Update XRC721 as a 0.8.17

XRC721/Address.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
 
 /**
  * @dev Collection of functions related to the address type,

XRC721/Counters.sol

@@ -1,38 +1,39 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
 
-	import "./SafeMath.sol";
-
-	/**
-	 * @title Counters
-	 * @author Matt Condon (@shrugs)
-	 * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
-	 * of elements in a mapping, issuing XRC721 ids, or counting request ids.
-	 *
-	 * Include with `using Counters for Counters.Counter;`
-	 * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the SafeMath
-	 * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
-	 * directly accessed.
-	 */
-	library Counters {
-	    using SafeMath for uint256;
-
-	    struct Counter {
-	        // This variable should never be directly accessed by users of the library: interactions must be restricted to
-	        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
-	        // this feature: see https://github.com/XDC/solidity/issues/4637
-	        uint256 _value; // default: 0
-	    }
-
-	    function current(Counter storage counter) internal view returns (uint256) {
-	        return counter._value;
-	    }
-
-	    function increment(Counter storage counter) internal {
-	        counter._value += 1;
-	    }
-
-	    function decrement(Counter storage counter) internal {
-	        counter._value = counter._value.sub(1);
-	    }
+import "./SafeMath.sol";
+
+/**
+	* @title Counters
+	* @author Matt Condon (@shrugs)
+	* @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
+	* of elements in a mapping, issuing XRC721 ids, or counting request ids.
+	*
+	* Include with `using Counters for Counters.Counter;`
+	* Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the SafeMath
+	* overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
+	* directly accessed.
+	*/
+library Counters {
+	using SafeMath for uint256;
+
+	struct Counter {
+		// This variable should never be directly accessed by users of the library: interactions must be restricted to
+		// the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
+		// this feature: see https://github.com/XDC/solidity/issues/4637
+		uint256 _value; // default: 0
+	}
+
+	function current(Counter storage counter) internal view returns (uint256) {
+		return counter._value;
+	}
+
+	function increment(Counter storage counter) internal {
+		counter._value += 1;
+	}
+
+	function decrement(Counter storage counter) internal {
+		counter._value = counter._value.sub(1);
 	}
+}
 

XRC721/IXRC165.sol

@@ -1,21 +1,22 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
 
+/**
+* @dev Interface of the XRC165 standard
+*
+* Implementers can declare support of contract interfaces, which can then be
+* queried by others (`XRC165Checker`).
+*
+* For an implementation, see `XRC165`.
+*/
+interface IXRC165 {
 	/**
-	 * @dev Interface of the XRC165 standard
-	 *
-	 * Implementers can declare support of contract interfaces, which can then be
-	 * queried by others (`XRC165Checker`).
-	 *
-	 * For an implementation, see `XRC165`.
-	 */
-	interface IXRC165 {
-	    /**
-	     * @dev Returns true if this contract implements the interface defined by
-	     * `interfaceId`.
-	     * to learn more about how these ids are created.
-	     *
-	     * This function call must use less than 30 000 gas.
-	     */
-	    function supportsInterface(bytes4 interfaceId) external view returns (bool);
-	}
+	* @dev Returns true if this contract implements the interface defined by
+	* `interfaceId`.
+	* to learn more about how these ids are created.
+	*
+	* This function call must use less than 30 000 gas.
+	*/
+	function supportsInterface(bytes4 interfaceId) external view returns (bool);
+}
 

XRC721/IXRC721.sol

@@ -1,54 +1,55 @@
-pragma solidity ^0.5.0;
-
-	import "./IXRC165.sol";
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
 
+import "./IXRC165.sol";
+
+/**
+* @dev Required interface of an XRC721 compliant contract.
+*/
+interface IXRC721 is IXRC165 {
+	event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
+	event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
+	event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
+
 	/**
-	 * @dev Required interface of an XRC721 compliant contract.
-	 */
-	contract IXRC721 is IXRC165 {
-	    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
-	    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
-	    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
-
-	    /**
-	     * @dev Returns the number of NFTs in `owner`'s account.
-	     */
-	    function balanceOf(address owner) public view returns (uint256 balance);
-
-	    /**
-	     * @dev Returns the owner of the NFT specified by `tokenId`.
-	     */
-	    function ownerOf(uint256 tokenId) public view returns (address owner);
-
-	    /**
-	     * @dev Transfers a specific NFT (`tokenId`) from one account (`from`) to
-	     * another (`to`).
-	     *
-	     * 
-	     *
-	     * Requirements:
-	     * - `from`, `to` cannot be zero.
-	     * - `tokenId` must be owned by `from`.
-	     * - If the caller is not `from`, it must be have been allowed to move this
-	     * NFT by either `approve` or `setApproveForAll`.
-	     */
-	    function safeTransferFrom(address from, address to, uint256 tokenId) public;
-	    /**
-	     * @dev Transfers a specific NFT (`tokenId`) from one account (`from`) to
-	     * another (`to`).
-	     *
-	     * Requirements:
-	     * - If the caller is not `from`, it must be approved to move this NFT by
-	     * either `approve` or `setApproveForAll`.
-	     */
-	    function transferFrom(address from, address to, uint256 tokenId) public;
-	    function approve(address to, uint256 tokenId) public;
-	    function getApproved(uint256 tokenId) public view returns (address operator);
-
-	    function setApprovalForAll(address operator, bool _approved) public;
-	    function isApprovedForAll(address owner, address operator) public view returns (bool);
-
-
-	    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data) public;
-	}
+	* @dev Returns the number of NFTs in `owner`'s account.
+	*/
+	function balanceOf(address owner) external view returns (uint256 balance);
+
+	/**
+	* @dev Returns the owner of the NFT specified by `tokenId`.
+	*/
+	function ownerOf(uint256 tokenId) external view returns (address owner);
+
+	/**
+	* @dev Transfers a specific NFT (`tokenId`) from one account (`from`) to
+	* another (`to`).
+	*
+	* 
+	*
+	* Requirements:
+	* - `from`, `to` cannot be zero.
+	* - `tokenId` must be owned by `from`.
+	* - If the caller is not `from`, it must be have been allowed to move this
+	* NFT by either `approve` or `setApproveForAll`.
+	*/
+	function safeTransferFrom(address from, address to, uint256 tokenId) external;
+	/**
+	* @dev Transfers a specific NFT (`tokenId`) from one account (`from`) to
+	* another (`to`).
+	*
+	* Requirements:
+	* - If the caller is not `from`, it must be approved to move this NFT by
+	* either `approve` or `setApproveForAll`.
+	*/
+	function transferFrom(address from, address to, uint256 tokenId) external;
+	function approve(address to, uint256 tokenId) external;
+	function getApproved(uint256 tokenId) external view returns (address operator);
+
+	function setApprovalForAll(address operator, bool _approved) external;
+	function isApprovedForAll(address owner, address operator) external view returns (bool);
+
+
+	function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data) external;
+}
 

XRC721/IXRC721Receiver.sol

@@ -1,26 +1,26 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
 
+/**
+* @title XRC721 token receiver interface
+* @dev Interface for any contract that wants to support safeTransfers
+* from XRC721 asset contracts.
+*/
+interface IXRC721Receiver {
 	/**
-	 * @title XRC721 token receiver interface
-	 * @dev Interface for any contract that wants to support safeTransfers
-	 * from XRC721 asset contracts.
-	 */
-	contract IXRC721Receiver {
-	    /**
-	     * @notice Handle the receipt of an NFT
-	     * @dev The XRC721 smart contract calls this function on the recipient
-	     * after a `safeTransfer`. This function MUST return the function selector,
-	     * otherwise the caller will revert the transaction. The selector to be
-	     * returned can be obtained as `this.onXRC721Received.selector`. This
-	     * function MAY throw to revert and reject the transfer.
-	     * Note: the XRC721 contract address is always the message sender.
-	     * @param operator The address which called `safeTransferFrom` function
-	     * @param from The address which previously owned the token
-	     * @param tokenId The NFT identifier which is being transferred
-	     * @param data Additional data with no specified format
-	     * @return bytes4 `bytes4(keccak256("onXRC721Received(address,address,uint256,bytes)"))`
-	     */
-	    function onXRC721Received(address operator, address from, uint256 tokenId, bytes memory data)
-	    public returns (bytes4);
-	}
+	* @notice Handle the receipt of an NFT
+	* @dev The XRC721 smart contract calls this function on the recipient
+	* after a `safeTransfer`. This function MUST return the function selector,
+	* otherwise the caller will revert the transaction. The selector to be
+	* returned can be obtained as `this.onXRC721Received.selector`. This
+	* function MAY throw to revert and reject the transfer.
+	* Note: the XRC721 contract address is always the message sender.
+	* @param operator The address which called `safeTransferFrom` function
+	* @param from The address which previously owned the token
+	* @param tokenId The NFT identifier which is being transferred
+	* @param data Additional data with no specified format
+	* @return bytes4 `bytes4(keccak256("onXRC721Received(address,address,uint256,bytes)"))`
+	*/
+	function onXRC721Received(address operator, address from, uint256 tokenId, bytes memory data) external returns (bytes4);
+}