/*
    * 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:
    *
    * 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.http2;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.http.FullHttpMessage;
  import io.netty.handler.codec.http.FullHttpRequest;
  import io.netty.handler.codec.http.FullHttpResponse;
  import io.netty.handler.codec.http.HttpHeaderNames;
  import io.netty.handler.codec.http.HttpStatusClass;
  import io.netty.handler.codec.http.HttpUtil;
  import io.netty.util.internal.UnstableApi;
  
  import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
  import static io.netty.handler.codec.http2.Http2Error.PROTOCOL_ERROR;
  import static io.netty.handler.codec.http2.Http2Exception.connectionError;
  import static io.netty.handler.codec.http.HttpResponseStatus.OK;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  
  /**
   * This adapter provides just header/data events from the HTTP message flow defined
   * in <a href="https://tools.ietf.org/html/rfc7540#section-8.1">[RFC 7540], Section 8.1</a>.
   * <p>
   * See {@link HttpToHttp2ConnectionHandler} to get translation from HTTP/1.x objects to HTTP/2 frames for writes.
   */
  @UnstableApi
  public class InboundHttp2ToHttpAdapter extends Http2EventAdapter {
      private static final ImmediateSendDetector DEFAULT_SEND_DETECTOR = new ImmediateSendDetector() {
          @Override
          public boolean mustSendImmediately(FullHttpMessage msg) {
              if (msg instanceof FullHttpResponse) {
                  return ((FullHttpResponse) msg).status().codeClass() == HttpStatusClass.INFORMATIONAL;
              }
              if (msg instanceof FullHttpRequest) {
                  return msg.headers().contains(HttpHeaderNames.EXPECT);
              }
              return false;
          }
  
          @Override
          public FullHttpMessage copyIfNeeded(ByteBufAllocator allocator, FullHttpMessage msg) {
              if (msg instanceof FullHttpRequest) {
                  FullHttpRequest copy = ((FullHttpRequest) msg).replace(allocator.buffer(0));
                  copy.headers().remove(HttpHeaderNames.EXPECT);
                  return copy;
              }
              return null;
          }
      };
  
      private final int maxContentLength;
      private final ImmediateSendDetector sendDetector;
      private final Http2Connection.PropertyKey messageKey;
      private final boolean propagateSettings;
      protected final Http2Connection connection;
      protected final boolean validateHttpHeaders;
  
      protected InboundHttp2ToHttpAdapter(Http2Connection connection, int maxContentLength,
                                          boolean validateHttpHeaders, boolean propagateSettings) {
          this.connection = checkNotNull(connection, "connection");
          this.maxContentLength = checkPositive(maxContentLength, "maxContentLength");
          this.validateHttpHeaders = validateHttpHeaders;
          this.propagateSettings = propagateSettings;
          sendDetector = DEFAULT_SEND_DETECTOR;
          messageKey = connection.newKey();
      }
  
      /**
       * The stream is out of scope for the HTTP message flow and will no longer be tracked
       * @param stream The stream to remove associated state with
       * @param release {@code true} to call release on the value if it is present. {@code false} to not call release.
       */
      protected final void removeMessage(Http2Stream stream, boolean release) {
          FullHttpMessage msg = stream.removeProperty(messageKey);
          if (release && msg != null) {
              msg.release();
          }
      }
  
      /**
       * Get the {@link FullHttpMessage} associated with {@code stream}.
       * @param stream The stream to get the associated state from
       * @return The {@link FullHttpMessage} associated with {@code stream}.
       */
     protected final FullHttpMessage getMessage(Http2Stream stream) {
         return (FullHttpMessage) stream.getProperty(messageKey);
     }
 
     /**
      * Make {@code message} be the state associated with {@code stream}.
      * @param stream The stream which {@code message} is associated with.
      * @param message The message which contains the HTTP semantics.
      */
     protected final void putMessage(Http2Stream stream, FullHttpMessage message) {
         FullHttpMessage previous = stream.setProperty(messageKey, message);
         if (previous != message && previous != null) {
             previous.release();
         }
     }
 
     @Override
     public void onStreamRemoved(Http2Stream stream) {
         removeMessage(stream, true);
     }
 
     /**
      * Set final headers and fire a channel read event
      *
      * @param ctx The context to fire the event on
      * @param msg The message to send
      * @param release {@code true} to call release on the value if it is present. {@code false} to not call release.
      * @param stream the stream of the message which is being fired
      */
     protected void fireChannelRead(ChannelHandlerContext ctx, FullHttpMessage msg, boolean release,
                                    Http2Stream stream) {
         removeMessage(stream, release);
         HttpUtil.setContentLength(msg, msg.content().readableBytes());
         ctx.fireChannelRead(msg);
     }
 
     /**
      * Create a new {@link FullHttpMessage} based upon the current connection parameters
      *
      * @param stream The stream to create a message for
      * @param headers The headers associated with {@code stream}
      * @param validateHttpHeaders
      * <ul>
      * <li>{@code true} to validate HTTP headers in the http-codec</li>
      * <li>{@code false} not to validate HTTP headers in the http-codec</li>
      * </ul>
      * @param alloc The {@link ByteBufAllocator} to use to generate the content of the message
      * @throws Http2Exception If there is an error when creating {@link FullHttpMessage} from
      *                        {@link Http2Stream} and {@link Http2Headers}
      */
     protected FullHttpMessage newMessage(Http2Stream stream, Http2Headers headers, boolean validateHttpHeaders,
                                          ByteBufAllocator alloc) throws Http2Exception {
         return connection.isServer() ? HttpConversionUtil.toFullHttpRequest(stream.id(), headers, alloc,
                 validateHttpHeaders) : HttpConversionUtil.toFullHttpResponse(stream.id(), headers, alloc,
                 validateHttpHeaders);
     }
 
     /**
      * Provides translation between HTTP/2 and HTTP header objects while ensuring the stream
      * is in a valid state for additional headers.
      *
      * @param ctx The context for which this message has been received.
      * Used to send informational header if detected.
      * @param stream The stream the {@code headers} apply to
      * @param headers The headers to process
      * @param endOfStream {@code true} if the {@code stream} has received the end of stream flag
      * @param allowAppend
      * <ul>
      * <li>{@code true} if headers will be appended if the stream already exists.</li>
      * <li>if {@code false} and the stream already exists this method returns {@code null}.</li>
      * </ul>
      * @param appendToTrailer
      * <ul>
      * <li>{@code true} if a message {@code stream} already exists then the headers
      * should be added to the trailing headers.</li>
      * <li>{@code false} then appends will be done to the initial headers.</li>
      * </ul>
      * @return The object used to track the stream corresponding to {@code stream}. {@code null} if
      *         {@code allowAppend} is {@code false} and the stream already exists.
      * @throws Http2Exception If the stream id is not in the correct state to process the headers request
      */
     protected FullHttpMessage processHeadersBegin(ChannelHandlerContext ctx, Http2Stream stream, Http2Headers headers,
                                                   boolean endOfStream, boolean allowAppend, boolean appendToTrailer)
             throws Http2Exception {
         FullHttpMessage msg = getMessage(stream);
         boolean release = true;
         if (msg == null) {
             msg = newMessage(stream, headers, validateHttpHeaders, ctx.alloc());
         } else if (allowAppend) {
             release = false;
             HttpConversionUtil.addHttp2ToHttpHeaders(stream.id(), headers, msg, appendToTrailer);
         } else {
             release = false;
             msg = null;
         }
 
         if (sendDetector.mustSendImmediately(msg)) {
             // Copy the message (if necessary) before sending. The content is not expected to be copied (or used) in
             // this operation but just in case it is used do the copy before sending and the resource may be released
             final FullHttpMessage copy = endOfStream ? null : sendDetector.copyIfNeeded(ctx.alloc(), msg);
             fireChannelRead(ctx, msg, release, stream);
             return copy;
         }
 
         return msg;
     }
 
     /**
      * After HTTP/2 headers have been processed by {@link #processHeadersBegin} this method either
      * sends the result up the pipeline or retains the message for future processing.
      *
      * @param ctx The context for which this message has been received
      * @param stream The stream the {@code objAccumulator} corresponds to
      * @param msg The object which represents all headers/data for corresponding to {@code stream}
      * @param endOfStream {@code true} if this is the last event for the stream
      */
     private void processHeadersEnd(ChannelHandlerContext ctx, Http2Stream stream, FullHttpMessage msg,
                                    boolean endOfStream) {
         if (endOfStream) {
             // Release if the msg from the map is different from the object being forwarded up the pipeline.
             fireChannelRead(ctx, msg, getMessage(stream) != msg, stream);
         } else {
             putMessage(stream, msg);
         }
     }
 
     @Override
     public int onDataRead(ChannelHandlerContext ctx, int streamId, ByteBuf data, int padding, boolean endOfStream)
             throws Http2Exception {
         Http2Stream stream = connection.stream(streamId);
         FullHttpMessage msg = getMessage(stream);
         if (msg == null) {
             throw connectionError(PROTOCOL_ERROR, "Data Frame received for unknown stream id %d", streamId);
         }
 
         ByteBuf content = msg.content();
         final int dataReadableBytes = data.readableBytes();
         if (content.readableBytes() > maxContentLength - dataReadableBytes) {
             throw connectionError(INTERNAL_ERROR,
                     "Content length exceeded max of %d for stream id %d", maxContentLength, streamId);
         }
 
         content.writeBytes(data, data.readerIndex(), dataReadableBytes);
 
         if (endOfStream) {
             fireChannelRead(ctx, msg, false, stream);
         }
 
         // All bytes have been processed.
         return dataReadableBytes + padding;
     }
 
     @Override
     public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers, int padding,
                               boolean endOfStream) throws Http2Exception {
         Http2Stream stream = connection.stream(streamId);
         FullHttpMessage msg = processHeadersBegin(ctx, stream, headers, endOfStream, true, true);
         if (msg != null) {
             processHeadersEnd(ctx, stream, msg, endOfStream);
         }
     }
 
     @Override
     public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers, int streamDependency,
                               short weight, boolean exclusive, int padding, boolean endOfStream)
             throws Http2Exception {
         Http2Stream stream = connection.stream(streamId);
         FullHttpMessage msg = processHeadersBegin(ctx, stream, headers, endOfStream, true, true);
         if (msg != null) {
             // Add headers for dependency and weight.
             // See https://github.com/netty/netty/issues/5866
             if (streamDependency != Http2CodecUtil.CONNECTION_STREAM_ID) {
                 msg.headers().setInt(HttpConversionUtil.ExtensionHeaderNames.STREAM_DEPENDENCY_ID.text(),
                         streamDependency);
             }
             msg.headers().setShort(HttpConversionUtil.ExtensionHeaderNames.STREAM_WEIGHT.text(), weight);
 
             processHeadersEnd(ctx, stream, msg, endOfStream);
         }
     }
 
     @Override
     public void onRstStreamRead(ChannelHandlerContext ctx, int streamId, long errorCode) throws Http2Exception {
         Http2Stream stream = connection.stream(streamId);
         FullHttpMessage msg = getMessage(stream);
         if (msg != null) {
             onRstStreamRead(stream, msg);
         }
         ctx.fireExceptionCaught(Http2Exception.streamError(streamId, Http2Error.valueOf(errorCode),
                 "HTTP/2 to HTTP layer caught stream reset"));
     }
 
     @Override
     public void onPushPromiseRead(ChannelHandlerContext ctx, int streamId, int promisedStreamId,
                                   Http2Headers headers, int padding) throws Http2Exception {
         // A push promise should not be allowed to add headers to an existing stream
         Http2Stream promisedStream = connection.stream(promisedStreamId);
         if (headers.status() == null) {
             // A PUSH_PROMISE frame has no Http response status.
             // https://tools.ietf.org/html/rfc7540#section-8.2.1
             // Server push is semantically equivalent to a server responding to a
             // request; however, in this case, that request is also sent by the
             // server, as a PUSH_PROMISE frame.
             headers.status(OK.codeAsText());
         }
         FullHttpMessage msg = processHeadersBegin(ctx, promisedStream, headers, false, false, false);
         if (msg == null) {
             throw connectionError(PROTOCOL_ERROR, "Push Promise Frame received for pre-existing stream id %d",
                     promisedStreamId);
         }
 
         msg.headers().setInt(HttpConversionUtil.ExtensionHeaderNames.STREAM_PROMISE_ID.text(), streamId);
         msg.headers().setShort(HttpConversionUtil.ExtensionHeaderNames.STREAM_WEIGHT.text(),
                 Http2CodecUtil.DEFAULT_PRIORITY_WEIGHT);
 
         processHeadersEnd(ctx, promisedStream, msg, false);
     }
 
     @Override
     public void onSettingsRead(ChannelHandlerContext ctx, Http2Settings settings) throws Http2Exception {
         if (propagateSettings) {
             // Provide an interface for non-listeners to capture settings
             ctx.fireChannelRead(settings);
         }
     }
 
     /**
      * Called if a {@code RST_STREAM} is received but we have some data for that stream.
      */
     protected void onRstStreamRead(Http2Stream stream, FullHttpMessage msg) {
         removeMessage(stream, true);
     }
 
     /**
      * Allows messages to be sent up the pipeline before the next phase in the
      * HTTP message flow is detected.
      */
     private interface ImmediateSendDetector {
         /**
          * Determine if the response should be sent immediately, or wait for the end of the stream
          *
          * @param msg The response to test
          * @return {@code true} if the message should be sent immediately
          *         {@code false) if we should wait for the end of the stream
          */
         boolean mustSendImmediately(FullHttpMessage msg);
 
         /**
          * Determine if a copy must be made after an immediate send happens.
          * <p>
          * An example of this use case is if a request is received
          * with a 'Expect: 100-continue' header. The message will be sent immediately,
          * and the data will be queued and sent at the end of the stream.
          *
          * @param allocator The {@link ByteBufAllocator} that can be used to allocate
          * @param msg The message which has just been sent due to {@link #mustSendImmediately(FullHttpMessage)}
          * @return A modified copy of the {@code msg} or {@code null} if a copy is not needed.
          */
         FullHttpMessage copyIfNeeded(ByteBufAllocator allocator, FullHttpMessage msg);
     }
 }