log4j-core/src/main/java/org/apache/logging/log4j/core/layout/AbstractStringLayout.java

/*
 * 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.logging.log4j.core.layout;

import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

import org.apache.logging.log4j.core.LogEvent;

/**
 * Abstract base class for Layouts that result in a String.
 * <p>
 * Since 2.4.1, this class has custom logic to convert ISO-8859-1 or US-ASCII Strings to byte[] arrays to improve
 * performance: all characters are simply cast to bytes.
 */
/*
 * Implementation note: prefer String.getBytes(String) to String.getBytes(Charset) for performance reasons. See
 * https://issues.apache.org/jira/browse/LOG4J2-935 for details.
 */
public abstract class AbstractStringLayout extends AbstractLayout<String> {

    /**
     * Default length for new StringBuilder instances: {@value} .
     */
    protected static final int DEFAULT_STRING_BUILDER_SIZE = 1024;

    private final static ThreadLocal<StringBuilder> threadLocal = new ThreadLocal<>();

    private static final long serialVersionUID = 1L;

    /**
     * The charset for the formatted message.
     */
    // TODO: Charset is not serializable. Implement read/writeObject() ?
    private final Charset charset;
    private final String charsetName;
    private final boolean useCustomEncoding;

    protected AbstractStringLayout(final Charset charset) {
        this(charset, null, null);
    }

    protected AbstractStringLayout(final Charset charset, final byte[] header, final byte[] footer) {
        super(header, footer);
        this.charset = charset == null ? StandardCharsets.UTF_8 : charset;
        this.charsetName = this.charset.name();
        useCustomEncoding = isPreJava8()
                && (StandardCharsets.ISO_8859_1.equals(charset) || StandardCharsets.US_ASCII.equals(charset));
    }

    // LOG4J2-1151: If the built-in JDK 8 encoders are available we should use them.
    private static boolean isPreJava8() {
        final String version = System.getProperty("java.version");
        final String[] parts = version.split("\\.");
        try {
            int major = Integer.parseInt(parts[1]);
            return major < 8;
        } catch (Exception ex) {
            return true;
        }
    }

    /**
     * Converts a String to a byte[].
     * 
     * @param str if null, return null.
     * @param charset if null, use the default charset.
     * @return a byte[]
     */
    static byte[] toBytes(final String str, final Charset charset) {
        if (str != null) {
            if (StandardCharsets.ISO_8859_1.equals(charset)) {
                return encodeSingleByteChars(str);
            }
            final Charset actual = charset != null ? charset : Charset.defaultCharset();
            try { // LOG4J2-935: String.getBytes(String) gives better performance
                return str.getBytes(actual.name());
            } catch (UnsupportedEncodingException e) {
                return str.getBytes(actual);
            }
        }
        return null;
    }

    /**
     * Returns a {@code StringBuilder} that this Layout implementation can use to write the formatted log event to.
     * 
     * @return a {@code StringBuilder}
     */
    protected StringBuilder getStringBuilder() {
        StringBuilder result = threadLocal.get();
        if (result == null) {
            result = new StringBuilder(DEFAULT_STRING_BUILDER_SIZE);
            threadLocal.set(result);
        }
        result.setLength(0);
        return result;
    }

    protected byte[] getBytes(final String s) {
        if (useCustomEncoding) { // rely on branch prediction to eliminate this check if false
            return encodeSingleByteChars(s);
        }
        try { // LOG4J2-935: String.getBytes(String) gives better performance
            return s.getBytes(charsetName);
        } catch (UnsupportedEncodingException e) {
            return s.getBytes(charset);
        }
    }

    /**
     * Encode the specified string by casting each character to a byte.
     * 
     * @param s the string to encode
     * @return the encoded String
     * @see https://issues.apache.org/jira/browse/LOG4J2-1151
     */
    private static byte[] encodeSingleByteChars(String s) {
        final int length = s.length();
        final byte[] result = new byte[length];
        encodeString(s, 0, length, result);
        return result;
    }

    // LOG4J2-1151
    /*
     * Implementation note: this is the fast path. If the char array contains only ISO-8859-1 characters, all the work
     * will be done here.
     */
    private static int encodeIsoChars(String charArray, int charIndex, byte[] byteArray, int byteIndex, int length) {
        int i = 0;
        for (; i < length; i++) {
            char c = charArray.charAt(charIndex++);
            if (c > 255) {
                break;
            }
            byteArray[(byteIndex++)] = ((byte) c);
        }
        return i;
    }

    // LOG4J2-1151
    private static int encodeString(String charArray, int charOffset, int charLength, byte[] byteArray) {
        int byteOffset = 0;
        int length = Math.min(charLength, byteArray.length);
        int charDoneIndex = charOffset + length;
        while (charOffset < charDoneIndex) {
            int done = encodeIsoChars(charArray, charOffset, byteArray, byteOffset, length);
            charOffset += done;
            byteOffset += done;
            if (done != length) {
                char c = charArray.charAt(charOffset++);
                if ((Character.isHighSurrogate(c)) && (charOffset < charDoneIndex)
                        && (Character.isLowSurrogate(charArray.charAt(charOffset)))) {
                    if (charLength > byteArray.length) {
                        charDoneIndex++;
                        charLength--;
                    }
                    charOffset++;
                }
                byteArray[(byteOffset++)] = '?';
                length = Math.min(charDoneIndex - charOffset, byteArray.length - byteOffset);
            }
        }
        return byteOffset;
    }

    protected Charset getCharset() {
        return charset;
    }

    /**
     * @return The default content type for Strings.
     */
    @Override
    public String getContentType() {
        return "text/plain";
    }

    /**
     * Formats the Log Event as a byte array.
     *
     * @param event The Log Event.
     * @return The formatted event as a byte array.
     */
    @Override
    public byte[] toByteArray(final LogEvent event) {
        return getBytes(toSerializable(event));
    }

}