feat(Python): Add ExitFee hook.

python/src/hooks/exit_fee_hook.py

@@ -0,0 +1,89 @@
+from src.remove_liquidity import RemoveKind
+from src.maths import mul_down_fixed
+
+
+# This hook implements the ExitFeeHookExample found in mono-repo: https://github.com/balancer/balancer-v3-monorepo/blob/c848c849cb44dc35f05d15858e4fba9f17e92d5e/pkg/pool-hooks/contracts/ExitFeeHookExample.sol
+class ExitFeeHook:
+    def __init__(self):
+        self.should_call_compute_dynamic_swap_fee = False
+        self.should_call_before_swap = False
+        self.should_call_after_swap = False
+        self.should_call_before_add_liquidity = False
+        self.should_call_after_add_liquidity = False
+        self.should_call_before_remove_liquidity = False
+        self.should_call_after_remove_liquidity = True
+        self.enable_hook_adjusted_amounts = True
+
+    def on_before_add_liquidity(self):
+        return {"success": False, "hook_adjusted_balances_scaled18": []}
+
+    def on_after_add_liquidity(
+        self,
+    ):
+        return {"success": False, "hook_adjusted_amounts_in_raw": []}
+
+    def on_before_remove_liquidity(self):
+        return {"success": False, "hook_adjusted_balances_scaled18": []}
+
+    def on_after_remove_liquidity(
+        self,
+        kind,
+        _bpt_amount_in,
+        _amounts_out_scaled18,
+        amounts_out_raw,
+        _balances_scaled18,
+        hook_state,
+    ):
+        if not (
+            isinstance(hook_state, dict)
+            and hook_state is not None
+            and "removeLiquidityHookFeePercentage" in hook_state
+            and "tokens" in hook_state
+        ):
+            raise ValueError("Unexpected hookState")
+
+        # // Our current architecture only supports fees on tokens. Since we must always respect exact `amountsOut`, and
+        # // non-proportional remove liquidity operations would require taking fees in BPT, we only support proportional
+        # // removeLiquidity.
+        if kind != RemoveKind.PROPORTIONAL.value:
+            raise ValueError("ExitFeeHook: Unsupported RemoveKind: ", kind)
+
+        accrued_fees = [0] * len(hook_state["tokens"])
+        hook_adjusted_amounts_out_raw = amounts_out_raw[:]
+        if hook_state["removeLiquidityHookFeePercentage"] > 0:
+            # Charge fees proportional to amounts out of each token
+
+            for i in range(len(amounts_out_raw)):
+                hook_fee = mul_down_fixed(
+                    amounts_out_raw[i],
+                    hook_state["removeLiquidityHookFeePercentage"],
+                )
+                accrued_fees[i] = hook_fee
+                hook_adjusted_amounts_out_raw[i] -= hook_fee
+                # Fees don't need to be transferred to the hook, because donation will reinsert them in the vault
+
+            # // In SC Hook Donates accrued fees back to LPs
+            # // _vault.addLiquidity(
+            # //     AddLiquidityParams({
+            # //         pool: pool,
+            # //         to: msg.sender, // It would mint BPTs to router, but it's a donation so no BPT is minted
+            # //         maxAmountsIn: accruedFees, // Donate all accrued fees back to the pool (i.e. to the LPs)
+            # //         minBptAmountOut: 0, // Donation does not return BPTs, any number above 0 will revert
+            # //         kind: AddLiquidityKind.DONATION,
+            # //         userData: bytes(''), // User data is not used by donation, so we can set to an empty string
+            # //     }),
+            # // );
+
+        return {
+            "success": True,
+            "hook_adjusted_amounts_out_raw": hook_adjusted_amounts_out_raw,
+        }
+
+    def on_before_swap(self):
+        return {"success": False, "hook_adjusted_balances_scaled18": []}
+
+    def on_after_swap(self):
+        return {"success": False, "hook_adjusted_amount_calculated_raw": 0}
+
+    def on_compute_dynamic_swap_fee(self):
+        return {"success": False, "dynamic_swap_fee": 0}

python/src/vault.py

@@ -1,3 +1,4 @@
+from src.hooks.exit_fee_hook import ExitFeeHook
 from .swap import swap
 from .add_liquidity import add_liquidity
 from .remove_liquidity import remove_liquidity
@@ -6,17 +7,16 @@
 from .pools.stable import Stable
 from .hooks.default_hook import DefaultHook
 
-
 class Vault:
     def __init__(self, *, custom_pool_classes=None, custom_hook_classes=None):
         self.pool_classes = {
             "Weighted": Weighted,
             "Stable": Stable,
         }
+        self.hook_classes = {"ExitFee": ExitFeeHook}
         if custom_pool_classes is not None:
             self.pool_classes.update(custom_pool_classes)
 
-        self.hook_classes = {}
         if custom_hook_classes is not None:
             self.hook_classes.update(custom_hook_classes)
 

python/test/hooks/exit_fee.py

@@ -0,0 +1,83 @@
+import pytest
+import sys
+import os
+
+# Get the directory of the current file
+current_file_dir = os.path.dirname(os.path.abspath(__file__))
+# Get the parent directory (one level up)
+parent_dir = os.path.dirname(os.path.dirname(current_file_dir))
+
+# Insert the parent directory at the start of sys.path
+sys.path.insert(0, parent_dir)
+
+from src.pools.weighted import Weighted
+from src.remove_liquidity import RemoveKind
+
+# Get the directory of the current file
+current_file_dir = os.path.dirname(os.path.abspath(__file__))
+# Get the parent directory (one level up)
+parent_dir = os.path.dirname(os.path.dirname(current_file_dir))
+
+# Insert the parent directory at the start of sys.path
+sys.path.insert(0, parent_dir)
+
+from src.vault import Vault
+
+remove_liquidity_input = {
+    "pool": '0x03722034317d8fb16845213bd3ce15439f9ce136',
+    "min_amounts_out_raw": [1, 1],
+    "max_bpt_amount_in_raw": 10000000000000,
+    "kind": RemoveKind.PROPORTIONAL.value,
+}
+
+pool = {
+    "poolType": "Weighted",
+    "hookType": "ExitFee",
+    "chainId": "11155111",
+    "blockNumber": "5955145",
+    "poolAddress": "0x03722034317d8fb16845213bd3ce15439f9ce136",
+    "tokens": [
+        "0x7b79995e5f793A07Bc00c21412e50Ecae098E7f9",
+        "0xb19382073c7A0aDdbb56Ac6AF1808Fa49e377B75",
+    ],
+    "scalingFactors": [1000000000000000000, 1000000000000000000],
+    "weights": [500000000000000000, 500000000000000000],
+    "swapFee": 100000000000000000,
+    "balancesLiveScaled18": [5000000000000000, 5000000000000000000],
+    "tokenRates": [1000000000000000000, 1000000000000000000],
+    "totalSupply": 158113883008415798,
+    "aggregateSwapFee": 0,
+}
+
+vault = Vault()
+
+def test_hook_exit_fee_no_fee():
+    input_hook_state = {
+            'removeLiquidityHookFeePercentage': 0,
+            'tokens': pool['tokens'],
+        }
+    test = vault.remove_liquidity(
+        remove_liquidity_input,
+        pool,
+        hook_state=input_hook_state
+    )
+    assert test["amounts_out_raw"] == [
+            316227766016,
+            316227766016840
+        ]
+
+def test_hook_exit_fee_with_fee():
+    # 5% fee
+    input_hook_state = {
+            'removeLiquidityHookFeePercentage': 50000000000000000,
+            'tokens': pool['tokens'],
+        }
+    test = vault.remove_liquidity(
+        remove_liquidity_input,
+        pool,
+        hook_state=input_hook_state
+    )
+    assert test["amounts_out_raw"] == [
+            300416377716,
+            300416377715998
+        ]

typescript/test/hooks/beforeRemoveLiquidity.test.ts

@@ -47,7 +47,7 @@ describe('hook - afterRemoveLiquidity', () => {
         },
     });
 
-    test('aggregateSwapFee of 50% should take half of remaining', () => {
+    test('should alter pool balances', () => {
         /*
             hook state is used to pass new balances which give expected result
         */