Limit the number of nested documents

Add an index level setting `index.mapping.nested_objects.limit` to control
the number of nested json objects that can be in a single document
across all fields. Defaults to 10000.

Throw an error if the number of created nested documents exceed this
limit during the parsing of a document.

Closes #26962

Author: mayya-sharipova

core/src/test/java/org/elasticsearch/index/mapper/NestedObjectMapperTests.java

@@ -525,35 +525,42 @@ public void testParentObjectMapperAreNested() throws Exception {
     }
 
     public void testLimitNestedDocsDefaultSettings() throws Exception{
-        MapperService mapperService = createIndex("test1", Settings.builder().build()).mapperService();
+        Settings settings = Settings.builder().build();
+        MapperService mapperService = createIndex("test1", settings).mapperService();
         String mapping = XContentFactory.jsonBuilder().startObject().startObject("type").startObject("properties")
             .startObject("nested1").field("type", "nested").endObject()
             .endObject().endObject().endObject().string();
         DocumentMapper docMapper = mapperService.documentMapperParser().parse("type", new CompressedXContent(mapping));
+        long defaultMaxNoNestedDocs = MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.get(settings);
 
-        // parsing a doc with 3 nested objects succeeds
+        // parsing a doc with No. nested objects > defaultMaxNoNestedDocs fails
         XContentBuilder docBuilder = XContentFactory.jsonBuilder();
         docBuilder.startObject();
         {
             docBuilder.startArray("nested1");
             {
-                docBuilder.startObject().field("field1", "11").field("field2", "21").endObject();
-                docBuilder.startObject().field("field1", "12").field("field2", "22").endObject();
-                docBuilder.startObject().field("field1", "13").field("field2", "23").endObject();
+                for(int i=0; i<=defaultMaxNoNestedDocs; i++) {
+                    docBuilder.startObject().field("f", i).endObject();
+                }
             }
             docBuilder.endArray();
         }
         docBuilder.endObject();
         SourceToParse source1 = SourceToParse.source("test1", "type", "1", docBuilder.bytes(), XContentType.JSON);
-        ParsedDocument doc = docMapper.parse(source1);
-        assertThat(doc.docs().size(), equalTo(4));
+        MapperParsingException e = expectThrows(MapperParsingException.class, () -> docMapper.parse(source1));
+        assertEquals(
+            "The number of nested documents has exceeded the allowed limit of [" + defaultMaxNoNestedDocs
+                + "]. This limit can be set by changing the [" + MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey()
+                + "] index level setting.",
+            e.getMessage()
+        );
     }
 
     public void testLimitNestedDocs() throws Exception{
         // setting limit to allow only two nested objects in the whole doc
-        long nested_docs_limit = 2L;
+        long maxNoNestedDocs = 2L;
         MapperService mapperService = createIndex("test1", Settings.builder()
-            .put(MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey(), nested_docs_limit).build()).mapperService();
+            .put(MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey(), maxNoNestedDocs).build()).mapperService();
         String mapping = XContentFactory.jsonBuilder().startObject().startObject("type").startObject("properties")
             .startObject("nested1").field("type", "nested").endObject()
             .endObject().endObject().endObject().string();
@@ -591,7 +598,7 @@ public void testLimitNestedDocs() throws Exception{
         SourceToParse source2 = SourceToParse.source("test1", "type", "2", docBuilder2.bytes(), XContentType.JSON);
         MapperParsingException e = expectThrows(MapperParsingException.class, () -> docMapper.parse(source2));
         assertEquals(
-            "The number of nested documents has exceeded the allowed limit of [" + nested_docs_limit
+            "The number of nested documents has exceeded the allowed limit of [" + maxNoNestedDocs
             + "]. This limit can be set by changing the [" + MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey()
             + "] index level setting.",
             e.getMessage()
@@ -600,9 +607,9 @@ public void testLimitNestedDocs() throws Exception{
 
     public void testLimitNestedDocsMultipleNestedFields() throws Exception{
         // setting limit to allow only two nested objects in the whole doc
-        long nested_docs_limit = 2L;
+        long maxNoNestedDocs = 2L;
         MapperService mapperService = createIndex("test1", Settings.builder()
-            .put(MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey(), nested_docs_limit).build()).mapperService();
+            .put(MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey(), maxNoNestedDocs).build()).mapperService();
         String mapping = XContentFactory.jsonBuilder().startObject().startObject("type").startObject("properties")
             .startObject("nested1").field("type", "nested").endObject()
             .startObject("nested2").field("type", "nested").endObject()
@@ -650,7 +657,7 @@ public void testLimitNestedDocsMultipleNestedFields() throws Exception{
         SourceToParse source2 = SourceToParse.source("test1", "type", "2", docBuilder2.bytes(), XContentType.JSON);
         MapperParsingException e = expectThrows(MapperParsingException.class, () -> docMapper.parse(source2));
         assertEquals(
-            "The number of nested documents has exceeded the allowed limit of [" + nested_docs_limit
+            "The number of nested documents has exceeded the allowed limit of [" + maxNoNestedDocs
                 + "]. This limit can be set by changing the [" + MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING.getKey()
                 + "] index level setting.",
             e.getMessage()

rest-api-spec/src/main/resources/rest-api-spec/test/create/70_nested.yml

@@ -16,7 +16,7 @@ setup:
 "Indexing a doc with No. nested objects less or equal to index.mapping.nested_objects.limit should succeed":
   - skip:
       version: " - 6.99.99"
-      reason:  index.mapping.nested_objects setting was introduced from this version
+      reason:  index.mapping.nested_objects setting has been added in 7.0.0
   - do:
       create:
           index:  test_1
@@ -30,7 +30,7 @@ setup:
 "Indexing a doc with No. nested objects more than index.mapping.nested_objects.limit should fail":
   - skip:
       version: " - 6.99.99"
-      reason:  index.mapping.nested_objects setting was introduced from this version
+      reason:  index.mapping.nested_objects setting has been added in 7.0.0
   - do:
       catch: /The number of nested documents has exceeded the allowed limit of \[2\]. This limit can be set by changing the \[index.mapping.nested_objects.limit\] index level setting\./
       create: