>
seth send $CONTRACT 'approve(address,uint256)' <account1-address> 1

From account1, call takeOwnership() of the zombie:

export ETH_FROM=<account1-address>
seth send $CONTRACT 'takeOwnership(uint256)'  1

Verify the number of zombies each account now has:

seth call $CONTRACT 'balanceOf(address)' <account1-address>
seth call $CONTRACT 'balanceOf(address)' <account2-address>

Sign and publish separately

With the seth send command used in the previous section, we perform both signing the transaction and publishing to the blockchain. In some cases, we would like to do them separately, for security purpose. Signing can be performed on a offline machine and then publishing can be done on another machine connected to the network.

To create a signed transaction data, seth mktx can be used, with similar syntax to seth send.

seth mktx $CONTRACT 'createRandomZombie(string)' 'a1'

It will output a signed transaction data to the console which can be published with seth publish.

Read-only on etherscan

All contract reads can be done interactively on the browser via etherscan site: https://kovan.etherscan.io/address/0xc4e157d452fbaa20767cfd051099a4ccb7a9a911#readContract

View contract event logs

We need to set the SETH_ABI environment variable:

export SETH_ABI=$(seth --decorate-abi $(cat out/ZombieOwnership.abi))

View the event logs with seth:

seth events $CONTRACT