Implemented expectedGasLimit from spec

CHANGELOG.md

@@ -18,3 +18,4 @@
 - Set `is_syncing` to `false` instead of `true` for the `/eth/v1/node/syncing` API endpoint when the head is optimistic and the sync distance is 0
 - Fix libp2p direct peers handling
 - Added check for gossip message maximum uncompressed size
+- Updated the gas change check for block building so that warnings only get raised if the change is off spec.

ethereum/executionlayer/src/main/java/tech/pegasys/teku/ethereum/executionlayer/BuilderBidValidatorImpl.java

@@ -122,20 +122,21 @@ public void validateBuilderBid(
     final UInt64 preferredGasLimit = validatorRegistration.getGasLimit();
     final UInt64 proposedGasLimit = executionPayloadHeader.getGasLimit();
 
-    if (parentGasLimit.equals(preferredGasLimit) && proposedGasLimit.equals(parentGasLimit)) {
-      return;
-    }
-
-    if (preferredGasLimit.isGreaterThan(parentGasLimit)
-        && proposedGasLimit.isGreaterThan(parentGasLimit)) {
-      return;
+    final UInt64 expectedGasLimit = expectedGasLimit(parentGasLimit, preferredGasLimit);
+    if (!expectedGasLimit.equals(preferredGasLimit)) {
+      eventLogger.builderBidNotHonouringGasLimit(
+          parentGasLimit, proposedGasLimit, preferredGasLimit);
     }
+  }
 
-    if (preferredGasLimit.isLessThan(parentGasLimit)
-        && proposedGasLimit.isLessThan(parentGasLimit)) {
-      return;
+  static UInt64 expectedGasLimit(final UInt64 parentGasLimit, final UInt64 targetGasLimit) {
+    final UInt64 maxGasLimitDifference = parentGasLimit.dividedBy(1024L).minusMinZero(1);
+    if (targetGasLimit.isGreaterThan(parentGasLimit)) {
+      final UInt64 gasDiff = targetGasLimit.minusMinZero(parentGasLimit);
+      return parentGasLimit.plus(maxGasLimitDifference.min(gasDiff));
+    } else {
+      final UInt64 gasDiff = parentGasLimit.minusMinZero(targetGasLimit);
+      return parentGasLimit.minusMinZero(maxGasLimitDifference.min(gasDiff));
     }
-
-    eventLogger.builderBidNotHonouringGasLimit(parentGasLimit, proposedGasLimit, preferredGasLimit);
   }
 }

ethereum/executionlayer/src/test/java/tech/pegasys/teku/ethereum/executionlayer/BuilderBidValidatorTest.java

@@ -13,6 +13,7 @@
 
 package tech.pegasys.teku.ethereum.executionlayer;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doNothing;
@@ -24,12 +25,16 @@
 import static tech.pegasys.teku.spec.schemas.ApiSchemas.VALIDATOR_REGISTRATION_SCHEMA;
 
 import java.util.Optional;
+import java.util.stream.Stream;
 import org.apache.tuweni.bytes.Bytes;
 import org.apache.tuweni.bytes.Bytes32;
 import org.apache.tuweni.units.bigints.UInt256;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 import tech.pegasys.teku.bls.BLS;
 import tech.pegasys.teku.bls.BLSConstants;
 import tech.pegasys.teku.bls.BLSKeyPair;
@@ -148,10 +153,21 @@ void shouldBeInvalidIfLocalPayloadWithdrawalsRootDoesNotMatchTheRootOfTheBid() {
                 .orElseThrow());
   }
 
+  @ParameterizedTest(name = "parent.{0}_target.{1}_result.{2}")
+  @MethodSource("expectedGasLimitPermutations")
+  void expectedGasLimitTestCases(
+      final long parentGasLimit, final long targetGasLimit, final long expectedGasLimit) {
+    final UInt64 computedGasLimit =
+        BuilderBidValidatorImpl.expectedGasLimit(
+            UInt64.valueOf(parentGasLimit), UInt64.valueOf(targetGasLimit));
+
+    assertThat(computedGasLimit).isEqualTo(UInt64.valueOf(expectedGasLimit));
+  }
+
   @Test
   void shouldNotLogEventIfGasLimitDecreases() throws BuilderBidValidationException {
-
-    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1022_000), UInt64.valueOf(1023_000));
+    // 1023001 is as high as it can move in 1 shot
+    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1022_000), UInt64.valueOf(1023_001));
 
     builderBidValidatorWithMockSpec.validateBuilderBid(
         signedBuilderBid, validatorRegistration, state, Optional.empty());
@@ -161,8 +177,8 @@ void shouldNotLogEventIfGasLimitDecreases() throws BuilderBidValidationException
 
   @Test
   void shouldNotLogEventIfGasLimitIncreases() throws BuilderBidValidationException {
-
-    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1025_000), UInt64.valueOf(2048_000));
+    // 1024999 is as high as it can move in 1 shot
+    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1025_000), UInt64.valueOf(1024_999));
 
     builderBidValidatorWithMockSpec.validateBuilderBid(
         signedBuilderBid, validatorRegistration, state, Optional.empty());
@@ -184,27 +200,44 @@ void shouldNotLogEventIfGasLimitStaysTheSame() throws BuilderBidValidationExcept
   @Test
   void shouldLogEventIfGasLimitDoesNotDecrease() throws BuilderBidValidationException {
 
-    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1024_000), UInt64.valueOf(1023_100));
+    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1024_000), UInt64.valueOf(1020_000));
 
     builderBidValidatorWithMockSpec.validateBuilderBid(
         signedBuilderBid, validatorRegistration, state, Optional.empty());
 
     verify(eventLogger)
         .builderBidNotHonouringGasLimit(
-            UInt64.valueOf(1024_000), UInt64.valueOf(1024_000), UInt64.valueOf(1023_100));
+            UInt64.valueOf(1024_000), UInt64.valueOf(1024_000), UInt64.valueOf(1020_000));
   }
 
   @Test
   void shouldLogEventIfGasLimitDoesNotIncrease() throws BuilderBidValidationException {
 
-    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1020_000), UInt64.valueOf(1024_100));
+    prepareGasLimit(UInt64.valueOf(1024_000), UInt64.valueOf(1020_000), UInt64.valueOf(1028_000));
 
     builderBidValidatorWithMockSpec.validateBuilderBid(
         signedBuilderBid, validatorRegistration, state, Optional.empty());
 
     verify(eventLogger)
         .builderBidNotHonouringGasLimit(
-            UInt64.valueOf(1024_000), UInt64.valueOf(1020_000), UInt64.valueOf(1024_100));
+            UInt64.valueOf(1024_000), UInt64.valueOf(1020_000), UInt64.valueOf(1028_000));
+  }
+
+  static Stream<Arguments> expectedGasLimitPermutations() {
+    return Stream.of(
+        // same, expect no change
+        Arguments.of(36_000_000L, 36_000_000L, 36_000_000L),
+        Arguments.of(1024_000L, 1024_000L, 1024_000L),
+        // down inside bounds
+        Arguments.of(1024_000L, 1023_500L, 1023_500L),
+        // down outside bounds - results in a partial move
+        Arguments.of(36_000_000L, 35_000_000L, 35_964_845L),
+        Arguments.of(1024_000L, 1020_000L, 1023_001L),
+        // increase outside bounds - results in a partial move
+        Arguments.of(1024_000L, 1025_000L, 1024_999L),
+        Arguments.of(30_000_000L, 36_000_000L, 30_029_295L),
+        // increase inside bounds
+        Arguments.of(1024_000L, 1024_500L, 1024_500L));
   }
 
   private void prepareValidSignedBuilderBid() {