fix(CA): proper bridging fee calculation (#921)

Author: geekbrother

integration/chain_orchestrator.test.ts

@@ -33,8 +33,6 @@ describe('Chain abstraction orchestrator', () => {
 
   // Amount to send to Optimism
   const amount_to_send = 3_000_000
-  // Amount bridging slippage
-  const amount_slippage = 2; // +2% topup
 
   let usdc_contracts = {};
   usdc_contracts[chain_id_optimism] = "0x0b2c639c533813f4aa9d7837caf62653d097ff85";
@@ -133,7 +131,6 @@ describe('Chain abstraction orchestrator', () => {
 
     // How much needs to be topped up
     const amount_to_topup = Math.round(amount_to_send - usdc_funds[chain_id_optimism]);
-    const amount_to_topup_with_fees = Math.round(((amount_to_topup * amount_slippage) / 100) + amount_to_topup);
 
     const data_encoded = erc20Interface.encodeFunctionData('transfer', [
       receiver_address,
@@ -167,7 +164,7 @@ describe('Chain abstraction orchestrator', () => {
     expect(approvalTransaction.nonce).not.toBe("0x00")
     expect(() => BigInt(approvalTransaction.gasLimit)).not.toThrow();
     const decodedData = erc20Interface.decodeFunctionData('approve', approvalTransaction.input);
-    if (decodedData.amount < BigInt(amount_to_topup_with_fees)) {
+    if (decodedData.amount <= BigInt(amount_to_topup)) {
       throw new Error(`Expected amount is lower then the minimal required`);
     }
 
@@ -188,10 +185,10 @@ describe('Chain abstraction orchestrator', () => {
     expect(fundingFrom.chainId).toBe(chain_id_base)
     expect(fundingFrom.symbol).toBe(usdc_token_symbol)
     expect(fundingFrom.tokenContract).toBe(usdc_contracts[chain_id_base].toLowerCase())
-    if (BigInt(fundingFrom.amount) <= BigInt(amount_to_topup_with_fees)) {
+    if (BigInt(fundingFrom.amount) <= BigInt(amount_to_topup)) {
       throw new Error(`Expected amount is lower then the minimal required`);
     }
-    if (BigInt(fundingFrom.bridgingFee) != BigInt(fundingFrom.amount - amount_to_topup)){
+    if (BigInt(fundingFrom.bridgingFee) < BigInt(fundingFrom.amount - amount_to_topup)){
       throw new Error(`Expected bridging fee is incorrect. `);
     }
     // Check the initialTransaction metadata
@@ -212,7 +209,6 @@ describe('Chain abstraction orchestrator', () => {
 
     // How much needs to be topped up
     const amount_to_topup = Math.round(amount_to_send - usdt_funds[chain_id_optimism]);
-    const amount_to_topup_with_fees = Math.round(((amount_to_topup * amount_slippage) / 100) + amount_to_topup);
 
     const data_encoded = erc20Interface.encodeFunctionData('transfer', [
       receiver_address,
@@ -246,7 +242,7 @@ describe('Chain abstraction orchestrator', () => {
     expect(approvalTransaction.nonce).not.toBe("0x00")
     expect(() => BigInt(approvalTransaction.gasLimit)).not.toThrow();
     const decodedData = erc20Interface.decodeFunctionData('approve', approvalTransaction.input);
-    if (decodedData.amount < BigInt(amount_to_topup_with_fees)) {
+    if (decodedData.amount <= BigInt(amount_to_topup)) {
       throw new Error(`Expected amount is lower then the minimal required`);
     }
 
@@ -267,10 +263,10 @@ describe('Chain abstraction orchestrator', () => {
     expect(fundingFrom.chainId).toBe(chain_id_arbitrum)
     expect(fundingFrom.symbol).toBe(usdt_token_symbol)
     expect(fundingFrom.tokenContract).toBe(usdt_contracts[chain_id_arbitrum].toLowerCase())
-    if (BigInt(fundingFrom.amount) <= BigInt(amount_to_topup_with_fees)) {
+    if (BigInt(fundingFrom.amount) <= BigInt(amount_to_topup)) {
       throw new Error(`Expected amount is lower then the minimal required`);
     }
-    if (BigInt(fundingFrom.bridgingFee) != BigInt(fundingFrom.amount - amount_to_topup)){
+    if (BigInt(fundingFrom.bridgingFee) < BigInt(fundingFrom.amount - amount_to_topup)){
       throw new Error(`Expected bridging fee is incorrect. `);
     }
     // Check the initialTransaction metadata

src/handlers/chain_agnostic/mod.rs

@@ -22,8 +22,8 @@ pub mod assets;
 pub mod route;
 pub mod status;
 
-/// How much to multiply the amount by when bridging to cover bridging differences
-pub const BRIDGING_AMOUNT_SLIPPAGE: i8 = 50; // 50%
+/// How much to multiply the bridging fee amount to cover bridging fee volatility
+pub const BRIDGING_FEE_SLIPPAGE: i8 = 50; // 50%
 
 /// Bridging timeout in seconds
 pub const BRIDGING_TIMEOUT: u64 = 1800; // 30 minutes

src/handlers/chain_agnostic/route.rs

@@ -2,7 +2,7 @@ use {
     super::{
         super::HANDLER_TASK_METRICS, check_bridging_for_erc20_transfer,
         find_supported_bridging_asset, get_assets_changes_from_simulation, BridgingStatus,
-        StorageBridgingItem, BRIDGING_AMOUNT_SLIPPAGE, STATUS_POLLING_INTERVAL,
+        StorageBridgingItem, BRIDGING_FEE_SLIPPAGE, STATUS_POLLING_INTERVAL,
     },
     crate::{
         analytics::{
@@ -314,9 +314,10 @@ async fn handler_internal(
         U256::from_str(&bridging_amount).map_err(|_| RpcError::InvalidValue(bridging_amount))?;
     let bridging_fee = erc20_topup_value - bridging_amount;
 
-    // Calculate the required bridging topup amount with the bridging fee and slippage
+    // Calculate the required bridging topup amount with the bridging fee
+    // and bridging fee * slippage to cover volatility
     let required_topup_amount = erc20_topup_value + bridging_fee;
-    let required_topup_amount = ((required_topup_amount * U256::from(BRIDGING_AMOUNT_SLIPPAGE))
+    let required_topup_amount = ((bridging_fee * U256::from(BRIDGING_FEE_SLIPPAGE))
         / U256::from(100))
         + required_topup_amount;
     if current_bridging_asset_balance < required_topup_amount {
@@ -362,7 +363,7 @@ async fn handler_internal(
         );
         return Err(RpcError::BridgingFinalAmountLess);
     }
-    let final_bridging_fee = bridging_amount - erc20_topup_value;
+    let final_bridging_fee = bridging_amount - required_topup_amount;
 
     // Build bridging transaction
     let bridge_tx = state