Add `max_token_length` setting to the CharGroupTokenizer (#56860)

Adds `max_token_length` option to the CharGroupTokenizer.
Updates documentation as well to reflect the changes.

Closes #56676

docs/reference/analysis/tokenizers/chargroup-tokenizer.asciidoc

@@ -13,11 +13,15 @@ The `char_group` tokenizer accepts one parameter:
 
 [horizontal]
 `tokenize_on_chars`::
-    A list containing a list of characters to tokenize the string on. Whenever a character 
+    A list containing a list of characters to tokenize the string on. Whenever a character
     from this list is encountered, a new token is started. This accepts either single
     characters like e.g. `-`, or character groups: `whitespace`, `letter`, `digit`,
     `punctuation`, `symbol`.
 
+`max_token_length`::
+    The maximum token length. If a token is seen that exceeds this length then
+    it is split at `max_token_length` intervals. Defaults to `255`.
+
 
 [float]
 === Example output

modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/CharGroupTokenizerFactory.java

@@ -21,6 +21,7 @@ package org.elasticsearch.analysis.common;
 
 import org.apache.lucene.analysis.Tokenizer;
 import org.apache.lucene.analysis.util.CharTokenizer;
+import org.apache.lucene.util.AttributeFactory;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.index.IndexSettings;
@@ -31,7 +32,10 @@ import java.util.Set;
 
 public class CharGroupTokenizerFactory extends AbstractTokenizerFactory{
 
+    static final String MAX_TOKEN_LENGTH = "max_token_length";
+
     private final Set<Integer> tokenizeOnChars = new HashSet<>();
+    private final Integer maxTokenLength;
     private boolean tokenizeOnSpace = false;
     private boolean tokenizeOnLetter = false;
     private boolean tokenizeOnDigit = false;
@@ -41,6 +45,8 @@ public class CharGroupTokenizerFactory extends AbstractTokenizerFactory{
     public CharGroupTokenizerFactory(IndexSettings indexSettings, Environment environment, String name, Settings settings) {
         super(indexSettings, settings, name);
 
+        maxTokenLength = settings.getAsInt(MAX_TOKEN_LENGTH, CharTokenizer.DEFAULT_MAX_WORD_LEN);
+
         for (final String c : settings.getAsList("tokenize_on_chars")) {
             if (c == null || c.length() == 0) {
                 throw new RuntimeException("[tokenize_on_chars] cannot contain empty characters");
@@ -110,7 +116,7 @@ public class CharGroupTokenizerFactory extends AbstractTokenizerFactory{
 
     @Override
     public Tokenizer create() {
-        return new CharTokenizer() {
+        return new CharTokenizer(AttributeFactory.DEFAULT_ATTRIBUTE_FACTORY, maxTokenLength) {
             @Override
             protected boolean isTokenChar(int c) {
                 if (tokenizeOnSpace && Character.isWhitespace(c)) {

modules/analysis-common/src/test/java/org/elasticsearch/analysis/common/CharGroupTokenizerFactoryTests.java

@@ -19,7 +19,9 @@
 
 package org.elasticsearch.analysis.common;
 
+import com.carrotsearch.randomizedtesting.generators.RandomStrings;
 import org.apache.lucene.analysis.Tokenizer;
+import org.apache.lucene.analysis.util.CharTokenizer;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexSettings;
@@ -27,11 +29,12 @@ import org.elasticsearch.test.ESTokenStreamTestCase;
 import org.elasticsearch.test.IndexSettingsModule;
 
 import java.io.IOException;
+import java.io.Reader;
 import java.io.StringReader;
 import java.util.Arrays;
 
-
 public class CharGroupTokenizerFactoryTests extends ESTokenStreamTestCase {
+
     public void testParseTokenChars() {
         final Index index = new Index("test", "_na_");
         final Settings indexSettings = newAnalysisSettingsBuilder().build();
@@ -61,6 +64,53 @@ public class CharGroupTokenizerFactoryTests extends ESTokenStreamTestCase {
         }
     }
 
+    public void testMaxTokenLength() throws IOException {
+        final Index index = new Index("test", "_na_");
+        final Settings indexSettings = newAnalysisSettingsBuilder().build();
+        IndexSettings indexProperties = IndexSettingsModule.newIndexSettings(index, indexSettings);
+        final String name = "cg";
+
+        String[] conf = new String[] {"-"};
+
+        final Settings defaultLengthSettings = newAnalysisSettingsBuilder()
+            .putList("tokenize_on_chars", conf)
+            .build();
+        CharTokenizer tokenizer = (CharTokenizer) new CharGroupTokenizerFactory(indexProperties, null, name, defaultLengthSettings)
+            .create();
+        String textWithVeryLongToken = RandomStrings.randomAsciiAlphanumOfLength(random(), 256).concat("-trailing");
+        try (Reader reader = new StringReader(textWithVeryLongToken)) {
+            tokenizer.setReader(reader);
+            assertTokenStreamContents(tokenizer, new String[] { textWithVeryLongToken.substring(0, 255),
+                textWithVeryLongToken.substring(255, 256), "trailing"});
+        }
+
+        final Settings analysisSettings = newAnalysisSettingsBuilder()
+            .putList("tokenize_on_chars", conf)
+            .put("max_token_length", 2)
+            .build();
+        tokenizer = (CharTokenizer) new CharGroupTokenizerFactory(indexProperties, null, name, analysisSettings).create();
+        try (Reader reader = new StringReader("one-two-three")) {
+            tokenizer.setReader(reader);
+            assertTokenStreamContents(tokenizer, new String[] { "on", "e", "tw", "o", "th", "re", "e" });
+        }
+
+        final Settings tooLongLengthSettings = newAnalysisSettingsBuilder()
+            .putList("tokenize_on_chars", conf)
+            .put("max_token_length", 1024 * 1024 + 1)
+            .build();
+        IllegalArgumentException e = expectThrows(IllegalArgumentException.class,
+            () -> new CharGroupTokenizerFactory(indexProperties, null, name, tooLongLengthSettings).create());
+        assertEquals("maxTokenLen must be greater than 0 and less than 1048576 passed: 1048577", e.getMessage());
+
+        final Settings negativeLengthSettings = newAnalysisSettingsBuilder()
+            .putList("tokenize_on_chars", conf)
+            .put("max_token_length", -1)
+            .build();
+        e = expectThrows(IllegalArgumentException.class,
+            () -> new CharGroupTokenizerFactory(indexProperties, null, name, negativeLengthSettings).create());
+        assertEquals("maxTokenLen must be greater than 0 and less than 1048576 passed: -1", e.getMessage());
+    }
+
     public void testTokenization() throws IOException {
         final Index index = new Index("test", "_na_");
         final String name = "cg";