CyberGirlsCafe - ERC721 Contract

This contract is based on the OpenZeppelin template. We have optimized it to use gas more efficiently. The efficiency reaches 45-75% compared to the basic implementation. We partially retain support for the Enumerable interface, so that third-party applications, such as marketplaces, could easily interact with the contract.

Below is a table of how gas is used for token minting. Let's imagine that the price of gas is 60 Gwei and the price of Ethereum is 4000 USD.

Number of tokens	Gas used	Transaction fee in USD
1	75123	18.02952
2	99935	23.9844
5	174371	41.84904
10	298432	71.62368
20	546554	131.17296

Note: The MainNet consumes slightly more gas (~6%) than the test environment.

Smart contract address in MainNet - 0xf8c0acb14328aa09398f1cfd949fa2bdfeaa1cd7

ProxyRegistry

Our contract interacts with OpenSea's ProxyRegistry. This allows users to avoid paying gas for SetApprovalForAll when trading. This is a safe feature that is recommended to be installed in smart contracts in the official OpenSea technical documentation. Read more here - OpenSea Whitelisting.

In our contract, this is implemented in the file CyberGirlsCafe.sol (line 133).

In the template from OpenSea this is implemented here - ERC721Tradable.sol

Provenance Hash

We use Provenance Hash technology (more details here - Provenance Hash solution), to prove to the community that each Cyber Girl is created in a certain order before the smart contract is published. This order and images cannot be changed afterwards.

Each image is hashed using the SHA-256 algorithm. Then all the hashes are combined in the proper order into a single hash string CONCATENATED HASH STRING. This string is hashed using the SHA-256 algorithm and results in a FINAL PROOF HASH.

CONCATENATED HASH STRING = sha256('Token 1 Hash' + 'Token 2 Hash' + ... + 'Token 10010 Hash')
FINAL PROOF HASH = sha256(CONCATENATED HASH STRING)

Our contract stores the FINAL PROOF HASH in the file CyberGirlsCafe.sol on line 22.

string public constant PROVENANCE = "8fef626f47a65408f131274eefff04588dbd9a2eee69460efe986e72ae3c119c";

You can see the full list of hashes here - CyberGirlsCafe Provenance.

Whitelist

We have implemented the whitelist in the contract, which allows users from that list to mint a token for 0.045 ETH (the discount is 0.025 ETH). One user from the whitelist can mint a maximum of 4 tokens.

Development

The project is made using Truffle, so you need Node.js and this package to work with it.

Install

npm install -g truffle

Run tests

We have completely tested the contract using OpenZeppelin tests as a basis. Running the tests takes a long time.

cd path/to/CyberGirlsCafe
truffle test

Deploy

To deploy the contract you need:

1. Install the truffle-hdwallet-provider package.
2. Specify the mnemonic and providerUrl arguments in truffle-config.js.
3. Specify the contract constructor arguments in migrations/1_initial_migration.js.

npm install truffle-hdwallet-provider
truffle compile
truffle migrate --network rinkeby