Snap server GetTrieNodes to return empty bytes when trienode doesn't exist (#7305)

Signed-off-by: Jason Frame <jason.frame@consensys.net>

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/snap/SnapServer.java

@@ -518,15 +518,13 @@ class SnapServer implements BesuEvents.InitialSyncCompletionListener {
                     if (optStorage.isEmpty() && location.isEmpty()) {
                       optStorage = Optional.of(MerkleTrie.EMPTY_TRIE_NODE);
                     }
-                    if (optStorage.isPresent()) {
-                      if (!trieNodes.isEmpty()
-                          && (sumListBytes(trieNodes) + optStorage.get().size() > maxResponseBytes
-                              || stopWatch.getTime() > StatefulPredicate.MAX_MILLIS_PER_REQUEST)) {
-                        break;
-                      }
-                      trieNodes.add(optStorage.get());
+                    var trieNode = optStorage.orElse(Bytes.EMPTY);
+                    if (!trieNodes.isEmpty()
+                        && (sumListBytes(trieNodes) + trieNode.size() > maxResponseBytes
+                            || stopWatch.getTime() > StatefulPredicate.MAX_MILLIS_PER_REQUEST)) {
+                      break;
                     }
-
+                    trieNodes.add(trieNode);
                   } else {
                     // There must be at least one element in the path otherwise it is invalid
                     if (triePath.isEmpty()) {
@@ -537,7 +535,11 @@ class SnapServer implements BesuEvents.InitialSyncCompletionListener {
                     // otherwise the first element should be account hash, and subsequent paths
                     // are compact encoded account storage paths
 
-                    final Bytes accountPrefix = Bytes32.leftPad(triePath.getFirst());
+                    final Bytes32 accountPrefix = Bytes32.leftPad(triePath.getFirst());
+                    var optAccount = storage.getAccount(Hash.wrap(accountPrefix));
+                    if (optAccount.isEmpty()) {
+                      continue;
+                    }
 
                     List<Bytes> storagePaths = triePath.subList(1, triePath.size());
                     for (var path : storagePaths) {
@@ -547,14 +549,12 @@ class SnapServer implements BesuEvents.InitialSyncCompletionListener {
                       if (optStorage.isEmpty() && location.isEmpty()) {
                         optStorage = Optional.of(MerkleTrie.EMPTY_TRIE_NODE);
                       }
-                      if (optStorage.isPresent()) {
-                        if (!trieNodes.isEmpty()
-                            && sumListBytes(trieNodes) + optStorage.get().size()
-                                > maxResponseBytes) {
-                          break;
-                        }
-                        trieNodes.add(optStorage.get());
+                      var trieNode = optStorage.orElse(Bytes.EMPTY);
+                      if (!trieNodes.isEmpty()
+                          && sumListBytes(trieNodes) + trieNode.size() > maxResponseBytes) {
+                        break;
                       }
+                      trieNodes.add(trieNode);
                     }
                   }
                 }

ethereum/eth/src/test/java/org/hyperledger/besu/ethereum/eth/manager/snap/SnapServerTest.java

@@ -531,7 +531,25 @@ public class SnapServerTest {
     assertThat(trieNodeRequest).isNotNull();
     List<Bytes> trieNodes = trieNodeRequest.nodes(false);
     assertThat(trieNodes).isNotNull();
-    assertThat(trieNodes.size()).isEqualTo(4);
+    assertThat(trieNodes.size()).isEqualTo(6);
+    assertThat(trieNodes.get(2)).isEqualTo(Bytes.EMPTY);
+    assertThat(trieNodes.get(5)).isEqualTo(Bytes.EMPTY);
+  }
+
+  @Test
+  public void assertStorageTriePathRequest_accountNotPresent() {
+    insertTestAccounts(acct4);
+    var pathToSlot11 = CompactEncoding.encode(Bytes.fromHexStringLenient("0x0101"));
+    var trieNodeRequest =
+        requestTrieNodes(
+            storageTrie.getRootHash(),
+            List.of(
+                List.of(acct3.addressHash, pathToSlot11) // account not present
+                ));
+    assertThat(trieNodeRequest).isNotNull();
+    List<Bytes> trieNodes = trieNodeRequest.nodes(false);
+    assertThat(trieNodes).isNotNull();
+    assertThat(trieNodes.size()).isEqualTo(0);
   }
 
   @Test
@@ -582,8 +600,7 @@ public class SnapServerTest {
     assertThat(trieNodeRequest).isNotNull();
     List<Bytes> trieNodes = trieNodeRequest.nodes(false);
     assertThat(trieNodes).isNotNull();
-    // TODO: adjust this assertion after sorting out the request fudge factor
-    assertThat(trieNodes.size()).isEqualTo(trieNodeLimit * 90 / 100);
+    assertThat(trieNodes.size()).isEqualTo(3);
   }
 
   @Test