Uniswap V2 (uniswap-v2)

In a Sauce program, swap with @sauce/router’s function for the venue (uniswapV2, uniswapV3, uniswapV4, curve, balancerV2, …; Slipstream, PancakeSwap V3 and Algebra pools through uniswapV3), with a minimum output and, where the pool takes one, a price limit (the @sauce/router reference; several pools under one limit, the distributed swap).

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When to use it

• Constant-product pairs, one per token pair, with a 0.3% fee. Simple and everywhere, but with more price impact than a V3 pool for the same trade.
• The pair fills in full or reverts, so its Router, with an exact approval and amountOutMin, strands nothing. A Sauce program trades the pair itself with @sauce/router’s uniswapV2, with no Router and no approval.

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Pitfalls for a program

• amountOutMin is the only bound: there is no price limit.
• Through the Router, approve it for exactly amountIn, and give a deadline (ctx.timestamp() is this block). uniswapV2 needs neither: it pushes the input to the pair.
• A fee-on-transfer token needs the ...SupportingFeeOnTransferTokens variants, which the registry ABI does not declare.
• The pair must exist: Factory.getPair returns 0 where it does not.

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In a Sauce program

import { uniswapV2 } from "@sauce/router";

function main(amountIn: Uint256, minOut: Uint256, recipient: Address) {
  const pair = UniswapV2.Factory.getPair(USDC, WETH);
  require(pair != 0, "no USDC/WETH pair");
  uniswapV2(pair, USDC, WETH, amountIn, 3000, minOut, recipient);
}

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What it offers

• swap: Swap an exact amount of input tokens for as many output tokens as possible, routed through a path of pairs
• addLiquidity: Deposit two tokens into a pair to mint LP tokens proportional to pool share
• removeLiquidity: Burn LP tokens to withdraw both underlying tokens from a pair

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Notes

• Path array defines the swap route: [tokenIn, tokenOut] for direct swaps, [tokenIn, WETH, tokenOut] for multi-hop through WETH
• 0.3% fee per hop, taken from input amount before swap
• Both tokens must be ERC20-approved to the Router before addLiquidity/swap
• LP tokens must be ERC20-approved to the Router before removeLiquidity
• For tokens with transfer taxes (fee-on-transfer), use swapExactTokensForTokensSupportingFeeOnTransferTokens instead (not in SDK but available on-chain)
• Prefer V3 for better capital efficiency, but V2 for maximum compatibility and simplicity
• On Arc (5042) the router’s WETH() is a stub that always reverts with UnsupportedProtocolError(), so the ETH paths (swapExactETHForTokens, addLiquidityETH, …) revert. Trade USDC’s ERC-20 0x3600000000000000000000000000000000000000; Arc’s native coin is USDC and it has no canonical wrapped native
• From a Pot program, @sauce/router trades a Uniswap V2 pair directly, with no router and no approval: uniswapV2(pair, tokenIn, tokenOut, amountIn, 3000, minOut, recipient) reads the pair’s getReserves, prices the output in the program with the pair’s fee in parts per million, transfers the input to the pair and calls pair.swap with empty data, returning the amount out. The direction is the sort order of tokenIn and tokenOut (token0 is the lower address), so there is no argument to get wrong. The swap consumes its whole input or reverts; there is no refund path. tryUniswapV2 takes the same arguments and returns 0, moving nothing, when the pair cannot fill the whole input at the floor. The uniswapV2Swap action is the same call

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Its names in a program

function main() {
  // Ethereum's factory, `0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f`.
  require(UniswapV2.Factory != 0);
}

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Deployments

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ABI

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UniswapV2FactoryABI

• getPair(address tokenA, address tokenB) view returns (address pair): the address is a UniswapV2.Pair
• createPair(address tokenA, address tokenB) returns (address pair)

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UniswapV2PairABI

• getReserves() view returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast)
• token0() view returns (address): the address is a token
• token1() view returns (address): the address is a token
• swap(uint256 amount0Out, uint256 amount1Out, address to, bytes data)

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UniswapV2RouterABI

• swapExactTokensForTokens(uint256 amountIn, uint256 amountOutMin, address[] path, address to, uint256 deadline) returns (uint256[] amounts)
• swapTokensForExactTokens(uint256 amountOut, uint256 amountInMax, address[] path, address to, uint256 deadline) returns (uint256[] amounts)
• addLiquidity(address tokenA, address tokenB, uint256 amountADesired, uint256 amountBDesired, uint256 amountAMin, uint256 amountBMin, address to, uint256 deadline) returns (uint256 amountA, uint256 amountB, uint256 liquidity)
• removeLiquidity(address tokenA, address tokenB, uint256 liquidity, uint256 amountAMin, uint256 amountBMin, address to, uint256 deadline) returns (uint256 amountA, uint256 amountB)
• getAmountsOut(uint256 amountIn, address[] path) view returns (uint256[] amounts)

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Next steps

• Protocols: the other protocols, by what they do.
• Protocols and tokens: calling a contract by its namespace, or through its ABI.
• Glossary: the words these pages use, in plain terms.