An oracle is a midpoint that makes HTTP requests from contracts to off-chain endpoints. Unlike traditional oracle networks - midpoints allow developers to define arbitrarily complex requests with components such as parameters/headers defined on-chain, multistep authentication workflows, private off-chain data for keys, and cross-chain functionality.
/*
* SPDX-License-Identifier: MIT
* Midpoint Sample Storage Contract v3.0.0
*
* This is a contract generated at 2023-02-28 20:07:34 for testing requests to midpoint 160.
* This contract is intended to serve as a guide for interfacing with a midpoint and should not be used
* as is in a production environment.
* For more information on setting up a midpoint and using this contract see docs.midpointapi.com
*/
pragma solidity>=0.8.0;
interface IMidpoint {
function callMidpoint(uint64 midpointId, bytes calldata _data) external returns(uint64 requestId);
}
contract TestMidpointOracleContract {
// These events can be removed without impacting the functionality of your midpoint
event RequestForWikipediaSummaryMade(string article);
event WikipediaSummaryReceived(uint64 Request_ID, uint64 Midpoint_ID, string wikipedia_summary);
// A verified startpoint for Goerli Testnet
address constant startpointAddress = 0x795c5292b9630d473d568079b73850F29344403c;
// A verified midpoint transact to EVM function EOA for Goerli Testnet
address constant whitelistedCallbackAddress = 0xC0FFEE4a3A2D488B138d090b8112875B90b5e6D9;
// The globally unique identifier for your midpoint
uint64 constant midpointID = 160;
// Mapping of Request ID to a flag that is checked when the request is satisfied
// This can be removed without impacting the functionality of your midpoint
mapping(uint64 => bool) public request_id_satisfied;
// Mappings from Request ID to each of your results
// This can be removed without impacting the functionality of your midpoint
mapping(uint64 => string) public request_id_to_wikipedia_summary;
/*
* This function makes a call to your midpoint with On-Chain Variables specified as function inputs.
*
* Note that this is a public function and will allow any address or contract to call midpoint 160.
* Configure your midpoint to permit calls from this contract when testing. Before using your midpoint
* in a production environment, ensure that calls to 'callMidpoint' are protected.
* Any call to 'callMidpoint' from a whitelisted contract will make a call to your midpoint;
* there may be multiple places in this contract that call the midpoint or multiple midpoints called by the same contract.
*/
function getWikipediaSummary(string memory article) public {
// This packs together all of the On-Chain Variables for your midpoint into a single bytestring
bytes memory args = abi.encodePacked(article, bytes1(0x00));
// This makes the call to your midpoint
uint64 requestId = IMidpoint(startpointAddress).callMidpoint(midpointID, args);
// This logs that the call has been made, and can be removed without impacting your midpoint
emit RequestForWikipediaSummaryMade(article);
request_id_satisfied[requestId] = false;
}
/*
* This function is the callback target specified in your midpoint callback definition.
* Note that the callback is placed in the same contract as the call to callMidpoint for simplicity when testing.
* The callback does not need to be defined in the same contract as the request or live on the same chain.
*/
function requestedWikipediaSummary(uint64 midpointId, uint64 requestId, string memory wikipediaSummary) public {
// Only allow a verified callback address to submit information for your midpoint.
require(tx.origin == whitelistedCallbackAddress, "Invalid callback address");
// Only allow requests that came from your midpoint ID
require(midpointID == midpointId, "Invalid Midpoint ID");
// This stores each of your response variables. This is where you would place any logic associated with your callback.
// Your midpoint can transact to a callback with arbitrary execution and gas cost.
request_id_to_wikipedia_summary[requestId] = wikipediaSummary;
// This logs that a response has been received, and can be removed without impacting your midpoint
emit WikipediaSummaryReceived(requestId, midpointId, wikipediaSummary);
request_id_satisfied[requestId] = true;
}
}
