io.netty.buffer.search.AbstractMultiSearchProcessorFactory Maven / Gradle / Ivy
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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including
all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and
JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up
with different versions on classes on the class path).
/*
* Copyright 2020 The Netty Project
*
* The Netty Project 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:
*
* https://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 io.netty.buffer.search;
/**
* Base class for precomputed factories that create {@link MultiSearchProcessor}s.
*
* The purpose of {@link MultiSearchProcessor} is to perform efficient simultaneous search for multiple {@code needles}
* in the {@code haystack}, while scanning every byte of the input sequentially, only once. While it can also be used
* to search for just a single {@code needle}, using a {@link SearchProcessorFactory} would be more efficient for
* doing that.
*
* See the documentation of {@link AbstractSearchProcessorFactory} for a comprehensive description of common usage.
* In addition to the functionality provided by {@link SearchProcessor}, {@link MultiSearchProcessor} adds
* a method to get the index of the {@code needle} found at the current position of the {@link MultiSearchProcessor} -
* {@link MultiSearchProcessor#getFoundNeedleId()}.
*
* Note: in some cases one {@code needle} can be a suffix of another {@code needle}, eg. {@code {"BC", "ABC"}},
* and there can potentially be multiple {@code needles} found ending at the same position of the {@code haystack}.
* In such case {@link MultiSearchProcessor#getFoundNeedleId()} returns the index of the longest matching {@code needle}
* in the array of {@code needles}.
*
* Usage example (given that the {@code haystack} is a {@link io.netty.buffer.ByteBuf} containing "ABCD" and the
* {@code needles} are "AB", "BC" and "CD"):
*
* MultiSearchProcessorFactory factory = MultiSearchProcessorFactory.newAhoCorasicSearchProcessorFactory(
* "AB".getBytes(CharsetUtil.UTF_8), "BC".getBytes(CharsetUtil.UTF_8), "CD".getBytes(CharsetUtil.UTF_8));
* MultiSearchProcessor processor = factory.newSearchProcessor();
*
* int idx1 = haystack.forEachByte(processor);
* // idx1 is 1 (index of the last character of the occurrence of "AB" in the haystack)
* // processor.getFoundNeedleId() is 0 (index of "AB" in needles[])
*
* int continueFrom1 = idx1 + 1;
* // continue the search starting from the next character
*
* int idx2 = haystack.forEachByte(continueFrom1, haystack.readableBytes() - continueFrom1, processor);
* // idx2 is 2 (index of the last character of the occurrence of "BC" in the haystack)
* // processor.getFoundNeedleId() is 1 (index of "BC" in needles[])
*
* int continueFrom2 = idx2 + 1;
*
* int idx3 = haystack.forEachByte(continueFrom2, haystack.readableBytes() - continueFrom2, processor);
* // idx3 is 3 (index of the last character of the occurrence of "CD" in the haystack)
* // processor.getFoundNeedleId() is 2 (index of "CD" in needles[])
*
* int continueFrom3 = idx3 + 1;
*
* int idx4 = haystack.forEachByte(continueFrom3, haystack.readableBytes() - continueFrom3, processor);
* // idx4 is -1 (no more occurrences of any of the needles)
*
* // This search session is complete, processor should be discarded.
* // To search for the same needles again, reuse the same {@link AbstractMultiSearchProcessorFactory}
* // to get a new MultiSearchProcessor.
*
*/
public abstract class AbstractMultiSearchProcessorFactory implements MultiSearchProcessorFactory {
/**
* Creates a {@link MultiSearchProcessorFactory} based on
* Aho–Corasick
* string search algorithm.
*
* Precomputation (this method) time is linear in the size of input ({@code O(Σ|needles|)}).
*
* The factory allocates and retains an array of 256 * X ints plus another array of X ints, where X
* is the sum of lengths of each entry of {@code needles} minus the sum of lengths of repeated
* prefixes of the {@code needles}.
*
* Search (the actual application of {@link MultiSearchProcessor}) time is linear in the size of
* {@link io.netty.buffer.ByteBuf} on which the search is performed ({@code O(|haystack|)}).
* Every byte of {@link io.netty.buffer.ByteBuf} is processed only once, sequentually, regardles of
* the number of {@code needles} being searched for.
*
* @param needles a varargs array of arrays of bytes to search for
* @return a new instance of {@link AhoCorasicSearchProcessorFactory} precomputed for the given {@code needles}
*/
public static AhoCorasicSearchProcessorFactory newAhoCorasicSearchProcessorFactory(byte[] ...needles) {
return new AhoCorasicSearchProcessorFactory(needles);
}
}