UniversalRouter

The UniversalRouter is a single entry-point contract that routes swaps across all three protocol versions (V2.5, V3, and V4) using a command-based execution model. Instead of calling version-specific routers directly, callers encode a sequence of commands and their ABI-encoded inputs, then dispatch everything in one execute() call.

Deployment (Arc Testnet)

Execute Interface

All interactions go through a single payable function:

function execute(
  bytes  calldata commands,   // packed command bytes, one byte per command
  bytes[] calldata inputs,    // ABI-encoded args for each command
  uint256 deadline            // unix timestamp after which the call reverts
) external payable

Each byte in commands maps to one entry in inputs. Commands are executed sequentially in the order they appear.

Command Reference

V4 Inner Actions

The V4_SWAP command takes a nested actions bytes payload that encodes V4-specific operations from v4-periphery Actions.sol:

Init Code Hashes

The UniversalRouter uses init code hashes to compute pool addresses without an on-chain lookup. The values for Arc Testnet are:

Usage Example: V3 Exact-Input Swap

import { encodePacked, encodeAbiParameters, parseUnits } from 'viem'

// Command: V3_SWAP_EXACT_IN (0x00)
const commands = '0x00'

// Encode the path: tokenIn -> fee -> tokenOut
const path = encodePacked(
  ['address', 'uint24', 'address'],
  [tokenInAddress, 3000, tokenOutAddress]  // 0.30% fee tier
)

// Encode the swap input params
const input = encodeAbiParameters(
  [
    { type: 'address' },   // recipient
    { type: 'uint256' },   // amountIn
    { type: 'uint256' },   // amountOutMinimum
    { type: 'bytes' },     // path
    { type: 'bool' },      // payerIsUser (true = pull from msg.sender via Permit2)
  ],
  [recipientAddress, parseUnits('1', 6), parseUnits('0.99', 6), path, true]
)

await walletClient.writeContract({
  address: '0xC43cC6A1E0F6EB48Cd4131522C1C73B13f3Da0F1',
  abi: UNIVERSAL_ROUTER_ABI,
  functionName: 'execute',
  args: [commands, [input], BigInt(Math.floor(Date.now() / 1000) + 300)],
})

Usage Example: V4 Exact-Input Single Swap

// Command: V4_SWAP (0x10)
const commands = '0x10'

// Inner V4 actions: SWAP_EXACT_IN_SINGLE (0x06) + SETTLE_ALL (0x0c) + TAKE_ALL (0x0f)
const v4Actions = encodePacked(
  ['uint8', 'uint8', 'uint8'],
  [0x06, 0x0c, 0x0f]
)

const swapParams = encodeAbiParameters(
  [{
    type: 'tuple',
    components: [
      { name: 'poolKey', type: 'tuple', components: [
        { name: 'currency0', type: 'address' },
        { name: 'currency1', type: 'address' },
        { name: 'fee', type: 'uint24' },
        { name: 'tickSpacing', type: 'int24' },
        { name: 'hooks', type: 'address' },
      ]},
      { name: 'zeroForOne', type: 'bool' },
      { name: 'amountIn', type: 'uint128' },
      { name: 'sqrtPriceLimitX96', type: 'uint160' },
      { name: 'hookData', type: 'bytes' },
    ],
  }],
  [{ poolKey, zeroForOne: true, amountIn: parseUnits('1', 6), sqrtPriceLimitX96: 0n, hookData: '0x' }]
)

const settleParams = encodeAbiParameters(
  [{ type: 'address' }, { type: 'uint256' }],
  [currency0Address, parseUnits('1', 6)]
)

const takeParams = encodeAbiParameters(
  [{ type: 'address' }, { type: 'uint256' }],
  [currency1Address, 0n]  // 0 = take all
)

const v4Input = encodeAbiParameters(
  [{ type: 'bytes' }, { type: 'bytes[]' }],
  [v4Actions, [swapParams, settleParams, takeParams]]
)

await walletClient.writeContract({
  address: '0xC43cC6A1E0F6EB48Cd4131522C1C73B13f3Da0F1',
  abi: UNIVERSAL_ROUTER_ABI,
  functionName: 'execute',
  args: [commands, [v4Input], BigInt(Math.floor(Date.now() / 1000) + 300)],
})

Source Reference

The UniversalRouter configuration lives in src/config/universalRouter.ts in the DEX repository. It exports:

• UNIVERSAL_ROUTER_ADDRESS - contract address (overridable via NEXT_PUBLIC_UNIVERSAL_ROUTER_ADDRESS)
• PERMIT2_ADDRESS - shared Permit2 address
• UR_COMMANDS - command byte constants
• V4_ACTIONS - V4 inner action byte constants
• UNIVERSAL_ROUTER_ABI - minimal ABI for the execute function
• V3_POOL_INIT_CODE_HASH - V3 pool init code hash for Arc Testnet