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how-to-write-a-fetch-adapter.md

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How to write a fetch adapter

Fetch adapters export a function, called fetch, which returns a project's total TVL (in USD) as a number. The following basic adapter would just always return a TVL of 100$:

async function fetch() {
  return 100;
}

module.exports = {
  fetch
}

Fetch adapters only allow us to get the TVL at the current time, so it's impossible to fill old values on a protocol's TVL chart or recompute them, thus leading to charts that look jumpy. To solve this we introduced SDK adapters, which allow us to retrieve a protocol's TVL at any point in time.

{% hint style="info" %} Fetch adapters can only be used for projects on non-EVM chains. Where possible, SDK adapters are preferred to fetch adapters because on-chain calls are more transparent. {% endhint %}

Third party APIs should be used where possible to reduce bias. If third party APIs are not available for the data you need, proprietary APIs can be used if they're open source.

Examples

{% code title="projects/balancer.js" %}

const retry = require('async-retry')
const { GraphQLClient, gql } = require('graphql-request')

async function fetch() {
  var endpoint ='https://api.thegraph.com/subgraphs/name/balancer-labs/balancer';
  var graphQLClient = new GraphQLClient(endpoint)

  var query = gql`
  {
    balancers(first: 5) {
      totalLiquidity,
      totalSwapVolume
    }
  }
  `;
  const results = await retry(async bail => await graphQLClient.request(query))
  return parseFloat(results.balancers[0].totalLiquidity);
}

module.exports = {
  fetch
}

{% endcode %}

{% code title="projects/ren.js" %}

const retry = require('async-retry')
const axios = require("axios");
const BigNumber = require("bignumber.js");

async function fetch() {
  let price_feed = await retry(async bail => await axios.get('https://api.coingecko.com/api/v3/simple/price?ids=bitcoin&vs_currencies=usd&include_market_cap=true&include_24hr_vol=true&include_24hr_change=true'))
  let response = await retry(async bail => await axios.get('https://api.etherscan.io/api?module=stats&action=tokensupply&contractaddress=0xeb4c2781e4eba804ce9a9803c67d0893436bb27d&apikey=H6NGIGG7N74TUH8K2X31J1KB65HFBH2E82'))
  let tvl = new BigNumber(response.data.result).div(10 ** 8).toFixed(2);
  return (tvl * price_feed.data.bitcoin.usd);
}

module.exports = {
  fetch
}

{% endcode %}

{% code title="projects/thorchain.js" %}

const retry = require('async-retry')
const axios = require("axios");
const BigNumber = require("bignumber.js");

async function fetch() {
  var price_feed = await retry(async bail => await axios.get('https://api.coingecko.com/api/v3/simple/price?ids=thorchain&vs_currencies=usd&include_market_cap=true&include_24hr_vol=true&include_24hr_change=true'))

  var res = await retry(async bail => await axios.get('https://chaosnet-midgard.bepswap.com/v1/network'))
  var tvl = await new BigNumber((parseFloat(res.data.totalStaked) * 2) + parseFloat(res.data.bondMetrics.totalActiveBond) + parseFloat(res.data.bondMetrics.totalStandbyBond)).div(10 ** 8).toFixed(2);
  tvl = tvl * price_feed.data.thorchain.usd;
  return tvl;
}

module.exports = {
  fetch
}

{% endcode %}