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Posted to issues@lucene.apache.org by GitBox <gi...@apache.org> on 2021/03/17 14:14:27 UTC
[GitHub] [lucene] rmuir commented on a change in pull request #15: LUCENE-8972: Add ICUTransformCharFilter, to support pre-tokenizer ICU text transformation
rmuir commented on a change in pull request #15:
URL: https://github.com/apache/lucene/pull/15#discussion_r595948260
##########
File path: lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUTransformFilter.java
##########
@@ -77,17 +77,26 @@
@SuppressWarnings("deprecation")
public ICUTransformFilter(TokenStream input, Transliterator transform) {
super(input);
- this.transform = transform;
+ this.transform = optimizeForCommonCase(transform);
+ }
- /*
- * This is cheating, but speeds things up a lot.
- * If we wanted to use pkg-private APIs we could probably do better.
- */
+ /**
+ * Configures the specified {@link Transliterator} to optimize common use case when the input
+ * doesn't match the filter anyway.
+ *
+ * <p>This is cheating, but speeds things up a lot. If we wanted to use pkg-private APIs we could
+ * probably do better.
+ *
+ * @param transform {@link Transliterator} to be optimized
+ * @return the input argument, optionally configured to optimize common case.
+ */
+ static Transliterator optimizeForCommonCase(Transliterator transform) {
Review comment:
I'd suggest a more descriptive name such as `hoistFilter`: that is all that happens here, we apply the same filter from the rules to transform itself, to save cycles for chars that don't match it.
##########
File path: lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUTransformCharFilter.java
##########
@@ -0,0 +1,686 @@
+/*
+ * 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 com.ibm.icu.impl.Utility;
+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 java.io.IOException;
+import java.io.Reader;
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Locale;
+import java.util.WeakHashMap;
+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>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;
+ private int offsetDiffAdjust = 0;
+
+ private static final int HARD_MAX_ROLLBACK_BUFFER_CAPACITY =
+ Integer.highestOneBit(Integer.MAX_VALUE);
+ 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;
+
+ static final boolean DEFAULT_FAIL_ON_ROLLBACK_BUFFER_OVERFLOW = true;
+ private final boolean failOnRollbackBufferOverflow;
+
+ ICUTransformCharFilter(Reader in, Transliterator transform) {
+ this(
+ in,
+ transform,
+ DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY,
+ DEFAULT_FAIL_ON_ROLLBACK_BUFFER_OVERFLOW);
+ }
+
+ /**
+ * 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". It is illegal to specify a
+ * negative value. There is no power of 2 greater than <code>
+ * Integer.highestOneBit(Integer.MAX_VALUE))</code>, so to prevent overflow, values in this
+ * range will resolve to an enforced limit of <code>Integer.highestOneBit(Integer.MAX_VALUE))
+ * </code>. Specifying "0" (or "1", in practice) disables rollback. Larger values can in some
+ * cases yield more accurate transliteration, at the cost of performance and
+ * resolution/accuracy of offset correction. This is intended primarily as a failsafe, with a
+ * relatively large default value of {@value
+ * ICUTransformCharFilter#DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY}. See comments "To understand
+ * the need for rollback" in private method: {@link
+ * Transliterator#filteredTransliterate(com.ibm.icu.text.Replaceable, Position, boolean,
+ * boolean)}
+ * @param failOnRollbackBufferOverflow if true, transliteration failing to complete within the
+ * specified rollbackBuffer window will fail with an exception. If false, transliteration
+ * forges ahead with possibly-inconsistent results.
+ */
+ ICUTransformCharFilter(
+ Reader in,
+ Transliterator transform,
+ int maxRollbackBufferCapacityHint,
+ boolean failOnRollbackBufferOverflow) {
+ super(in);
+ this.transform = ICUTransformFilter.optimizeForCommonCase(transform);
+ this.failOnRollbackBufferOverflow = failOnRollbackBufferOverflow;
+ if (maxRollbackBufferCapacityHint < 0) {
+ throw new IllegalArgumentException(
+ "It is illegal to request negative rollback buffer max capacity");
+ } else if (maxRollbackBufferCapacityHint >= HARD_MAX_ROLLBACK_BUFFER_CAPACITY) {
+ // arg is positive, so user wants the largest possible buffer capacity limit
+ // we know what that is (static), protecting for overflow.
+ this.maxRollbackBufferCapacity = HARD_MAX_ROLLBACK_BUFFER_CAPACITY;
+ this.rollbackBuffer = new char[DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY];
+ } else {
+ // greatest power of 2 (excluding "1") less than or equal to the specified hint
+ this.maxRollbackBufferCapacity =
+ Integer.highestOneBit(maxRollbackBufferCapacityHint - 1) << 1;
+ if (this.maxRollbackBufferCapacity == 0) {
+ this.rollbackBuffer = null;
+ } else {
+ this.rollbackBuffer = new char[DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY];
+ }
+ }
+ }
+
+ /**
+ * Reads characters into a portion of an array. This method will block until some input is
+ * available, an I/O error occurs, or the end of the stream is reached.
+ *
+ * @param cbuf Destination buffer
+ * @param off Offset at which to start storing characters
+ * @param len Maximum number of characters to read
+ * @return The number of characters read, or -1 if the end of the stream has been reached
+ * @throws IOException If an I/O error occurs
+ */
+ @Override
+ public int read(char[] cbuf, int off, int len) throws IOException {
+ while (!inputFinished || position.start > outputCursor) {
+ // (expecting more input) || (output remains that has not been flushed)
+ if (position.start > outputCursor) {
+ return outputFromResultBuffer(cbuf, off, len);
+ }
+
+ int resLen = transliterateBufferContents();
+ if (resLen > 0) {
+ return outputFromResultBuffer(cbuf, off, len);
+ }
+
+ if (!readInputToBuffer()) {
+ final int preStart = position.start;
+ final int preLimit;
+ final int bufferLength = buffer.length();
+ if (preStart < bufferLength) {
+ if (UTF16.isLeadSurrogate(buffer.charAt(bufferLength - 1))) {
+ // if last char is a lead surrogate, transform won't handle it properly
+ // preLimit = bufferLength - 1; // could simply pass the malformed input along
+ throw new RuntimeException(
+ "malformed input; final UTF16 character is a lead surrogate");
+ } else {
+ preLimit = bufferLength;
+ }
+ position.contextLimit = preLimit;
+ position.limit = preLimit;
+ transform.finishTransliteration(replaceable, position);
+ } else if (offsetDiffAdjust == 0) {
+ break;
+ } else {
+ preLimit = bufferLength;
+ }
+ cursorAdvanced(preStart, preLimit);
+ }
+ }
+
+ return -1;
+ }
+
+ private void rollback(int preStart, int preLimit) {
+ buffer.delete(preStart, position.limit); // delete uncommitted chars
+ buffer.insert(preStart, rollbackBuffer, 0, rollbackBufferSize);
+ position.start = preStart;
+ position.contextLimit = preLimit;
+ position.limit = preLimit;
+ }
+
+ /**
+ * Grow rollback buffer if necessary, within constraints of {@link #maxRollbackBufferCapacity}.
+ * This imposes an arbitrary failsafe to prevent the possibility that the rollback buffer could
+ * grow indefinitely.
+ *
+ * @return true if upon return, rollback buffer has sufficient capacity for new input chars,
+ * otherwise false.
+ */
+ private boolean ensureRollbackBufferCapacity() {
+ // ensure space for at least 2 chars (surrogate pair, max possible space needed)
+ if (rollbackBuffer.length - rollbackBufferSize < 2) {
+ if (rollbackBuffer.length < maxRollbackBufferCapacity) {
+ rollbackBuffer = ArrayUtil.growExact(rollbackBuffer, rollbackBuffer.length << 1);
+ } else {
+ // hit threshold; not going to increase the buffer size
+ if (failOnRollbackBufferOverflow) {
+ throw new RuntimeException(
+ "input could not be transliterated without overflowing maxRollbackBufferCapacity ("
+ + maxRollbackBufferCapacity
+ + "); "
+ + "try increasing maxRollbackBufferCapacity, or setting failOnRollbackBufferOverflow=false");
+ }
+ return false;
+ }
+ }
+ return true;
+ }
+
+ private int pushRollbackBuffer(int idx, int bufferLength) {
+ if (idx >= bufferLength) {
+ return 0;
+ } else {
+ // note: we have already ensured sufficient buffer capacity
+ final char candidate = buffer.charAt(idx);
+ if (!UTF16.isLeadSurrogate(candidate)) {
+ if (rollbackBuffer != null) {
+ rollbackBuffer[rollbackBufferSize++] = candidate;
+ }
+ return 1;
+ } else {
+ if (++idx < bufferLength) {
+ if (rollbackBuffer != null) {
+ rollbackBuffer[rollbackBufferSize++] = candidate;
+ rollbackBuffer[rollbackBufferSize++] = buffer.charAt(idx);
+ }
+ return 2;
+ } else {
+ // we don't yet have the high surrogate
+ if (inputFinished) {
+ // no more input available; proceed with the char we have; rollback not needed
+ return 1;
+ } else {
+ return 0; // wait for more input to be available
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Transliterate as much of the contents of {@link #buffer} as possible.
+ *
+ * @return number of output characters transliterated (possibly 0)
+ */
+ private int transliterateBufferContents() {
+ int nextCharLength = pushRollbackBuffer(position.limit, buffer.length());
+ if (nextCharLength == 0) {
+ return 0;
+ }
+ final int preCharCount = charCount;
+ int preStart = position.start;
+ int preLimit;
+ do {
+ position.limit += nextCharLength;
+ preLimit = position.limit;
+ position.contextLimit = preLimit;
+ transform.filteredTransliterate(replaceable, position, true);
+ boolean rollbackSizeWithinBounds = true;
+ if (rollbackBuffer != null
+ && position.start < position.limit
+ && (rollbackSizeWithinBounds = ensureRollbackBufferCapacity())) {
+ // complete pass not transliterated, and not yet at rollback buffer threshold cap.
+ // N.b.: rollback buffer threshold cap is arbitrary, so we check here (somewhat
+ // counterintuitively, *before* rolling back, as opposed to before pushing to
+ // the buffer) so that we can fall through to the else clause, clear the rollback
+ // buffer, and proceed.
+ rollback(preStart, preLimit);
+ } else {
+ rollbackBufferSize = 0;
+ if (position.start > preStart) {
+ // cursor advanced
+ cursorAdvanced(preStart, preLimit);
+
+ // N.b.: advancing contextStart precludes support for quantifiers, but is crucial for
+ // streaming,
+ // so we'll do it anyway.
+ // See comments in Transliterator source code:
+ // TODO
+ // This doesn't work once we add quantifier support. Need to rewrite
+ // this code to support quantifiers and 'use maximum backup <n>;'.
+ //
+ // index.contextStart = Math.max(index.start - getMaximumContextLength(),
+ // originalStart);
+ position.contextStart =
+ Math.max(position.start - transform.getMaximumContextLength(), preStart);
+ preStart = position.start;
+ if (!rollbackSizeWithinBounds) {
+ // prepopulate newly cleared rollback buffer with all top-level uncommitted characters
+ rollbackBufferSize = position.limit - preStart;
+ if (rollbackBuffer.length - rollbackBufferSize < 2) {
+ // even after flushing all committed text, there's not enough space in the rollback
+ // buffer.
+ // This is an edge case of an edge case, when the last char32 read into the rollback
+ // buffer
+ // is a surrogate pair (completely filling the rollback buffer), *and* the last
+ // transliteration pass advanced position.start by exactly one char16 (not a surrogate
+ // pair).
+ preStart = forceAdvance(preStart, preLimit);
+ rollbackBufferSize = position.limit - preStart;
+ }
+ buffer.getChars(preStart, position.limit, rollbackBuffer, 0);
+ }
+ } else if (preLimit != position.limit) {
+ // cursor hasn't advanced; incoming characters have probably been deleted
+ offsetDiffAdjust += preLimit - position.limit;
+ // edge case of !rollbackSizeWithinBounds needs no special handling here, since input
+ // characters *are* being
+ // processed (deleted) -- we *are* progressing through the input stream, although the
+ // output stream hasn't changed.
+ } else if (!rollbackSizeWithinBounds) {
+ // cursor hasn't advanced, no incoming characters have been deleted, and the rollback
+ // buffer is full.
+ preStart = forceAdvance(preStart, preLimit);
+ }
+ }
+ } while ((nextCharLength = pushRollbackBuffer(position.limit, buffer.length())) > 0);
+
+ return charCount - preCharCount;
+ }
+
+ private static final int FORCE_THRESHOLD = 2; // conservative; the length of a surrogate pair
+
+ private int forceAdvance(int preStart, int preLimit) {
+ int shift;
+ if (maxRollbackBufferCapacity == 2) {
+ rollbackBufferSize = 0;
+ shift = 2;
+ } else {
+ shift = 0;
+ do {
+ shift += UTF16.isLeadSurrogate(rollbackBuffer[shift]) ? 2 : 1;
+ } while (shift < FORCE_THRESHOLD && shift < maxRollbackBufferCapacity);
+ rollbackBufferSize -= shift;
+ System.arraycopy(rollbackBuffer, shift, rollbackBuffer, 0, rollbackBufferSize);
+ }
+ position.start += shift; // mock transliterator advance
+ cursorAdvanced(preStart, preLimit);
+ position.contextStart =
+ Math.max(position.start - transform.getMaximumContextLength(), preStart);
+ return position.start;
+ }
+
+ private void cursorAdvanced(int preStart, int preLimit) {
+ final int outputLength = position.start - preStart;
+ final int diff = preLimit - position.limit + offsetDiffAdjust;
+ offsetDiffAdjust = 0;
+ if (diff == 0) {
+ // increment charCount; no offset correction necessary
+ charCount += outputLength;
+ } else {
+ // limit change indicates change in length of replacement text; correct offsets accordingly
+ // we correct offsets as frequently as possible, for every incremental change. This will
+ // sometimes be for a range of characters, but that's the best we can do as far as the level
+ // of granularity that's available to us via the Transliterator API.
+ recordOffsetDiff(diff, outputLength);
+ }
+ }
+
+ private void recordOffsetDiff(int diff, int outputLength) {
+ final int cumuDiff = getLastCumulativeDiff();
+ if (diff < 0) {
+ // positive diff indicates an increase in character count wrt input
+ for (int i = 1; i <= -diff; ++i) {
+ addOffCorrectMap(charCount + i, cumuDiff - i);
+ }
+ } else {
+ // positive diff indicates an decrease in character count wrt input
+ addOffCorrectMap(charCount + outputLength, cumuDiff + diff);
+ }
+ charCount += outputLength;
+ }
+
+ private boolean readInputToBuffer() throws IOException {
+ int res = input.read(tmpBuffer, 0, tmpBuffer.length);
+ if (res == -1) {
+ inputFinished = true;
+ return false;
+ } else {
+ buffer.append(tmpBuffer, 0, res);
+ return true;
+ }
+ }
+
+ private int outputFromResultBuffer(char[] cbuf, int begin, int len) {
+ len = Math.min(position.start - outputCursor, len);
+ buffer.getChars(outputCursor, outputCursor + len, cbuf, begin);
+ outputCursor += len;
+ if (outputCursor > BUFFER_PRUNE_THRESHOLD && position.contextStart > BUFFER_PRUNE_THRESHOLD) {
+ final int pruneSize = Math.min(outputCursor, position.contextStart);
+ buffer.delete(0, pruneSize);
+ position.contextStart -= pruneSize;
+ position.start -= pruneSize;
+ position.limit -= pruneSize;
+ position.contextLimit -= pruneSize;
+ outputCursor -= pruneSize;
+ }
+ return len;
+ }
+
+ /**
+ * Strips off Unicode character normalization form rules from a Transliterator. Do this if, as is
+ * typical, your analysis chain already includes another component that does normalization, like
+ * {@link ICUNormalizer2CharFilter}.
+ *
+ * @return a new Transliterator with no normalization, or the original Transliterator if it
+ * already did no normalization.
+ */
+ public static Transliterator withoutUnicodeNormalization(Transliterator transliterator) {
+ final String modifiedRules = modifyRules(false, transliterator);
+ if (modifiedRules == null) {
+ return transliterator;
+ }
+ String baseId = transliterator.getID();
+ String modId = baseId.concat(baseId.lastIndexOf('/') < 0 ? "/X_NO_NORM_IO" : "_X_NO_NORM_IO");
+ return Transliterator.createFromRules(modId, modifiedRules, Transliterator.FORWARD);
+ }
Review comment:
btw I also think its ok to extend the optimization for the case where we know for sure previous stream gives us the input normalization we already need, so in this example:
```
if (!(charstream instanceof ICUNormalizer2CharFilter and in [NFD, NFKD])) {
charstream = new ICUNormalizer2CharFilter(charstream, NFD);
}
charstream = new ICUTransformCharCharter(charstream, X);
charstream = new ICUNormalizer2CharFilter(charstream, NFC);
return charstream;
```
The filters don't even have to know about such optimizations and we can write tests for them too.
##########
File path: lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUTransformCharFilter.java
##########
@@ -0,0 +1,686 @@
+/*
+ * 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 com.ibm.icu.impl.Utility;
+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 java.io.IOException;
+import java.io.Reader;
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Locale;
+import java.util.WeakHashMap;
+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>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;
+ private int offsetDiffAdjust = 0;
+
+ private static final int HARD_MAX_ROLLBACK_BUFFER_CAPACITY =
+ Integer.highestOneBit(Integer.MAX_VALUE);
+ 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;
+
+ static final boolean DEFAULT_FAIL_ON_ROLLBACK_BUFFER_OVERFLOW = true;
+ private final boolean failOnRollbackBufferOverflow;
+
+ ICUTransformCharFilter(Reader in, Transliterator transform) {
+ this(
+ in,
+ transform,
+ DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY,
+ DEFAULT_FAIL_ON_ROLLBACK_BUFFER_OVERFLOW);
+ }
+
+ /**
+ * 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". It is illegal to specify a
+ * negative value. There is no power of 2 greater than <code>
+ * Integer.highestOneBit(Integer.MAX_VALUE))</code>, so to prevent overflow, values in this
+ * range will resolve to an enforced limit of <code>Integer.highestOneBit(Integer.MAX_VALUE))
+ * </code>. Specifying "0" (or "1", in practice) disables rollback. Larger values can in some
+ * cases yield more accurate transliteration, at the cost of performance and
+ * resolution/accuracy of offset correction. This is intended primarily as a failsafe, with a
+ * relatively large default value of {@value
+ * ICUTransformCharFilter#DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY}. See comments "To understand
+ * the need for rollback" in private method: {@link
+ * Transliterator#filteredTransliterate(com.ibm.icu.text.Replaceable, Position, boolean,
+ * boolean)}
+ * @param failOnRollbackBufferOverflow if true, transliteration failing to complete within the
+ * specified rollbackBuffer window will fail with an exception. If false, transliteration
+ * forges ahead with possibly-inconsistent results.
+ */
+ ICUTransformCharFilter(
+ Reader in,
+ Transliterator transform,
+ int maxRollbackBufferCapacityHint,
+ boolean failOnRollbackBufferOverflow) {
+ super(in);
+ this.transform = ICUTransformFilter.optimizeForCommonCase(transform);
+ this.failOnRollbackBufferOverflow = failOnRollbackBufferOverflow;
+ if (maxRollbackBufferCapacityHint < 0) {
+ throw new IllegalArgumentException(
+ "It is illegal to request negative rollback buffer max capacity");
+ } else if (maxRollbackBufferCapacityHint >= HARD_MAX_ROLLBACK_BUFFER_CAPACITY) {
+ // arg is positive, so user wants the largest possible buffer capacity limit
+ // we know what that is (static), protecting for overflow.
+ this.maxRollbackBufferCapacity = HARD_MAX_ROLLBACK_BUFFER_CAPACITY;
+ this.rollbackBuffer = new char[DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY];
+ } else {
+ // greatest power of 2 (excluding "1") less than or equal to the specified hint
+ this.maxRollbackBufferCapacity =
+ Integer.highestOneBit(maxRollbackBufferCapacityHint - 1) << 1;
+ if (this.maxRollbackBufferCapacity == 0) {
+ this.rollbackBuffer = null;
+ } else {
+ this.rollbackBuffer = new char[DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY];
+ }
+ }
+ }
+
+ /**
+ * Reads characters into a portion of an array. This method will block until some input is
+ * available, an I/O error occurs, or the end of the stream is reached.
+ *
+ * @param cbuf Destination buffer
+ * @param off Offset at which to start storing characters
+ * @param len Maximum number of characters to read
+ * @return The number of characters read, or -1 if the end of the stream has been reached
+ * @throws IOException If an I/O error occurs
+ */
+ @Override
+ public int read(char[] cbuf, int off, int len) throws IOException {
+ while (!inputFinished || position.start > outputCursor) {
+ // (expecting more input) || (output remains that has not been flushed)
+ if (position.start > outputCursor) {
+ return outputFromResultBuffer(cbuf, off, len);
+ }
+
+ int resLen = transliterateBufferContents();
+ if (resLen > 0) {
+ return outputFromResultBuffer(cbuf, off, len);
+ }
+
+ if (!readInputToBuffer()) {
+ final int preStart = position.start;
+ final int preLimit;
+ final int bufferLength = buffer.length();
+ if (preStart < bufferLength) {
+ if (UTF16.isLeadSurrogate(buffer.charAt(bufferLength - 1))) {
+ // if last char is a lead surrogate, transform won't handle it properly
+ // preLimit = bufferLength - 1; // could simply pass the malformed input along
+ throw new RuntimeException(
+ "malformed input; final UTF16 character is a lead surrogate");
+ } else {
+ preLimit = bufferLength;
+ }
+ position.contextLimit = preLimit;
+ position.limit = preLimit;
+ transform.finishTransliteration(replaceable, position);
+ } else if (offsetDiffAdjust == 0) {
+ break;
+ } else {
+ preLimit = bufferLength;
+ }
+ cursorAdvanced(preStart, preLimit);
+ }
+ }
+
+ return -1;
+ }
+
+ private void rollback(int preStart, int preLimit) {
+ buffer.delete(preStart, position.limit); // delete uncommitted chars
+ buffer.insert(preStart, rollbackBuffer, 0, rollbackBufferSize);
+ position.start = preStart;
+ position.contextLimit = preLimit;
+ position.limit = preLimit;
+ }
+
+ /**
+ * Grow rollback buffer if necessary, within constraints of {@link #maxRollbackBufferCapacity}.
+ * This imposes an arbitrary failsafe to prevent the possibility that the rollback buffer could
+ * grow indefinitely.
+ *
+ * @return true if upon return, rollback buffer has sufficient capacity for new input chars,
+ * otherwise false.
+ */
+ private boolean ensureRollbackBufferCapacity() {
+ // ensure space for at least 2 chars (surrogate pair, max possible space needed)
+ if (rollbackBuffer.length - rollbackBufferSize < 2) {
+ if (rollbackBuffer.length < maxRollbackBufferCapacity) {
+ rollbackBuffer = ArrayUtil.growExact(rollbackBuffer, rollbackBuffer.length << 1);
+ } else {
+ // hit threshold; not going to increase the buffer size
+ if (failOnRollbackBufferOverflow) {
+ throw new RuntimeException(
+ "input could not be transliterated without overflowing maxRollbackBufferCapacity ("
+ + maxRollbackBufferCapacity
+ + "); "
+ + "try increasing maxRollbackBufferCapacity, or setting failOnRollbackBufferOverflow=false");
+ }
+ return false;
+ }
+ }
+ return true;
+ }
+
+ private int pushRollbackBuffer(int idx, int bufferLength) {
+ if (idx >= bufferLength) {
+ return 0;
+ } else {
+ // note: we have already ensured sufficient buffer capacity
+ final char candidate = buffer.charAt(idx);
+ if (!UTF16.isLeadSurrogate(candidate)) {
+ if (rollbackBuffer != null) {
+ rollbackBuffer[rollbackBufferSize++] = candidate;
+ }
+ return 1;
+ } else {
+ if (++idx < bufferLength) {
+ if (rollbackBuffer != null) {
+ rollbackBuffer[rollbackBufferSize++] = candidate;
+ rollbackBuffer[rollbackBufferSize++] = buffer.charAt(idx);
+ }
+ return 2;
+ } else {
+ // we don't yet have the high surrogate
+ if (inputFinished) {
+ // no more input available; proceed with the char we have; rollback not needed
+ return 1;
+ } else {
+ return 0; // wait for more input to be available
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Transliterate as much of the contents of {@link #buffer} as possible.
+ *
+ * @return number of output characters transliterated (possibly 0)
+ */
+ private int transliterateBufferContents() {
+ int nextCharLength = pushRollbackBuffer(position.limit, buffer.length());
+ if (nextCharLength == 0) {
+ return 0;
+ }
+ final int preCharCount = charCount;
+ int preStart = position.start;
+ int preLimit;
+ do {
+ position.limit += nextCharLength;
+ preLimit = position.limit;
+ position.contextLimit = preLimit;
+ transform.filteredTransliterate(replaceable, position, true);
+ boolean rollbackSizeWithinBounds = true;
+ if (rollbackBuffer != null
+ && position.start < position.limit
+ && (rollbackSizeWithinBounds = ensureRollbackBufferCapacity())) {
+ // complete pass not transliterated, and not yet at rollback buffer threshold cap.
+ // N.b.: rollback buffer threshold cap is arbitrary, so we check here (somewhat
+ // counterintuitively, *before* rolling back, as opposed to before pushing to
+ // the buffer) so that we can fall through to the else clause, clear the rollback
+ // buffer, and proceed.
+ rollback(preStart, preLimit);
+ } else {
+ rollbackBufferSize = 0;
+ if (position.start > preStart) {
+ // cursor advanced
+ cursorAdvanced(preStart, preLimit);
+
+ // N.b.: advancing contextStart precludes support for quantifiers, but is crucial for
+ // streaming,
+ // so we'll do it anyway.
+ // See comments in Transliterator source code:
+ // TODO
+ // This doesn't work once we add quantifier support. Need to rewrite
+ // this code to support quantifiers and 'use maximum backup <n>;'.
+ //
+ // index.contextStart = Math.max(index.start - getMaximumContextLength(),
+ // originalStart);
+ position.contextStart =
+ Math.max(position.start - transform.getMaximumContextLength(), preStart);
+ preStart = position.start;
+ if (!rollbackSizeWithinBounds) {
+ // prepopulate newly cleared rollback buffer with all top-level uncommitted characters
+ rollbackBufferSize = position.limit - preStart;
+ if (rollbackBuffer.length - rollbackBufferSize < 2) {
+ // even after flushing all committed text, there's not enough space in the rollback
+ // buffer.
+ // This is an edge case of an edge case, when the last char32 read into the rollback
+ // buffer
+ // is a surrogate pair (completely filling the rollback buffer), *and* the last
+ // transliteration pass advanced position.start by exactly one char16 (not a surrogate
+ // pair).
+ preStart = forceAdvance(preStart, preLimit);
+ rollbackBufferSize = position.limit - preStart;
+ }
+ buffer.getChars(preStart, position.limit, rollbackBuffer, 0);
+ }
+ } else if (preLimit != position.limit) {
+ // cursor hasn't advanced; incoming characters have probably been deleted
+ offsetDiffAdjust += preLimit - position.limit;
+ // edge case of !rollbackSizeWithinBounds needs no special handling here, since input
+ // characters *are* being
+ // processed (deleted) -- we *are* progressing through the input stream, although the
+ // output stream hasn't changed.
+ } else if (!rollbackSizeWithinBounds) {
+ // cursor hasn't advanced, no incoming characters have been deleted, and the rollback
+ // buffer is full.
+ preStart = forceAdvance(preStart, preLimit);
+ }
+ }
+ } while ((nextCharLength = pushRollbackBuffer(position.limit, buffer.length())) > 0);
+
+ return charCount - preCharCount;
+ }
+
+ private static final int FORCE_THRESHOLD = 2; // conservative; the length of a surrogate pair
+
+ private int forceAdvance(int preStart, int preLimit) {
+ int shift;
+ if (maxRollbackBufferCapacity == 2) {
+ rollbackBufferSize = 0;
+ shift = 2;
+ } else {
+ shift = 0;
+ do {
+ shift += UTF16.isLeadSurrogate(rollbackBuffer[shift]) ? 2 : 1;
+ } while (shift < FORCE_THRESHOLD && shift < maxRollbackBufferCapacity);
+ rollbackBufferSize -= shift;
+ System.arraycopy(rollbackBuffer, shift, rollbackBuffer, 0, rollbackBufferSize);
+ }
+ position.start += shift; // mock transliterator advance
+ cursorAdvanced(preStart, preLimit);
+ position.contextStart =
+ Math.max(position.start - transform.getMaximumContextLength(), preStart);
+ return position.start;
+ }
+
+ private void cursorAdvanced(int preStart, int preLimit) {
+ final int outputLength = position.start - preStart;
+ final int diff = preLimit - position.limit + offsetDiffAdjust;
+ offsetDiffAdjust = 0;
+ if (diff == 0) {
+ // increment charCount; no offset correction necessary
+ charCount += outputLength;
+ } else {
+ // limit change indicates change in length of replacement text; correct offsets accordingly
+ // we correct offsets as frequently as possible, for every incremental change. This will
+ // sometimes be for a range of characters, but that's the best we can do as far as the level
+ // of granularity that's available to us via the Transliterator API.
+ recordOffsetDiff(diff, outputLength);
+ }
+ }
+
+ private void recordOffsetDiff(int diff, int outputLength) {
+ final int cumuDiff = getLastCumulativeDiff();
+ if (diff < 0) {
+ // positive diff indicates an increase in character count wrt input
+ for (int i = 1; i <= -diff; ++i) {
+ addOffCorrectMap(charCount + i, cumuDiff - i);
+ }
+ } else {
+ // positive diff indicates an decrease in character count wrt input
+ addOffCorrectMap(charCount + outputLength, cumuDiff + diff);
+ }
+ charCount += outputLength;
+ }
+
+ private boolean readInputToBuffer() throws IOException {
+ int res = input.read(tmpBuffer, 0, tmpBuffer.length);
+ if (res == -1) {
+ inputFinished = true;
+ return false;
+ } else {
+ buffer.append(tmpBuffer, 0, res);
+ return true;
+ }
+ }
+
+ private int outputFromResultBuffer(char[] cbuf, int begin, int len) {
+ len = Math.min(position.start - outputCursor, len);
+ buffer.getChars(outputCursor, outputCursor + len, cbuf, begin);
+ outputCursor += len;
+ if (outputCursor > BUFFER_PRUNE_THRESHOLD && position.contextStart > BUFFER_PRUNE_THRESHOLD) {
+ final int pruneSize = Math.min(outputCursor, position.contextStart);
+ buffer.delete(0, pruneSize);
+ position.contextStart -= pruneSize;
+ position.start -= pruneSize;
+ position.limit -= pruneSize;
+ position.contextLimit -= pruneSize;
+ outputCursor -= pruneSize;
+ }
+ return len;
+ }
+
+ /**
+ * Strips off Unicode character normalization form rules from a Transliterator. Do this if, as is
+ * typical, your analysis chain already includes another component that does normalization, like
+ * {@link ICUNormalizer2CharFilter}.
+ *
+ * @return a new Transliterator with no normalization, or the original Transliterator if it
+ * already did no normalization.
+ */
+ public static Transliterator withoutUnicodeNormalization(Transliterator transliterator) {
+ final String modifiedRules = modifyRules(false, transliterator);
+ if (modifiedRules == null) {
+ return transliterator;
+ }
+ String baseId = transliterator.getID();
+ String modId = baseId.concat(baseId.lastIndexOf('/') < 0 ? "/X_NO_NORM_IO" : "_X_NO_NORM_IO");
+ return Transliterator.createFromRules(modId, modifiedRules, Transliterator.FORWARD);
+ }
Review comment:
I would move this logic to the factory for now. If we see `NFD; X; NFC` we can instead do this:
```
charstream = new ICUNormalizer2CharFilter(charstream, NFD);
charstream = new ICUTransformCharCharter(charstream, X);
charstream = new ICUNormalizer2CharFilter(charstream, NFC);
return charstream;
```
This way, the performance is improved automatically but in a safe way, without any option: we just "hoist" normalization out of the transform and implement it with faster component behind the scenes.
##########
File path: lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUTransformCharFilter.java
##########
@@ -0,0 +1,686 @@
+/*
+ * 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 com.ibm.icu.impl.Utility;
+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 java.io.IOException;
+import java.io.Reader;
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Locale;
+import java.util.WeakHashMap;
+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>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;
+ private int offsetDiffAdjust = 0;
+
+ private static final int HARD_MAX_ROLLBACK_BUFFER_CAPACITY =
+ Integer.highestOneBit(Integer.MAX_VALUE);
+ 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;
+
+ static final boolean DEFAULT_FAIL_ON_ROLLBACK_BUFFER_OVERFLOW = true;
+ private final boolean failOnRollbackBufferOverflow;
+
+ ICUTransformCharFilter(Reader in, Transliterator transform) {
+ this(
+ in,
+ transform,
+ DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY,
+ DEFAULT_FAIL_ON_ROLLBACK_BUFFER_OVERFLOW);
+ }
+
+ /**
+ * 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". It is illegal to specify a
+ * negative value. There is no power of 2 greater than <code>
+ * Integer.highestOneBit(Integer.MAX_VALUE))</code>, so to prevent overflow, values in this
+ * range will resolve to an enforced limit of <code>Integer.highestOneBit(Integer.MAX_VALUE))
+ * </code>. Specifying "0" (or "1", in practice) disables rollback. Larger values can in some
+ * cases yield more accurate transliteration, at the cost of performance and
+ * resolution/accuracy of offset correction. This is intended primarily as a failsafe, with a
+ * relatively large default value of {@value
+ * ICUTransformCharFilter#DEFAULT_MAX_ROLLBACK_BUFFER_CAPACITY}. See comments "To understand
+ * the need for rollback" in private method: {@link
+ * Transliterator#filteredTransliterate(com.ibm.icu.text.Replaceable, Position, boolean,
+ * boolean)}
+ * @param failOnRollbackBufferOverflow if true, transliteration failing to complete within the
+ * specified rollbackBuffer window will fail with an exception. If false, transliteration
+ * forges ahead with possibly-inconsistent results.
+ */
+ ICUTransformCharFilter(
+ Reader in,
+ Transliterator transform,
+ int maxRollbackBufferCapacityHint,
+ boolean failOnRollbackBufferOverflow) {
+ super(in);
+ this.transform = ICUTransformFilter.optimizeForCommonCase(transform);
+ this.failOnRollbackBufferOverflow = failOnRollbackBufferOverflow;
+ if (maxRollbackBufferCapacityHint < 0) {
+ throw new IllegalArgumentException(
+ "It is illegal to request negative rollback buffer max capacity");
+ } else if (maxRollbackBufferCapacityHint >= HARD_MAX_ROLLBACK_BUFFER_CAPACITY) {
+ // arg is positive, so user wants the largest possible buffer capacity limit
+ // we know what that is (static), protecting for overflow.
+ this.maxRollbackBufferCapacity = HARD_MAX_ROLLBACK_BUFFER_CAPACITY;
+ this.rollbackBuffer = new char[DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY];
+ } else {
+ // greatest power of 2 (excluding "1") less than or equal to the specified hint
+ this.maxRollbackBufferCapacity =
+ Integer.highestOneBit(maxRollbackBufferCapacityHint - 1) << 1;
+ if (this.maxRollbackBufferCapacity == 0) {
+ this.rollbackBuffer = null;
+ } else {
+ this.rollbackBuffer = new char[DEFAULT_INITIAL_ROLLBACK_BUFFER_CAPACITY];
+ }
+ }
+ }
+
+ /**
+ * Reads characters into a portion of an array. This method will block until some input is
+ * available, an I/O error occurs, or the end of the stream is reached.
+ *
+ * @param cbuf Destination buffer
+ * @param off Offset at which to start storing characters
+ * @param len Maximum number of characters to read
+ * @return The number of characters read, or -1 if the end of the stream has been reached
+ * @throws IOException If an I/O error occurs
+ */
+ @Override
+ public int read(char[] cbuf, int off, int len) throws IOException {
+ while (!inputFinished || position.start > outputCursor) {
+ // (expecting more input) || (output remains that has not been flushed)
+ if (position.start > outputCursor) {
+ return outputFromResultBuffer(cbuf, off, len);
+ }
+
+ int resLen = transliterateBufferContents();
+ if (resLen > 0) {
+ return outputFromResultBuffer(cbuf, off, len);
+ }
+
+ if (!readInputToBuffer()) {
+ final int preStart = position.start;
+ final int preLimit;
+ final int bufferLength = buffer.length();
+ if (preStart < bufferLength) {
+ if (UTF16.isLeadSurrogate(buffer.charAt(bufferLength - 1))) {
+ // if last char is a lead surrogate, transform won't handle it properly
+ // preLimit = bufferLength - 1; // could simply pass the malformed input along
+ throw new RuntimeException(
+ "malformed input; final UTF16 character is a lead surrogate");
+ } else {
+ preLimit = bufferLength;
+ }
+ position.contextLimit = preLimit;
+ position.limit = preLimit;
+ transform.finishTransliteration(replaceable, position);
+ } else if (offsetDiffAdjust == 0) {
+ break;
+ } else {
+ preLimit = bufferLength;
+ }
+ cursorAdvanced(preStart, preLimit);
+ }
+ }
+
+ return -1;
+ }
+
+ private void rollback(int preStart, int preLimit) {
+ buffer.delete(preStart, position.limit); // delete uncommitted chars
+ buffer.insert(preStart, rollbackBuffer, 0, rollbackBufferSize);
+ position.start = preStart;
+ position.contextLimit = preLimit;
+ position.limit = preLimit;
+ }
+
+ /**
+ * Grow rollback buffer if necessary, within constraints of {@link #maxRollbackBufferCapacity}.
+ * This imposes an arbitrary failsafe to prevent the possibility that the rollback buffer could
+ * grow indefinitely.
+ *
+ * @return true if upon return, rollback buffer has sufficient capacity for new input chars,
+ * otherwise false.
+ */
+ private boolean ensureRollbackBufferCapacity() {
+ // ensure space for at least 2 chars (surrogate pair, max possible space needed)
+ if (rollbackBuffer.length - rollbackBufferSize < 2) {
+ if (rollbackBuffer.length < maxRollbackBufferCapacity) {
+ rollbackBuffer = ArrayUtil.growExact(rollbackBuffer, rollbackBuffer.length << 1);
+ } else {
+ // hit threshold; not going to increase the buffer size
+ if (failOnRollbackBufferOverflow) {
+ throw new RuntimeException(
+ "input could not be transliterated without overflowing maxRollbackBufferCapacity ("
+ + maxRollbackBufferCapacity
+ + "); "
+ + "try increasing maxRollbackBufferCapacity, or setting failOnRollbackBufferOverflow=false");
+ }
+ return false;
+ }
+ }
+ return true;
+ }
+
+ private int pushRollbackBuffer(int idx, int bufferLength) {
+ if (idx >= bufferLength) {
+ return 0;
+ } else {
+ // note: we have already ensured sufficient buffer capacity
+ final char candidate = buffer.charAt(idx);
+ if (!UTF16.isLeadSurrogate(candidate)) {
+ if (rollbackBuffer != null) {
+ rollbackBuffer[rollbackBufferSize++] = candidate;
+ }
+ return 1;
+ } else {
+ if (++idx < bufferLength) {
+ if (rollbackBuffer != null) {
+ rollbackBuffer[rollbackBufferSize++] = candidate;
+ rollbackBuffer[rollbackBufferSize++] = buffer.charAt(idx);
+ }
+ return 2;
+ } else {
+ // we don't yet have the high surrogate
+ if (inputFinished) {
+ // no more input available; proceed with the char we have; rollback not needed
+ return 1;
+ } else {
+ return 0; // wait for more input to be available
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Transliterate as much of the contents of {@link #buffer} as possible.
+ *
+ * @return number of output characters transliterated (possibly 0)
+ */
+ private int transliterateBufferContents() {
+ int nextCharLength = pushRollbackBuffer(position.limit, buffer.length());
+ if (nextCharLength == 0) {
+ return 0;
+ }
+ final int preCharCount = charCount;
+ int preStart = position.start;
+ int preLimit;
+ do {
+ position.limit += nextCharLength;
+ preLimit = position.limit;
+ position.contextLimit = preLimit;
+ transform.filteredTransliterate(replaceable, position, true);
+ boolean rollbackSizeWithinBounds = true;
+ if (rollbackBuffer != null
+ && position.start < position.limit
+ && (rollbackSizeWithinBounds = ensureRollbackBufferCapacity())) {
+ // complete pass not transliterated, and not yet at rollback buffer threshold cap.
+ // N.b.: rollback buffer threshold cap is arbitrary, so we check here (somewhat
+ // counterintuitively, *before* rolling back, as opposed to before pushing to
+ // the buffer) so that we can fall through to the else clause, clear the rollback
+ // buffer, and proceed.
+ rollback(preStart, preLimit);
+ } else {
+ rollbackBufferSize = 0;
+ if (position.start > preStart) {
+ // cursor advanced
+ cursorAdvanced(preStart, preLimit);
+
+ // N.b.: advancing contextStart precludes support for quantifiers, but is crucial for
+ // streaming,
+ // so we'll do it anyway.
+ // See comments in Transliterator source code:
+ // TODO
+ // This doesn't work once we add quantifier support. Need to rewrite
+ // this code to support quantifiers and 'use maximum backup <n>;'.
+ //
+ // index.contextStart = Math.max(index.start - getMaximumContextLength(),
+ // originalStart);
+ position.contextStart =
+ Math.max(position.start - transform.getMaximumContextLength(), preStart);
+ preStart = position.start;
+ if (!rollbackSizeWithinBounds) {
+ // prepopulate newly cleared rollback buffer with all top-level uncommitted characters
+ rollbackBufferSize = position.limit - preStart;
+ if (rollbackBuffer.length - rollbackBufferSize < 2) {
+ // even after flushing all committed text, there's not enough space in the rollback
+ // buffer.
+ // This is an edge case of an edge case, when the last char32 read into the rollback
+ // buffer
+ // is a surrogate pair (completely filling the rollback buffer), *and* the last
+ // transliteration pass advanced position.start by exactly one char16 (not a surrogate
+ // pair).
+ preStart = forceAdvance(preStart, preLimit);
+ rollbackBufferSize = position.limit - preStart;
+ }
+ buffer.getChars(preStart, position.limit, rollbackBuffer, 0);
+ }
+ } else if (preLimit != position.limit) {
+ // cursor hasn't advanced; incoming characters have probably been deleted
+ offsetDiffAdjust += preLimit - position.limit;
+ // edge case of !rollbackSizeWithinBounds needs no special handling here, since input
+ // characters *are* being
+ // processed (deleted) -- we *are* progressing through the input stream, although the
+ // output stream hasn't changed.
+ } else if (!rollbackSizeWithinBounds) {
+ // cursor hasn't advanced, no incoming characters have been deleted, and the rollback
+ // buffer is full.
+ preStart = forceAdvance(preStart, preLimit);
+ }
+ }
+ } while ((nextCharLength = pushRollbackBuffer(position.limit, buffer.length())) > 0);
+
+ return charCount - preCharCount;
+ }
+
+ private static final int FORCE_THRESHOLD = 2; // conservative; the length of a surrogate pair
+
+ private int forceAdvance(int preStart, int preLimit) {
+ int shift;
+ if (maxRollbackBufferCapacity == 2) {
+ rollbackBufferSize = 0;
+ shift = 2;
+ } else {
+ shift = 0;
+ do {
+ shift += UTF16.isLeadSurrogate(rollbackBuffer[shift]) ? 2 : 1;
+ } while (shift < FORCE_THRESHOLD && shift < maxRollbackBufferCapacity);
+ rollbackBufferSize -= shift;
+ System.arraycopy(rollbackBuffer, shift, rollbackBuffer, 0, rollbackBufferSize);
+ }
+ position.start += shift; // mock transliterator advance
+ cursorAdvanced(preStart, preLimit);
+ position.contextStart =
+ Math.max(position.start - transform.getMaximumContextLength(), preStart);
+ return position.start;
+ }
+
+ private void cursorAdvanced(int preStart, int preLimit) {
+ final int outputLength = position.start - preStart;
+ final int diff = preLimit - position.limit + offsetDiffAdjust;
+ offsetDiffAdjust = 0;
+ if (diff == 0) {
+ // increment charCount; no offset correction necessary
+ charCount += outputLength;
+ } else {
+ // limit change indicates change in length of replacement text; correct offsets accordingly
+ // we correct offsets as frequently as possible, for every incremental change. This will
+ // sometimes be for a range of characters, but that's the best we can do as far as the level
+ // of granularity that's available to us via the Transliterator API.
+ recordOffsetDiff(diff, outputLength);
+ }
+ }
+
+ private void recordOffsetDiff(int diff, int outputLength) {
+ final int cumuDiff = getLastCumulativeDiff();
+ if (diff < 0) {
+ // positive diff indicates an increase in character count wrt input
+ for (int i = 1; i <= -diff; ++i) {
+ addOffCorrectMap(charCount + i, cumuDiff - i);
+ }
+ } else {
+ // positive diff indicates an decrease in character count wrt input
+ addOffCorrectMap(charCount + outputLength, cumuDiff + diff);
+ }
+ charCount += outputLength;
+ }
+
+ private boolean readInputToBuffer() throws IOException {
+ int res = input.read(tmpBuffer, 0, tmpBuffer.length);
+ if (res == -1) {
+ inputFinished = true;
+ return false;
+ } else {
+ buffer.append(tmpBuffer, 0, res);
+ return true;
+ }
+ }
+
+ private int outputFromResultBuffer(char[] cbuf, int begin, int len) {
+ len = Math.min(position.start - outputCursor, len);
+ buffer.getChars(outputCursor, outputCursor + len, cbuf, begin);
+ outputCursor += len;
+ if (outputCursor > BUFFER_PRUNE_THRESHOLD && position.contextStart > BUFFER_PRUNE_THRESHOLD) {
+ final int pruneSize = Math.min(outputCursor, position.contextStart);
+ buffer.delete(0, pruneSize);
+ position.contextStart -= pruneSize;
+ position.start -= pruneSize;
+ position.limit -= pruneSize;
+ position.contextLimit -= pruneSize;
+ outputCursor -= pruneSize;
+ }
+ return len;
+ }
+
+ /**
+ * Strips off Unicode character normalization form rules from a Transliterator. Do this if, as is
+ * typical, your analysis chain already includes another component that does normalization, like
+ * {@link ICUNormalizer2CharFilter}.
+ *
+ * @return a new Transliterator with no normalization, or the original Transliterator if it
+ * already did no normalization.
+ */
+ public static Transliterator withoutUnicodeNormalization(Transliterator transliterator) {
+ final String modifiedRules = modifyRules(false, transliterator);
+ if (modifiedRules == null) {
+ return transliterator;
+ }
+ String baseId = transliterator.getID();
+ String modId = baseId.concat(baseId.lastIndexOf('/') < 0 ? "/X_NO_NORM_IO" : "_X_NO_NORM_IO");
+ return Transliterator.createFromRules(modId, modifiedRules, Transliterator.FORWARD);
+ }
Review comment:
And finally for the ICUNormalizer2CharFilterFactory I am ok with it inspecting the input stream and just returning it bare to complete the optimization. For example if you ask to normalize to NFC:
```
if (!(charstream instanceof ICUNormalizer2CharFilter and in [NFC, NFKC]])) {
charstream = new ICUNormalizer2CharFilter(charstream, NFC);
}
return charstream;
```
It is just a safe optimization to do, to remove double normalization in this way. Although really it shouldn't be that expensive especially on already-normalized strings, as normalization is optimized for that.
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