Address 1559 config assumption (#2193)

* address assumption that if 1559 is enabled there is a london fork block config
fixes #2192

Signed-off-by: garyschulte <garyschulte@gmail.com>

* fix tests

Signed-off-by: garyschulte <garyschulte@gmail.com>

* spotless. bump

Signed-off-by: garyschulte <garyschulte@gmail.com>

Co-authored-by: Sally MacFarlane <sally.macfarlane@consensys.net>

config/src/main/java/org/hyperledger/besu/config/GenesisConfigFile.java

@@ -18,6 +18,7 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.hyperledger.besu.config.JsonUtil.normalizeKeys;
 
 import java.io.IOException;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -118,7 +119,7 @@ public class GenesisConfigFile {
   }
 
   public long getGasLimit() {
-    return parseLong("gasLimit", getRequiredString("gaslimit"));
+    return parseLong("gasLimit", getFirstRequiredString("gaslimit", "gastarget"));
   }
 
   public String getMixHash() {
@@ -138,11 +139,21 @@ public class GenesisConfigFile {
   }
 
   private String getRequiredString(final String key) {
-    if (!configRoot.has(key)) {
-      throw new IllegalArgumentException(
-          String.format("Invalid genesis block configuration, missing value for '%s'", key));
-    }
-    return configRoot.get(key).asText();
+    return getFirstRequiredString(key);
+  }
+
+  private String getFirstRequiredString(final String... keys) {
+    List<String> keysList = Arrays.asList(keys);
+    return keysList.stream()
+        .filter(key -> configRoot.has(key))
+        .findFirst()
+        .map(key -> configRoot.get(key).asText())
+        .orElseThrow(
+            () ->
+                new IllegalArgumentException(
+                    String.format(
+                        "Invalid genesis block configuration, missing value for one of '%s'",
+                        keysList)));
   }
 
   private long parseLong(final String name, final String value) {

config/src/test/java/org/hyperledger/besu/config/GenesisConfigFileTest.java

@@ -102,6 +102,11 @@ public class GenesisConfigFileTest {
     assertThat(configWithProperty("gasLimit", "1000").getGasLimit()).isEqualTo(1000);
   }
 
+  @Test
+  public void shouldGetGasTarget() {
+    assertThat(configWithProperty("gasTarget", "9999").getGasLimit()).isEqualTo(9999);
+  }
+
   @Test
   public void shouldRequireGasLimit() {
     assertInvalidConfiguration(EMPTY_CONFIG::getGasLimit);

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

@@ -248,7 +248,8 @@ public class ProtocolScheduleBuilder {
     if (ExperimentalEIPs.eip1559Enabled) {
       final Optional<TransactionPriceCalculator> transactionPriceCalculator =
           Optional.of(TransactionPriceCalculator.eip1559());
-      final long eip1559Block = config.getEIP1559BlockNumber().getAsLong();
+      // if we do not have a 1559 block number, assume we are running pre-London config:
+      final long eip1559Block = config.getEIP1559BlockNumber().orElse(Long.MAX_VALUE);
       builders.put(
           eip1559Block,
           new BuilderMapEntry(