[Segment Replication] Add components for segment replication to perform file copy.

server/src/main/java/org/opensearch/indices/RunUnderPrimaryPermit.java

@@ -0,0 +1,72 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.indices;
+
+import org.apache.logging.log4j.Logger;
+import org.opensearch.action.ActionListener;
+import org.opensearch.common.lease.Releasable;
+import org.opensearch.common.util.CancellableThreads;
+import org.opensearch.common.util.concurrent.FutureUtils;
+import org.opensearch.index.shard.IndexShard;
+import org.opensearch.index.shard.IndexShardRelocatedException;
+import org.opensearch.threadpool.ThreadPool;
+
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * Execute a Runnable after acquiring the primary's operation permit.
+ *
+ * @opensearch.internal
+ */
+public final class RunUnderPrimaryPermit {
+
+    public static void run(
+        CancellableThreads.Interruptible runnable,
+        String reason,
+        IndexShard primary,
+        CancellableThreads cancellableThreads,
+        Logger logger
+    ) {
+        cancellableThreads.execute(() -> {
+            CompletableFuture<Releasable> permit = new CompletableFuture<>();
+            final ActionListener<Releasable> onAcquired = new ActionListener<>() {
+                @Override
+                public void onResponse(Releasable releasable) {
+                    if (permit.complete(releasable) == false) {
+                        releasable.close();
+                    }
+                }
+
+                @Override
+                public void onFailure(Exception e) {
+                    permit.completeExceptionally(e);
+                }
+            };
+            primary.acquirePrimaryOperationPermit(onAcquired, ThreadPool.Names.SAME, reason);
+            try (Releasable ignored = FutureUtils.get(permit)) {
+                // check that the IndexShard still has the primary authority. This needs to be checked under operation permit to prevent
+                // races, as IndexShard will switch its authority only when it holds all operation permits, see IndexShard.relocated()
+                if (primary.isRelocatedPrimary()) {
+                    throw new IndexShardRelocatedException(primary.shardId());
+                }
+                runnable.run();
+            } finally {
+                // just in case we got an exception (likely interrupted) while waiting for the get
+                permit.whenComplete((r, e) -> {
+                    if (r != null) {
+                        r.close();
+                    }
+                    if (e != null) {
+                        logger.trace("suppressing exception on completion (it was already bubbled up or the operation was aborted)", e);
+                    }
+                });
+            }
+        });
+    }
+}

server/src/main/java/org/opensearch/indices/recovery/FileChunkWriter.java

@@ -0,0 +1,31 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.indices.recovery;
+
+import org.opensearch.action.ActionListener;
+import org.opensearch.common.bytes.BytesReference;
+import org.opensearch.index.store.StoreFileMetadata;
+
+/**
+ * Writes a partial file chunk to the target store.
+ *
+ * @opensearch.internal
+ */
+@FunctionalInterface
+public interface FileChunkWriter {
+
+    void writeFileChunk(
+        StoreFileMetadata fileMetadata,
+        long position,
+        BytesReference content,
+        boolean lastChunk,
+        int totalTranslogOps,
+        ActionListener<Void> listener
+    );
+}