Add a max-fee-per-gas headroom factor to the driver gas config

crates/driver/src/infra/blockchain/gas.rs

@@ -78,12 +78,25 @@ impl GasPriceEstimator {
             )
         };
 
+        // Add headroom on top of the estimate so a base-fee increase between
+        // submission and inclusion does not strand the tx below the new base
+        // fee. max_fee_per_gas is a ceiling, not the amount paid.
+        let factor_as_bps = self.adjustments.max_fee_per_gas_factor * 10000.0;
+        let suggested_max_fee_per_gas = eth::U256::from(estimate.max_fee_per_gas)
+            .checked_mul(eth::U256::from(factor_as_bps as u128))
+            .ok_or_else(|| {
+                Error::GasPrice(anyhow!(
+                    "overflow on multiplication (max_fee_per_gas * max_fee_per_gas_factor)"
+                ))
+            })?
+            / eth::U256::from(10000u128);
+
         // make sure the used max fee per gas is at least big enough to cover
         // the tip - otherwise the tx will be rejected by the node
         // immediately
-        let suggested_max_fee_per_gas = eth::U256::from(estimate.max_fee_per_gas);
         let suggested_max_fee_per_gas =
             std::cmp::max(suggested_max_fee_per_gas, max_priority_fee_per_gas);
+
         if suggested_max_fee_per_gas > self.adjustments.max_fee_per_gas {
             return Err(Error::GasPrice(anyhow::anyhow!(
                 "suggested gas price is higher than maximum allowed gas price (network is too \
@@ -123,6 +136,9 @@ pub struct GasPriceParameters {
     max_fee_per_gas: eth::U256,
     /// We'll always tip at least this value for `max_priority_fee_per_gas`.
     min_priority_fee: eth::U256,
+    /// The `max_fee_per_gas` suggested by the estimator gets multiplied with
+    /// this factor to leave headroom for a base-fee increase before inclusion.
+    max_fee_per_gas_factor: f64,
 }
 
 pub fn adjustments(mempools: &[mempool::Config]) -> GasPriceParameters {
@@ -133,19 +149,22 @@ pub fn adjustments(mempools: &[mempool::Config]) -> GasPriceParameters {
     let mut additional_tip_percentage = 0.0f64;
     let mut max_fee_per_gas = eth::U256::MAX;
     let mut min_priority_fee = eth::U256::ZERO;
+    let mut max_fee_per_gas_factor = 1.0f64;
 
     for mempool in mempools {
         max_additional_tip = max_additional_tip.max(mempool.max_additional_tip);
         additional_tip_percentage =
             additional_tip_percentage.max(mempool.additional_tip_percentage);
         max_fee_per_gas = max_fee_per_gas.min(mempool.gas_price_cap);
         min_priority_fee = min_priority_fee.max(mempool.min_priority_fee);
+        max_fee_per_gas_factor = max_fee_per_gas_factor.max(mempool.max_fee_per_gas_factor);
     }
 
     GasPriceParameters {
         max_additional_tip,
         additional_tip_factor: additional_tip_percentage,
         max_fee_per_gas,
         min_priority_fee,
+        max_fee_per_gas_factor,
     }
 }

crates/driver/src/infra/config/file/load.rs

@@ -334,6 +334,7 @@ pub async fn load(chain: Chain, path: &Path) -> infra::Config {
             .map(|(index, mempool)| mempool::Config {
                 min_priority_fee: config.submission.min_priority_fee,
                 gas_price_cap: config.submission.gas_price_cap,
+                max_fee_per_gas_factor: config.submission.max_fee_per_gas_factor,
                 target_confirm_time: config.submission.target_confirm_time,
                 retry_interval: config.submission.retry_interval,
                 nonce_block_number: config.submission.nonce_block_number.map(Into::into),

crates/driver/src/infra/config/file/mod.rs

@@ -111,6 +111,11 @@ struct SubmissionConfig {
     #[serde_as(as = "serde_ext::U256")]
     gas_price_cap: eth::U256,
 
+    /// Factor applied to the estimated `max_fee_per_gas` to leave headroom for
+    /// a base-fee increase between submission and inclusion.
+    #[serde(default = "default_max_fee_per_gas_factor")]
+    max_fee_per_gas_factor: f64,
+
     /// The target confirmation time for settlement transactions used
     /// to estimate gas price.
     #[serde(with = "humantime_serde", default = "default_target_confirm_time")]
@@ -213,6 +218,11 @@ fn default_gas_price_cap() -> eth::U256 {
     eth::U256::from(1000) * eth::U256::from(10).pow(eth::U256::from(9))
 }
 
+/// No headroom over the estimated `max_fee_per_gas` by default.
+fn default_max_fee_per_gas_factor() -> f64 {
+    1.0
+}
+
 fn default_target_confirm_time() -> Duration {
     Duration::from_secs(30)
 }

crates/driver/src/infra/mempool/mod.rs

@@ -22,6 +22,7 @@ use {
 pub struct Config {
     pub min_priority_fee: eth::U256,
     pub gas_price_cap: eth::U256,
+    pub max_fee_per_gas_factor: f64,
     pub target_confirm_time: std::time::Duration,
     pub retry_interval: std::time::Duration,
     /// Optional block number to use when fetching nonces. If None, uses the
@@ -40,6 +41,7 @@ impl Config {
         Self {
             min_priority_fee: Default::default(),
             gas_price_cap: eth::U256::from(1000000000000_u128),
+            max_fee_per_gas_factor: 1.,
             target_confirm_time: Default::default(),
             retry_interval: Default::default(),
             name: "default_rpc".to_string(),