/*
    * Copyright 2014 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.http2;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.embedded.EmbeddedChannel;
  import io.netty.handler.codec.ByteToMessageDecoder;
  import io.netty.handler.codec.compression.ZlibCodecFactory;
  import io.netty.handler.codec.compression.ZlibWrapper;
  import io.netty.util.internal.UnstableApi;
  
  import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_ENCODING;
  import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_LENGTH;
  import static io.netty.handler.codec.http.HttpHeaderValues.DEFLATE;
  import static io.netty.handler.codec.http.HttpHeaderValues.GZIP;
  import static io.netty.handler.codec.http.HttpHeaderValues.IDENTITY;
  import static io.netty.handler.codec.http.HttpHeaderValues.X_DEFLATE;
  import static io.netty.handler.codec.http.HttpHeaderValues.X_GZIP;
  import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
  import static io.netty.handler.codec.http2.Http2Exception.streamError;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * A HTTP2 frame listener that will decompress data frames according to the {@code content-encoding} header for each
   * stream. The decompression provided by this class will be applied to the data for the entire stream.
   */
  @UnstableApi
  public class DelegatingDecompressorFrameListener extends Http2FrameListenerDecorator {
  
      private final Http2Connection connection;
      private final boolean strict;
      private boolean flowControllerInitialized;
      private final Http2Connection.PropertyKey propertyKey;
  
      public DelegatingDecompressorFrameListener(Http2Connection connection, Http2FrameListener listener) {
          this(connection, listener, true);
      }
  
      public DelegatingDecompressorFrameListener(Http2Connection connection, Http2FrameListener listener,
                      boolean strict) {
          super(listener);
          this.connection = connection;
          this.strict = strict;
  
          propertyKey = connection.newKey();
          connection.addListener(new Http2ConnectionAdapter() {
              @Override
              public void onStreamRemoved(Http2Stream stream) {
                  final Http2Decompressor decompressor = decompressor(stream);
                  if (decompressor != null) {
                      cleanup(decompressor);
                  }
              }
          });
      }
  
      @Override
      public int onDataRead(ChannelHandlerContext ctx, int streamId, ByteBuf data, int padding, boolean endOfStream)
              throws Http2Exception {
          final Http2Stream stream = connection.stream(streamId);
          final Http2Decompressor decompressor = decompressor(stream);
          if (decompressor == null) {
              // The decompressor may be null if no compatible encoding type was found in this stream's headers
              return listener.onDataRead(ctx, streamId, data, padding, endOfStream);
          }
  
          final EmbeddedChannel channel = decompressor.decompressor();
          final int compressedBytes = data.readableBytes() + padding;
          decompressor.incrementCompressedBytes(compressedBytes);
          try {
              // call retain here as it will call release after its written to the channel
              channel.writeInbound(data.retain());
              ByteBuf buf = nextReadableBuf(channel);
              if (buf == null && endOfStream && channel.finish()) {
                  buf = nextReadableBuf(channel);
              }
              if (buf == null) {
                  if (endOfStream) {
                      listener.onDataRead(ctx, streamId, Unpooled.EMPTY_BUFFER, padding, true);
                  }
                  // No new decompressed data was extracted from the compressed data. This means the application could
                  // not be provided with data and thus could not return how many bytes were processed. We will assume
                  // there is more data coming which will complete the decompression block. To allow for more data we
                  // return all bytes to the flow control window (so the peer can send more data).
                  decompressor.incrementDecompressedBytes(compressedBytes);
                 return compressedBytes;
             }
             try {
                 Http2LocalFlowController flowController = connection.local().flowController();
                 decompressor.incrementDecompressedBytes(padding);
                 for (;;) {
                     ByteBuf nextBuf = nextReadableBuf(channel);
                     boolean decompressedEndOfStream = nextBuf == null && endOfStream;
                     if (decompressedEndOfStream && channel.finish()) {
                         nextBuf = nextReadableBuf(channel);
                         decompressedEndOfStream = nextBuf == null;
                     }
 
                     decompressor.incrementDecompressedBytes(buf.readableBytes());
                     // Immediately return the bytes back to the flow controller. ConsumedBytesConverter will convert
                     // from the decompressed amount which the user knows about to the compressed amount which flow
                     // control knows about.
                     flowController.consumeBytes(stream,
                             listener.onDataRead(ctx, streamId, buf, padding, decompressedEndOfStream));
                     if (nextBuf == null) {
                         break;
                     }
 
                     padding = 0; // Padding is only communicated once on the first iteration.
                     buf.release();
                     buf = nextBuf;
                 }
                 // We consume bytes each time we call the listener to ensure if multiple frames are decompressed
                 // that the bytes are accounted for immediately. Otherwise the user may see an inconsistent state of
                 // flow control.
                 return 0;
             } finally {
                 buf.release();
             }
         } catch (Http2Exception e) {
             throw e;
         } catch (Throwable t) {
             throw streamError(stream.id(), INTERNAL_ERROR, t,
                     "Decompressor error detected while delegating data read on streamId %d", stream.id());
         }
     }
 
     @Override
     public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers, int padding,
                     boolean endStream) throws Http2Exception {
         initDecompressor(ctx, streamId, headers, endStream);
         listener.onHeadersRead(ctx, streamId, headers, padding, endStream);
     }
 
     @Override
     public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers, int streamDependency,
                     short weight, boolean exclusive, int padding, boolean endStream) throws Http2Exception {
         initDecompressor(ctx, streamId, headers, endStream);
         listener.onHeadersRead(ctx, streamId, headers, streamDependency, weight, exclusive, padding, endStream);
     }
 
     /**
      * Returns a new {@link EmbeddedChannel} that decodes the HTTP2 message content encoded in the specified
      * {@code contentEncoding}.
      *
      * @param contentEncoding the value of the {@code content-encoding} header
      * @return a new {@link ByteToMessageDecoder} if the specified encoding is supported. {@code null} otherwise
      *         (alternatively, you can throw a {@link Http2Exception} to block unknown encoding).
      * @throws Http2Exception If the specified encoding is not not supported and warrants an exception
      */
     protected EmbeddedChannel newContentDecompressor(final ChannelHandlerContext ctx, CharSequence contentEncoding)
             throws Http2Exception {
         if (GZIP.contentEqualsIgnoreCase(contentEncoding) || X_GZIP.contentEqualsIgnoreCase(contentEncoding)) {
             return new EmbeddedChannel(ctx.channel().id(), ctx.channel().metadata().hasDisconnect(),
                     ctx.channel().config(), ZlibCodecFactory.newZlibDecoder(ZlibWrapper.GZIP));
         }
         if (DEFLATE.contentEqualsIgnoreCase(contentEncoding) || X_DEFLATE.contentEqualsIgnoreCase(contentEncoding)) {
             final ZlibWrapper wrapper = strict ? ZlibWrapper.ZLIB : ZlibWrapper.ZLIB_OR_NONE;
             // To be strict, 'deflate' means ZLIB, but some servers were not implemented correctly.
             return new EmbeddedChannel(ctx.channel().id(), ctx.channel().metadata().hasDisconnect(),
                     ctx.channel().config(), ZlibCodecFactory.newZlibDecoder(wrapper));
         }
         // 'identity' or unsupported
         return null;
     }
 
     /**
      * Returns the expected content encoding of the decoded content. This getMethod returns {@code "identity"} by
      * default, which is the case for most decompressors.
      *
      * @param contentEncoding the value of the {@code content-encoding} header
      * @return the expected content encoding of the new content.
      * @throws Http2Exception if the {@code contentEncoding} is not supported and warrants an exception
      */
     protected CharSequence getTargetContentEncoding(@SuppressWarnings("UnusedParameters") CharSequence contentEncoding)
                     throws Http2Exception {
         return IDENTITY;
     }
 
     /**
      * Checks if a new decompressor object is needed for the stream identified by {@code streamId}.
      * This method will modify the {@code content-encoding} header contained in {@code headers}.
      *
      * @param ctx The context
      * @param streamId The identifier for the headers inside {@code headers}
      * @param headers Object representing headers which have been read
      * @param endOfStream Indicates if the stream has ended
      * @throws Http2Exception If the {@code content-encoding} is not supported
      */
     private void initDecompressor(ChannelHandlerContext ctx, int streamId, Http2Headers headers, boolean endOfStream)
             throws Http2Exception {
         final Http2Stream stream = connection.stream(streamId);
         if (stream == null) {
             return;
         }
 
         Http2Decompressor decompressor = decompressor(stream);
         if (decompressor == null && !endOfStream) {
             // Determine the content encoding.
             CharSequence contentEncoding = headers.get(CONTENT_ENCODING);
             if (contentEncoding == null) {
                 contentEncoding = IDENTITY;
             }
             final EmbeddedChannel channel = newContentDecompressor(ctx, contentEncoding);
             if (channel != null) {
                 decompressor = new Http2Decompressor(channel);
                 stream.setProperty(propertyKey, decompressor);
                 // Decode the content and remove or replace the existing headers
                 // so that the message looks like a decoded message.
                 CharSequence targetContentEncoding = getTargetContentEncoding(contentEncoding);
                 if (IDENTITY.contentEqualsIgnoreCase(targetContentEncoding)) {
                     headers.remove(CONTENT_ENCODING);
                 } else {
                     headers.set(CONTENT_ENCODING, targetContentEncoding);
                 }
             }
         }
 
         if (decompressor != null) {
             // The content length will be for the compressed data. Since we will decompress the data
             // this content-length will not be correct. Instead of queuing messages or delaying sending
             // header frames...just remove the content-length header
             headers.remove(CONTENT_LENGTH);
 
             // The first time that we initialize a decompressor, decorate the local flow controller to
             // properly convert consumed bytes.
             if (!flowControllerInitialized) {
                 flowControllerInitialized = true;
                 connection.local().flowController(new ConsumedBytesConverter(connection.local().flowController()));
             }
         }
     }
 
     Http2Decompressor decompressor(Http2Stream stream) {
         return stream == null ? null : (Http2Decompressor) stream.getProperty(propertyKey);
     }
 
     /**
      * Release remaining content from the {@link EmbeddedChannel}.
      *
      * @param decompressor The decompressor for {@code stream}
      */
     private static void cleanup(Http2Decompressor decompressor) {
         decompressor.decompressor().finishAndReleaseAll();
     }
 
     /**
      * Read the next decompressed {@link ByteBuf} from the {@link EmbeddedChannel}
      * or {@code null} if one does not exist.
      *
      * @param decompressor The channel to read from
      * @return The next decoded {@link ByteBuf} from the {@link EmbeddedChannel} or {@code null} if one does not exist
      */
     private static ByteBuf nextReadableBuf(EmbeddedChannel decompressor) {
         for (;;) {
             final ByteBuf buf = decompressor.readInbound();
             if (buf == null) {
                 return null;
             }
             if (!buf.isReadable()) {
                 buf.release();
                 continue;
             }
             return buf;
         }
     }
 
     /**
      * A decorator around the local flow controller that converts consumed bytes from uncompressed to compressed.
      */
     private final class ConsumedBytesConverter implements Http2LocalFlowController {
         private final Http2LocalFlowController flowController;
 
         ConsumedBytesConverter(Http2LocalFlowController flowController) {
             this.flowController = checkNotNull(flowController, "flowController");
         }
 
         @Override
         public Http2LocalFlowController frameWriter(Http2FrameWriter frameWriter) {
             return flowController.frameWriter(frameWriter);
         }
 
         @Override
         public void channelHandlerContext(ChannelHandlerContext ctx) throws Http2Exception {
             flowController.channelHandlerContext(ctx);
         }
 
         @Override
         public void initialWindowSize(int newWindowSize) throws Http2Exception {
             flowController.initialWindowSize(newWindowSize);
         }
 
         @Override
         public int initialWindowSize() {
             return flowController.initialWindowSize();
         }
 
         @Override
         public int windowSize(Http2Stream stream) {
             return flowController.windowSize(stream);
         }
 
         @Override
         public void incrementWindowSize(Http2Stream stream, int delta) throws Http2Exception {
             flowController.incrementWindowSize(stream, delta);
         }
 
         @Override
         public void receiveFlowControlledFrame(Http2Stream stream, ByteBuf data, int padding,
                 boolean endOfStream) throws Http2Exception {
             flowController.receiveFlowControlledFrame(stream, data, padding, endOfStream);
         }
 
         @Override
         public boolean consumeBytes(Http2Stream stream, int numBytes) throws Http2Exception {
             Http2Decompressor decompressor = decompressor(stream);
             if (decompressor != null) {
                 // Convert the decompressed bytes to compressed (on the wire) bytes.
                 numBytes = decompressor.consumeBytes(stream.id(), numBytes);
             }
             try {
                 return flowController.consumeBytes(stream, numBytes);
             } catch (Http2Exception e) {
                 throw e;
             } catch (Throwable t) {
                 // The stream should be closed at this point. We have already changed our state tracking the compressed
                 // bytes, and there is no guarantee we can recover if the underlying flow controller throws.
                 throw streamError(stream.id(), INTERNAL_ERROR, t, "Error while returning bytes to flow control window");
             }
         }
 
         @Override
         public int unconsumedBytes(Http2Stream stream) {
             return flowController.unconsumedBytes(stream);
         }
 
         @Override
         public int initialWindowSize(Http2Stream stream) {
             return flowController.initialWindowSize(stream);
         }
     }
 
     /**
      * Provides the state for stream {@code DATA} frame decompression.
      */
     private static final class Http2Decompressor {
         private final EmbeddedChannel decompressor;
         private int compressed;
         private int decompressed;
 
         Http2Decompressor(EmbeddedChannel decompressor) {
             this.decompressor = decompressor;
         }
 
         /**
          * Responsible for taking compressed bytes in and producing decompressed bytes.
          */
         EmbeddedChannel decompressor() {
             return decompressor;
         }
 
         /**
          * Increment the number of bytes received prior to doing any decompression.
          */
         void incrementCompressedBytes(int delta) {
             assert delta >= 0;
             compressed += delta;
         }
 
         /**
          * Increment the number of bytes after the decompression process.
          */
         void incrementDecompressedBytes(int delta) {
             assert delta >= 0;
             decompressed += delta;
         }
 
         /**
          * Determines the ratio between {@code numBytes} and {@link Http2Decompressor#decompressed}.
          * This ratio is used to decrement {@link Http2Decompressor#decompressed} and
          * {@link Http2Decompressor#compressed}.
          * @param streamId the stream ID
          * @param decompressedBytes The number of post-decompressed bytes to return to flow control
          * @return The number of pre-decompressed bytes that have been consumed.
          */
         int consumeBytes(int streamId, int decompressedBytes) throws Http2Exception {
             if (decompressedBytes < 0) {
                 throw new IllegalArgumentException("decompressedBytes must not be negative: " + decompressedBytes);
             }
             if (decompressed - decompressedBytes < 0) {
                 throw streamError(streamId, INTERNAL_ERROR,
                         "Attempting to return too many bytes for stream %d. decompressed: %d " +
                                 "decompressedBytes: %d", streamId, decompressed, decompressedBytes);
             }
             double consumedRatio = decompressedBytes / (double) decompressed;
             int consumedCompressed = Math.min(compressed, (int) Math.ceil(compressed * consumedRatio));
             if (compressed - consumedCompressed < 0) {
                 throw streamError(streamId, INTERNAL_ERROR,
                         "overflow when converting decompressed bytes to compressed bytes for stream %d." +
                                 "decompressedBytes: %d decompressed: %d compressed: %d consumedCompressed: %d",
                         streamId, decompressedBytes, decompressed, compressed, consumedCompressed);
             }
             decompressed -= decompressedBytes;
             compressed -= consumedCompressed;
 
             return consumedCompressed;
         }
     }
 }