Client / Frontend integration

In this chapter we cover how a client (Web-frontend or backend) can create and sign an order.

Structure of an order

Example signed order.

{  
  "hash": "0x30ba20598b4e977f26465c25f7ba7bd6f4724924ae28cd3b81f67627ce323786",  
  "sig": "0x3f89a18f83ca12b65c94394f50ff9c7107bee18d4d22c1f067a4558c6b51f0213b38e2791042fab700c75560295bf40236f66a4efb2e2428933613867977c6d71c",  
  "order": {  
    "maker": "0x92e56418297664a34a91f0e3a6a81aa092f268f1",  
    "nftAddress": "0xec455e43adf3b073d9fef311205305ccf8e7574a",  
    "nftTokenId": "8680783491275350067",  
    "orderType": 0,  
    "maxNbrOfNftsToTrade": "1",  
    "erc20PaymentToken": "0x0000000000000000000000000000000000000000",  
    "pricePerNft": "1000000000000000",  
    "ttl": 1667329052257,  
    "nonce": 4914140582696146000  
  }  
}

Property	Description
maker	The one who created and signed the order
nftAddress	The NFT smart contract address (ERC721, ERC1155)
nftTokenId	The NFT tokenId
orderType	0: SELL_ERC721, 1: SELL_ERC1155, 2: BID_FOR_ERC721, 3: BID_FOR_ERC1155
maxNbrOfNftsToTrade	In case of ERC721: Must be 1. In case of ERC1155: Must be 1..n.
erc20PaymentToken	The ERC20 token required to fill this order. If address is 0x0 then it's an Ether payment
pricePerNft	Price for a single NFT. For ERC721 it's the price. For ERC1155 multiply with amount the buyer wants to trade.
ttl	Unixtimestamp in seconds. How long the order is valid
nonce	Unique nonce. Clients must always create a new unique nonce. This is a security feature

Create the hash

The hash is a keccak256 over all the properties of the order. To create this hash the most simple way is to call the DEX smart contract createMakerHash function.

function createMakerHash(
    address payable maker,
    address nftAddress,
    uint256 nftTokenId,
    OrderType orderType,
    uint256 maxNbrOfNftsToTrade,
    address erc20PaymentToken,
    uint256 pricePerNft,
    uint256 ttl,
    uint256 nonce
) external pure returns (bytes32)

This function returns a bytes32 which represents the hash.

In JavaScript this could look like this:

// Returns Promise
createMakerHash(order) {
    console.dir("Create Maker Hash:", order);
    var dex3 = this.getDex3Instance();
    return dex3.methods.createMakerHash(
        order.maker,
        order.nftAddress,
        order.nftTokenId,
        order.orderType,
        order.maxNbrOfNftsToTrade,
        order.erc20PaymentToken,
        order.pricePerNft,
        order.ttl,
        order.nonce
    ).call();
}

Create the signature

Using JavaScript with Web3js

web3.eth.personal.sign(hash, usersAddress);

It's important to use the web3.personal.sign function. See web3js doc

Using Java with Web3j

public static String sign(Credentials credentials, String hash) {  
    byte[] hashBytes = HexUtil.fromHexString(hash);  
    Sign.SignatureData sd = Sign.signPrefixedMessage(hashBytes, credentials.getEcKeyPair());  
    return SignatureDataToHexString(sd);  
}  

public static String SignatureDataToHexString(Sign.SignatureData sd) {  
    byte[] subrRev = Arrays.copyOfRange(sd.getR(), 0, 32);  
    byte[] subsRev = Arrays.copyOfRange(sd.getS(), 0, 32);  
    byte[] result = new byte[65];  
    for (int i = 0; i < 32; i++) {  
        result[i] = subrRev[i];  
    }  

    for (int i = 0; i < 32; i++) {  
        result[i + 32] = subsRev[i];  
    }  

    result[64] = sd.getV()[0];  

    return HexUtil.toHexString0xPrefix(result);  
}