Set nowInMillis to search context created by the explain api so that "NOW" can be used within queries

Added nowInMillis to ExplainRequest in a backwards compatible manner

Fixes #3626

src/main/java/org/elasticsearch/action/explain/ExplainRequest.java

@@ -19,11 +19,11 @@
 
 package org.elasticsearch.action.explain;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.ValidateActions;
 import org.elasticsearch.action.support.single.shard.SingleShardOperationRequest;
 import org.elasticsearch.client.Requests;
-import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -51,6 +51,8 @@ public class ExplainRequest extends SingleShardOperationRequest<ExplainRequest>
 
     private String[] filteringAlias = Strings.EMPTY_ARRAY;
 
+    long nowInMillis;
+
     ExplainRequest() {
     }
 
@@ -196,6 +198,12 @@ public class ExplainRequest extends SingleShardOperationRequest<ExplainRequest>
         }
 
         fetchSourceContext = FetchSourceContext.optionalReadFromStream(in);
+
+        if (in.getVersion().onOrAfter(Version.V_0_90_6)) {
+            nowInMillis = in.readVLong();
+        } else {
+            nowInMillis = System.currentTimeMillis();
+        }
     }
 
     @Override
@@ -215,5 +223,9 @@ public class ExplainRequest extends SingleShardOperationRequest<ExplainRequest>
         }
 
         FetchSourceContext.optionalWriteToStream(fetchSourceContext, out);
+
+        if (out.getVersion().onOrAfter(Version.V_0_90_6)) {
+            out.writeVLong(nowInMillis);
+        }
     }
 }

src/main/java/org/elasticsearch/action/explain/TransportExplainAction.java

@@ -22,6 +22,7 @@ package org.elasticsearch.action.explain;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.Explanation;
 import org.elasticsearch.ElasticSearchException;
+import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.support.single.shard.TransportShardSingleOperationAction;
 import org.elasticsearch.cache.recycler.CacheRecycler;
 import org.elasticsearch.cluster.ClusterService;
@@ -75,6 +76,12 @@ public class TransportExplainAction extends TransportShardSingleOperationAction<
         this.cacheRecycler = cacheRecycler;
     }
 
+    @Override
+    protected void doExecute(ExplainRequest request, ActionListener<ExplainResponse> listener) {
+        request.nowInMillis = System.currentTimeMillis();
+        super.doExecute(request, listener);
+    }
+
     protected String transportAction() {
         return ExplainAction.NAME;
     }
@@ -102,7 +109,8 @@ public class TransportExplainAction extends TransportShardSingleOperationAction<
         SearchContext context = new DefaultSearchContext(
                 0,
                 new ShardSearchRequest().types(new String[]{request.type()})
-                        .filteringAliases(request.filteringAlias()),
+                        .filteringAliases(request.filteringAlias())
+                        .nowInMillis(request.nowInMillis),
                 null, result.searcher(), indexService, indexShard,
                 scriptService, cacheRecycler
         );

src/test/java/org/elasticsearch/explain/ExplainActionTests.java

@@ -24,11 +24,15 @@ import org.elasticsearch.common.settings.ImmutableSettings;
 import org.elasticsearch.index.query.FilterBuilders;
 import org.elasticsearch.index.query.QueryBuilders;
 import org.elasticsearch.test.AbstractIntegrationTest;
+import org.joda.time.DateTime;
+import org.joda.time.DateTimeZone;
+import org.joda.time.format.ISODateTimeFormat;
 import org.junit.Test;
 
 import java.util.Map;
 
 import static org.elasticsearch.common.xcontent.XContentFactory.jsonBuilder;
+import static org.elasticsearch.index.query.QueryBuilders.queryString;
 import static org.hamcrest.Matchers.equalTo;
 
 /**
@@ -218,4 +222,19 @@ public class ExplainActionTests extends AbstractIntegrationTest {
         assertFalse(response.isMatch());
     }
 
+    @Test
+    public void explainDateRangeInQueryString() {
+        client().admin().indices().prepareCreate("test").setSettings(ImmutableSettings.settingsBuilder().put("index.number_of_shards", 1)).get();
+
+        String aMonthAgo = ISODateTimeFormat.yearMonthDay().print(new DateTime(DateTimeZone.UTC).minusMonths(1));
+        String aMonthFromNow = ISODateTimeFormat.yearMonthDay().print(new DateTime(DateTimeZone.UTC).plusMonths(1));
+
+        client().prepareIndex("test", "type", "1").setSource("past", aMonthAgo, "future", aMonthFromNow).get();
+
+        refresh();
+
+        ExplainResponse explainResponse = client().prepareExplain("test", "type", "1").setQuery(queryString("past:[now-2M/d TO now/d]")).get();
+        assertThat(explainResponse.isExists(), equalTo(true));
+        assertThat(explainResponse.isMatch(), equalTo(true));
+    }
 }