Adapt BWC after backporting #78765 (#79350)

Author: ywelsch

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

@@ -8,9 +8,11 @@
 
 package org.elasticsearch.action.search;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.OriginalIndices;
 import org.elasticsearch.action.support.IndicesOptions;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -149,6 +151,14 @@ public CanMatchNodeRequest(StreamInput in) throws IOException {
         source = in.readOptionalWriteable(SearchSourceBuilder::new);
         indicesOptions = IndicesOptions.readIndicesOptions(in);
         searchType = SearchType.fromId(in.readByte());
+        if (in.getVersion().before(Version.V_8_0_0)) {
+            // types no longer relevant so ignore
+            String[] types = in.readStringArray();
+            if (types.length > 0) {
+                throw new IllegalStateException(
+                    "types are no longer supported in search requests but found [" + Arrays.toString(types) + "]");
+            }
+        }
         scroll = in.readOptionalWriteable(Scroll::new);
         requestCache = in.readOptionalBoolean();
         allowPartialSearchResults = in.readBoolean();
@@ -167,6 +177,10 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalWriteable(source);
         indicesOptions.writeIndicesOptions(out);
         out.writeByte(searchType.id());
+        if (out.getVersion().before(Version.V_8_0_0)) {
+            // types not supported so send an empty array to previous versions
+            out.writeStringArray(Strings.EMPTY_ARRAY);
+        }
         out.writeOptionalWriteable(scroll);
         out.writeOptionalBoolean(requestCache);
         out.writeBoolean(allowPartialSearchResults);

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

@@ -131,8 +131,8 @@ public void sendCanMatch(Transport.Connection connection, final ShardSearchReque
 
     public void sendCanMatch(Transport.Connection connection, final CanMatchNodeRequest request, SearchTask task, final
                              ActionListener<CanMatchNodeResponse> listener) {
-        if (connection.getVersion().onOrAfter(Version.V_8_0_0) &&
-            connection.getNode().getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (connection.getVersion().onOrAfter(Version.V_7_16_0) &&
+            connection.getNode().getVersion().onOrAfter(Version.V_7_16_0)) {
             transportService.sendChildRequest(connection, QUERY_CAN_MATCH_NODE_NAME, request, task,
                 TransportRequestOptions.EMPTY, new ActionListenerResponseHandler<>(listener, CanMatchNodeResponse::new));
         } else {