magibney commented on a change in pull request #892: LUCENE-8972: Add ICUTransformCharFilter, to support pre-tokenizer ICU text transformation URL: https://github.com/apache/lucene-solr/pull/892#discussion_r329744248
########## File path: lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUTransformCharFilter.java ########## @@ -0,0 +1,322 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.lucene.analysis.icu; + +import java.io.IOException; +import java.io.Reader; + +import com.ibm.icu.text.ReplaceableString; +import com.ibm.icu.text.Transliterator; +import com.ibm.icu.text.Transliterator.Position; +import com.ibm.icu.text.UTF16; + +import org.apache.lucene.analysis.CharFilter; +import org.apache.lucene.analysis.charfilter.BaseCharFilter; +import org.apache.lucene.util.ArrayUtil; + +/** + * A {@link CharFilter} that transforms text with ICU. + * <p> + * ICU provides text-transformation functionality via its Transliteration API. + * Although script conversion is its most common use, a Transliterator can + * actually perform a more general class of tasks. In fact, Transliterator + * defines a very general API which specifies only that a segment of the input + * text is replaced by new text. The particulars of this conversion are + * determined entirely by subclasses of Transliterator. + * </p> + * <p> + * Some useful transformations for search are built-in: + * <ul> + * <li>Conversion from Traditional to Simplified Chinese characters + * <li>Conversion from Hiragana to Katakana + * <li>Conversion from Fullwidth to Halfwidth forms. + * <li>Script conversions, for example Serbian Cyrillic to Latin + * </ul> + * <p> + * Example usage: <blockquote>stream = new ICUTransformCharFilter(reader, + * Transliterator.getInstance("Traditional-Simplified"));</blockquote> + * <br> + * For more details, see the <a + * href="http://userguide.icu-project.org/transforms/general";>ICU User + * Guide</a>. + */ +public final class ICUTransformCharFilter extends BaseCharFilter { + + // Transliterator to transform the text + private final Transliterator transform; + + // Reusable position object + private final Position position = new Position(); + + private static final int READ_BUFFER_SIZE = 1024; + private final char[] tmpBuffer = new char[READ_BUFFER_SIZE]; + + private static final int INITIAL_TRANSLITERATE_BUFFER_SIZE = 1024; + private final StringBuffer buffer = new StringBuffer(INITIAL_TRANSLITERATE_BUFFER_SIZE); + private final ReplaceableString replaceable = new ReplaceableString(buffer); + + private static final int BUFFER_PRUNE_THRESHOLD = 1024; + + private int outputCursor = 0; + private boolean inputFinished = false; + private int charCount = 0; + + static final int DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY = 8192; + private final int maxRollbackBufferCapacity; + + private static final int DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY = 4; // must be power of 2 + private char[] rollbackBuffer; + private int rollbackBufferSize = 0; + + ICUTransformCharFilter(Reader in, Transliterator transform) { + this(in, transform, DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY); + } + + /** + * Construct new {@link ICUTransformCharFilter} with the specified {@link Transliterator}, backed by + * the specified {@link Reader}. + * @param in input source + * @param transform used to perform transliteration + * @param maxRollbackBufferCapacityHint used to control the maximum size to which this + * {@link ICUTransformCharFilter} will buffer and rollback partial transliteration of input sequences. + * The provided hint will be converted to an enforced limit of "the greatest power of 2 (excluding '1') + * less than or equal to the specified value". Specifying a negative value allows the rollback buffer to Review comment: +1. This was here more as a convenience targeted at the external schema config API, so I've preserved that convenience, but moved it out to the `ICUTransformCharFilterFactory` instead (to allow users who essentially want to configure "no limit" to avoid having to explicitly write something like "2147483647" in their config files). Does that sound ok? I also noticed that there is no power of 2 greater than or equal to hint, for hint greater than `Integer.highestOneBit(Integer.MAX_VALUE)`, so I added special handling for that range of hint. It's a little fiddly, but basically we're protecting against overflow while recognizing that if the user specifies a very large value, it makes sense to resolve to the largest _legal_ value, even though it's smaller than the specified hint. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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