feat(java): enable Java API to read file checksum

Updates the `SstFileMetaData` class and its native transform method to
pass in the full file checksum if present. If absent, a null byte array
is passed.

This gives minimum support to the Full File Checksum feature for the
Java API; users can enable the feature via
`DBOptions#getOptionsFromProps`, and read the checksums via
`RocksDB#getLiveFilesMetadata`.

java/rocksjni/portal.h

@@ -7327,7 +7327,7 @@ class LiveFileMetaDataJni : public JavaClass {
 
     jmethodID mid = env->GetMethodID(
         jclazz, "<init>",
-        "([BILjava/lang/String;Ljava/lang/String;JJJ[B[BJZJJ)V");
+        "([BILjava/lang/String;Ljava/lang/String;JJJ[B[BJZJJ[B)V");
     if (mid == nullptr) {
       // exception thrown: NoSuchMethodException or OutOfMemoryError
       return nullptr;
@@ -7378,6 +7378,18 @@ class LiveFileMetaDataJni : public JavaClass {
       return nullptr;
     }
 
+    jbyteArray jfile_checksum = ROCKSDB_NAMESPACE::JniUtil::copyBytes(
+        env, live_file_meta_data->file_checksum);
+    if (env->ExceptionCheck()) {
+      // exception occurred creating java string
+      env->DeleteLocalRef(jcolumn_family_name);
+      env->DeleteLocalRef(jfile_name);
+      env->DeleteLocalRef(jpath);
+      env->DeleteLocalRef(jsmallest_key);
+      env->DeleteLocalRef(jlargest_key);
+      return nullptr;
+    }
+
     jobject jlive_file_meta_data = env->NewObject(
         jclazz, mid, jcolumn_family_name,
         static_cast<jint>(live_file_meta_data->level), jfile_name, jpath,
@@ -7388,14 +7400,15 @@ class LiveFileMetaDataJni : public JavaClass {
         static_cast<jlong>(live_file_meta_data->num_reads_sampled),
         static_cast<jboolean>(live_file_meta_data->being_compacted),
         static_cast<jlong>(live_file_meta_data->num_entries),
-        static_cast<jlong>(live_file_meta_data->num_deletions));
+        static_cast<jlong>(live_file_meta_data->num_deletions), jfile_checksum);
 
     if (env->ExceptionCheck()) {
       env->DeleteLocalRef(jcolumn_family_name);
       env->DeleteLocalRef(jfile_name);
       env->DeleteLocalRef(jpath);
       env->DeleteLocalRef(jsmallest_key);
       env->DeleteLocalRef(jlargest_key);
+      env->DeleteLocalRef(jfile_checksum);
       return nullptr;
     }
 
@@ -7405,6 +7418,7 @@ class LiveFileMetaDataJni : public JavaClass {
     env->DeleteLocalRef(jpath);
     env->DeleteLocalRef(jsmallest_key);
     env->DeleteLocalRef(jlargest_key);
+    env->DeleteLocalRef(jfile_checksum);
 
     return jlive_file_meta_data;
   }

java/src/main/java/org/rocksdb/LiveFileMetaData.java

@@ -15,22 +15,13 @@ public class LiveFileMetaData extends SstFileMetaData {
   /**
    * Called from JNI C++
    */
-  private LiveFileMetaData(
-      final byte[] columnFamilyName,
-      final int level,
-      final String fileName,
-      final String path,
-      final long size,
-      final long smallestSeqno,
-      final long largestSeqno,
-      final byte[] smallestKey,
-      final byte[] largestKey,
-      final long numReadsSampled,
-      final boolean beingCompacted,
-      final long numEntries,
-      final long numDeletions) {
-    super(fileName, path, size, smallestSeqno, largestSeqno, smallestKey,
-        largestKey, numReadsSampled, beingCompacted, numEntries, numDeletions);
+  private LiveFileMetaData(final byte[] columnFamilyName, final int level, final String fileName,
+      final String path, final long size, final long smallestSeqno, final long largestSeqno,
+      final byte[] smallestKey, final byte[] largestKey, final long numReadsSampled,
+      final boolean beingCompacted, final long numEntries, final long numDeletions,
+      final byte[] fileChecksum) {
+    super(fileName, path, size, smallestSeqno, largestSeqno, smallestKey, largestKey,
+        numReadsSampled, beingCompacted, numEntries, numDeletions, fileChecksum);
     this.columnFamilyName = columnFamilyName;
     this.level = level;
   }

java/src/main/java/org/rocksdb/SstFileMetaData.java

@@ -20,6 +20,7 @@ public class SstFileMetaData {
   private final boolean beingCompacted;
   private final long numEntries;
   private final long numDeletions;
+  private final byte[] fileChecksum;
 
   /**
    * Called from JNI C++
@@ -35,19 +36,12 @@ public class SstFileMetaData {
    * @param beingCompacted true if the file is being compacted, false otherwise
    * @param numEntries the number of entries
    * @param numDeletions the number of deletions
+   * @param fileChecksum the full file checksum (if enabled)
    */
-  protected SstFileMetaData(
-      final String fileName,
-      final String path,
-      final long size,
-      final long smallestSeqno,
-      final long largestSeqno,
-      final byte[] smallestKey,
-      final byte[] largestKey,
-      final long numReadsSampled,
-      final boolean beingCompacted,
-      final long numEntries,
-      final long numDeletions) {
+  protected SstFileMetaData(final String fileName, final String path, final long size,
+      final long smallestSeqno, final long largestSeqno, final byte[] smallestKey,
+      final byte[] largestKey, final long numReadsSampled, final boolean beingCompacted,
+      final long numEntries, final long numDeletions, final byte[] fileChecksum) {
     this.fileName = fileName;
     this.path = path;
     this.size = size;
@@ -59,6 +53,7 @@ protected SstFileMetaData(
     this.beingCompacted = beingCompacted;
     this.numEntries = numEntries;
     this.numDeletions = numDeletions;
+    this.fileChecksum = fileChecksum;
   }
 
   /**
@@ -159,4 +154,13 @@ public long numEntries() {
   public long numDeletions() {
     return numDeletions;
   }
+
+  /**
+   * Get the full file checksum iff full file checksum is enabled.
+   *
+   * @return the file's checksum
+   */
+  public byte[] fileChecksum() {
+    return fileChecksum;
+  }
 }