Percolator response now always returns the `matches` key.

Closes #4881

rest-api-spec/test/percolate/17_empty.yaml

@@ -0,0 +1,31 @@
+---
+"Basic percolation tests on an empty cluster":
+
+  - do:
+      indices.create:
+        index: test_index
+
+  - do:
+      indices.refresh: {}
+
+  - do:
+      percolate:
+        index: test_index
+        type:  test_type
+        body:
+          doc:
+            foo: bar
+
+  - match: {'total': 0}
+  - match: {'matches': []}
+
+  - do:
+      count_percolate:
+        index: test_index
+        type:  test_type
+        body:
+          doc:
+            foo: bar
+
+  - is_false:  matches
+  - match: {'total': 0}

src/main/java/org/elasticsearch/action/percolate/PercolateResponse.java

@@ -42,7 +42,7 @@ import java.util.*;
  */
 public class PercolateResponse extends BroadcastOperationResponse implements Iterable<PercolateResponse.Match>, ToXContent {
 
-    private static final Match[] EMPTY = new Match[0];
+    public static final Match[] EMPTY = new Match[0];
 
     private long tookInMillis;
     private Match[] matches;
@@ -60,10 +60,10 @@ public class PercolateResponse extends BroadcastOperationResponse implements Ite
         this.aggregations = aggregations;
     }
 
-    public PercolateResponse(int totalShards, int successfulShards, int failedShards, List<ShardOperationFailedException> shardFailures, long tookInMillis) {
+    public PercolateResponse(int totalShards, int successfulShards, int failedShards, List<ShardOperationFailedException> shardFailures, long tookInMillis, Match[] matches) {
         super(totalShards, successfulShards, failedShards, shardFailures);
         this.tookInMillis = tookInMillis;
-        this.matches = EMPTY;
+        this.matches = matches;
     }
 
     PercolateResponse() {
@@ -87,18 +87,30 @@ public class PercolateResponse extends BroadcastOperationResponse implements Ite
         return tookInMillis;
     }
 
+    /**
+     * @return The queries that match with the document being percolated. This can return <code>null</code> if th.
+     */
     public Match[] getMatches() {
         return this.matches;
     }
 
+    /**
+     * @return The total number of queries that have matched with the document being percolated.
+     */
     public long getCount() {
         return count;
     }
 
+    /**
+     * @return Any facet that has been executed on the query metadata. This can return <code>null</code>.
+     */
     public InternalFacets getFacets() {
         return facets;
     }
 
+    /**
+     * @return Any aggregations that has been executed on the query metadata. This can return <code>null</code>.
+     */
     public InternalAggregations getAggregations() {
         return aggregations;
     }
@@ -116,7 +128,7 @@ public class PercolateResponse extends BroadcastOperationResponse implements Ite
         RestActions.buildBroadcastShardsHeader(builder, this);
 
         builder.field(Fields.TOTAL, count);
-        if (matches.length != 0) {
+        if (matches != null) {
             builder.startArray(Fields.MATCHES);
             boolean justIds = "ids".equals(params.param("percolate_format"));
             if (justIds) {
@@ -171,11 +183,13 @@ public class PercolateResponse extends BroadcastOperationResponse implements Ite
         tookInMillis = in.readVLong();
         count = in.readVLong();
         int size = in.readVInt();
+        if (size != -1) {
             matches = new Match[size];
             for (int i = 0; i < size; i++) {
                 matches[i] = new Match();
                 matches[i].readFrom(in);
             }
+        }
         facets = InternalFacets.readOptionalFacets(in);
         aggregations = InternalAggregations.readOptionalAggregations(in);
     }
@@ -185,10 +199,14 @@ public class PercolateResponse extends BroadcastOperationResponse implements Ite
         super.writeTo(out);
         out.writeVLong(tookInMillis);
         out.writeVLong(count);
+        if (matches == null) {
+            out.writeVInt(-1);
+        } else {
             out.writeVInt(matches.length);
             for (Match match : matches) {
                 match.writeTo(out);
             }
+        }
         out.writeOptionalStreamable(facets);
         out.writeOptionalStreamable(aggregations);
     }

src/main/java/org/elasticsearch/action/percolate/TransportPercolateAction.java

@@ -155,7 +155,8 @@ public class TransportPercolateAction extends TransportBroadcastOperationAction<
 
         if (shardResults == null) {
             long tookInMillis = System.currentTimeMillis() - request.startTime;
-            return new PercolateResponse(shardsResponses.length(), successfulShards, failedShards, shardFailures, tookInMillis);
+            PercolateResponse.Match[] matches = request.onlyCount() ? null : PercolateResponse.EMPTY;
+            return new PercolateResponse(shardsResponses.length(), successfulShards, failedShards, shardFailures, tookInMillis, matches);
         } else {
             PercolatorService.ReduceResult result = percolatorService.reduce(percolatorTypeId, shardResults);
             long tookInMillis = System.currentTimeMillis() - request.startTime;

src/main/java/org/elasticsearch/percolator/PercolatorService.java

@@ -795,8 +795,6 @@ public class PercolatorService extends AbstractComponent {
 
     public final static class ReduceResult {
 
-        private static PercolateResponse.Match[] EMPTY = new PercolateResponse.Match[0];
-
         private final long count;
         private final PercolateResponse.Match[] matches;
         private final InternalFacets reducedFacets;
@@ -811,7 +809,7 @@ public class PercolatorService extends AbstractComponent {
 
         public ReduceResult(long count, InternalFacets reducedFacets, InternalAggregations reducedAggregations) {
             this.count = count;
-            this.matches = EMPTY;
+            this.matches = null;
             this.reducedFacets = reducedFacets;
             this.reducedAggregations = reducedAggregations;
         }

src/test/java/org/elasticsearch/percolator/PercolatorTests.java

@@ -931,7 +931,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setPercolateDoc(docBuilder().setDoc(jsonBuilder().startObject().field("field1", "b").endObject()))
                 .execute().actionGet();
         assertMatchCount(response, 2l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate doc with field1=c");
         response = client().preparePercolate()
@@ -939,7 +939,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setPercolateDoc(docBuilder().setDoc(yamlBuilder().startObject().field("field1", "c").endObject()))
                 .execute().actionGet();
         assertMatchCount(response, 2l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate doc with field1=b c");
         response = client().preparePercolate()
@@ -947,7 +947,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setPercolateDoc(docBuilder().setDoc(smileBuilder().startObject().field("field1", "b c").endObject()))
                 .execute().actionGet();
         assertMatchCount(response, 4l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate doc with field1=d");
         response = client().preparePercolate()
@@ -955,7 +955,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setPercolateDoc(docBuilder().setDoc(jsonBuilder().startObject().field("field1", "d").endObject()))
                 .execute().actionGet();
         assertMatchCount(response, 1l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate non existing doc");
         try {
@@ -1003,7 +1003,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setGetRequest(Requests.getRequest("test").type("type").id("1"))
                 .execute().actionGet();
         assertMatchCount(response, 2l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate existing doc with id 2");
         response = client().preparePercolate()
@@ -1011,7 +1011,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setGetRequest(Requests.getRequest("test").type("type").id("2"))
                 .execute().actionGet();
         assertMatchCount(response, 2l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate existing doc with id 3");
         response = client().preparePercolate()
@@ -1019,7 +1019,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setGetRequest(Requests.getRequest("test").type("type").id("3"))
                 .execute().actionGet();
         assertMatchCount(response, 4l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
 
         logger.info("--> Count percolate existing doc with id 4");
         response = client().preparePercolate()
@@ -1027,7 +1027,7 @@ public class PercolatorTests extends ElasticsearchIntegrationTest {
                 .setGetRequest(Requests.getRequest("test").type("type").id("4"))
                 .execute().actionGet();
         assertMatchCount(response, 1l);
-        assertThat(response.getMatches(), emptyArray());
+        assertThat(response.getMatches(), nullValue());
     }
 
     @Test