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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * 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 org.jboss.netty.handler.codec.http.websocketx;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.TooLongFrameException;
import org.jboss.netty.handler.codec.replay.ReplayingDecoder;
import org.jboss.netty.handler.codec.replay.VoidEnum;

/**
 * Decodes {@link ChannelBuffer}s into {@link WebSocketFrame}s.
 * 
 * For the detailed instruction on adding add Web Socket support to your HTTP server, take a look into the
 * WebSocketServer example located in the {@code org.jboss.netty.example.http.websocket} package.
 *
 * @apiviz.landmark
 * @apiviz.uses org.jboss.netty.handler.codec.http.websocket.WebSocketFrame
 */
public class WebSocket00FrameDecoder extends ReplayingDecoder {

    private static final long DEFAULT_MAX_FRAME_SIZE = 16384;

    private final long maxFrameSize;
    private boolean receivedClosingHandshake;

    public WebSocket00FrameDecoder() {
        this(DEFAULT_MAX_FRAME_SIZE);
    }

    /**
     * Creates a new instance of {@code WebSocketFrameDecoder} with the specified {@code maxFrameSize}. If the client
     * sends a frame size larger than {@code maxFrameSize}, the channel will be closed.
     *
     * @param maxFrameSize
     *            the maximum frame size to decode
     * @deprecated
     */
    @Deprecated
    public WebSocket00FrameDecoder(int maxFrameSize) {
        this.maxFrameSize = maxFrameSize;
    }

    /**
     * Creates a new instance of {@code WebSocketFrameDecoder} with the specified {@code maxFrameSize}. If the client
     * sends a frame size larger than {@code maxFrameSize}, the channel will be closed.
     *
     * @param maxFrameSize
     *            the maximum frame size to decode
     */
    public WebSocket00FrameDecoder(long maxFrameSize) {
        this.maxFrameSize = maxFrameSize;
    }

    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer, VoidEnum state)
            throws Exception {

        // Discard all data received if closing handshake was received before.
        if (receivedClosingHandshake) {
            buffer.skipBytes(actualReadableBytes());
            return null;
        }

        // Decode a frame otherwise.
        byte type = buffer.readByte();
        if ((type & 0x80) == 0x80) {
            // If the MSB on type is set, decode the frame length
            return decodeBinaryFrame(type, buffer);
        } else {
            // Decode a 0xff terminated UTF-8 string
            return decodeTextFrame(buffer);
        }
    }

    private WebSocketFrame decodeBinaryFrame(byte type, ChannelBuffer buffer) throws TooLongFrameException {
        long frameSize = 0;
        int lengthFieldSize = 0;
        byte b;
        do {
            b = buffer.readByte();
            frameSize <<= 7;
            frameSize |= b & 0x7f;
            if (frameSize > maxFrameSize) {
                throw new TooLongFrameException();
            }
            lengthFieldSize++;
            if (lengthFieldSize > 8) {
                // Perhaps a malicious peer?
                throw new TooLongFrameException();
            }
        } while ((b & 0x80) == 0x80);

        if (type == (byte) 0xFF && frameSize == 0) {
            receivedClosingHandshake = true;
            return new CloseWebSocketFrame();
        }

        return new BinaryWebSocketFrame(buffer.readBytes((int) frameSize));
    }

    private WebSocketFrame decodeTextFrame(ChannelBuffer buffer) throws TooLongFrameException {
        int ridx = buffer.readerIndex();
        int rbytes = actualReadableBytes();
        int delimPos = buffer.indexOf(ridx, ridx + rbytes, (byte) 0xFF);
        if (delimPos == -1) {
            // Frame delimiter (0xFF) not found
            if (rbytes > maxFrameSize) {
                // Frame length exceeded the maximum
                throw new TooLongFrameException();
            } else {
                // Wait until more data is received
                return null;
            }
        }

        int frameSize = delimPos - ridx;
        if (frameSize > maxFrameSize) {
            throw new TooLongFrameException();
        }

        ChannelBuffer binaryData = buffer.readBytes(frameSize);
        buffer.skipBytes(1);

        int ffDelimPos = binaryData.indexOf(binaryData.readerIndex(), binaryData.writerIndex(), (byte) 0xFF);
        if (ffDelimPos >= 0) {
            throw new IllegalArgumentException("a text frame should not contain 0xFF.");
        }

        return new TextWebSocketFrame(binaryData);
    }
}