Warn only once per multisearch request

Author: pawankartik-elastic

server/src/main/java/org/elasticsearch/action/search/MultiSearchRequest.java

@@ -18,7 +18,9 @@
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.logging.HeaderWarning;
 import org.elasticsearch.common.xcontent.XContentHelper;
+import org.elasticsearch.rest.action.search.SearchParamsParser;
 import org.elasticsearch.tasks.CancellableTask;
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.tasks.TaskId;
@@ -204,6 +206,7 @@ public static void readMultiLineFormat(
     ) throws IOException {
         int from = 0;
         byte marker = xContent.bulkSeparator();
+        boolean warnedMrtForCps = false;
         while (true) {
             int nextMarker = findNextMarker(marker, from, data);
             if (nextMarker == -1) {
@@ -256,6 +259,10 @@ public static void readMultiLineFormat(
                             searchRequest.searchType(nodeStringValue(value, null));
                         } else if ("ccs_minimize_roundtrips".equals(entry.getKey()) || "ccsMinimizeRoundtrips".equals(entry.getKey())) {
                             searchRequest.setCcsMinimizeRoundtrips(crossProjectEnabled.orElse(false) || nodeBooleanValue(value));
+                            if (warnedMrtForCps == false) {
+                                HeaderWarning.addWarning(SearchParamsParser.MRT_SET_IN_CPS_WARN);
+                                warnedMrtForCps = true;
+                            }
                         } else if ("request_cache".equals(entry.getKey()) || "requestCache".equals(entry.getKey())) {
                             searchRequest.requestCache(nodeBooleanValue(value, entry.getKey()));
                         } else if ("preference".equals(entry.getKey())) {

server/src/main/java/org/elasticsearch/rest/action/search/SearchParamsParser.java

@@ -15,8 +15,9 @@
 import java.util.Optional;
 
 public class SearchParamsParser {
-    private static final String MRT_SET_IN_CPS_WARN = "ccs_minimize_roundtrips always defaults to true in Cross Project Search context."
-        + " Setting it explicitly has no effect irrespective of the value specified and is ignored.";
+    public static final String MRT_SET_IN_CPS_WARN = "ccs_minimize_roundtrips always defaults to true in Cross Project Search context."
+        + " Setting it explicitly has no effect irrespective of the value specified and is ignored."
+        + " It will soon be deprecated and made unavailable for Cross project Search.";
 
     /**
      * For CPS, we do not necessarily want to use the MRT value that the user has provided.