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LANDCHAIN

This repository contains smart contracts for an advanced NFT-based land ownership and rental system with an integrated marketplace. The system allows for tokenization of land ownership, facilitates various trading mechanisms, and supports temporary transfers of usage rights.

Contracts

1. IERC4907

Purpose: This interface extends the ERC721 standard to include user and expires functionality, enabling time-limited permissions on NFTs. It's crucial for implementing rental or time-limited usage features for NFTs.

Key Functions:

  • setUser(uint256 tokenId, address user, uint64 expires): Assigns user rights to an address for a specific NFT with an expiration time.
  • userOf(uint256 tokenId): Retrieves the current user of an NFT.
  • userExpires(uint256 tokenId): Returns the expiration timestamp of the current user's rights.

Events:

  • UpdateUser(uint256 indexed tokenId, address indexed user, uint64 expires): Emitted when user rights are updated.

2. LandChain 0x4d6D7E6E807452Fb07780C2B443fdc310dC0842A

Purpose: This is the core NFT contract representing land ownership as non-fungible tokens. It implements ERC721 and IERC4907 standards, allowing for ownership and time-limited usage rights.

Key Features:

  • ERC721 Compatibility: Implements standard NFT functions like transfer, approve, etc.
  • Minting: Allows creation of new land NFTs with associated metadata.
  • User Rights Management: Implements IERC4907 for managing temporary usage rights.
  • Supply Control: Includes a maximum supply limit and tracking of total supply.
  • Metadata Management: Uses ERC721URIStorage for flexible metadata handling.

Key Functions:

  • mint(string calldata MtokenURI): Mints a new land NFT with specified metadata.
  • setUser(uint256 tokenId, address user, uint64 expires): Sets temporary user rights for an NFT.
  • userOf(uint256 tokenId): Returns the current user of an NFT.
  • userExpires(uint256 tokenId): Returns the expiration time of user rights.
  • setMaxSupply(uint256 maxSupply_): Allows owner to adjust the maximum supply.

Security Measures:

  • Access Control: Uses OpenZeppelin's Ownable for restricted functions.
  • Checks: Implements various require statements to ensure valid operations.

3. Marketplace 0x3C4d70269737D5D930D2BE6bcBA7A4D8Ea574370

Purpose: This contract provides a comprehensive platform for trading and renting LandChain NFTs through various mechanisms including auctions, direct sales, and rentals.

Key Features:

  1. Auctions

    • Creation: Sellers can create time-limited auctions for their NFTs.
    • Bidding: Users can place bids on active auctions.
    • Automatic Extension: Auctions are extended if a bid is placed near the end time.
    • Settlement: Auctions can be settled after the end time, transferring the NFT and funds.

  2. Direct Sales

    • Listing: Sellers can list their NFTs for a fixed price.
    • Purchasing: Buyers can directly purchase listed NFTs.
    • Cancellation: Sellers can cancel their listings.

  3. Rentals

    • Listing: NFT owners can list their tokens for rent with a price and duration.
    • Renting: Users can rent NFTs, gaining temporary usage rights.
    • Cancellation: Owners can cancel their rental listings.

  4. Financial Management

    • Platform Fees: Implements a percentage-based fee on all transactions.
    • Withdrawals: Users can withdraw funds from outbid or cancelled transactions.
    • Owner Withdrawals: Contract owner can withdraw accumulated platform fees.

Key Functions:

  • Auction Functions: createAuction, placeBid, endAuction
  • Direct Sale Functions: createDirectSale, buyDirectSale, cancelDirectSale
  • Rental Functions: createRentSale, rentNFT, cancelRentSale
  • Financial Functions: withdraw, withdrawPlatformFees
  • Management Functions: setNftContract, setPlatformFee, pause, unpause

Security Measures:

  • Reentrancy Guard: Uses OpenZeppelin's ReentrancyGuard to prevent reentrancy attacks.
  • Pausability: Implements Pausable for emergency stops.
  • Access Control: Utilizes Ownable for restricted functions.
  • Checks-Effects-Interactions Pattern: Follows best practices to prevent potential vulnerabilities.

System Workflow

  1. NFT Creation: Users mint land NFTs using the LandChain contract.
  2. Marketplace Interaction: NFT owners can list their tokens on the Marketplace contract.
  3. Trading Options:
    • Sellers can create auctions, direct sales, or rental listings.
    • Buyers can bid on auctions, purchase directly, or rent NFTs.
  4. Transaction Settlement: The marketplace handles transfers of NFTs and funds, including fee calculations.
  5. Rental Management: For rented NFTs, the system manages temporary user rights and expirations.

Security Considerations

  • The contracts inherit from OpenZeppelin's audited contracts for enhanced security.
  • Reentrancy guards are implemented to prevent common attack vectors.
  • The system uses a checks-effects-interactions pattern to ensure state consistency.
  • Pausability allows for emergency stops in case of detected issues.
  • Access control mechanisms restrict sensitive functions to authorized users only.

Deployment and Integration

When deploying these contracts:

  1. Deploy the LandChain contract first.
  2. Deploy the Marketplace contract, passing the address of the LandChain contract.
  3. Call setApprovalForAll on the LandChain contract to approve the Marketplace for trading.

Future Improvements

  • Implementation of API of UK Real Estate System for verification of the owner of the property
  • Integration with real-world land registry systems for increased utility.
  • Addition of fractional ownership capabilities for land NFTs.

This system provides a robust, secure, and flexible solution for tokenizing land ownership, facilitating various trading mechanisms, and managing temporary usage rights, all secured on the blockchain.