/*
    * Copyright 2019 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.http.websocketx;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.ReplayingDecoder;
  import io.netty.handler.codec.TooLongFrameException;
  import io.netty.util.internal.ObjectUtil;
  
  import java.util.List;
  
  import static io.netty.buffer.ByteBufUtil.readBytes;
  
  /**
   * Decodes {@link ByteBuf}s into {@link WebSocketFrame}s.
   * <p>
   * For the detailed instruction on adding add Web Socket support to your HTTP server, take a look into the
   * <tt>WebSocketServer</tt> example located in the {@code io.netty.example.http.websocket} package.
   */
  public class WebSocket00FrameDecoder extends ReplayingDecoder<Void> implements WebSocketFrameDecoder {
  
      static final int 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
       */
      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 decoderConfig
       *            Frames decoder configuration.
       */
      public WebSocket00FrameDecoder(WebSocketDecoderConfig decoderConfig) {
          this.maxFrameSize = ObjectUtil.checkNotNull(decoderConfig, "decoderConfig").maxFramePayloadLength();
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
          // Discard all data received if closing handshake was received before.
          if (receivedClosingHandshake) {
              in.skipBytes(actualReadableBytes());
              return;
          }
  
          // Decode a frame otherwise.
          byte type = in.readByte();
          WebSocketFrame frame;
          if ((type & 0x80) == 0x80) {
              // If the MSB on type is set, decode the frame length
              frame = decodeBinaryFrame(ctx, type, in);
          } else {
              // Decode a 0xff terminated UTF-8 string
              frame = decodeTextFrame(ctx, in);
          }
  
          if (frame != null) {
              out.add(frame);
          }
      }
  
      private WebSocketFrame decodeBinaryFrame(ChannelHandlerContext ctx, byte type, ByteBuf buffer) {
          long frameSize = 0;
          int lengthFieldSize = 0;
          byte b;
          do {
              b = buffer.readByte();
              frameSize <<= 7;
              frameSize |= b & 0x7f;
              if (frameSize > maxFrameSize) {
                 throw new TooLongFrameException("frame length exceeds " + maxFrameSize + ": " + frameSize);
             }
             lengthFieldSize++;
             if (lengthFieldSize > 8) {
                 // Perhaps a malicious peer?
                 throw new TooLongFrameException("frame length field size exceeds 8: " + lengthFieldSize);
             }
         } while ((b & 0x80) == 0x80);
 
         if (type == (byte) 0xFF && frameSize == 0) {
             receivedClosingHandshake = true;
             return new CloseWebSocketFrame(true, 0, ctx.alloc().buffer(0));
         }
         ByteBuf payload = readBytes(ctx.alloc(), buffer, (int) frameSize);
         return new BinaryWebSocketFrame(payload);
     }
 
     private WebSocketFrame decodeTextFrame(ChannelHandlerContext ctx, ByteBuf buffer) {
         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("frame length exceeds " + maxFrameSize + ": " + rbytes);
             } else {
                 // Wait until more data is received
                 return null;
             }
         }
 
         int frameSize = delimPos - ridx;
         if (frameSize > maxFrameSize) {
             throw new TooLongFrameException("frame length exceeds " + maxFrameSize + ": " + frameSize);
         }
 
         ByteBuf binaryData = readBytes(ctx.alloc(), buffer, frameSize);
         buffer.skipBytes(1);
 
         int ffDelimPos = binaryData.indexOf(binaryData.readerIndex(), binaryData.writerIndex(), (byte) 0xFF);
         if (ffDelimPos >= 0) {
             binaryData.release();
             throw new IllegalArgumentException("a text frame should not contain 0xFF.");
         }
 
         return new TextWebSocketFrame(binaryData);
     }
 }