LineBasedFrameDecoder.java — netty Source File

Source Code

/*
 * Copyright 2012 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.handler.codec;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.util.ByteProcessor;

import java.util.List;

/**
 * A decoder that splits the received {@link ByteBuf}s on line endings.
 * <p>
 * Both {@code "\n"} and {@code "\r\n"} are handled.
 * <p>
 * The byte stream is expected to be in UTF-8 character encoding or ASCII. The current implementation
 * uses direct {@code byte} to {@code char} cast and then compares that {@code char} to a few low range
 * ASCII characters like {@code '\n'} or {@code '\r'}. UTF-8 is not using low range [0..0x7F]
 * byte values for multibyte codepoint representations therefore fully supported by this implementation.
 * <p>
 * For a more general delimiter-based decoder, see {@link DelimiterBasedFrameDecoder}.
 * <p>
 * Users should be aware that used as is, the lenient approach on lone {@code '\n} might result on a parser
 * diffenrencial on line based protocols requiring the use of {@code "\r\n"} delimiters like SMTP and can
 * result in attacks similar to
 * <a href="https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/">SMTP smuggling</a>.
 * Validating afterward the end of line pattern can be a possible mitigation.
 */
public class LineBasedFrameDecoder extends ByteToMessageDecoder {

    /** Maximum length of a frame we're willing to decode.  */
    private final int maxLength;
    /** Whether or not to throw an exception as soon as we exceed maxLength. */
    private final boolean failFast;
    private final boolean stripDelimiter;

    /** True if we're discarding input because we're already over maxLength.  */
    private boolean discarding;
    private int discardedBytes;

    /** Last scan position. */
    private int offset;

    /**
     * Creates a new decoder.
     * @param maxLength  the maximum length of the decoded frame.
     *                   A {@link TooLongFrameException} is thrown if
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