Astroport Constant Product Pair with Sale Tax

The constant product pool uses the widely known xy=k formula. More details around how the pool functions can be found here.

This is a modified version of the standard Astroport XYK pair which adds a configurable sale tax. The tax can be added on each of the assets in the pair and is taken on the offered asset before calculating the return amount.

Liquidity Providers

A user can provide liquidity to a constant product pool by calling provide_liquidity. Users can also withdraw liquidity by calling withdraw_liquidity.

Whenever liquidity is deposited into a pool, special tokens known as "liquidity tokens" are minted to the provider’s address, in proportion to how much liquidity they contributed to the pool. These tokens are a representation of a liquidity provider’s contribution to a pool. Whenever a trade occurs, the lp_commission is distributed pro-rata to all LPs in the pool at the moment of the trade. To receive the underlying liquidity back plus accrued LP fees, LPs must burn their liquidity tokens.

When providing liquidity from a smart contract, the most important thing to keep in mind is that the amount of tokens deposited into a pool and the amount of tokens withdrawn later from the pool will most likely not be the same. This is because of the way constant product pools work where, as the token prices in the pool change, so do the respective token amounts that a LP can withdraw.

As an example, let's say the global ratio between two tokens x:y is 10:2 (i.e. 1 x = 0.2 y), but the current ratio between the tokens in an Astroport pair is 5:2 (1 x = 0.4 y). Let's also say that someone may decide to LP in the x:y Astroport pool at the current 5:2 ratio. As the Astroport pool gets arbitraged to the global ratio, the amount of x & y tokens that the LP can withdraw changes because the total amounts of x & y tokens in the pool also change.

Note that before executing the provide_liqudity operation, a user must allow the pool contract to take tokens from their wallet

Slippage Tolerance for Providing Liquidity

If a user specifies a slippage tolerance when they provide liquidity in a constant product pool, the pool contract makes sure that the transaction goes through only if the pool price does not change more than tolerance.

As an example, let's say someone LPs in a pool and specifies a 1% slippage tolerance. The user LPs 200 UST and 1 ASSET. With a 1% slippage tolerance, amountUSTMin (the minimum amount of UST to LP) should be set to 198 UST, and amountASSETMin (the minimum amount of ASSET to LP) should be set to .99 ASSET. This means that, in a worst case scenario, liquidity will be added at a pool rate of 198 ASSET/1 UST or 202.02 UST/1 ASSET (200 UST + .99 ASSET). If the contract cannot add liquidity within these bounds (because the pool ratio changed more than the tolerance), the transaction will revert.

Traders

Slippage Tolerance for Swaps

Astroport has two options to protect traders against slippage during swaps:

1. Providing max_spread The spread is calculated as the difference between the ask amount (using the constant pool price) before and after the swap operation. Once max_spread is set, it will be compared against the actual swap spread. In case the swap spread exceeds the provided max limit, the swap will fail.

Note that the spread is calculated before commission deduction in order to properly represent the pool's ratio change.

2. Providing max_spread + belief_price If belief_price is provided in combination with max_spread, the pool will check the difference between the return amount (using belief_price) and the real pool price.

Please note that Astroport has the default value for the spread set to 0.5% and the max allowed spread set to 50%.

InstantiateMsg

Initializes a new x*y=k pair.

{
  "token_code_id": 123,
  "factory_addr": "terra...",
  "asset_infos": [
    {
      "token": {
        "contract_addr": "terra..."
      }
    },
    {
      "native_token": {
        "denom": "uusd"
      }
    }
  ],
  "init_params": "<base64_encoded_json_string: optional binary serialised parameters for custom pool types>"
}

ExecuteMsg

receive

Withdraws liquidity or assets that were swapped to (ask assets in a swap operation).

{
  "receive": {
    "sender": "terra...",
    "amount": "123",
    "msg": "<base64_encoded_json_string>"
  }
}

provide_liquidity

Provides liquidity by sending a user's native or token assets to the pool.

NOTE: you should increase your token allowance for the pool before providing liquidity!

1. Providing Liquidity Without Specifying Slippage Tolerance

{
  "provide_liquidity": {
    "assets": [
      {
        "info": {
          "token": {
            "contract_addr": "terra..."
          }
        },
        "amount": "1000000"
      },
      {
        "info": {
          "native_token": {
            "denom": "uusd"
          }
        },
        "amount": "1000000"
      }
    ],
    "auto_stake": false,
    "receiver": "terra..."
  }
}

2. Providing Liquidity With Slippage Tolerance

{
  "provide_liquidity": {
    "assets": [
      {
        "info": {
          "token": {
            "contract_addr": "terra..."
          }
        },
        "amount": "1000000"
      },
      {
        "info": {
          "native_token": {
            "denom": "uusd"
          }
        },
        "amount": "1000000"
      }
    ],
    "slippage_tolerance": "0.01",
    "auto_stake": false,
    "receiver": "terra..."
  }
}

withdraw_liquidity

Burn LP tokens and withdraw liquidity from a pool. This call must be sent to a LP token contract associated with the pool from which you want to withdraw liquidity from.

{
  "withdraw_liquidity": {}
}

swap

Perform a swap. offer_asset is your source asset and to is the address that will receive the ask assets. All fields are optional except offer_asset.

NOTE: You should increase token allowance before swap.

{
  "swap": {
    "offer_asset": {
      "info": {
        "native_token": {
          "denom": "uluna"
        }
      },
      "amount": "123"
    },
    "belief_price": "123",
    "max_spread": "123",
    "to": "terra..."
  }
}

update_config

The contract configuration cannot be updated.

{
  "update_config": {
    "params": "<base64_encoded_json_string>"
  }
}

QueryMsg

All query messages are described below. A custom struct is defined for each query response.

pair

Retrieve a pair's configuration (type, assets traded in it etc)

{
  "pair": {}
}

pool

Returns the amount of tokens in the pool for all assets as well as the amount of LP tokens issued.

{
  "pool": {}
}

config

Get the pair contract configuration.

{
  "config": {}
}

share

Return the amount of assets someone would get from the pool if they were to burn a specific amount of LP tokens.

{
  "share": {
    "amount": "123"
  }
}

simulation

Simulates a swap and returns the spread and commission amounts.

{
  "simulation": {
    "offer_asset": {
      "info": {
        "native_token": {
          "denom": "uusd"
        }
      },
      "amount": "1000000"
    }
  }
}

reverse_simulation

Reverse simulates a swap (specifies the ask instead of the offer) and returns the offer amount, spread and commission.

{
  "reverse_simulation": {
    "ask_asset": {
      "info": {
        "token": {
          "contract_addr": "terra..."
        }
      },
      "amount": "1000000"
    }
  }
}

cumulative_prices

Returns the cumulative prices for the assets in the pair.

{
  "cumulative_prices": {}
}

asset_balance_at

Returns the balance of the specified asset that was in the pool just preceeding the moment of the specified block height creation. It will return None (null) if the balance was not tracked up to the specified block height.

{
  "asset_balance_at": {
    "asset_info": {
      "native_token": {
        "denom": "stake"
      }
    },
    "block_height": "12345678"
  }
}