Swap Development: Implementing BlockchainDecentralized TradingTechnical implementation details of the

As a blockchain developer, we often need to come into contact with Swap, an important transaction method on the blockchain that enables fast exchange of assets. In this article, we will introduce the source code aspects of Swap and quote some relevant experts.

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Swap Architecture Solutions

Swap's architectural scheme generally consists of the following components.

1. Front-end interaction layer

The front-end interaction layer generally usesWeb3.jsIt interacts with the back-end through Web3.js, showing the user information about Swap and providing operations such as selection of trading pairs, pending orders, and withdrawal of orders.

2. Back-end trading layer

The back-end transaction layer generally usesSoliditySmart contracts, through Solidity smart contracts to implement Swap's core functions, such as order aggregation, asset transfer, etc.

3. On-chain transaction layer

The on-chain transaction layer generally refers to blockchain nodes, including Ethernet nodes, etc. In the transaction process, it is necessary to send a transaction request to the blockchain node and wait for the response from the blockchain node.

4. Database layer

The database layer generally uses a NoSQL database, for exampleMongoDBetc. In Swap, the user's transaction history, asset balance and other information need to be recorded for easy access.

Swap's source code analysis

The source code of Swap mainly includes the front-end interaction layer, the back-end transaction layer and the on-chain transaction layer. The source code of each of these parts will be introduced below.

1. Front-end interaction layer

The front-end interaction layer generally uses Web3.js, which can be used to implement Swap-related functions through the following code.

// Connect to the ethernet node
let web3 = new Web3(new Web3.providers.HttpProvider('https://mainnet.infura.io/v3/'));

//get the user wallet address
let accounts = await web3.eth.getAccounts();
let account = accounts[0];

//Get the transaction pair information
let pairContract = new web3.eth.Contract(pairABI, pairAddress);
let token0 = await pairContract.methods.token0().call();
let token1 = await pairContract.methods.token1().call();

// pending order
let amountIn = web3.utils.toWei('1', 'ether');
let amountOut = 0;
let deadline = Math.floor(Date.now() / 1000) + 60 * 10; //10 minutes
let path = [token0, token1];
let swapContract = new web3.eth.Contract(swapABI, swapAddress);
await swapContract.methods.swapExactTokensForTokens(amountIn, amountOut, path, account, deadline).send({from: account});

//Query the balance
let tokenContract = new web3.eth.Contract(tokenABI, tokenAddress);
let balance = await tokenContract.methods.balanceOf(account).call();

In the above code, we first connect to the ethereum node and get the user wallet address. Then, we can get the transaction pair information through the contract ABI and contract address, and make pending orders. Finally, we can query the user's asset balance through the contract ABI and contract address.

2. Back-end trading layer

The back-end transaction layer generally uses Solidity smart contracts, which can be used to implement the core functionality of Swap through the following code.

pragma solidity ^0.8.0;

interface IUniswapV2Router {
    function swapExactTokensForTokens(uint amountIn, uint amountOutMin, address[] calldata path, address to, uint deadline) external returns (uint[] memory amounts);
}

contract MySwap {
    address constant uniswapV2RouterAddress = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;

    function swapTokens(address tokenIn, address tokenOut, uint amountIn) external {
        address[] memory path = new address[](2);
        path[0] = tokenIn;
        path[1] = tokenOut;
        uint deadline = block.timestamp + 60 * 10; //10 minutes
        uint[] memory amounts = IUniswapV2Router(uniswapV2RouterAddress).swapExactTokensForTokens(amountIn, 0, path, msg.sender, deadline);
    }
}

In the above code, we define a MySwap contract and introduce the IUniswapV2Router interface. Then, we can implement the core functionality of Swap by calling the swapExactTokensForTokens function. Where amountIn indicates the number of assets to be swapped, path indicates the transaction pair, and deadline indicates the deadline of the transaction. Finally, we can send the swapped assets to the caller.

3. On-chain transaction layer

The on-chain transaction layer generally refers to blockchain nodes, including Ethernet nodes, etc. In the transaction process, you need to send a transaction request to the blockchain node and wait for the response from the blockchain node. We can implement the sending of transaction requests by the following code.

let tx = await web3.eth.sendTransaction({
    from: account,
    to: contractAddress,
    gas: gasLimit,
    data: encodedData
});

// Connect to the MongoDB database
const MongoClient = require('mongodb').MongoClient;
const uri = "mongodb+srv://:@.mongodb.net/?retryWrites=true&w=majority";
const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true });
await client.connect();
const db = client.db("mydb");

//query user transaction history
let collection = db.collection('transactions');
let transactions = await collection.find({user: account}).toArray();

//Update the user's asset balance
collection = db.collection('balances');
await collection.updateOne({user: account, token: tokenAddress}, {$inc: {balance: amount}});

let accounts = await web3.eth.getAccounts();

let contract = new web3.eth.Contract(abi, contractAddress);
let balance = await contract.methods.balanceOf(accounts[0]).call();

let result = await contract.methods.transfer(toAddress, amount).send({from: accounts[0]});