Fix reindex-from-remote for parent/child from <2.0

Versions before 2.0 needed to be told to return interesting fields
like `_parent`, `_routing`, `_ttl`, and `_timestamp`. And they come
back inside a `fields` block which we need to parse.

Closes #21044

modules/reindex/src/main/java/org/elasticsearch/index/reindex/remote/RemoteRequestBuilders.java

@@ -89,6 +89,10 @@ final class RemoteRequestBuilders {
                 params.put("sort", sorts.toString());
             }
         }
+        if (remoteVersion.before(Version.V_2_0_0)) {
+            // Versions before 2.0.0 need prompting to return interesting fields. Note that timestamp isn't available at all....
+            searchRequest.source().storedField("_parent").storedField("_routing").storedField("_ttl");
+        }
         if (searchRequest.source().storedFields() != null && false == searchRequest.source().storedFields().fieldNames().isEmpty()) {
             StringBuilder fields = new StringBuilder(searchRequest.source().storedFields().fieldNames().get(0));
             for (int i = 1; i < searchRequest.source().storedFields().fieldNames().size(); i++) {
@@ -97,6 +101,8 @@ final class RemoteRequestBuilders {
             String storedFieldsParamName = remoteVersion.before(Version.V_5_0_0_alpha4) ? "fields" : "stored_fields";
             params.put(storedFieldsParamName, fields.toString());
         }
+        // We always want the _source document and this will force it to be returned.
+        params.put("_source", "true");
         return params;
     }
 

modules/reindex/src/main/java/org/elasticsearch/index/reindex/remote/RemoteResponseParsers.java

@@ -83,10 +83,28 @@ final class RemoteResponseParsers {
                 throw new ParsingException(p.getTokenLocation(), "[hit] failed to parse [_source]", e);
             }
         }, new ParseField("_source"));
-        HIT_PARSER.declareString(BasicHit::setRouting, new ParseField("_routing"));
+        ParseField routingField = new ParseField("_routing");
-        HIT_PARSER.declareString(BasicHit::setParent, new ParseField("_parent"));
+        ParseField parentField = new ParseField("_parent");
-        HIT_PARSER.declareLong(BasicHit::setTTL, new ParseField("_ttl"));
+        ParseField ttlField = new ParseField("_ttl");
+        HIT_PARSER.declareString(BasicHit::setRouting, routingField);
+        HIT_PARSER.declareString(BasicHit::setParent, parentField);
+        HIT_PARSER.declareLong(BasicHit::setTTL, ttlField);
         HIT_PARSER.declareLong(BasicHit::setTimestamp, new ParseField("_timestamp"));
+        // Pre-2.0.0 parent and routing come back in "fields"
+        class Fields {
+            String routing;
+            String parent;
+            long ttl;
+        }
+        ObjectParser<Fields, ParseFieldMatcherSupplier> fieldsParser = new ObjectParser<>("fields", Fields::new);
+        HIT_PARSER.declareObject((hit, fields) -> {
+            hit.setRouting(fields.routing);
+            hit.setParent(fields.parent);
+            hit.setTTL(fields.ttl);
+        }, fieldsParser, new ParseField("fields"));
+        fieldsParser.declareString((fields, routing) -> fields.routing = routing, routingField);
+        fieldsParser.declareString((fields, parent) -> fields.parent = parent, parentField);
+        fieldsParser.declareLong((fields, ttl) -> fields.ttl = ttl, ttlField);
     }
 
     /**

modules/reindex/src/test/java/org/elasticsearch/index/reindex/remote/RemoteRequestBuildersTests.java

@@ -113,7 +113,7 @@ public class RemoteRequestBuildersTests extends ESTestCase {
         SearchRequest searchRequest = new SearchRequest().source(new SearchSourceBuilder());
 
         // Test request without any fields
-        Version remoteVersion = Version.fromId(between(0, Version.CURRENT.id));
+        Version remoteVersion = Version.fromId(between(Version.V_2_0_0_beta1_ID, Version.CURRENT.id));
         assertThat(initialSearchParams(searchRequest, remoteVersion),
                 not(either(hasKey("stored_fields")).or(hasKey("fields"))));
 
@@ -125,8 +125,12 @@ public class RemoteRequestBuildersTests extends ESTestCase {
         assertThat(initialSearchParams(searchRequest, remoteVersion), hasEntry("stored_fields", "_source,_id"));
 
         // Test fields for versions that support it
-        remoteVersion = Version.fromId(between(0, Version.V_5_0_0_alpha4_ID - 1));
+        remoteVersion = Version.fromId(between(Version.V_2_0_0_beta1_ID, Version.V_5_0_0_alpha4_ID - 1));
         assertThat(initialSearchParams(searchRequest, remoteVersion), hasEntry("fields", "_source,_id"));
+
+        // Test extra fields for versions that need it
+        remoteVersion = Version.fromId(between(0, Version.V_2_0_0_beta1_ID - 1));
+        assertThat(initialSearchParams(searchRequest, remoteVersion), hasEntry("fields", "_source,_id,_parent,_routing,_ttl"));
     }
 
     public void testInitialSearchParamsMisc() {
@@ -151,6 +155,7 @@ public class RemoteRequestBuildersTests extends ESTestCase {
         assertThat(params, scroll == null ? not(hasKey("scroll")) : hasEntry("scroll", scroll.toString()));
         assertThat(params, hasEntry("size", Integer.toString(size)));
         assertThat(params, fetchVersion == null || fetchVersion == true ? hasEntry("version", null) : not(hasEntry("version", null)));
+        assertThat(params, hasEntry("_source", "true"));
     }
 
     public void testInitialSearchEntity() throws IOException {

modules/reindex/src/test/java/org/elasticsearch/index/reindex/remote/RemoteScrollableHitSourceTests.java

@@ -192,7 +192,7 @@ public class RemoteScrollableHitSourceTests extends ESTestCase {
     }
 
     /**
-     * Test for parsing _ttl, _timestamp, and _routing.
+     * Test for parsing _ttl, _timestamp, _routing, and _parent.
      */
     public void testParseScrollFullyLoaded() throws Exception {
         AtomicBoolean called = new AtomicBoolean();
@@ -208,6 +208,24 @@ public class RemoteScrollableHitSourceTests extends ESTestCase {
         assertTrue(called.get());
     }
 
+    /**
+     * Test for parsing _ttl, _routing, and _parent. _timestamp isn't available.
+     */
+    public void testParseScrollFullyLoadedFrom1_7() throws Exception {
+        AtomicBoolean called = new AtomicBoolean();
+        sourceWithMockedRemoteCall("scroll_fully_loaded_1_7.json").doStartNextScroll("", timeValueMillis(0), r -> {
+            assertEquals("AVToMiDL50DjIiBO3yKA", r.getHits().get(0).getId());
+            assertEquals("{\"test\":\"test3\"}", r.getHits().get(0).getSource().utf8ToString());
+            assertEquals((Long) 1234L, r.getHits().get(0).getTTL());
+            assertNull(r.getHits().get(0).getTimestamp()); // Not available from 1.7
+            assertEquals("testrouting", r.getHits().get(0).getRouting());
+            assertEquals("testparent", r.getHits().get(0).getParent());
+            called.set(true);
+        });
+        assertTrue(called.get());
+    }
+
+
     /**
      * Versions of Elasticsearch before 2.1.0 don't support sort:_doc and instead need to use search_type=scan. Scan doesn't return
      * documents the first iteration but reindex doesn't like that. So we jump start strait to the next iteration.

modules/reindex/src/test/resources/responses/scroll_fully_loaded_1_7.json

@@ -0,0 +1,31 @@
+{
+  "_scroll_id" : "DnF1ZXJ5VGhlbkZldGNoBQAAAfakescroll",
+  "took" : 3,
+  "timed_out" : false,
+  "terminated_early" : true,
+  "_shards" : {
+    "total" : 5,
+    "successful" : 5,
+    "failed" : 0
+  },
+  "hits" : {
+    "total" : 4,
+    "max_score" : null,
+    "hits" : [ {
+      "_index" : "test",
+      "_type" : "test",
+      "_id" : "AVToMiDL50DjIiBO3yKA",
+      "_version" : 1,
+      "_score" : null,
+      "_source" : {
+        "test" : "test3"
+      },
+      "sort" : [ 0 ],
+      "fields" : {
+        "_routing" : "testrouting",
+        "_ttl" : 1234,
+        "_parent" : "testparent"
+      }
+    } ]
+  }
+}