---
title: Sample 721 with GSN support
tags: GSN
---

# Sample 721 with GSN support

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
import "@opengsn/contracts/src/BaseRelayRecipient.sol";

contract GSN is ERC721, BaseRelayRecipient {
    using Counters for Counters.Counter;

    string public override versionRecipient = "2.2.0+opengsn.batched.irelayrecipient";
    
    Counters.Counter private currentTokenId;

    /// @dev Base token URI used as a prefix by tokenURI().
    string public baseTokenURI;
    mapping(uint256 => string) private _tokenURIs;

    constructor(address forwarder_) ERC721("GSN", "GSN") {
        baseTokenURI = "";
        _setTrustedForwarder(forwarder_);
    }

    function _msgSender()
        internal
        view
        override(Context, BaseRelayRecipient)
        returns (address sender)
    {
        sender = BaseRelayRecipient._msgSender();
    }

    function _msgData()
        internal
        view
        override(Context, BaseRelayRecipient)
        returns (bytes calldata)
    {
        return BaseRelayRecipient._msgData();
    }

    function mintTo(address recipient, string memory tokenURI_)
        public
        returns (uint256)
    {
        currentTokenId.increment();
        uint256 newItemId = currentTokenId.current();
        _safeMint(recipient, newItemId);
        _setTokenURI(newItemId, tokenURI_);
        return newItemId;
    }

    /// @dev Returns an URI for a given token ID
    function _baseURI() internal view virtual override returns (string memory) {
        return baseTokenURI;
    }

    function showBaseURI() public view returns (string memory) {
        return baseTokenURI;
    }

    /// @dev Sets the base token URI prefix.
    function setBaseTokenURI(string memory _baseTokenURI) public {
        baseTokenURI = _baseTokenURI;
    }

    function _setTokenURI(uint256 tokenId, string memory _tokenURI)
        internal
        virtual
    {
        require(
            _exists(tokenId),
            "ERC721Metadata: URI set of nonexistent token"
        );
        _tokenURIs[tokenId] = _tokenURI;
    }

    function tokenURI(uint256 tokenId)
        public
        view
        virtual
        override
        returns (string memory)
    {
        require(
            _exists(tokenId),
            "ERC721Metadata: URI query for nonexistent token"
        );

        string memory _tokenURI = _tokenURIs[tokenId];
        string memory base = _baseURI();

        // If there is no base URI, return the token URI.
        if (bytes(base).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(base, _tokenURI));
        }
        // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
        return string(abi.encodePacked(base, tokenId));
    }
}