OPNXSWAP

What we built

OPN Mini Swap is a minimal Uniswap V2-style AMM DEX deployed on the IOPn Testnet (chainId 984), with a built-in faucet so reviewers can claim test tokens and run a full swap end-to-end without needing pre-existing balances.

6 contracts deployed, all pragma solidity =0.8.20, zero external dependencies:

• OPNSwapFactory — creates and indexes liquidity pairs via deterministic CREATE2 (pair addresses are predictable, immune to front-running).
• OPNSwapRouter — the entry point for swaps and liquidity. Every state-changing call enforces an on-chain deadline plus an explicit amountOutMin/amountInMax slippage check — real guarantees, not just UI hints. User tokens flow straight to the Pair via transferFrom; they never sit in the Router's balance.
• WOPN — Wrapped OPN, a WETH9-style wrapper for the native token, checks-effects-interactions on withdraw.
• TestToken — minimal ERC-20, deployed twice (TKA / TKB) to form the tradeable pair.
• Faucet — 10 TKA per wallet, 24h cooldown. No mint power: it only redistributes a balance the owner funds manually, so a worst-case compromise leaks at most its own reserve.

Two supporting files complete the system: OPNSwapPair (the AMM pool — constant-product invariant, LP mint/burn) and OPNSwapERC20 (base ERC-20 the Pair inherits to issue LP tokens).

Why this design

OPN Chain is fully EVM-compatible, so instead of trusting an undocumented third-party router, every contract here is deployed from scratch on the audited Uniswap V2 pattern — Factory + Pair + Router, 0.3% fee, reentrancy-safe by construction. No OpenZeppelin, no proxies, no upgradeability: access control, the ERC-20 standard, and the fixed-point math are all hand-written, keeping the whole system small enough to read end-to-end in one sitting.

Testnet only. Tokens carry no real value; contracts are unaudited — do not deploy to mainnet or use with real funds.