Add JNI for IngestExternalFileOptions::link_files

Add linkFiles() and setLinkFiles() methods to the Java API to expose
the link_files option for hard linking SST files during ingestion.

Author: corydolphin

java/rocksjni/ingest_external_file_options.cc

@@ -185,6 +185,31 @@ Java_org_rocksdb_IngestExternalFileOptions_setWriteGlobalSeqno(
   options->write_global_seqno = jwrite_global_seqno == JNI_TRUE;
 }
 
+/*
+ * Class:     org_rocksdb_IngestExternalFileOptions
+ * Method:    linkFiles
+ * Signature: (J)Z
+ */
+JNIEXPORT jboolean JNICALL
+Java_org_rocksdb_IngestExternalFileOptions_linkFiles(JNIEnv*, jclass,
+                                                     jlong jhandle) {
+  auto* options =
+      reinterpret_cast<ROCKSDB_NAMESPACE::IngestExternalFileOptions*>(jhandle);
+  return options->link_files == JNI_TRUE;
+}
+
+/*
+ * Class:     org_rocksdb_IngestExternalFileOptions
+ * Method:    setLinkFiles
+ * Signature: (JZ)V
+ */
+JNIEXPORT void JNICALL Java_org_rocksdb_IngestExternalFileOptions_setLinkFiles(
+    JNIEnv*, jclass, jlong jhandle, jboolean jlink_files) {
+  auto* options =
+      reinterpret_cast<ROCKSDB_NAMESPACE::IngestExternalFileOptions*>(jhandle);
+  options->link_files = jlink_files == JNI_TRUE;
+}
+
 /*
  * Class:     org_rocksdb_IngestExternalFileOptions
  * Method:    disposeInternal

java/src/main/java/org/rocksdb/IngestExternalFileOptions.java

@@ -201,6 +201,35 @@ public IngestExternalFileOptions setWriteGlobalSeqno(
     return this;
   }
 
+  /**
+   * Returns true if files will be hard linked instead of copied.
+   * <p>
+   * See {@link #setLinkFiles(boolean)}.
+   *
+   * @return true if files will be hard linked, false otherwise.
+   */
+  public boolean linkFiles() {
+    return linkFiles(nativeHandle_);
+  }
+
+  /**
+   * Set to true to hard link ingested files to the DB directory instead of
+   * copying them. This preserves the original file links after ingestion.
+   * <p>
+   * Only one of {@link #setMoveFiles(boolean)} and {@link #setLinkFiles(boolean)}
+   * can be set to true at the same time.
+   * <p>
+   * Default: false
+   *
+   * @param linkFiles true to hard link files instead of copying
+   *
+   * @return the reference to the current IngestExternalFileOptions.
+   */
+  public IngestExternalFileOptions setLinkFiles(final boolean linkFiles) {
+    setLinkFiles(nativeHandle_, linkFiles);
+    return this;
+  }
+
   private static native long newIngestExternalFileOptions();
   private static native long newIngestExternalFileOptions(final boolean moveFiles,
       final boolean snapshotConsistency, final boolean allowGlobalSeqNo,
@@ -226,4 +255,6 @@ private static native void setAllowBlockingFlush(
   private static native void setIngestBehind(final long handle, final boolean ingestBehind);
   private static native boolean writeGlobalSeqno(final long handle);
   private static native void setWriteGlobalSeqno(final long handle, final boolean writeGlobalSeqNo);
+  private static native boolean linkFiles(final long handle);
+  private static native void setLinkFiles(final long handle, final boolean linkFiles);
 }

java/src/test/java/org/rocksdb/IngestExternalFileOptionsTest.java

@@ -104,4 +104,14 @@ public void writeGlobalSeqno() {
       assertThat(options.writeGlobalSeqno()).isTrue();
     }
   }
+
+  @Test
+  public void linkFiles() {
+    try (final IngestExternalFileOptions options =
+             new IngestExternalFileOptions()) {
+      assertThat(options.linkFiles()).isFalse();
+      options.setLinkFiles(true);
+      assertThat(options.linkFiles()).isTrue();
+    }
+  }
 }