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Java example source code file (LineBasedFrameDecoder.java)

This example Java source code file (LineBasedFrameDecoder.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

bytebuf, bytetomessagedecoder, channelhandlercontext, exception, linebasedframedecoder, list, object, override, string, toolongframeexception, util

The LineBasedFrameDecoder.java Java example 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:
 *
 *   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 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.
 * For a more general delimiter-based decoder, see {@link DelimiterBasedFrameDecoder}.
 */
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;

    /**
     * Creates a new decoder.
     * @param maxLength  the maximum length of the decoded frame.
     *                   A {@link TooLongFrameException} is thrown if
     *                   the length of the frame exceeds this value.
     */
    public LineBasedFrameDecoder(final int maxLength) {
        this(maxLength, true, false);
    }

    /**
     * Creates a new decoder.
     * @param maxLength  the maximum length of the decoded frame.
     *                   A {@link TooLongFrameException} is thrown if
     *                   the length of the frame exceeds this value.
     * @param stripDelimiter  whether the decoded frame should strip out the
     *                        delimiter or not
     * @param failFast  If <tt>true, a {@link TooLongFrameException} is
     *                  thrown as soon as the decoder notices the length of the
     *                  frame will exceed <tt>maxFrameLength regardless of
     *                  whether the entire frame has been read.
     *                  If <tt>false, a {@link TooLongFrameException} is
     *                  thrown after the entire frame that exceeds
     *                  <tt>maxFrameLength has been read.
     */
    public LineBasedFrameDecoder(final int maxLength, final boolean stripDelimiter, final boolean failFast) {
        this.maxLength = maxLength;
        this.failFast = failFast;
        this.stripDelimiter = stripDelimiter;
    }

    @Override
    protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        Object decoded = decode(ctx, in);
        if (decoded != null) {
            out.add(decoded);
        }
    }

    /**
     * Create a frame out of the {@link ByteBuf} and return it.
     *
     * @param   ctx             the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
     * @param   buffer          the {@link ByteBuf} from which to read data
     * @return  frame           the {@link ByteBuf} which represent the frame or {@code null} if no frame could
     *                          be created.
     */
    protected Object decode(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {
        final int eol = findEndOfLine(buffer);
        if (!discarding) {
            if (eol >= 0) {
                final ByteBuf frame;
                final int length = eol - buffer.readerIndex();
                final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1;

                if (length > maxLength) {
                    buffer.readerIndex(eol + delimLength);
                    fail(ctx, length);
                    return null;
                }

                if (stripDelimiter) {
                    frame = buffer.readRetainedSlice(length);
                    buffer.skipBytes(delimLength);
                } else {
                    frame = buffer.readRetainedSlice(length + delimLength);
                }

                return frame;
            } else {
                final int length = buffer.readableBytes();
                if (length > maxLength) {
                    discardedBytes = length;
                    buffer.readerIndex(buffer.writerIndex());
                    discarding = true;
                    if (failFast) {
                        fail(ctx, "over " + discardedBytes);
                    }
                }
                return null;
            }
        } else {
            if (eol >= 0) {
                final int length = discardedBytes + eol - buffer.readerIndex();
                final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1;
                buffer.readerIndex(eol + delimLength);
                discardedBytes = 0;
                discarding = false;
                if (!failFast) {
                    fail(ctx, length);
                }
            } else {
                discardedBytes += buffer.readableBytes();
                buffer.readerIndex(buffer.writerIndex());
            }
            return null;
        }
    }

    private void fail(final ChannelHandlerContext ctx, int length) {
        fail(ctx, String.valueOf(length));
    }

    private void fail(final ChannelHandlerContext ctx, String length) {
        ctx.fireExceptionCaught(
                new TooLongFrameException(
                        "frame length (" + length + ") exceeds the allowed maximum (" + maxLength + ')'));
    }

    /**
     * Returns the index in the buffer of the end of line found.
     * Returns -1 if no end of line was found in the buffer.
     */
    private static int findEndOfLine(final ByteBuf buffer) {
        int i = buffer.forEachByte(ByteProcessor.FIND_LF);
        if (i > 0 && buffer.getByte(i - 1) == '\r') {
            i--;
        }
        return i;
    }
}

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