This is a simple kit demonstrating how the Lit Network can be used to sign data pulled from the web (or another blockchain) and write it to chain. This may be a useful primitive for several different use cases, such as generating verifiable data proofs, using off-chain data to trigger blockchain transactions, or performing cross-chain message passing with chain signatures (using a state change on Chain A to trigger a state change on Chain B.)
The Lit Oracle Kit uses an PKP Wallet (Programmable Key Pair) to sign the data that is written to the chain using a Lit Action (JS code that runs on Lit Nodes). The PKP is irrevocably bound to the code that retrieves and writes the data to chain, so you know that if this PKP wrote the data, it was by running that Lit Action JS code.
When you call writeToChain, the kit does the following:
- Checks if there is already a PKP Wallet for the given IPFS CID. If not, it creates a new one and stores it in local storage.
- Sends the JS code to the Lit Nodes to be executed
- On the Lit Nodes, the JS code uses the PKP Wallet to sign the data and broadcast it to chain.
npm i lit-oracle-kitimport { LitOracleKit } from "lit-oracle-kit";
const sdk = new LitOracleKit(
"datil-dev",
process.env.LIT_ORACLE_KIT_PRIVATE_KEY!
);
await sdk.connect();
const result = await sdk.writeToChain({
dataSource: `
const url = "https://api.weather.gov/gridpoints/LWX/97,71/forecast";
const response = await fetch(url).then((res) => res.json());
const nearestForecast = response.properties.periods[0];
const temp = nearestForecast.temperature;
const probabilityOfPrecipitation = nearestForecast.probabilityOfPrecipitation.value || 0;
return [ temp, probabilityOfPrecipitation ];
`,
functionAbi:
"function updateWeather(int256 temperature, uint8 precipitationProbability) external",
toAddress: "0xE2c2A8A1f52f8B19A46C97A6468628db80d31673",
chain: "yellowstone",
});The examples/hardhat-weather-oracle directory contains a simple example of how to use this kit to fetch weather data from the NOAA API and write it to a chain using the Lit Oracle Kit.
The script update-weather.ts fetches the weather data and writes it to the chain by calling the updateWeather function on the deployed WeatherOracle contract.
You can test your data source retrieval code using the testDataSource() function. This will simply run your code on the Lit Nodes and return the result, so you can confirm that it's retrieving the correct values.
import { LitOracleKit } from "lit-oracle-kit";
const sdk = new LitOracleKit(
"datil-dev",
process.env.LIT_ORACLE_KIT_PRIVATE_KEY!
);
await sdk.connect();
const result = await sdk.testDataSource(`
const url = "https://api.weather.gov/gridpoints/LWX/97,71/forecast";
const response = await fetch(url).then((res) => res.json());
const nearestForecast = response.properties.periods[0];
const temp = nearestForecast.temperature;
const probabilityOfPrecipitation = nearestForecast.probabilityOfPrecipitation.value || 0;
return [ temp, probabilityOfPrecipitation ];
`);
// this will output your return value, so you can confirm it's correct
console.log(result.response);MIT
You can find support information, including Discord and Telegram support channels, here: https://developer.litprotocol.com/support/intro