Account for gwei overflows while multiplying

shared/src/ledger/eth_bridge/bridge_pool.rs

@@ -649,27 +649,41 @@ mod recommendations {
                             );
                             return None;
                         }
-                        Some(rate)
+                        Some(Uint::from(rate))
                     })?;
 
+                // And this the amount of gas tokens a user is willing to
+                // pay for the transfer
+                let gas_amount: Uint = pending.gas_fee.amount.into();
+
+                // Multiply both to acquire the amount of earned gwei,
+                // after the relay operation completes
+                let amt_of_earned_gwei = if let Some(gwei) =
+                    gas_amount.checked_mul(gas_token_to_gwei_conversion_rate)
+                {
+                    gwei
+                } else {
+                    return Some(Err("Overflowing error while calculating \
+                                     earned gwei amount"
+                        .into()));
+                };
+
                 Some(
-                    I256::try_from(
-                        pending.gas_fee.amount
-                            * gas_token_to_gwei_conversion_rate,
-                    )
-                    .map_err(|err| err.to_string())
-                    .and_then(|amt_of_earned_gwei| {
-                        transfer_fee()
-                            .checked_sub(&amt_of_earned_gwei)
-                            .ok_or_else(|| {
-                                "Underflowed calculating relaying cost".into()
-                            })
-                    })
-                    .map(|cost| EligibleRecommendation {
-                        cost,
-                        pending_transfer: pending,
-                        transfer_hash: pending_hash,
-                    }),
+                    I256::try_from(amt_of_earned_gwei)
+                        .map_err(|err| err.to_string())
+                        .and_then(|amt_of_earned_gwei| {
+                            transfer_fee()
+                                .checked_sub(&amt_of_earned_gwei)
+                                .ok_or_else(|| {
+                                    "Underflowed calculating relaying cost"
+                                        .into()
+                                })
+                        })
+                        .map(|cost| EligibleRecommendation {
+                            cost,
+                            pending_transfer: pending,
+                            transfer_hash: pending_hash,
+                        }),
                 )
             })
             .maybe_collect_result()