Support pruned chain history in peer validators (#6698)

* dao fork block presence is optional in peer validator to support peers with pruned chain history

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

* Update ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/peervalidation/AbstractPeerBlockValidator.java

Co-authored-by: Sally MacFarlane <macfarla.github@gmail.com>
Signed-off-by: garyschulte <garyschulte@gmail.com>

---------

Signed-off-by: garyschulte <garyschulte@gmail.com>
Co-authored-by: Sally MacFarlane <macfarla.github@gmail.com>

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/peervalidation/AbstractPeerBlockValidator.java

@@ -86,12 +86,20 @@ abstract class AbstractPeerBlockValidator implements PeerValidator {
               }
               final List<BlockHeader> headers = res.getResult();
               if (headers.size() == 0) {
-                // If no headers are returned, fail
-                LOG.debug(
-                    "Peer {} is invalid because required block ({}) is unavailable.",
-                    ethPeer,
-                    blockNumber);
-                return false;
+                if (blockIsRequired()) {
+                  // If no headers are returned, fail
+                  LOG.debug(
+                      "Peer {} is invalid because required block ({}) is unavailable.",
+                      ethPeer,
+                      blockNumber);
+                  return false;
+                } else {
+                  LOG.debug(
+                      "Peer {} deemed valid because unavailable block ({}) is not required.",
+                      ethPeer,
+                      blockNumber);
+                  return true;
+                }
               }
               final BlockHeader header = headers.get(0);
               return validateBlockHeader(ethPeer, header);
@@ -105,6 +113,10 @@ abstract class AbstractPeerBlockValidator implements PeerValidator {
     return ethPeer.chainState().getEstimatedHeight() >= (blockNumber + chainHeightEstimationBuffer);
   }
 
+  protected boolean blockIsRequired() {
+    return true;
+  }
+
   @Override
   public Duration nextValidationCheckTimeout(final EthPeer ethPeer) {
     if (!ethPeer.chainState().hasEstimatedHeight()) {

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/peervalidation/DaoForkPeerValidator.java

@@ -49,4 +49,13 @@ public class DaoForkPeerValidator extends AbstractPeerBlockValidator {
     }
     return validDaoBlock;
   }
+
+  /**
+   * In order to support chain history pruning, clients do not need to have the dao fork block to be
+   * deemed valid.
+   */
+  @Override
+  protected boolean blockIsRequired() {
+    return false;
+  }
 }

ethereum/eth/src/test/java/org/hyperledger/besu/ethereum/eth/peervalidation/DaoForkPeerValidatorTest.java

@@ -98,4 +98,28 @@ public class DaoForkPeerValidatorTest extends AbstractPeerBlockValidatorTest {
     assertThat(result).isDone();
     assertThat(result).isCompletedWithValue(false);
   }
+
+  @Test
+  public void validatePeer_responsivePeerDoesNotHaveBlockWhenPastForkHeight() {
+    final EthProtocolManager ethProtocolManager = EthProtocolManagerTestUtil.create();
+    final long daoBlockNumber = 500;
+
+    final PeerValidator validator =
+        new DaoForkPeerValidator(
+            ProtocolScheduleFixture.MAINNET, new NoOpMetricsSystem(), daoBlockNumber, 0);
+
+    final RespondingEthPeer peer =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, daoBlockNumber);
+
+    final CompletableFuture<Boolean> result =
+        validator.validatePeer(ethProtocolManager.ethContext(), peer.getEthPeer());
+
+    assertThat(result).isNotDone();
+
+    // Respond to block header request with empty
+    peer.respond(RespondingEthPeer.emptyResponder());
+
+    assertThat(result).isDone();
+    assertThat(result).isCompletedWithValue(true);
+  }
 }

ethereum/eth/src/test/java/org/hyperledger/besu/ethereum/eth/peervalidation/RequiredBlocksPeerValidatorTest.java

@@ -104,4 +104,26 @@ public class RequiredBlocksPeerValidatorTest extends AbstractPeerBlockValidatorT
     assertThat(result).isDone();
     assertThat(result).isCompletedWithValue(false);
   }
+
+  @Test
+  public void validatePeer_responsivePeerDoesNotHaveBlockWhenPastForkHeight() {
+    final EthProtocolManager ethProtocolManager = EthProtocolManagerTestUtil.create();
+
+    final PeerValidator validator =
+        new RequiredBlocksPeerValidator(
+            ProtocolScheduleFixture.MAINNET, new NoOpMetricsSystem(), 1, Hash.ZERO);
+
+    final RespondingEthPeer peer = EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1);
+
+    final CompletableFuture<Boolean> result =
+        validator.validatePeer(ethProtocolManager.ethContext(), peer.getEthPeer());
+
+    assertThat(result).isNotDone();
+
+    // Respond to block header request with empty
+    peer.respond(RespondingEthPeer.emptyResponder());
+
+    assertThat(result).isDone();
+    assertThat(result).isCompletedWithValue(false);
+  }
 }