Addressed review comments:

- added missing @nonnull and @nullable annotations
- added missing final modifiers
- extracted helper methods
- added null check for `snapshotMetrics`

Signed-off-by: Ivan Malygin <ivan@swirldslabs.com>

platform-sdk/swirlds-common/src/main/java/com/swirlds/common/io/streams/SerializableStreamConstants.java

@@ -39,7 +39,7 @@ private SerializableStreamConstants() {}
     public static final int VERSION_BYTES = Integer.BYTES;
 
     /**
-     * The previous version of the serialization protocol implemented by {@link SerializableDataOutputStream} and
+     * The current version of the serialization protocol implemented by {@link SerializableDataOutputStream} and
      * {@link SerializableDataInputStream}
      */
     public static final int SERIALIZATION_PROTOCOL_VERSION = 1;

platform-sdk/swirlds-platform-core/src/main/java/com/swirlds/platform/state/MerkleStateRoot.java

@@ -1110,9 +1110,11 @@ public void createSnapshot(Path targetPath) {
         throwIfDestroyed();
         long start = System.nanoTime();
         createSnapshot(this, targetPath);
-        snapshotMetrics
-                .getWriteStateToDiskTimeMetric()
-                .update(TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start));
+        if (snapshotMetrics != null) {
+            snapshotMetrics
+                    .getWriteStateToDiskTimeMetric()
+                    .update(TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start));
+        }
     }
 
     static void createSnapshot(MerkleRoot merkleRoot, Path targetPath) {

platform-sdk/swirlds-platform-core/src/main/java/com/swirlds/platform/state/snapshot/SignedStateFileReader.java

@@ -37,6 +37,7 @@
 import com.swirlds.platform.state.signed.SigSet;
 import com.swirlds.platform.state.signed.SignedState;
 import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
 import java.io.BufferedInputStream;
 import java.io.File;
 import java.io.FileInputStream;
@@ -71,7 +72,15 @@ public static List<SavedStateInfo> getSavedStateFiles(
                 .getSavedStateFiles(mainClassName, platformId, swirldName);
     }
 
-    public record StateFileData(MerkleRoot state, Hash hash, SigSet sigSet, int fileVersion) {}
+    /**
+     * This is a helper class to hold the data read from a state file.
+     * @param state the Merkle tree state
+     * @param hash the hash of the state
+     * @param sigSet the signature set
+     * @param fileVersion the version of the file
+     */
+    public record StateFileData(
+            @NonNull MerkleRoot state, @NonNull Hash hash, @Nullable SigSet sigSet, int fileVersion) {}
 
     /**
      * Reads a SignedState from disk using the provided snapshot reader function. If the reader throws
@@ -95,16 +104,16 @@ public record StateFileData(MerkleRoot state, Hash hash, SigSet sigSet, int file
         checkSignedStatePath(stateFile);
 
         final DeserializedSignedState returnState;
-        StateFileData data = readStateFileData(stateFile, snapshotStateReader);
+        final StateFileData data = readStateFileData(stateFile, snapshotStateReader);
 
         final StateFileData normalizedData;
         if (data.sigSet == null) {
-            File sigSetFile =
+            final File sigSetFile =
                     stateFile.getParent().resolve(SIGNATURE_SET_FILE_NAME).toFile();
             normalizedData = deserializeAndDebugOnFailure(
                     () -> new BufferedInputStream(new FileInputStream(sigSetFile)),
                     (final MerkleDataInputStream in) -> {
-                        int fileVersion = readAndCheckSigSetFileVersion(in);
+                        final int fileVersion = readAndCheckSigSetFileVersion(in);
                         final SigSet sigSet = in.readSerializable();
                         return new StateFileData(data.state, data.hash, sigSet, fileVersion);
                     });
@@ -129,8 +138,17 @@ public record StateFileData(MerkleRoot state, Hash hash, SigSet sigSet, int file
         return returnState;
     }
 
+    /**
+     * Reads a SignedState from disk using the provided snapshot reader function.
+     * @param stateFile the file to read from
+     * @param snapshotStateReader state snapshot reading function
+     * @return a signed state with it's associated hash (as computed when the state was serialized)
+     * @throws IOException if there is any problems with reading from a file
+     */
+    @NonNull
     public static StateFileData readStateFileData(
-            Path stateFile, CheckedBiFunction<MerkleDataInputStream, Path, MerkleRoot, IOException> snapshotStateReader)
+            final Path stateFile,
+            final CheckedBiFunction<MerkleDataInputStream, Path, MerkleRoot, IOException> snapshotStateReader)
             throws IOException {
         return deserializeAndDebugOnFailure(
                 () -> new BufferedInputStream(new FileInputStream(stateFile.toFile())),
@@ -139,29 +157,51 @@ public static StateFileData readStateFileData(
 
                     final Path directory = stateFile.getParent();
                     if (fileVersion == INIT_FILE_VERSION) {
-                        try {
-                            final MerkleRoot state = snapshotStateReader.apply(in, directory);
-                            final Hash hash = in.readSerializable();
-                            final SigSet sigSet = in.readSerializable();
-                            return new StateFileData(state, hash, sigSet, fileVersion);
-                        } catch (final IOException e) {
-                            throw new IOException("Failed to read snapshot file " + stateFile.toFile(), e);
-                        }
+                        return readStateFileDataV1(stateFile, snapshotStateReader, in, directory, fileVersion);
                     } else if (fileVersion == SIG_SET_SEPARATE_VERSION) {
-                        try {
-                            final MerkleRoot state = snapshotStateReader.apply(in, directory);
-                            final Hash hash = in.readSerializable();
-                            return new StateFileData(state, hash, null, fileVersion);
-
-                        } catch (final IOException e) {
-                            throw new IOException("Failed to read snapshot file " + stateFile.toFile(), e);
-                        }
+                        return createStateFileDataV2(stateFile, snapshotStateReader, in, directory, fileVersion);
                     } else {
                         throw new IOException("Unsupported protocol version: " + fileVersion);
                     }
                 });
     }
 
+    @NonNull
+    private static StateFileData createStateFileDataV2(
+            @NonNull Path stateFile,
+            @NonNull CheckedBiFunction<MerkleDataInputStream, Path, MerkleRoot, IOException> snapshotStateReader,
+            @NonNull MerkleDataInputStream in,
+            @NonNull Path directory,
+            int fileVersion)
+            throws IOException {
+        try {
+            final MerkleRoot state = snapshotStateReader.apply(in, directory);
+            final Hash hash = in.readSerializable();
+            return new StateFileData(state, hash, null, fileVersion);
+
+        } catch (final IOException e) {
+            throw new IOException("Failed to read snapshot file " + stateFile.toFile(), e);
+        }
+    }
+
+    @NonNull
+    private static StateFileData readStateFileDataV1(
+            @NonNull Path stateFile,
+            @NonNull CheckedBiFunction<MerkleDataInputStream, Path, MerkleRoot, IOException> snapshotStateReader,
+            @NonNull MerkleDataInputStream in,
+            @NonNull Path directory,
+            int fileVersion)
+            throws IOException {
+        try {
+            final MerkleRoot state = snapshotStateReader.apply(in, directory);
+            final Hash hash = in.readSerializable();
+            final SigSet sigSet = in.readSerializable();
+            return new StateFileData(state, hash, sigSet, fileVersion);
+        } catch (final IOException e) {
+            throw new IOException("Failed to read snapshot file " + stateFile.toFile(), e);
+        }
+    }
+
     /**
      * Check the path of a signed state file
      *

platform-sdk/swirlds-platform-core/src/main/java/com/swirlds/platform/state/snapshot/SignedStateFileUtils.java

@@ -53,7 +53,8 @@ public final class SignedStateFileUtils {
     public static final int INIT_FILE_VERSION = 1;
 
     /**
-     * The current version of the signed state file
+     * The current version of the signed state file. A file of this version no longer contains the signature set,
+     * instead the signature set is stored in a separate file.
      */
     public static final int SIG_SET_SEPARATE_VERSION = 2;
 

platform-sdk/swirlds-platform-core/src/testFixtures/java/com/swirlds/platform/test/fixtures/state/BlockingSwirldState.java

@@ -31,6 +31,7 @@
 import com.swirlds.platform.system.Round;
 import com.swirlds.platform.system.SwirldState;
 import com.swirlds.state.merkle.singleton.StringLeaf;
+import edu.umd.cs.findbugs.annotations.NonNull;
 import java.io.IOException;
 import java.util.Objects;
 import java.util.concurrent.CountDownLatch;
@@ -84,6 +85,7 @@ public void handleConsensusRound(final Round round, final PlatformStateAccessor
     /**
      * {@inheritDoc}
      */
+    @NonNull
     @Override
     public BlockingSwirldState copy() {
         throwIfImmutable();

platform-sdk/swirlds-state-api/src/main/java/com/swirlds/state/State.java

@@ -78,6 +78,7 @@ default void unregisterCommitListener(@NonNull final StateChangeListener listene
     /**
      * {@inheritDoc}
      */
+    @NonNull
     @Override
     default State copy() {
         throw new UnsupportedOperationException();
@@ -102,7 +103,7 @@ default void computeHash() {
      * Creates a snapshots for the state. The state has to be hashed and immutable before calling this method.
      * @param targetPath The path to save the snapshot.
      */
-    default void createSnapshot(Path targetPath) {
+    default void createSnapshot(final @NonNull Path targetPath) {
         throw new UnsupportedOperationException();
     }
 }