[ERC1185] DNS情報をENSに保存する仕組みを理解しよう！

pragma solidity ^0.7.4;
import "../ResolverBase.sol";
import "@ensdomains/dnssec-oracle/contracts/RRUtils.sol";

abstract contract DNSResolver is ResolverBase {
    using RRUtils for *;
    using BytesUtils for bytes;

    bytes4 constant private DNS_RECORD_INTERFACE_ID = 0xa8fa5682;
    bytes4 constant private DNS_ZONE_INTERFACE_ID = 0x5c47637c;

    // DNSRecordChanged is emitted whenever a given node/name/resource's RRSET is updated.
    event DNSRecordChanged(bytes32 indexed node, bytes name, uint16 resource, bytes record);
    // DNSRecordDeleted is emitted whenever a given node/name/resource's RRSET is deleted.
    event DNSRecordDeleted(bytes32 indexed node, bytes name, uint16 resource);
    // DNSZoneCleared is emitted whenever a given node's zone information is cleared.
    event DNSZoneCleared(bytes32 indexed node);

    // DNSZonehashChanged is emitted whenever a given node's zone hash is updated.
    event DNSZonehashChanged(bytes32 indexed node, bytes lastzonehash, bytes zonehash);

    // Zone hashes for the domains.
    // A zone hash is an ERC-1577 content hash in binary format that should point to a
    // resource containing a single zonefile.
    // node => contenthash
    mapping(bytes32=>bytes) private zonehashes;

    // Version the mapping for each zone.  This allows users who have lost
    // track of their entries to effectively delete an entire zone by bumping
    // the version number.
    // node => version
    mapping(bytes32=>uint256) private versions;

    // The records themselves.  Stored as binary RRSETs
    // node => version => name => resource => data
    mapping(bytes32=>mapping(uint256=>mapping(bytes32=>mapping(uint16=>bytes)))) private records;

    // Count of number of entries for a given name.  Required for DNS resolvers
    // when resolving wildcards.
    // node => version => name => number of records
    mapping(bytes32=>mapping(uint256=>mapping(bytes32=>uint16))) private nameEntriesCount;

    /**
     * Set one or more DNS records.  Records are supplied in wire-format.
     * Records with the same node/name/resource must be supplied one after the
     * other to ensure the data is updated correctly. For example, if the data
     * was supplied:
     *     a.example.com IN A 1.2.3.4
     *     a.example.com IN A 5.6.7.8
     *     www.example.com IN CNAME a.example.com.
     * then this would store the two A records for a.example.com correctly as a
     * single RRSET, however if the data was supplied:
     *     a.example.com IN A 1.2.3.4
     *     www.example.com IN CNAME a.example.com.
     *     a.example.com IN A 5.6.7.8
     * then this would store the first A record, the CNAME, then the second A
     * record which would overwrite the first.
     *
     * @param node the namehash of the node for which to set the records
     * @param data the DNS wire format records to set
     */
    function setDNSRecords(bytes32 node, bytes calldata data) external authorised(node) {
        uint16 resource = 0;
        uint256 offset = 0;
        bytes memory name;
        bytes memory value;
        bytes32 nameHash;
        // Iterate over the data to add the resource records
        for (RRUtils.RRIterator memory iter = data.iterateRRs(0); !iter.done(); iter.next()) {
            if (resource == 0) {
                resource = iter.dnstype;
                name = iter.name();
                nameHash = keccak256(abi.encodePacked(name));
                value = bytes(iter.rdata());
            } else {
                bytes memory newName = iter.name();
                if (resource != iter.dnstype || !name.equals(newName)) {
                    setDNSRRSet(node, name, resource, data, offset, iter.offset - offset, value.length == 0);
                    resource = iter.dnstype;
                    offset = iter.offset;
                    name = newName;
                    nameHash = keccak256(name);
                    value = bytes(iter.rdata());
                }
            }
        }
        if (name.length > 0) {
            setDNSRRSet(node, name, resource, data, offset, data.length - offset, value.length == 0);
        }
    }

    /**
     * Obtain a DNS record.
     * @param node the namehash of the node for which to fetch the record
     * @param name the keccak-256 hash of the fully-qualified name for which to fetch the record
     * @param resource the ID of the resource as per https://en.wikipedia.org/wiki/List_of_DNS_record_types
     * @return the DNS record in wire format if present, otherwise empty
     */
    function dnsRecord(bytes32 node, bytes32 name, uint16 resource) public view returns (bytes memory) {
        return records[node][versions[node]][name][resource];
    }

    /**
     * Check if a given node has records.
     * @param node the namehash of the node for which to check the records
     * @param name the namehash of the node for which to check the records
     */
    function hasDNSRecords(bytes32 node, bytes32 name) public view returns (bool) {
        return (nameEntriesCount[node][versions[node]][name] != 0);
    }

    /**
     * Clear all information for a DNS zone.
     * @param node the namehash of the node for which to clear the zone
     */
    function clearDNSZone(bytes32 node) public authorised(node) {
        versions[node]++;
        emit DNSZoneCleared(node);
    }

    /**
     * setZonehash sets the hash for the zone.
     * May only be called by the owner of that node in the ENS registry.
     * @param node The node to update.
     * @param hash The zonehash to set
     */
    function setZonehash(bytes32 node, bytes calldata hash) external authorised(node) {
        bytes memory oldhash = zonehashes[node];
        zonehashes[node] = hash;
        emit DNSZonehashChanged(node, oldhash, hash);
    }

    /**
     * zonehash obtains the hash for the zone.
     * @param node The ENS node to query.
     * @return The associated contenthash.
     */
    function zonehash(bytes32 node) external view returns (bytes memory) {
        return zonehashes[node];
    }

    function supportsInterface(bytes4 interfaceID) virtual override public pure returns(bool) {
        return interfaceID == DNS_RECORD_INTERFACE_ID ||
               interfaceID == DNS_ZONE_INTERFACE_ID ||
               super.supportsInterface(interfaceID);
    }

    function setDNSRRSet(
        bytes32 node,
        bytes memory name,
        uint16 resource,
        bytes memory data,
        uint256 offset,
        uint256 size,
        bool deleteRecord) private
    {
        uint256 version = versions[node];
        bytes32 nameHash = keccak256(name);
        bytes memory rrData = data.substring(offset, size);
        if (deleteRecord) {
            if (records[node][version][nameHash][resource].length != 0) {
                nameEntriesCount[node][version][nameHash]--;
            }
            delete(records[node][version][nameHash][resource]);
            emit DNSRecordDeleted(node, name, resource);
        } else {
            if (records[node][version][nameHash][resource].length == 0) {
                nameEntriesCount[node][version][nameHash]++;
            }
            records[node][version][nameHash][resource] = rrData;
            emit DNSRecordChanged(node, name, resource, rrData);
        }
    }
}