Add a soft limit to the field name length (#40309)

Adds an optional limit to the length of field names, throws an IllegalArgumentException if the limit is breached. 
Closes #33651

docs/reference/mapping.asciidoc

@@ -97,6 +97,12 @@ causing a mapping explosion:
     100 objects within a nested field, will actually create 101 documents, as
     each nested object will be indexed as a separate hidden document.
 
+`index.mapping.field_name_length.limit`::
+    Setting for the maximum length of a field name. The default value is
+    Long.MAX_VALUE (no limit). This setting isn't really something that addresses
+    mappings explosion but might still be useful if you want to limit the field length.
+    It usually shouldn't be necessary to set this setting. The default is okay
+    unless a user starts to add a huge number of fields with really long names.
 
 [float]
 == Dynamic mapping

server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java

@@ -154,6 +154,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
         MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING,
         MapperService.INDEX_MAPPING_TOTAL_FIELDS_LIMIT_SETTING,
         MapperService.INDEX_MAPPING_DEPTH_LIMIT_SETTING,
+        MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING,
         BitsetFilterCache.INDEX_LOAD_RANDOM_ACCESS_FILTERS_EAGERLY_SETTING,
         IndexModule.INDEX_STORE_TYPE_SETTING,
         IndexModule.INDEX_STORE_PRE_LOAD_SETTING,

server/src/main/java/org/elasticsearch/index/mapper/MapperService.java

@@ -69,6 +69,7 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.function.Supplier;
+import java.util.stream.Stream;
 
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.unmodifiableMap;
@@ -102,6 +103,8 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
         Setting.longSetting("index.mapping.total_fields.limit", 1000L, 0, Property.Dynamic, Property.IndexScope);
     public static final Setting<Long> INDEX_MAPPING_DEPTH_LIMIT_SETTING =
         Setting.longSetting("index.mapping.depth.limit", 20L, 1, Property.Dynamic, Property.IndexScope);
+    public static final Setting<Long> INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING =
+        Setting.longSetting("index.mapping.field_name_length.limit", Long.MAX_VALUE, 1L, Property.Dynamic, Property.IndexScope);
     public static final boolean INDEX_MAPPER_DYNAMIC_DEFAULT = true;
     @Deprecated
     public static final Setting<Boolean> INDEX_MAPPER_DYNAMIC_SETTING =
@@ -503,6 +506,7 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
                 // Also, don't take metadata mappers into account for the field limit check
                 checkTotalFieldsLimit(objectMappers.size() + fieldMappers.size() - metadataMappers.length
                     + fieldAliasMappers.size() );
+                checkFieldNameSoftLimit(objectMappers, fieldMappers, fieldAliasMappers);
             }
 
             results.put(newMapper.type(), newMapper);
@@ -623,6 +627,24 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
         }
     }
 
+    private void checkFieldNameSoftLimit(Collection<ObjectMapper> objectMappers,
+                                         Collection<FieldMapper> fieldMappers,
+                                         Collection<FieldAliasMapper> fieldAliasMappers) {
+        final long maxFieldNameLength = indexSettings.getValue(INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING);
+
+        Stream.of(objectMappers.stream(), fieldMappers.stream(), fieldAliasMappers.stream())
+            .reduce(Stream::concat)
+            .orElseGet(Stream::empty)
+            .forEach(mapper -> {
+                String name = mapper.simpleName();
+                if (name.length() > maxFieldNameLength) {
+                    throw new IllegalArgumentException("Field name [" + name + "] in index [" + index().getName() +
+                        "] is too long. The limit is set to [" + maxFieldNameLength + "] characters but was ["
+                        + name.length() + "] characters");
+                }
+            });
+    }
+
     private void checkPartitionedIndexConstraints(DocumentMapper newMapper) {
         if (indexSettings.getIndexMetaData().isRoutingPartitionedIndex()) {
             if (!newMapper.routingFieldMapper().required()) {

server/src/test/java/org/elasticsearch/index/mapper/MapperServiceTests.java

@@ -323,4 +323,115 @@ public class MapperServiceTests extends ESSingleNodeTestCase {
             + " that indices can have at most one type.", e.getMessage());
     }
 
+    public void testFieldNameLengthLimit() throws Throwable {
+        int maxFieldNameLength = randomIntBetween(15, 20);
+        String testString = new String(new char[maxFieldNameLength + 1]).replace("\0", "a");
+        Settings settings = Settings.builder().put(MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING.getKey(), maxFieldNameLength)
+            .build();
+        MapperService mapperService = createIndex("test1", settings).mapperService();
+
+        CompressedXContent mapping = new CompressedXContent(BytesReference.bytes(
+            XContentFactory.jsonBuilder().startObject().startObject("type")
+                .startObject("properties")
+                    .startObject("field")
+                        .field("type", "text")
+                    .endObject()
+                .endObject()
+            .endObject().endObject()));
+
+        mapperService.merge("type", mapping, MergeReason.MAPPING_UPDATE);
+
+        CompressedXContent mappingUpdate = new CompressedXContent(BytesReference.bytes(
+            XContentFactory.jsonBuilder().startObject()
+                .startObject("properties")
+                    .startObject(testString)
+                        .field("type", "text")
+                    .endObject()
+                .endObject()
+            .endObject()));
+
+        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> {
+            mapperService.merge("type", mappingUpdate, MergeReason.MAPPING_UPDATE);
+        });
+
+        assertEquals("Field name [" + testString + "] in index [test1] is too long. " +
+            "The limit is set to [" + maxFieldNameLength + "] characters but was ["
+            + testString.length() + "] characters", e.getMessage());
+    }
+
+    public void testObjectNameLengthLimit() throws Throwable {
+        int maxFieldNameLength = randomIntBetween(15, 20);
+        String testString = new String(new char[maxFieldNameLength + 1]).replace("\0", "a");
+        Settings settings = Settings.builder().put(MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING.getKey(), maxFieldNameLength)
+            .build();
+        MapperService mapperService = createIndex("test1", settings).mapperService();
+
+        CompressedXContent mapping = new CompressedXContent(BytesReference.bytes(
+            XContentFactory.jsonBuilder().startObject().startObject("type")
+                .startObject("properties")
+                    .startObject(testString)
+                        .field("type", "object")
+                    .endObject()
+                .endObject()
+            .endObject().endObject()));
+
+        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> {
+            mapperService.merge("type", mapping, MergeReason.MAPPING_UPDATE);
+        });
+
+        assertEquals("Field name [" + testString + "] in index [test1] is too long. " +
+            "The limit is set to [" + maxFieldNameLength + "] characters but was ["
+            + testString.length() + "] characters", e.getMessage());
+    }
+
+    public void testAliasFieldNameLengthLimit() throws Throwable {
+        int maxFieldNameLength = randomIntBetween(15, 20);
+        String testString = new String(new char[maxFieldNameLength + 1]).replace("\0", "a");
+        Settings settings = Settings.builder().put(MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING.getKey(), maxFieldNameLength)
+            .build();
+        MapperService mapperService = createIndex("test1", settings).mapperService();
+
+        CompressedXContent mapping = new CompressedXContent(BytesReference.bytes(
+            XContentFactory.jsonBuilder().startObject().startObject("type")
+                .startObject("properties")
+                    .startObject(testString)
+                        .field("type", "alias")
+                        .field("path", "field")
+                    .endObject()
+                    .startObject("field")
+                        .field("type", "text")
+                    .endObject()
+                .endObject()
+            .endObject().endObject()));
+
+        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> {
+            mapperService.merge("type", mapping, MergeReason.MAPPING_UPDATE);
+        });
+
+        assertEquals("Field name [" + testString + "] in index [test1] is too long. " +
+            "The limit is set to [" + maxFieldNameLength + "] characters but was ["
+            + testString.length() + "] characters", e.getMessage());
+    }
+
+    public void testMappingRecoverySkipFieldNameLengthLimit() throws Throwable {
+        int maxFieldNameLength = randomIntBetween(15, 20);
+        String testString = new String(new char[maxFieldNameLength + 1]).replace("\0", "a");
+        Settings settings = Settings.builder().put(MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING.getKey(), maxFieldNameLength)
+            .build();
+        MapperService mapperService = createIndex("test1", settings).mapperService();
+
+        CompressedXContent mapping = new CompressedXContent(BytesReference.bytes(
+            XContentFactory.jsonBuilder().startObject().startObject("type")
+                .startObject("properties")
+                    .startObject(testString)
+                        .field("type", "text")
+                    .endObject()
+                .endObject()
+            .endObject().endObject()));
+
+        DocumentMapper documentMapper = mapperService.merge("type", mapping, MergeReason.MAPPING_RECOVERY);
+
+        assertEquals(testString, documentMapper.mappers().getMapper(testString).simpleName());
+    }
+
 }

x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowActionTests.java

@@ -230,6 +230,7 @@ public class TransportResumeFollowActionTests extends ESTestCase {
         replicatedSettings.add(MapperService.INDEX_MAPPING_NESTED_DOCS_LIMIT_SETTING);
         replicatedSettings.add(MapperService.INDEX_MAPPING_NESTED_FIELDS_LIMIT_SETTING);
         replicatedSettings.add(MapperService.INDEX_MAPPING_DEPTH_LIMIT_SETTING);
+        replicatedSettings.add(MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING);
         replicatedSettings.add(MapperService.INDEX_MAPPER_DYNAMIC_SETTING);
         replicatedSettings.add(IndexSettings.MAX_NGRAM_DIFF_SETTING);
         replicatedSettings.add(IndexSettings.MAX_SHINGLE_DIFF_SETTING);