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updated for v0.6 with fewer oracle details
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PatrickAlphaC
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@ -5,7 +5,7 @@ contributors:
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- ["Nemil Dalal", "https://www.nemil.com"]
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- ["Joseph Chow", ""]
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- ["Bhoomtawath Plinsut", "https://github.com/varshard"]
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- ["Shooter", "https://github.com/liushooter"]\
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- ["Shooter", "https://github.com/liushooter"]
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- ["Patrick Collins", "https://gist.github.com/PatrickAlphaC"]
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---
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@ -214,7 +214,8 @@ assert(c >= a); // assert tests for internal invariants; require is used for use
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// https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/math/SafeMath.sol
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// No random functions built in, see below for using Chainlink to get random numbers.
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// No random functions built in, you can get a pseduo-random number by hashing the current blockhash, or get a truely random number using something like Chainlink VRF.
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// https://docs.chain.link/docs/get-a-random-number
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// Type casting
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int x = int(b);
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@ -645,7 +646,6 @@ reveal(100, "mySecret");
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// All data to start of time is stored in blockchain, so
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// anyone can observe all previous data and changes
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// E. Oracles and External Data
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// Oracles are ways to interact with your smart contracts outside the blockchain.
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// They are used to get data from the real world, send post requests, to the real world
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@ -663,156 +663,12 @@ reveal(100, "mySecret");
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// multiple sources and delivered on-chain, and we can use it as a "data bank"
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// of sources.
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// We will need to be on a network that has the data already loaded.
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// Let's look at an example
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```
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# Oracles
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### Getting data from Chainlink Data Feeds
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// You can see other examples making API calls here:
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// https://docs.chain.link/docs/make-a-http-get-request
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We will be deploying to a testnet with Chainlink. This way we can get decentralized data into our smart contracts.
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// And you can of course build your own oracle network, just be sure to know
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// how centralized vs decentralized your application is.
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**Deploy the following contract with remix to the `Kovan` testnet. If unfamiliar, reference the start of this file.**
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[Work with this code in Remix](https://remix.ethereum.org/#version=soljson-v0.6.7+commit.b8d736ae.js&optimize=false&evmVersion=null&gist=0c5928a00094810d2ba01fd8d1083581&runs=200)
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We can get the price of any asset by using the `getLatestPrice` function. You can see a list of addresses for the Kovan network from the [Chainlink Documentation](https://docs.chain.link/docs/get-the-latest-price). You can also view any other address as well.
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```javascript
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/** This example code is designed to quickly deploy an example contract using Remix.
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* If you have never used Remix, try our example walkthrough: https://docs.chain.link/docs/example-walkthrough
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* You will need testnet ETH and LINK.
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* - Kovan ETH faucet: https://faucet.kovan.network/
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* - Kovan LINK faucet: https://kovan.chain.link/
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*/
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pragma solidity ^0.6.7;
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import "https://github.com/smartcontractkit/chainlink/blob/master/evm-contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";
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contract PriceConsumerV3 {
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AggregatorV3Interface internal priceFeed;
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/**
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* Network: Kovan
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* Aggregator: ETH/USD
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* Address: 0x9326BFA02ADD2366b30bacB125260Af641031331
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*/
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constructor() public {
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priceFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
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}
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/**
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* Returns the latest price
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*/
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function getLatestPrice() public view returns (int) {
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(
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uint80 roundID,
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int price,
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uint startedAt,
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uint timeStamp,
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uint80 answeredInRound
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) = priceFeed.latestRoundData();
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return price;
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}
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}
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```
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### Randomness / RNG
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Chainlink VRF (Verifiable Random Function) is a provably-fair and verifiable source of randomness designed for smart contracts. Randomness is difficult in blockchain, because blockchains are determanistic. We can get a random number by reaching outside the blockchain to an oracle.
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Chainlink VRF then cryptographically guarantees that the random number returned is random.
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**Deploy the following contract with remix to the `Kovan` testnet. If unfamiliar, reference the start of this file.**
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The only additional piece we need to do here is to fund our contract with LINK. [You can see a video on funding with LINK here.](https://www.youtube.com/watch?v=4ZgFijd02Jo)
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Once we deploy our Chainlink VRF contract, in order to `getRandomNumer` we need to fund the contract with LINK. Get some kovan testnet LINK [from this faucet](https://kovan.chain.link/). Once the transaction has gone through, in your metamask, hit `Add Token` and under `Custom Token` enter the address `0xa36085F69e2889c224210F603D836748e7dC0088`.
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NOTE: This is only the token address for Kovan.
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Once you deploy your contract, you'll need to fund it with LINK. You can fund it with link by copying your contract address from remix, and then sending that address a few LINK from your metamask. Remember this is all testnet LINK, and we can always get more for free.
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And you'll be able to work with the VRF. After deploying the content, enter a number of choice into the `getRandomNumber` function. After a delay of ~1 minute, you can hit the `randomResult` button to get the random number returned.
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```javascript
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/** This example code is designed to quickly deploy an example contract using Remix.
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* If you have never used Remix, try our example walkthrough: https://docs.chain.link/docs/example-walkthrough
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* You will need testnet ETH and LINK.
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* - Kovan ETH faucet: https://faucet.kovan.network/
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* - Kovan LINK faucet: https://kovan.chain.link/
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*/
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pragma solidity 0.6.6;
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import "https://raw.githubusercontent.com/smartcontractkit/chainlink/master/evm-contracts/src/v0.6/VRFConsumerBase.sol";
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contract RandomNumberConsumer is VRFConsumerBase {
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bytes32 internal keyHash;
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uint256 internal fee;
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uint256 public randomResult;
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/**
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* Constructor inherits VRFConsumerBase
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*
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* Network: Kovan
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* Chainlink VRF Coordinator address: 0xdD3782915140c8f3b190B5D67eAc6dc5760C46E9
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* LINK token address: 0xa36085F69e2889c224210F603D836748e7dC0088
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* Key Hash: 0x6c3699283bda56ad74f6b855546325b68d482e983852a7a82979cc4807b641f4
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*/
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constructor()
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VRFConsumerBase(
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0xdD3782915140c8f3b190B5D67eAc6dc5760C46E9, // VRF Coordinator
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0xa36085F69e2889c224210F603D836748e7dC0088 // LINK Token
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) public
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{
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keyHash = 0x6c3699283bda56ad74f6b855546325b68d482e983852a7a82979cc4807b641f4;
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fee = 0.1 * 10 ** 18; // 0.1 LINK
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}
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/**
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* Requests randomness from a user-provided seed
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*/
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function getRandomNumber(uint256 userProvidedSeed) public returns (bytes32 requestId) {
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require(LINK.balanceOf(address(this)) > fee, "Not enough LINK - fill contract with faucet");
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return requestRandomness(keyHash, fee, userProvidedSeed);
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}
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/**
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* Callback function used by VRF Coordinator
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*/
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function fulfillRandomness(bytes32 requestId, uint256 randomness) internal override {
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randomResult = randomness;
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}
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/**
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* Withdraw LINK from this contract
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*
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* DO NOT USE THIS IN PRODUCTION AS IT CAN BE CALLED BY ANY ADDRESS.
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* THIS IS PURELY FOR EXAMPLE PURPOSES.
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*/
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function withdrawLink() external {
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require(LINK.transfer(msg.sender, LINK.balanceOf(address(this))), "Unable to transfer");
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}
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}
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```
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[You can learn more about Chainlink from the documentation.](https://docs.chain.link/docs)
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You can [make API calls](https://docs.chain.link/docs/make-a-http-get-request), [set timing intervals](https://docs.chain.link/docs/chainlink-alarm-clock), and so much more.
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```javascript
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// Setting up oracle networks yourself
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// D. Cron Job
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@ -869,17 +725,17 @@ Work with the full example below using the [`Javascript VM` in remix here.](http
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// ** START EXAMPLE **
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// CrowdFunder.sol
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pragma solidity ^0.4.19;
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pragma solidity ^0.6.6;
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/// @title CrowdFunder
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/// @author nemild
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contract CrowdFunder {
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// Variables set on create by creator
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address public creator;
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address public fundRecipient; // creator may be different than recipient
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address payable public fundRecipient; // creator may be different than recipient, and must be payable
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uint public minimumToRaise; // required to tip, else everyone gets refund
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string campaignUrl;
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byte constant version = 1;
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byte version = "1";
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// Data structures
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enum State {
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@ -889,7 +745,7 @@ contract CrowdFunder {
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}
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struct Contribution {
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uint amount;
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address contributor;
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address payable contributor;
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}
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// State variables
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@ -919,10 +775,10 @@ contract CrowdFunder {
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_;
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}
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function CrowdFunder(
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function crowdFund(
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uint timeInHoursForFundraising,
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string _campaignUrl,
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address _fundRecipient,
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string memory _campaignUrl,
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address payable _fundRecipient,
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uint _minimumToRaise)
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public
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{
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@ -947,7 +803,7 @@ contract CrowdFunder {
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);
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totalRaised += msg.value;
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LogFundingReceived(msg.sender, msg.value, totalRaised);
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emit LogFundingReceived(msg.sender, msg.value, totalRaised);
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checkIfFundingCompleteOrExpired();
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return contributions.length - 1; // return id
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@ -971,7 +827,7 @@ contract CrowdFunder {
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public
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inState(State.Successful)
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{
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fundRecipient.transfer(this.balance);
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fundRecipient.transfer(address(this).balance);
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LogWinnerPaid(fundRecipient);
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}
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@ -1000,6 +856,7 @@ contract CrowdFunder {
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}
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}
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// ** END EXAMPLE **
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```
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Some more functions.
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@ -1085,6 +942,11 @@ someContractAddress.callcode('function_name');
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- [Modular design strategies for Ethereum Contracts](https://docs.erisindustries.com/tutorials/solidity/)
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- [Chainlink Documentation](https://docs.chain.link/docs/getting-started)
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## Smart Contract Development Frameworks
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- [Hardhat](https://hardhat.org/)
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- [Brownie](https://github.com/eth-brownie/brownie)
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- [Truffle](https://www.trufflesuite.com/)
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## Important libraries
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- [Zeppelin](https://github.com/OpenZeppelin/openzeppelin-contracts): Libraries that provide common contract patterns (crowdfuding, safemath, etc)
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- [Chainlink](https://github.com/smartcontractkit/chainlink): Code that allows you to interact with external data
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