Undo behaviour tweak and add tests

Author: pawankartik-elastic

x-pack/plugin/fleet/src/internalClusterTest/java/org/elasticsearch/xpack/fleet/action/FleetSearchRemoteIndicesDisallowedIT.java

@@ -52,30 +52,43 @@ public void testEndpointsShouldRejectRemoteIndices() {
             );
         }
 
+        {
+            /*
+             * It is possible, however, to sneak in multiple indices and a remote index if checkpoints are not specified.
+             * Unfortunately, that's the current behaviour and the Fleet team does not want us to touch it.
+             */
+            Request request = new Request("POST", "/foo,bar:baz/_fleet/_fleet_msearch");
+            request.setJsonEntity("{}\n{}\n");
+            try {
+                getRestClient().performRequest(request);
+            } catch (Exception e) {
+                throw new AssertionError(e);
+            }
+        }
+
         {
             // This is fine, there are no remote indices.
             Request request = new Request("POST", "/foo/_fleet/_fleet_msearch");
             request.setJsonEntity("{\"index\": \"bar*\"}\n{}\n");
             try {
                 getRestClient().performRequest(request);
-            } catch (Exception r) {
-                throw new AssertionError(r);
+            } catch (Exception e) {
+                throw new AssertionError(e);
             }
         }
 
         {
             // This is not valid. We shouldn't be passing multiple indices.
             Request request = new Request("POST", "/foo/_fleet/_fleet_msearch");
-            request.setJsonEntity("{\"index\": \"bar*,baz\"}\n{}\n");
-
+            request.setJsonEntity("{\"index\": \"bar,baz\", \"wait_for_checkpoints\": 1 }\n{}\n");
             ResponseException responseException = expectThrows(ResponseException.class, () -> getRestClient().performRequest(request));
             assertThat(responseException.getMessage(), Matchers.containsString("Fleet search API only supports searching a single index."));
         }
 
         {
             // This is not valid. We shouldn't be passing remote indices.
             Request request = new Request("POST", "/foo/_fleet/_fleet_msearch");
-            request.setJsonEntity("{\"index\": \"bar*\"}\n{}\n{\"index\": \"remote:index\"}\n{}\n");
+            request.setJsonEntity("{\"index\": \"bar:baz\", \"wait_for_checkpoints\": 1 }\n{}\n");
             ResponseException responseException = expectThrows(ResponseException.class, () -> getRestClient().performRequest(request));
             assertThat(responseException.getMessage(), Matchers.containsString("Fleet search API does not support remote indices. Found:"));
         }

x-pack/plugin/fleet/src/main/java/org/elasticsearch/xpack/fleet/rest/RestFleetMultiSearchAction.java

@@ -107,15 +107,14 @@ protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient cli
                         "Fleet search API param wait_for_checkpoints is only supported with an index to search specified. "
                             + "No index specified."
                     );
+                } else if (indices.length > 1) {
+                    throw new IllegalArgumentException(
+                        "Fleet search API only supports searching a single index. Found: [" + Arrays.toString(indices) + "]."
+                    );
                 }
             }
-            if (indices.length > 1) {
-                throw new IllegalArgumentException(
-                    "Fleet search API only supports searching a single index. Found: [" + Arrays.toString(indices) + "]."
-                );
-            }
 
-            if (RemoteClusterService.isRemoteIndexName(indices[0])) {
+            if (indices.length == 1 && RemoteClusterService.isRemoteIndexName(indices[0])) {
                 throw new IllegalArgumentException("Fleet search API does not support remote indices. Found: [" + indices[0] + "].");
             }
             long[] checkpoints = searchRequest.getWaitForCheckpoints().get("*");