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Merkle.sol

// taken here: https://github.com/maticnetwork/contracts/blob/main/contracts/common/lib/Merkle.sol
pragma solidity ^0.8.20;

library Merkle {
    function checkMembership(
        bytes32 leaf,
        uint256 index,
        bytes32 rootHash,
        bytes memory proof
    ) internal pure returns (bool) {
        require(proof.length % 32 == 0, "Invalid proof length");
        uint256 proofHeight = proof.length / 32;
        // Proof of size n means, height of the tree is n+1.
        // In a tree of height n+1, max #leafs possible is 2 ^ n
        require(index < 2 ** proofHeight, "Leaf index is too big");

        bytes32 proofElement;
        bytes32 computedHash = leaf;
        for (uint256 i = 32; i <= proof.length; i += 32) {
            assembly {
                proofElement := mload(add(proof, i))
            }

            if (index % 2 == 0) {
                computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
            } else {
                computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
            }

            index = index / 2;
        }
        return computedHash == rootHash;
    }
}

MerklePatriciaProof.sol

// taken here: https://github.com/maticnetwork/contracts/blob/main/contracts/common/lib/MerklePatriciaProof.sol

/*
 * @title MerklePatriciaVerifier
 * @author Sam Mayo ([email protected])
 *
 * @dev Library for verifing merkle patricia proofs.
 */
pragma solidity ^0.8.20;

import {RLPReader} from "solidity-rlp/contracts/RLPReader.sol";

library MerklePatriciaProof {
    /*
     * @dev Verifies a merkle patricia proof.
     * @param value The terminating value in the trie.
     * @param encodedPath The path in the trie leading to value.
     * @param rlpParentNodes The rlp encoded stack of nodes.
     * @param root The root hash of the trie.
     * @return The boolean validity of the proof.
     */
    function verify(
        bytes memory value,
        bytes memory encodedPath,
        bytes memory rlpParentNodes,
        bytes32 root
    ) internal pure returns (bool) {
        RLPReader.RLPItem memory item = RLPReader.toRlpItem(rlpParentNodes);
        RLPReader.RLPItem[] memory parentNodes = RLPReader.toList(item);

        bytes memory currentNode;
        RLPReader.RLPItem[] memory currentNodeList;

        bytes32 nodeKey = root;
        uint256 pathPtr = 0;

        bytes memory path = _getNibbleArray(encodedPath);
        if (path.length == 0) {
            return false;
        }

        for (uint256 i = 0; i < parentNodes.length; i++) {
            if (pathPtr > path.length) {
                return false;
            }

            currentNode = RLPReader.toRlpBytes(parentNodes[i]);
            if (nodeKey != keccak256(currentNode)) {
                return false;
            }
            currentNodeList = RLPReader.toList(parentNodes[i]);

            if (currentNodeList.length == 17) {
                if (pathPtr == path.length) {
                    if (keccak256(RLPReader.toBytes(currentNodeList[16])) == keccak256(value)) {
                        return true;
                    } else {
                        return false;
                    }
                }

                uint8 nextPathNibble = uint8(path[pathPtr]);
                if (nextPathNibble > 16) {
                    return false;
                }

                nodeKey = bytes32(RLPReader.toUintStrict(currentNodeList[nextPathNibble]));
                pathPtr += 1;
            } else if (currentNodeList.length == 2) {
                uint256 traversed = _nibblesToTraverse(RLPReader.toBytes(currentNodeList[0]), path, pathPtr);
                if (pathPtr + traversed == path.length) {
                    //leaf node
                    if (keccak256(RLPReader.toBytes(currentNodeList[1])) == keccak256(value)) {
                        return true;
                    } else {
                        return false;
                    }
                }

                //extension node
                if (traversed == 0) {
                    return false;
                }

                pathPtr += traversed;
                nodeKey = bytes32(RLPReader.toUintStrict(currentNodeList[1]));
            } else {
                return false;
            }
        }
    }

    // bytes b must be hp encoded
    function _getNibbleArray(bytes memory b) private pure returns (bytes memory) {
        bytes memory nibbles;
        if (b.length > 0) {
            uint8 offset;
            uint8 hpNibble = uint8(_getNthNibbleOfBytes(0, b));
            if (hpNibble == 1 || hpNibble == 3) {
                nibbles = new bytes(b.length * 2 - 1);
                bytes1 oddNibble = _getNthNibbleOfBytes(1, b);
                nibbles[0] = oddNibble;
                offset = 1;
            } else {
                nibbles = new bytes(b.length * 2 - 2);
                offset = 0;
            }

            for (uint256 i = offset; i < nibbles.length; i++) {
                nibbles[i] = _getNthNibbleOfBytes(i - offset + 2, b);
            }
        }
        return nibbles;
    }

    function _getNthNibbleOfBytes(uint256 n, bytes memory str) private pure returns (bytes1) {
        return bytes1(n % 2 == 0 ? uint8(str[n / 2]) / 0x10 : uint8(str[n / 2]) % 0x10);
    }

    function _nibblesToTraverse(
        bytes memory encodedPartialPath,
        bytes memory path,
        uint256 pathPtr
    ) private pure returns (uint256) {
        uint256 len;
        // encodedPartialPath has elements that are each two hex characters (1 byte), but partialPath
        // and slicedPath have elements that are each one hex character (1 nibble)
        bytes memory partialPath = _getNibbleArray(encodedPartialPath);
        bytes memory slicedPath = new bytes(partialPath.length);

        // pathPtr counts nibbles in path
        // partialPath.length is a number of nibbles
        for (uint256 i = pathPtr; i < pathPtr + partialPath.length; i++) {
            bytes1 pathNibble = path[i];
            slicedPath[i - pathPtr] = pathNibble;
        }

        if (keccak256(partialPath) == keccak256(slicedPath)) {
            len = partialPath.length;
        } else {
            len = 0;
        }
        return len;
    }
}

VerifyEvent.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity ^0.8.0;
import "solidity-rlp/contracts/RLPReader.sol";

import "./Hashi.sol";
import {Merkle} from "./libraries/Merkle.sol";
import {MerklePatriciaProof} from "./libraries/MerklePatriciaProof.sol";

 struct EventProof {
    bytes receiptsRootProofPath;         // proof path
    bytes receiptsRootProofParentNodes;  // proof parent nodes
    bytes receipt;      // receipt of the transaction to prove
    uint256 logIndex;   // log index of the event from receipt
    bytes blockHeader;  // rlp-encoded block header
 }

error InvalidEventEmitter(address proofEmitter, address actualEmitter);
error InvalidTopic(bytes32 topic, bytes32 expectedTopic);
error InvalidBlockHash(bytes32 blockHash, bytes32 expectedBlockHash);
error InvalidReceiptsRootMerkleProof();
error InvalidBlockHeaderLength(uint256 length);


contract VerifyEvent {

    Hashi public hashi;
    address public expectedPingPong;
    IOracleAdapter public ambAdapter;

    bytes32 public constant EVENT_SIGNATURE_TOPIC= 0x48257dc961b6f792c2b78a080dacfed693b660960a702de21cee364e20270e2f; //keccak256(ping(uint256))

    constructor(address hashi_, address pingpong_, address ambAdapter_){

        hashi = Hashi(hashi_);
        expectedPingPong = pingpong_;
        ambAdapter = IOracleAdapter(ambAdapter_);
    }



    /// @dev verify certain event of given block number and receipt
    /// @param proof The EventProof struct to prove for
    function verify(EventProof memory proof) external {
        
        // deserialze  block header data
        RLPReader.RLPItem memory blockHeaderRLP = RLPReader.toRlpItem(proof.blockHeader);
        RLPReader.RLPItem[] memory blockHeaderContent = RLPReader.toList(blockHeaderRLP);

        uint256 blockNumber = uint256(RLPReader.toUint(blockHeaderContent[8]));
        bytes32 receiptRoot = bytes32(RLPReader.toUint(blockHeaderContent[6]));
        

        // Get log from receipt
        RLPReader.RLPItem memory receiptRlpItem = RLPReader.toRlpItem(proof.receipt);
        RLPReader.RLPItem[] memory receiptData = RLPReader.toList(receiptRlpItem);
        RLPReader.RLPItem[] memory logs = RLPReader.toList(receiptData[3]); // index of 'logs[]' in receipt
        RLPReader.RLPItem[] memory log = RLPReader.toList(logs[proof.logIndex]); // index in 'logs[]' of the event to prove


        // Check block hash

        bytes32 reportedBlockHash = keccak256(proof.blockHeader);

        // check the block header with Hashi

        IOracleAdapter[] memory oracleAdapters = new IOracleAdapter[](1);
        oracleAdapters[0] = ambAdapter;
        uint256 sourceChainId = 5;
        bytes32[] memory expectedBlockHash = hashi.getHashesFromOracles(oracleAdapters, sourceChainId, blockNumber);
        if(expectedBlockHash[0]!=reportedBlockHash){
            revert InvalidBlockHash(reportedBlockHash, expectedBlockHash[0]);
        }


        // Check emitted address
        address  pingpong = RLPReader.toAddress(log[0]); // index of 'address' in log
        
        if(pingpong != expectedPingPong){
            revert InvalidEventEmitter(pingpong, expectedPingPong);
        }

        // Check event topic
        RLPReader.RLPItem[] memory topics = RLPReader.toList(log[7]); // index of 'topics' in log
        bytes32 pingPongTopic = bytes32(RLPReader.toBytes(topics[0]));  // first index of 'topics'
        
        if(EVENT_SIGNATURE_TOPIC != pingPongTopic){
            revert InvalidTopic(pingPongTopic, EVENT_SIGNATURE_TOPIC);
        }
        
        // Verify receipt trie

        if (
                !MerklePatriciaProof.verify(
                    proof.receipt,
                    proof.receiptsRootProofPath,
                    proof.receiptsRootProofParentNodes,
                    receiptRoot
                )
            ) 
            {
                revert InvalidReceiptsRootMerkleProof();
            }

        // Define your dApp logic here...

    }

}