curve-price-fetcher

curve-price-fetcher is a node package for interacting with curve smart contracts and finding the best price for swaps (not taking into account fees). you will need to provide a web3 instance for it to work.

Usage:

Firstly install the dependency to your project

npm i curve-price-fetcher --save

Import the dependency where you need it:

const CurvePriceFetcher = require('curve-price-fetcher');

Instantiate the fetcher and pass in a web3 instance:

const web3 = new Web3(new Web3.providers.HttpProvider(`https://localhost:8545`));

const fetcher = new CurvePriceFetcher();

above we are using the hardcoded set of pools and meta data.

alternatively, you can pass in a custom list of pool meta data.

const web3 = new Web3(new Web3.providers.HttpProvider(`https://localhost:8545`));

const customPoolData = [
    {
        "poolAddress": "0xa2b47e3d5c44877cca798226b7b8118f9bfb7a56",
        "coins": [
            "0x5d3a536e4d6dbd6114cc1ead35777bab948e3643",
            "0x39aa39c021dfbae8fac545936693ac917d5e7563"
        ],
        "underlying": [
            "0x6b175474e89094c44da98b954eedeac495271d0f",
            "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48"
        ]
    },
    {
        "poolAddress": "0x52ea46506b9cc5ef470c5bf89f17dc28bb35d85c",
        "coins": [
            "0x5d3a536e4d6dbd6114cc1ead35777bab948e3643",
            "0x39aa39c021dfbae8fac545936693ac917d5e7563",
            "0xdac17f958d2ee523a2206206994597c13d831ec7"
        ],
        "underlying": [
            "0x6b175474e89094c44da98b954eedeac495271d0f",
            "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48",
            "0xdac17f958d2ee523a2206206994597c13d831ec7"
        ]
    }
];

const fetcher = new CurvePriceFetcher({ web3, customPoolData });

finally, you can also pass in an array of addresses. you can then fetch pool metadata after creation and it will be used for subsequent pricing data.

const customPoolData = [
   {
       "poolAddress": "0xa2b47e3d5c44877cca798226b7b8118f9bfb7a56"
   },
   {
       "poolAddress": "0x52ea46506b9cc5ef470c5bf89f17dc28bb35d85c"
   }
];

const fetcher = new CurvePriceFetcher({ web3, customPoolData });

await fetcher.getAllPoolMetaData();

Fetching Prices:

Once you have your fetcher instantiated, you can fetch prices like so:

let prices = await fetcher.getPoolPrices(swapFrom, swapTo, '1000000000000000000000');

prices.forEach(
    pool => console.log(`Pool ${pool.poolAddress}: ${pool.price.toNumber()}`)
)

Prices are returned as a BigNumber object

Improvements

initially this was a quick and dirty script for a project i'm working on but then i packaged in a module. functionality is limited to fetching prices but some things that could be added (feel free to PR):

• take gas into account. the gas fees vary based on the underlying assets (quite vastly) due to different implementations, so the best price is not necessarily the best price.
• add support for performing swap
• route through multiple pools. for very large orders it will be more cost efficient to use multiple.
• fetch pool addresses from curve registry instead of json file. see here for details - https://www.curve.fi/contracts

Examples

There's example code in the examples folder. To use this you can rename the .env.example file to .env and change your infura project id in the file. If using a local node, replace the provider in the example with the RPC url of your local node before running.