refunder: Make gas price parameters configurable (#3897)

## Problem

The refunder was experiencing issues with hardcoded gas price parameters
that were too low for current network conditions:

### Errors observed:
1. `Refunding txs are likely not mined in time, as the current gas price
826120518137.4663 is higher than MAX_GAS_PRICE specified 800000000000`
2. `transaction gas price below minimum: gas tip cap 5773015156, minimum
needed 25000000000`

### Root cause:
- `MAX_GAS_PRICE` was hardcoded to 800 Gwei (current gas prices ~826
Gwei)
- `START_PRIORITY_FEE_TIP` was hardcoded to 2 Gwei (node requires
minimum 25 Gwei)

## Solution

This PR makes both gas price parameters configurable via CLI arguments
or environment variables:

- `--max-gas-price` / `MAX_GAS_PRICE` (default: 2000 Gwei /
2,000,000,000,000 wei)
- `--start-priority-fee-tip` / `START_PRIORITY_FEE_TIP` (default: 30
Gwei / 30,000,000,000 wei)

The new defaults are set higher to accommodate current network
conditions while still being configurable for future adjustments.

## Changes

- Added two new CLI arguments with environment variable support
- Refactored `Submitter` and `RefundService` to accept configurable
parameters
- Updated tests to use test-specific constants
- Updated argument display formatting to show new parameters

## Testing

- [x] Code compiles successfully (`cargo check -p refunder`)
- [x] No linter errors
- [x] Unit tests updated and passing

---------

Co-authored-by: ilya <[email protected]>

Author: ahhda

crates/e2e/tests/e2e/refunder.rs

@@ -142,6 +142,8 @@ async fn refunder_tx(web3: Web3) {
         validity_duration as i64 / 2,
         10i64,
         refunder_signer,
+        2_000_000_000_000, // max_gas_price: 2000 Gwei
+        30_000_000_000,    // start_priority_fee_tip: 30 Gwei
     );
 
     assert_ne!(

crates/refunder/src/arguments.rs

@@ -66,6 +66,16 @@ pub struct Arguments {
     /// The port at which we serve our metrics
     #[clap(long, env, default_value = "9590")]
     pub metrics_port: u16,
+
+    /// Maximum gas price (in wei) for submitting refund transactions
+    /// Default is 2000 Gwei (2_000_000_000_000 wei)
+    #[clap(long, env, default_value = "2000000000000")]
+    pub max_gas_price: u64,
+
+    /// Starting priority fee tip (in wei) for refund transactions
+    /// Default is 30 Gwei (30_000_000_000 wei)
+    #[clap(long, env, default_value = "30000000000")]
+    pub start_priority_fee_tip: u64,
 }
 
 impl std::fmt::Display for Arguments {
@@ -82,6 +92,8 @@ impl std::fmt::Display for Arguments {
             logging,
             db_url,
             refunder_pk,
+            max_gas_price,
+            start_priority_fee_tip,
         } = self;
 
         write!(f, "{http_client}")?;
@@ -97,6 +109,8 @@ impl std::fmt::Display for Arguments {
         let _intentionally_ignored = refunder_pk;
         writeln!(f, "refunder_pk: SECRET")?;
         writeln!(f, "metrics_port: {metrics_port}")?;
+        writeln!(f, "max_gas_price: {max_gas_price}")?;
+        writeln!(f, "start_priority_fee_tip: {start_priority_fee_tip}")?;
         Ok(())
     }
 }

crates/refunder/src/lib.rs

@@ -81,6 +81,8 @@ pub async fn run(args: arguments::Arguments) {
         i64::try_from(args.min_validity_duration.as_secs()).unwrap_or(i64::MAX),
         args.min_price_deviation_bps,
         refunder_account,
+        args.max_gas_price,
+        args.start_priority_fee_tip,
     );
     loop {
         tracing::info!("Staring a new refunding loop");

crates/refunder/src/refund_service.rs

@@ -31,6 +31,8 @@ pub struct RefundService {
     pub min_validity_duration: i64,
     pub min_price_deviation: f64,
     pub submitter: Submitter,
+    pub max_gas_price: u64,
+    pub start_priority_fee_tip: u64,
 }
 
 #[derive(Debug, Eq, PartialEq)]
@@ -41,13 +43,16 @@ enum RefundStatus {
 }
 
 impl RefundService {
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         db: PgPool,
         web3: Web3,
         ethflow_contracts: Vec<CoWSwapEthFlow::Instance>,
         min_validity_duration: i64,
         min_price_deviation_bps: i64,
         signer: Box<dyn TxSigner<Signature> + Send + Sync + 'static>,
+        max_gas_price: u64,
+        start_priority_fee_tip: u64,
     ) -> Self {
         let signer_address = signer.address();
         let gas_estimator = Box::new(web3.legacy.clone());
@@ -58,12 +63,16 @@ impl RefundService {
             ethflow_contracts,
             min_validity_duration,
             min_price_deviation: min_price_deviation_bps as f64 / 10000f64,
+            max_gas_price,
+            start_priority_fee_tip,
             submitter: Submitter {
                 web3,
                 signer_address,
                 gas_estimator,
                 gas_parameters_of_last_tx: None,
                 nonce_of_last_submission: None,
+                max_gas_price,
+                start_priority_fee_tip,
             },
         }
     }

crates/refunder/src/submitter.rs

@@ -18,16 +18,11 @@ use {
     std::time::Duration,
 };
 
-// Max gas price used for submitting transactions
-const MAX_GAS_PRICE: u64 = 800_000_000_000;
-
 // The gas price buffer determines the gas price buffer used to
 // send out EIP1559 txs.
 // Example: If the prevailing gas is 10Gwei and the buffer factor is 1.20
 // then the gas_price used will be 12.
 const GAS_PRICE_BUFFER_FACTOR: f64 = 1.3;
-// Starting priority fee that the refunder is willing to pay. (=2 Gwei)
-const START_PRIORITY_FEE_TIP: u64 = 2_000_000_000;
 
 // In order to resubmit a new tx with the same nonce, the gas tip and
 // max_fee_per_gas needs to be increased by at least 10 percent.
@@ -44,6 +39,8 @@ pub struct Submitter {
     pub gas_estimator: Box<dyn GasPriceEstimating>,
     pub gas_parameters_of_last_tx: Option<GasPrice1559>,
     pub nonce_of_last_submission: Option<u64>,
+    pub max_gas_price: u64,
+    pub start_priority_fee_tip: u64,
 }
 
 impl Submitter {
@@ -77,6 +74,8 @@ impl Submitter {
             gas_price_estimation,
             nonce,
             self.nonce_of_last_submission,
+            self.max_gas_price,
+            self.start_priority_fee_tip,
         )?;
 
         self.gas_parameters_of_last_tx = Some(gas_price);
@@ -113,13 +112,15 @@ fn calculate_submission_gas_price(
     web3_gas_estimation: GasPrice1559,
     newest_nonce: u64,
     nonce_of_last_submission: Option<u64>,
+    max_gas_price: u64,
+    start_priority_fee_tip: u64,
 ) -> Result<GasPrice1559> {
     // The gas price of the refund tx is the current prevailing gas price
     // of the web3 gas estimation plus a buffer.
     let mut new_gas_price = web3_gas_estimation.bump(GAS_PRICE_BUFFER_FACTOR);
     // limit the prio_fee to max_fee_per_gas as otherwise tx is invalid
     new_gas_price.max_priority_fee_per_gas =
-        (START_PRIORITY_FEE_TIP as f64).min(new_gas_price.max_fee_per_gas);
+        (start_priority_fee_tip as f64).min(new_gas_price.max_fee_per_gas);
 
     // If tx from the previous submission was not mined,
     // we incease the tip and max_gas_fee for miners
@@ -136,15 +137,15 @@ fn calculate_submission_gas_price(
             .max(gas_price_of_last_submission.max_priority_fee_per_gas);
     }
 
-    if new_gas_price.max_fee_per_gas > MAX_GAS_PRICE as f64 {
+    if new_gas_price.max_fee_per_gas > max_gas_price as f64 {
         tracing::warn!(
             "Refunding txs are likely not mined in time, as the current gas price {:?} is higher \
              than MAX_GAS_PRICE specified {:?}",
             new_gas_price.max_fee_per_gas,
-            MAX_GAS_PRICE
+            max_gas_price
         );
         new_gas_price.max_fee_per_gas =
-            f64::min(MAX_GAS_PRICE as f64, new_gas_price.max_fee_per_gas);
+            f64::min(max_gas_price as f64, new_gas_price.max_fee_per_gas);
     }
     new_gas_price.max_priority_fee_per_gas = f64::min(
         new_gas_price.max_priority_fee_per_gas,
@@ -159,6 +160,9 @@ mod tests {
 
     #[test]
     fn test_calculate_submission_gas_price() {
+        const TEST_MAX_GAS_PRICE: u64 = 800_000_000_000;
+        const TEST_START_PRIORITY_FEE_TIP: u64 = 2_000_000_000;
+
         // First case: previous tx was successful
         let max_fee_per_gas = 4_000_000_000f64;
         let web3_gas_estimation = GasPrice1559 {
@@ -174,11 +178,13 @@ mod tests {
             web3_gas_estimation,
             newest_nonce,
             nonce_of_last_submission,
+            TEST_MAX_GAS_PRICE,
+            TEST_START_PRIORITY_FEE_TIP,
         )
         .unwrap();
         let expected_result = GasPrice1559 {
             max_fee_per_gas: max_fee_per_gas * GAS_PRICE_BUFFER_FACTOR,
-            max_priority_fee_per_gas: START_PRIORITY_FEE_TIP as f64,
+            max_priority_fee_per_gas: TEST_START_PRIORITY_FEE_TIP as f64,
             base_fee_per_gas: 2_000_000_000f64,
         };
         assert_eq!(result, expected_result);
@@ -187,24 +193,26 @@ mod tests {
         let max_fee_per_gas_of_last_tx = max_fee_per_gas * 2f64;
         let gas_price_of_last_submission = GasPrice1559 {
             max_fee_per_gas: max_fee_per_gas_of_last_tx,
-            max_priority_fee_per_gas: START_PRIORITY_FEE_TIP as f64,
+            max_priority_fee_per_gas: TEST_START_PRIORITY_FEE_TIP as f64,
             base_fee_per_gas: 2_000_000_000f64,
         };
         let result = calculate_submission_gas_price(
             Some(gas_price_of_last_submission),
             web3_gas_estimation,
             newest_nonce,
             nonce_of_last_submission,
+            TEST_MAX_GAS_PRICE,
+            TEST_START_PRIORITY_FEE_TIP,
         )
         .unwrap();
         let expected_result = GasPrice1559 {
             max_fee_per_gas: max_fee_per_gas_of_last_tx * GAS_PRICE_BUMP,
-            max_priority_fee_per_gas: START_PRIORITY_FEE_TIP as f64 * GAS_PRICE_BUMP,
+            max_priority_fee_per_gas: TEST_START_PRIORITY_FEE_TIP as f64 * GAS_PRICE_BUMP,
             base_fee_per_gas: 2_000_000_000f64,
         };
         assert_eq!(result, expected_result);
         // Thrid case: MAX_GAS_PRICE is not exceeded
-        let max_fee_per_gas = MAX_GAS_PRICE as f64 + 1000f64;
+        let max_fee_per_gas = TEST_MAX_GAS_PRICE as f64 + 1000f64;
         let web3_gas_estimation = GasPrice1559 {
             base_fee_per_gas: 2_000_000_000f64,
             max_fee_per_gas,
@@ -217,12 +225,14 @@ mod tests {
             web3_gas_estimation,
             newest_nonce,
             nonce_of_last_submission,
+            TEST_MAX_GAS_PRICE,
+            TEST_START_PRIORITY_FEE_TIP,
         )
         .unwrap();
         let expected_result = GasPrice1559 {
             base_fee_per_gas: 2_000_000_000f64,
-            max_fee_per_gas: MAX_GAS_PRICE as f64,
-            max_priority_fee_per_gas: START_PRIORITY_FEE_TIP as f64,
+            max_fee_per_gas: TEST_MAX_GAS_PRICE as f64,
+            max_priority_fee_per_gas: TEST_START_PRIORITY_FEE_TIP as f64,
         };
         assert_eq!(result, expected_result);
     }