Smart Contract
The TUSDT protocol is a collateralized debt position (CDP) system built on ink! smart contracts. It allows users to lock native token collateral in vaults, borrow a synthetic stablecoin (TUSDT), and participate in liquidation auctions when vaults become undercollateralized. The system is composed of three interdependent contracts deployed together: TusdtVault, TusdtAuction, and TusdtErc20.
Contract Architecture
The three contracts have a strict ownership hierarchy. TusdtVault is the entry point for end users and is the owner of both TusdtErc20 and TusdtAuction. Neither the token nor the auction contract should be called directly by external integrators for write operations — all state-changing flows are orchestrated through the vault.
Figure : Contract Architecture
TusdtVault instantiates both child contracts at construction time using their code hashes and retains references to their on-chain addresses. Their addresses can be retrieved at any time via get_token_address() and get_auction_address().
TusdtVault
The core contract. Handles everything related to creating vaults, borrowing, repaying, and liquidations.
Key Parameters
Parameter
Default
Description
Collateral Ratio
150%
Minimum collateral required to borrow
Liquidation Ratio
120%
Threshold where vault can be liquidated
Interest Rate
10% p.a
Compounded hourly
Liquidation Fee
upto 11%
Extra collateral added when liquidating
Auction Duration
15 Minute
How long liquidation auctions run
Key Functions
Function
Description
create_vault()
Opens a new vault with attached native tokens as collateral
add_collateral(vault_id)
Tops up collateral in an existing vault
borrow_token(vault_id, amount)
Mints TUSDT to the caller against their collateral
repay_token(vault_id, amount)
Burns TUSDT from the caller to reduce vault debt
release_collateral(vault_id, amount)
Withdraws collateral back to the caller
trigger_liquidation_auction(owner, vault_id)
Starts a liquidation auction on an unsafe vault
settle_liquidation_auction(owner, vault_id)
Completes a finalized auction and clears vault debt
get_vault(owner, vault_id)
Returns full vault state
get_max_borrow(owner, vault_id)
Returns how much TUSDT can still be borrowed
set_contract_params(params)
Owner only — updates protocol parameter
TusdtErc20
Standard token contract for TUSDT. Mint and burn are restricted to the Vault contract. Users interact with it for transfers and approvals.
Key Functions
Function
Description
transfer(to, value)
Sends TUSDT to another account
approve(spender, value)
Approves another contract or account to spend TUSDT
transfer_from(from, to, value)
Transfers on behalf of another account using allowance
balance_of(owner)
Returns TUSDT balance of an account
mint(to, value)
Owner only — creates new TUSDT tokens
burn(from, value)
Owner only — destroys TUSDT tokens
TusdtAuction
Manages liquidation auctions. Created and settled by the Vault. Bidders interact with it directly to place bids and withdraw refunds.
Key Functions
Function
Description
place_bid(auction_id, amount, metadata)
Places or increases a bid using TUSDT
finalize_auction(auction_id)
Closes an expired auction and records the winner
withdraw_refund(auction_id, bid_id)
Returns TUSDT to losing bidders after finalization
get_active_auctions(page)
Lists all currently running auctions
get_auction(auction_id)
Returns full details of a specific auction
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