[EIP-1559] Handle case where gas price < base fee (due to the fee cap) (#776)

* Handle case where gas price < base fee (due to the fee cap)

Signed-off-by: Abdelhamid Bakhta <abdelhamid.bakhta@consensys.net>

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/core/fees/CoinbaseFeePriceCalculator.java

@@ -22,16 +22,17 @@ import java.util.Optional;
 
 @FunctionalInterface
 public interface CoinbaseFeePriceCalculator {
-  Wei price(Gas coinbaseFee, Wei transactionGasPrice, Optional<Long> baseFee);
+  long price(Gas coinbaseFee, Wei transactionGasPrice, Optional<Long> baseFee);
 
   static CoinbaseFeePriceCalculator frontier() {
-    return (coinbaseFee, transactionGasPrice, baseFee) -> coinbaseFee.priceFor(transactionGasPrice);
+    return (coinbaseFee, transactionGasPrice, baseFee) ->
+        coinbaseFee.priceFor(transactionGasPrice).toLong();
   }
 
   static CoinbaseFeePriceCalculator eip1559() {
     return (coinbaseFee, transactionGasPrice, baseFee) -> {
       ExperimentalEIPs.eip1559MustBeEnabled();
-      return coinbaseFee.priceFor(Wei.of(transactionGasPrice.toLong() - baseFee.orElseThrow()));
+      return coinbaseFee.toLong() * (transactionGasPrice.toLong() - baseFee.orElseThrow());
     };
   }
 }

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/mainnet/MainnetTransactionProcessor.java

@@ -327,10 +327,22 @@ public class MainnetTransactionProcessor implements TransactionProcessor {
 
     final MutableAccount coinbase = worldState.getOrCreate(miningBeneficiary).getMutable();
     final Gas coinbaseFee = Gas.of(transaction.getGasLimit()).minus(refunded);
-    final Wei coinbaseWei =
+    final long coinbaseWeiDelta =
         coinbaseFeePriceCalculator.price(
             coinbaseFee, transactionGasPrice, blockHeader.getBaseFee());
-    coinbase.incrementBalance(coinbaseWei);
+    if (coinbaseWeiDelta > 0) {
+      coinbase.incrementBalance(Wei.of(coinbaseWeiDelta));
+    } else if (coinbaseWeiDelta < 0) {
+      if (coinbaseWeiDelta > coinbase.getBalance().toLong()) {
+        return Result.failed(
+            refunded.toLong(),
+            ValidationResult.invalid(
+                TransactionValidator.TransactionInvalidReason.INSUFFICIENT_COINBASE_BALANCE,
+                "insufficient coinbase balance"),
+            Optional.empty());
+      }
+      coinbase.decrementBalance(Wei.of(Math.abs(coinbaseWeiDelta)));
+    }
 
     initialFrame.getSelfDestructs().forEach(worldState::deleteAccount);
 

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/mainnet/TransactionValidator.java

@@ -72,6 +72,7 @@ public interface TransactionValidator {
     CHAIN_HEAD_WORLD_STATE_NOT_AVAILABLE,
     EXCEEDS_PER_TRANSACTION_GAS_LIMIT,
     INVALID_TRANSACTION_FORMAT,
+    INSUFFICIENT_COINBASE_BALANCE,
     // Private Transaction Invalid Reasons
     PRIVATE_TRANSACTION_FAILED,
     PRIVATE_NONCE_TOO_LOW,

ethereum/core/src/test/java/org/hyperledger/besu/ethereum/core/fees/CoinbaseFeePriceCalculatorTest.java

@@ -42,14 +42,14 @@ public class CoinbaseFeePriceCalculatorTest {
   private final Gas coinbaseFee;
   private final Wei transactionGasPrice;
   private final Optional<Long> baseFee;
-  private final Wei expectedPrice;
+  private final long expectedPrice;
 
   public CoinbaseFeePriceCalculatorTest(
       final CoinbaseFeePriceCalculator coinbaseFeePriceCalculator,
       final Gas coinbaseFee,
       final Wei transactionGasPrice,
       final Optional<Long> baseFee,
-      final Wei expectedPrice) {
+      final long expectedPrice) {
     this.coinbaseFeePriceCalculator = coinbaseFeePriceCalculator;
     this.coinbaseFee = coinbaseFee;
     this.transactionGasPrice = transactionGasPrice;
@@ -62,9 +62,11 @@ public class CoinbaseFeePriceCalculatorTest {
     return Arrays.asList(
         new Object[][] {
           // legacy transaction must return gas price * gas
-          {FRONTIER_CALCULATOR, Gas.of(100), Wei.of(10L), Optional.empty(), Wei.of(1000L)},
+          {FRONTIER_CALCULATOR, Gas.of(100), Wei.of(10L), Optional.empty(), 1000L},
           // EIP-1559 must return gas * (gas price - base fee)
-          {EIP_1559_CALCULATOR, Gas.of(100), Wei.of(10L), Optional.of(4L), Wei.of(600L)}
+          {EIP_1559_CALCULATOR, Gas.of(100), Wei.of(10L), Optional.of(4L), 600L},
+          // Negative transaction gas price case
+          {EIP_1559_CALCULATOR, Gas.of(100), Wei.of(95L), Optional.of(100L), -500L}
         });
   }