Decrease liquidity

Source: https://docs.uniswap.org/contracts/v3/guides/providing-liquidity/decrease-liquidity

Make sure to go through the Setting Up Your Contract before continuing to this section

Here we decrease the liquidity of our position without withdrawing all of it.

This example assumes the contract already has possession of the position NFT, and requires the calling address to be the same address that deposited the position NFT to our contract.
In production, amount0Min and amount1Min should be adjusted to create slippage protections.

Decrease Liquidity


    /// @notice A function that decreases the current liquidity by half. An example to show how to call the `decreaseLiquidity` function defined in periphery.
    /// @param tokenId The id of the erc721 token
    /// @return amount0 The amount received back in token0
    /// @return amount1 The amount returned back in token1
    function decreaseLiquidityInHalf(uint256 tokenId) external returns (uint256 amount0, uint256 amount1) {
        // caller must be the owner of the NFT
        require(msg.sender == deposits[tokenId].owner, 'Not the owner');
        // get liquidity data for tokenId
        uint128 liquidity = deposits[tokenId].liquidity;
        uint128 halfLiquidity = liquidity / 2;
 
        // amount0Min and amount1Min are price slippage checks
        // if the amount received after burning is not greater than these minimums, transaction will fail
        INonfungiblePositionManager.DecreaseLiquidityParams memory params =
            INonfungiblePositionManager.DecreaseLiquidityParams({
                tokenId: tokenId,
                liquidity: halfLiquidity,
                amount0Min: 0,
                amount1Min: 0,
                deadline: block.timestamp
            });
 
        nonfungiblePositionManager.decreaseLiquidity(params);
 
        (amount0, amount1) = nonfungiblePositionManager.collect(
            INonfungiblePositionManager.CollectParams({
                tokenId: tokenId,
                recipient: address(this),
                amount0Max: type(uint128).max,
                amount1Max: type(uint128).max
            })
        );
 
        //send liquidity back to owner
        _sendToOwner(tokenId, amount0, amount1);
    }

Sending Fees To The Calling Address

This internal helper function sends any tokens, in the form of fees or position tokens, to the owner of an NFT.

In _sendToOwner, we pass the amount of fees due, previously populated in the last function, as arguments to safeTransfer, which transfers the fees to owner.


    /// @notice Transfers funds to owner of NFT
    /// @param tokenId The id of the erc721
    /// @param amount0 The amount of token0
    /// @param amount1 The amount of token1
    function _sendToOwner(
        uint256 tokenId,
        uint256 amount0,
        uint256 amount1
    ) internal {
        // get owner of contract
        address owner = deposits[tokenId].owner;
 
        address token0 = deposits[tokenId].token0;
        address token1 = deposits[tokenId].token1;
        // send collected fees to owner
        TransferHelper.safeTransfer(token0, owner, amount0);
        TransferHelper.safeTransfer(token1, owner, amount1);
    }