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Uses midpointapi.com to return a single cell value from any table or sql request on Tableland
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| // SPDX-License-Identifier: UNLICENSED | |
| pragma solidity ^0.8.17; | |
| import "@openzeppelin/contracts/utils/Strings.sol"; | |
| import "@openzeppelin/contracts/utils/structs/EnumerableMap.sol"; | |
| interface IMidpoint { | |
| function callMidpoint(uint64 midpointId, bytes calldata _data) external returns(uint256 requestId); | |
| } | |
| interface IStringCallback { | |
| function stringResponse(uint256 requestId, string memory data) external; | |
| } | |
| contract QueryController { | |
| // will be used for recalling callbacks | |
| using EnumerableMap for EnumerableMap.UintToAddressMap; | |
| // emits when requests come in | |
| event RequestMade(uint256 requestId, string network, string query); | |
| // emits when midpoint responses come in | |
| event ResponseReceived(uint256 requestId, string response); | |
| // the midpoint contract | |
| address constant midpoint = 0x9BEa2A4C2d84334287D60D6c36Ab45CB453821eB; | |
| // the addr of the midpoint responses | |
| address constant midpointOrigin = 0xC0FFEE4a3A2D488B138d090b8112875B90b5e6D9; | |
| // the id of our query type | |
| uint64 midpointID = 389; | |
| // recalling callbacks | |
| // mapping(uint256 => address) public callbacks; | |
| EnumerableMap.UintToAddressMap private callbacks; | |
| // just the basic call, no callback recorded | |
| function _queryString(string memory column, string memory query) private returns(uint256 requestId) { | |
| string memory wrapped = string.concat( | |
| "SELECT ", column, " as response FROM (", query,") LIMIT 1" | |
| ); | |
| bytes memory args = abi.encodePacked(wrapped, bytes1(0x00)); | |
| requestId = IMidpoint(midpoint).callMidpoint(midpointID, args); | |
| emit RequestMade(requestId, wrapped, query); | |
| return requestId; | |
| } | |
| // call midpoint w/ a callback to your own contract. contract must conform to IStringCallback | |
| function queryString(string memory column, string memory query, address endpoint) public returns(uint256 requestId) { | |
| // create a requestid from midpoint | |
| requestId = _queryString(column, query); | |
| EnumerableMap.set(callbacks, requestId, endpoint); | |
| return requestId; | |
| } | |
| function callback(uint256 _requestId, uint64 _midpointId, string memory response) public { | |
| // Only allow the verified callback address to submit information for your midpoint. | |
| require(tx.origin == midpointOrigin, "Invalid callback address"); | |
| require(midpointID == _midpointId, "Invalid Midpoint ID"); | |
| if (EnumerableMap.contains(callbacks, _requestId)) { | |
| address to = EnumerableMap.get(callbacks, _requestId); | |
| EnumerableMap.remove(callbacks, _requestId); | |
| IStringCallback(to).stringResponse(_requestId, response); | |
| } | |
| // For Demonstration Purposes Only | |
| emit ResponseReceived(_requestId, response); | |
| } | |
| } |
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