Special field visitor for _ignored_source

server/src/main/java/org/elasticsearch/index/fieldvisitor/CustomFieldsVisitor.java

@@ -10,6 +10,7 @@
 
 import org.apache.lucene.index.FieldInfo;
 import org.elasticsearch.index.mapper.IgnoredFieldMapper;
+import org.elasticsearch.index.mapper.IgnoredSourceFieldMapper;
 
 import java.util.HashSet;
 import java.util.Set;
@@ -50,6 +51,11 @@ public Status needsField(FieldInfo fieldInfo) {
         if (fields.contains(fieldInfo.name)) {
             return Status.YES;
         }
+
+        if (IgnoredSourceFieldMapper.NAME.equals(fieldInfo.name)) {
+            return Status.YES;
+        }
+
         return Status.NO;
     }
 }

server/src/main/java/org/elasticsearch/index/fieldvisitor/IgnoredSourceFieldLoader.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.index.fieldvisitor;
+
+import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.StoredFieldVisitor;
+import org.elasticsearch.common.CheckedBiConsumer;
+import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.lucene.index.SequentialStoredFieldsLeafReader;
+import org.elasticsearch.index.mapper.FallbackSyntheticSourceBlockLoader;
+import org.elasticsearch.index.mapper.IgnoredSourceFieldMapper;
+import org.elasticsearch.search.fetch.StoredFieldsSpec;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+class IgnoredSourceFieldLoader extends StoredFieldLoader {
+
+    final Set<String> potentialFieldsInIgnoreSource;
+
+    IgnoredSourceFieldLoader(StoredFieldsSpec spec) {
+        Set<String> potentialFieldsInIgnoreSource = new HashSet<>();
+        for (String requiredStoredField : spec.requiredStoredFields()) {
+            if (requiredStoredField.startsWith(IgnoredSourceFieldMapper.NAME)) {
+                String fieldName = requiredStoredField.substring(IgnoredSourceFieldMapper.NAME.length());
+                potentialFieldsInIgnoreSource.addAll(FallbackSyntheticSourceBlockLoader.splitIntoFieldPaths(fieldName));
+            }
+        }
+        this.potentialFieldsInIgnoreSource = potentialFieldsInIgnoreSource;
+    }
+
+    @Override
+    public LeafStoredFieldLoader getLoader(LeafReaderContext ctx, int[] docs) throws IOException {
+        var reader = sequentialReader(ctx);
+        var visitor = new SFV(potentialFieldsInIgnoreSource);
+        return new LeafStoredFieldLoader() {
+
+            private int doc = -1;
+
+            @Override
+            public void advanceTo(int doc) throws IOException {
+                if (doc != this.doc) {
+                    visitor.reset();
+                    reader.accept(doc, visitor);
+                    this.doc = doc;
+                }
+            }
+
+            @Override
+            public BytesReference source() {
+                return null;
+            }
+
+            @Override
+            public String id() {
+                return null;
+            }
+
+            @Override
+            public String routing() {
+                return null;
+            }
+
+            @Override
+            public Map<String, List<Object>> storedFields() {
+                return Map.of(IgnoredSourceFieldMapper.NAME, visitor.values);
+            }
+        };
+    }
+
+    @Override
+    public List<String> fieldsToLoad() {
+        return List.of(IgnoredSourceFieldMapper.NAME);
+    }
+
+    static class SFV extends StoredFieldVisitor {
+
+        final List<Object> values = new ArrayList<>();
+        final Set<String> potentialFieldsInIgnoreSource;
+
+        SFV(Set<String> potentialFieldsInIgnoreSource) {
+            this.potentialFieldsInIgnoreSource = potentialFieldsInIgnoreSource;
+        }
+
+        @Override
+        public Status needsField(FieldInfo fieldInfo) throws IOException {
+            if (IgnoredSourceFieldMapper.NAME.equals(fieldInfo.name)) {
+                return Status.YES;
+            } else {
+                return Status.NO;
+            }
+        }
+
+        @Override
+        public void binaryField(FieldInfo fieldInfo, byte[] value) throws IOException {
+            var result = IgnoredSourceFieldMapper.decodeIfMatch(value, potentialFieldsInIgnoreSource);
+            if (result != null) {
+                values.add(result);
+            }
+        }
+
+        void reset() {
+            values.clear();
+        }
+
+    }
+
+    static boolean supports(StoredFieldsSpec spec) {
+        if (spec.requiresSource() || spec.requiresMetadata()) {
+            return false;
+        }
+
+        for (String fieldName : spec.requiredStoredFields()) {
+            if (fieldName.startsWith(IgnoredSourceFieldMapper.NAME) == false) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    // TODO: use provided one
+    private static CheckedBiConsumer<Integer, StoredFieldVisitor, IOException> sequentialReader(LeafReaderContext ctx) throws IOException {
+        LeafReader leafReader = ctx.reader();
+        if (leafReader instanceof SequentialStoredFieldsLeafReader lf) {
+            return lf.getSequentialStoredFieldsReader()::document;
+        }
+        return leafReader.storedFields()::document;
+    }
+}

server/src/main/java/org/elasticsearch/index/fieldvisitor/StoredFieldLoader.java

@@ -50,6 +50,9 @@ public static StoredFieldLoader fromSpec(StoredFieldsSpec spec) {
         if (spec.noRequirements()) {
             return StoredFieldLoader.empty();
         }
+        if (IgnoredSourceFieldLoader.supports(spec)) {
+            return new IgnoredSourceFieldLoader(spec);
+        }
         return create(spec.requiresSource(), spec.requiredStoredFields());
     }
 
@@ -91,6 +94,10 @@ public static StoredFieldLoader fromSpecSequential(StoredFieldsSpec spec) {
         if (spec.noRequirements()) {
             return StoredFieldLoader.empty();
         }
+        if (IgnoredSourceFieldLoader.supports(spec)) {
+            return new IgnoredSourceFieldLoader(spec);
+        }
+
         List<String> fieldsToLoad = fieldsToLoad(spec.requiresSource(), spec.requiredStoredFields());
         return new StoredFieldLoader() {
             @Override

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

@@ -39,10 +39,12 @@
 public abstract class FallbackSyntheticSourceBlockLoader implements BlockLoader {
     private final Reader<?> reader;
     private final String fieldName;
+    private final Set<String> fieldPaths;
 
     protected FallbackSyntheticSourceBlockLoader(Reader<?> reader, String fieldName) {
         this.reader = reader;
         this.fieldName = fieldName;
+        this.fieldPaths = splitIntoFieldPaths(fieldName);
     }
 
     @Override
@@ -52,12 +54,12 @@ public ColumnAtATimeReader columnAtATimeReader(LeafReaderContext context) throws
 
     @Override
     public RowStrideReader rowStrideReader(LeafReaderContext context) throws IOException {
-        return new IgnoredSourceRowStrideReader<>(fieldName, reader);
+        return new IgnoredSourceRowStrideReader<>(fieldName, reader, fieldPaths);
     }
 
     @Override
     public StoredFieldsSpec rowStrideStoredFieldSpec() {
-        return new StoredFieldsSpec(false, false, Set.of(IgnoredSourceFieldMapper.NAME));
+        return new StoredFieldsSpec(false, false, Set.of(IgnoredSourceFieldMapper.NAME + "." + fieldName));
     }
 
     @Override
@@ -70,30 +72,29 @@ public SortedSetDocValues ordinals(LeafReaderContext context) throws IOException
         throw new UnsupportedOperationException();
     }
 
-    private static class IgnoredSourceRowStrideReader<T> implements RowStrideReader {
-        // Contains name of the field and all its parents
-        private final Set<String> fieldNames;
+    public static Set<String> splitIntoFieldPaths(String fieldName) {
+        var paths = new HashSet<String>();
+        paths.add("_doc");
+        var current = new StringBuilder();
+        for (var part : fieldName.split("\\.")) {
+            if (current.isEmpty() == false) {
+                current.append('.');
+            }
+            current.append(part);
+            paths.add(current.toString());
+        }
+        return paths;
+    }
+
+    private static final class IgnoredSourceRowStrideReader<T> implements RowStrideReader {
         private final String fieldName;
         private final Reader<T> reader;
+        private final Set<String> fieldPaths;
 
-        IgnoredSourceRowStrideReader(String fieldName, Reader<T> reader) {
+        private IgnoredSourceRowStrideReader(String fieldName, Reader<T> reader, Set<String> fieldPaths) {
             this.fieldName = fieldName;
             this.reader = reader;
-            this.fieldNames = new HashSet<>() {
-                {
-                    add("_doc");
-                }
-            };
-
-            var current = new StringBuilder();
-            for (String part : fieldName.split("\\.")) {
-                if (current.isEmpty() == false) {
-                    current.append('.');
-                }
-                current.append(part);
-                fieldNames.add(current.toString());
-            }
-
+            this.fieldPaths = fieldPaths;
         }
 
         @Override
@@ -105,10 +106,12 @@ public void read(int docId, StoredFields storedFields, Builder builder) throws I
             }
 
             Map<String, List<IgnoredSourceFieldMapper.NameValue>> valuesForFieldAndParents = new HashMap<>();
-
             for (Object value : ignoredSource) {
-                IgnoredSourceFieldMapper.NameValue nameValue = IgnoredSourceFieldMapper.decode(value);
-                if (fieldNames.contains(nameValue.name())) {
+                IgnoredSourceFieldMapper.NameValue nameValue = (value instanceof IgnoredSourceFieldMapper.NameValue nVal)
+                    ? nVal
+                    : IgnoredSourceFieldMapper.decode(value);
+
+                if (fieldPaths.contains(nameValue.name())) {
                     valuesForFieldAndParents.computeIfAbsent(nameValue.name(), k -> new ArrayList<>()).add(nameValue);
                 }
             }

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

@@ -186,6 +186,20 @@ static NameValue decode(Object field) {
         return new NameValue(name, parentOffset, value, null);
     }
 
+    public static NameValue decodeIfMatch(byte[] bytes, Set<String> potentialFieldsInIgnoreSource) {
+        int encodedSize = ByteUtils.readIntLE(bytes, 0);
+        int nameSize = encodedSize % PARENT_OFFSET_IN_NAME_OFFSET;
+        int parentOffset = encodedSize / PARENT_OFFSET_IN_NAME_OFFSET;
+
+        String name = new String(bytes, 4, nameSize, StandardCharsets.UTF_8);
+        if (potentialFieldsInIgnoreSource.contains(name)) {
+            BytesRef value = new BytesRef(bytes, 4 + nameSize, bytes.length - nameSize - 4);
+            return new NameValue(name, parentOffset, value, null);
+        } else {
+            return null;
+        }
+    }
+
     // In rare cases decoding values stored in this field can fail leading to entire source
     // not being available.
     // We would like to have an option to lose some values in synthetic source