A general purpose price feed oracle built on Uniswap v2 that supports arbitrary time windows (up to 256 blocks) and doesn't require any active maintenance.

Unlike other Uniswap v2 based oracles, this one does not require regular maintenance by either an altruistic or incentivized party. Anyone with access to an Ethereum node can generate a proof of Uniswap's storage from up to 256 blocks ago and submit it for on-chain validation. You can then use that validated proof to calculate the average price between the current block and the supplied proof's block so you are protected from short-term price manipulation.

https://medium.com/@epheph/using-uniswap-v2-oracle-with-storage-proofs-3530e699e1d3

npm install @keydonix/uniswap-oracle-contracts @keydonix/uniswap-oracle-sdk

Optionally:

npm install @keydonix/uniswap-oracle-sdk-adapter

See a fully functional example in demo/contracts/PriceEmitter.sol and demo/source/demo.ts. Documentation here is a bit terse because the example is so small that it is probably easier to just read it!

pragma solidity 0.6.8;
pragma experimental ABIEncoderV2;

import { UniswapOracle } from  '@Keydonix/uniswap-oracle-contracts/source/UniswapOracle.sol';
import { IUniswapV2Pair } from "@Keydonix/uniswap-oracle-contracts/source/IUniswapV2Pair.sol";

contract PriceEmitter is UniswapOracle {
	event Price(uint256 price);

	function emitPrice(IUniswapV2Pair exchange, address denominationToken, uint8 minBlocksBack, uint8 maxBlocksBack, UniswapOracle.ProofData memory proofData) public returns (uint256 price, uint256 blockNumber) {
		(price, blockNumber) = getPrice(exchange, denominationToken, minBlocksBack, maxBlocksBack, proofData);
		emit Price(price);
	}
}

import * as OracleSdk from '@keydonix/uniswap-oracle-sdk'
import * as OracleSdkAdapter from '@keydonix/uniswap-oracle-sdk-adapter'

// create the getters the SDK needs from an Ethereum instance off the window.  you could use `window.web3.currentProvider` instead of `window.ethereum` if that is what is available
const getStorageAt = OracleSdkAdapter.getStorageAtFactory(window.ethereum)
const getProof = OracleSdkAdapter.getProofFactory(window.ethereum)
const getBlockByNumber = OracleSdkAdapter.getBlockByNumberFactory(window.ethereum)

// estimate the moving average price off-chain for presentation in your UI
const estimatedPrice = OracleSdk.getPrice(getStorageAt, getblockByNumber, uniswapExchangeAddress, denominationTokenAddress, blockNumber)

// get the proof from the SDK
const proof = await OracleSdk.getProof(getStorageAt, getProof, getBlockByNumber, uniswapExchangeAddress, denominationTokenAddress, blockNumber)

// inside this contract call we'll have trustless access to a Uniswap average price between `blockNumber` and `currentBlockNumber`
await priceEmitter.emitPrice(uniswapExchangeAddress, denominationTokenAddress, minBlocksBackAllowed, maxBlocksBackAllowed, proof)

NodeJS, NPM, Docker

VSCode (life is simpler with this, but not required)

If you are using VSCode, you can run npm install in each directory (one time operation) and then Tasks Run Task > all the things to bootstrap everything. From there you can Debug: Select and Start Debugging > run demo or Debug: Select and Start Debugging > run tests.

These are published to NPM as-is, demo project compiles and tests them.

cd sdk
npm install # one time

npm run build

cd sdk-adapter
npm install # one time

npm run build

Depends on Contracts and SDK

cd demo
npm install # one time

npm run build # compiles contracts

cd demo
docker-compose up --force-recreate --always-recreate-deps --abort-on-container-exit --remove-orphans --renew-anon-volumes
npm run demo

cd demo
docker-compose up --force-recreate --always-recreate-deps --abort-on-container-exit --remove-orphans --renew-anon-volumes
npm run test