org.eclipse.jetty.util.SearchPattern Maven / Gradle / Ivy
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// Copyright (c) 1995-2022 Mort Bay Consulting Pty Ltd and others.
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// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
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// http://www.eclipse.org/legal/epl-v10.html
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// The Apache License v2.0 is available at
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package org.eclipse.jetty.util;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
/**
* SearchPattern
*
* Fast search for patterns within strings and arrays of bytes.
* Uses an implementation of the Boyer–Moore–Horspool algorithm
* with a 256 character alphabet.
*
* The algorithm has an average-case complexity of O(n)
* on random text and O(nm) in the worst case.
* where:
* m = pattern length
* n = length of data to search
*/
public class SearchPattern
{
private static final int ALPHABET_SIZE = 256;
private final int[] table = new int[ALPHABET_SIZE];
private final byte[] pattern;
/**
* Produces a SearchPattern instance which can be used
* to find matches of the pattern in data
*
* @param pattern byte array containing the pattern
* @return a new SearchPattern instance using the given pattern
*/
public static SearchPattern compile(byte[] pattern)
{
return new SearchPattern(Arrays.copyOf(pattern, pattern.length));
}
/**
* Produces a SearchPattern instance which can be used
* to find matches of the pattern in data
*
* @param pattern string containing the pattern
* @return a new SearchPattern instance using the given pattern
*/
public static SearchPattern compile(String pattern)
{
return new SearchPattern(pattern.getBytes(StandardCharsets.UTF_8));
}
/**
* @param pattern byte array containing the pattern used for matching
*/
private SearchPattern(byte[] pattern)
{
this.pattern = pattern;
if (pattern.length == 0)
throw new IllegalArgumentException("Empty Pattern");
//Build up the pre-processed table for this pattern.
Arrays.fill(table, pattern.length);
for (int i = 0; i < pattern.length - 1; ++i)
{
table[0xff & pattern[i]] = pattern.length - 1 - i;
}
}
/**
* Search for a complete match of the pattern within the data
*
* @param data The data in which to search for. The data may be arbitrary binary data,
* but the pattern will always be {@link StandardCharsets#US_ASCII} encoded.
* @param offset The offset within the data to start the search
* @param length The length of the data to search
* @return The index within the data array at which the first instance of the pattern or -1 if not found
*/
public int match(byte[] data, int offset, int length)
{
validateArgs(data, offset, length);
int skip = offset;
while (skip <= offset + length - pattern.length)
{
for (int i = pattern.length - 1; data[skip + i] == pattern[i]; i--)
{
if (i == 0)
return skip;
}
skip += table[0xff & data[skip + pattern.length - 1]];
}
return -1;
}
/**
* Search for a partial match of the pattern at the end of the data.
*
* @param data The data in which to search for. The data may be arbitrary binary data,
* but the pattern will always be {@link StandardCharsets#US_ASCII} encoded.
* @param offset The offset within the data to start the search
* @param length The length of the data to search
* @return the length of the partial pattern matched and 0 for no match.
*/
public int endsWith(byte[] data, int offset, int length)
{
validateArgs(data, offset, length);
int skip = (pattern.length <= length) ? (offset + length - pattern.length) : offset;
while (skip < offset + length)
{
for (int i = (offset + length - 1) - skip; data[skip + i] == pattern[i]; --i)
{
if (i == 0)
return (offset + length - skip);
}
// We can't use the pre-processed table as we are not matching on the full pattern.
skip++;
}
return 0;
}
/**
* Search for a possibly partial match of the pattern at the start of the data.
*
* @param data The data in which to search for. The data may be arbitrary binary data,
* but the pattern will always be {@link StandardCharsets#US_ASCII} encoded.
* @param offset The offset within the data to start the search
* @param length The length of the data to search
* @param matched The length of the partial pattern already matched
* @return the length of the partial pattern matched and 0 for no match.
*/
public int startsWith(byte[] data, int offset, int length, int matched)
{
validateArgs(data, offset, length);
int matchedCount = 0;
for (int i = 0; i < pattern.length - matched && i < length; i++)
{
if (data[offset + i] == pattern[i + matched])
matchedCount++;
else
return 0;
}
return matched + matchedCount;
}
/**
* Performs legality checks for standard arguments input into SearchPattern methods.
*
* @param data The data in which to search for. The data may be arbitrary binary data,
* but the pattern will always be {@link StandardCharsets#US_ASCII} encoded.
* @param offset The offset within the data to start the search
* @param length The length of the data to search
*/
private void validateArgs(byte[] data, int offset, int length)
{
if (offset < 0)
throw new IllegalArgumentException("offset was negative");
else if (length < 0)
throw new IllegalArgumentException("length was negative");
else if (offset + length > data.length)
throw new IllegalArgumentException("(offset+length) out of bounds of data[]");
}
/**
* @return The length of the pattern in bytes.
*/
public int getLength()
{
return pattern.length;
}
}