Make ThreadContext.stashAndMergeHeaders package-private

Signed-off-by: Craig Perkins <cwperx@amazon.com>

server/src/main/java/org/opensearch/client/support/AbstractClient.java

@@ -408,14 +408,13 @@
 import org.opensearch.client.AdminClient;
 import org.opensearch.client.Client;
 import org.opensearch.client.ClusterAdminClient;
-import org.opensearch.client.FilterClient;
 import org.opensearch.client.IndicesAdminClient;
 import org.opensearch.client.OpenSearchClient;
 import org.opensearch.cluster.metadata.IndexMetadata.APIBlock;
 import org.opensearch.common.Nullable;
 import org.opensearch.common.action.ActionFuture;
 import org.opensearch.common.settings.Settings;
-import org.opensearch.common.util.concurrent.ThreadContext;
+import org.opensearch.common.util.concurrent.StashAndMergeHeadersFilterClient;
 import org.opensearch.core.action.ActionListener;
 import org.opensearch.core.action.ActionResponse;
 import org.opensearch.core.common.bytes.BytesReference;
@@ -2140,18 +2139,6 @@ public ActionFuture<GetViewAction.Response> updateView(CreateViewAction.Request
 
     @Override
     public Client filterWithHeader(Map<String, String> headers) {
-        return new FilterClient(this) {
-            @Override
-            protected <Request extends ActionRequest, Response extends ActionResponse> void doExecute(
-                ActionType<Response> action,
-                Request request,
-                ActionListener<Response> listener
-            ) {
-                ThreadContext threadContext = threadPool().getThreadContext();
-                try (ThreadContext.StoredContext ctx = threadContext.stashAndMergeHeaders(headers)) {
-                    super.doExecute(action, request, listener);
-                }
-            }
-        };
+        return new StashAndMergeHeadersFilterClient(this, headers);
     }
 }

server/src/main/java/org/opensearch/common/util/concurrent/StashAndMergeHeadersFilterClient.java

@@ -0,0 +1,45 @@
+/*
+ * 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.common.util.concurrent;
+
+import org.opensearch.action.ActionRequest;
+import org.opensearch.action.ActionType;
+import org.opensearch.client.Client;
+import org.opensearch.client.FilterClient;
+import org.opensearch.core.action.ActionListener;
+import org.opensearch.core.action.ActionResponse;
+
+import java.util.Map;
+
+/**
+ * This class is used for simulating request headers for testing. Used in TasksIT to
+ * assert that request headers are carried to task info
+ *
+ * @opensearch.internal
+ */
+public class StashAndMergeHeadersFilterClient extends FilterClient {
+    private Map<String, String> headers;
+
+    public StashAndMergeHeadersFilterClient(Client in, Map<String, String> headers) {
+        super(in);
+        this.headers = headers;
+    }
+
+    @Override
+    protected <Request extends ActionRequest, Response extends ActionResponse> void doExecute(
+        ActionType<Response> action,
+        Request request,
+        ActionListener<Response> listener
+    ) {
+        ThreadContext threadContext = threadPool().getThreadContext();
+        try (ThreadContext.StoredContext ctx = threadContext.stashAndMergeHeaders(headers)) {
+            super.doExecute(action, request, listener);
+        }
+    }
+}

server/src/main/java/org/opensearch/common/util/concurrent/ThreadContext.java

@@ -217,7 +217,7 @@ public StoredContext stashWithOrigin(String origin) {
      * The removed context can be restored when closing the returned {@link StoredContext}. The merge strategy is that headers
      * that are already existing are preserved unless they are defaults.
      */
-    public StoredContext stashAndMergeHeaders(Map<String, String> headers) {
+    StoredContext stashAndMergeHeaders(Map<String, String> headers) {
         final ThreadContextStruct context = threadLocal.get();
         Map<String, String> newHeader = new HashMap<>(headers);
         newHeader.putAll(context.requestHeaders);