How to make a Chainlinked contract

Creating Chainlinked Contracts

Developers wanting to add external data to their contracts will need to import the Chainlinked contract into their project. The Chainlinked contract contains helper methods in order to simplify the process of making a Chainlink request on-chain for external data.

If you have any questions, feel free to ask us on Gitter!

Adding Chainlink to your project

Start off by adding Chainlink to your project, which is hosted on GitHub.

$ yarn add github:smartcontractkit/chainlink

Connect your smart contract to the Chainlink Network

Import Chainlinked.sol into your contract so you can inherit the Chainlinked behavior.

import "chainlink/solidity/contracts/Chainlinked.sol";

contract MyContract is Chainlinked {
  constructor()
    public
  {
    setLinkToken(0x20fE562d797A42Dcb3399062AE9546cd06f63280);
    setOracle(0xA39A4cC64C91267EC1376f6861aAC0622352de8F);
    ...

Or if using Remix, simply use the Github URL as your import path.

import "github.com/smartcontractkit/chainlink/solidity/contracts/Chainlinked.sol";

contract MyContract is Chainlinked {
  constructor()
    public
  {
    setLinkToken(0x20fE562d797A42Dcb3399062AE9546cd06f63280);
    setOracle(0xA39A4cC64C91267EC1376f6861aAC0622352de8F);
    ...

Requesting data

Here is an example of a Chainlink request from Solidity, called a run:

  function requestEthereumPrice(string _currency) public onlyOwner {
    ChainlinkLib.Run memory run = newRun(jobId, this, "requestedDataCallback(bytes32,uint256)");
    run.add("url", "https://min-api.cryptocompare.com/data/price?fsym=ETH&tsyms=USD,EUR,JPY");
    string[] memory path = new string[](1);
    path[0] = _currency;
    run.addStringArray("path", path);
    run.addInt("times", 100);
    requestId = chainlinkRequest(run, LINK(1));
  }

For details on which parameters to specify, see our adapters page.

Receiving data

In the example above requestedDataCallback is the callback method specified in the requestEthereumPrice method.

Be sure to add the checkChainlinkFulfillment modifier to ensure that only Chainlink can call this method. This modifier is included with the Chainlinked contract.

  function requestedDataCallback(bytes32 _requestId, uint256 _reportedPrice)
    public checkChainlinkFulfillment(_requestId)
  {
    calculatePayout(_reportedPrice); // run your calculation with the reported data
    ...

Deploying to the blockchain

In order for a contract to make use of the Chainlink network, you'll need to have the address of the LINK token contract and our oracle contract.

You will also need the JobID as bytes when invoking a new run. We have pre-made jobs available for you. Types with a Multiplier indicate that the value received from the given endpoint will be multiplied by the specified "times" value before being written to the blockchain. The string value of the JobIDs will need to be given to the Run as bytes.

Ropsten

LINK token address: "0x20fE562d797A42Dcb3399062AE9546cd06f63280"

Oracle address: "0xA39A4cC64C91267EC1376f6861aAC0622352de8F"

Rinkeby

LINK token address: "0x01BE23585060835E02B77ef475b0Cc51aA1e0709"

Oracle address: "0x32f5009789310dF4F971bf211E15a723269709C3"

Job Specs

Type	Job ID	Required Params
Bytes32	Ropsten: 0de7b99e32564e1cadf77ec5914f1734 Rinkeby: 7f075add62e5455bb527025930ceb4f5	url(string), path(array of strings)
Int256	Ropsten: 45f24e7f6da44657aaac1b92ab86cc82 Rinkeby: c8086213e8b9402c995fe37ee0f73043	url(string), path(array of strings)
Int256 Multiplier	Ropsten: aa07b77beabf42e596bd0f45a10aa1c7 Rinkeby: 80f21e24cdfb4e64be00a5408e316043	url(string), path(array of strings), times(int)
Uint256	Ropsten: e584d6df5f7046b388009e47a0752ba6 Rinkeby: cbbbd1d623c249299773198d6629b81a	url(string), path(array of strings)
Uint256 Multiplier	Ropsten: d4a0d580aba44bc09e43a7601025d793 Rinkeby: c3ac52b391df47ecab7bf9d4e37d8055	url(string), path(array of strings), times(int)