Fixing docsReceived counter (elastic#1840)

This commit fixes a bug that had been introduced to the "Documents Received" mapreduce counter. It had been
missing counting the first set of hits that were returned by each scroll.
Closes elastic#1470

Author: masseyke

mr/src/main/java/org/elasticsearch/hadoop/rest/ScrollQuery.java

@@ -100,7 +100,8 @@ public boolean hasNext() {
             } catch (IOException ex) {
                 throw new EsHadoopIllegalStateException(String.format("Cannot create scroll for query [%s/%s]", query, body), ex);
             }
-
+            read += batch.size();
+            stats.docsReceived += batch.size();
             // no longer needed
             body = null;
             query = null;

mr/src/test/java/org/elasticsearch/hadoop/rest/ScrollQueryTest.java

@@ -36,9 +36,8 @@
 
 public class ScrollQueryTest {
 
-    @Test
-    public void test() throws Exception {
-        RestRepository repository = mockRepository();
+    public void test(boolean firstScrollReturnsHits) throws Exception {
+        RestRepository repository = mockRepository(firstScrollReturnsHits);
         ScrollReader scrollReader = Mockito.mock(ScrollReader.class);
 
         String query = "/index/type/_search?scroll=10m&etc=etc";
@@ -54,23 +53,38 @@ public void test() throws Exception {
         Mockito.verify(repository).close();
         Stats stats = scrollQuery.stats();
         Assert.assertEquals(1, stats.docsReceived);
+        Assert.assertEquals(1, scrollQuery.getRead());
+    }
+
+    @Test
+    public void testWithEmptyFirstScroll() throws Exception {
+        test(false);
+    }
+
+    @Test
+    public void testWithNonEmptyFirstScroll() throws Exception {
+        test(true);
     }
 
-    private RestRepository mockRepository() throws Exception {
+    private RestRepository mockRepository(boolean firstScrollReturnsHits) throws Exception {
         Map<String, Object> data = new HashMap<String, Object>();
         data.put("field", "value");
         String id = "1";
         Object[] hit = new Object[]{id, data};
 
         RestRepository mocked = Mockito.mock(RestRepository.class);
 
-        ScrollReader.Scroll start = new ScrollReader.Scroll("abcd", 10, Collections.<Object[]>emptyList(), 5, 5);
+        ScrollReader.Scroll start = new ScrollReader.Scroll("abcd", 10,
+                firstScrollReturnsHits ? Collections.singletonList(hit) : Collections.<Object[]>emptyList(),
+                5, 5);
 
         Mockito.doReturn(start).when(mocked).scroll(Matchers.anyString(), Matchers.any(BytesArray.class), Matchers.any(ScrollReader.class));
 
         ScrollReader.Scroll middle = new ScrollReader.Scroll("efgh", 10, Collections.<Object[]>emptyList(), 3, 3);
         Mockito.doReturn(middle).when(mocked).scroll(Matchers.eq("abcd"), Matchers.any(ScrollReader.class));
-        ScrollReader.Scroll end = new ScrollReader.Scroll("ijkl", 10, Collections.singletonList(hit), 2, 1);
+        ScrollReader.Scroll end = new ScrollReader.Scroll("ijkl", 10,
+                firstScrollReturnsHits ? Collections.<Object[]>emptyList() : Collections.singletonList(hit),
+                2, 1);
         Mockito.doReturn(end).when(mocked).scroll(Matchers.eq("efgh"), Matchers.any(ScrollReader.class));
         ScrollReader.Scroll finalScroll = new ScrollReader.Scroll("mnop", 10, true);
         Mockito.doReturn(finalScroll).when(mocked).scroll(Matchers.eq("ijkl"), Matchers.any(ScrollReader.class));