/*
    * Copyright 2016 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.ByteBufAllocator;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelHandler;
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.EncoderException;
  import io.netty.handler.codec.MessageToMessageCodec;
  import io.netty.handler.codec.http.DefaultHttpContent;
  import io.netty.handler.codec.http.DefaultLastHttpContent;
  import io.netty.handler.codec.http.FullHttpMessage;
  import io.netty.handler.codec.http.FullHttpResponse;
  import io.netty.handler.codec.http.HttpContent;
  import io.netty.handler.codec.http.HttpHeaderNames;
  import io.netty.handler.codec.http.HttpHeaderValues;
  import io.netty.handler.codec.http.HttpMessage;
  import io.netty.handler.codec.http.HttpObject;
  import io.netty.handler.codec.http.HttpRequest;
  import io.netty.handler.codec.http.HttpResponse;
  import io.netty.handler.codec.http.HttpResponseStatus;
  import io.netty.handler.codec.http.HttpScheme;
  import io.netty.handler.codec.http.HttpStatusClass;
  import io.netty.handler.codec.http.HttpUtil;
  import io.netty.handler.codec.http.HttpVersion;
  import io.netty.handler.codec.http.LastHttpContent;
  import io.netty.handler.ssl.SslHandler;
  import io.netty.util.Attribute;
  import io.netty.util.AttributeKey;
  import io.netty.util.internal.UnstableApi;
  
  import java.util.List;
  
  /**
   * This handler converts from {@link Http2StreamFrame} to {@link HttpObject},
   * and back. It can be used as an adapter in conjunction with {@link
   * Http2MultiplexCodec} to make http/2 connections backward-compatible with
   * {@link ChannelHandler}s expecting {@link HttpObject}
   *
   * For simplicity, it converts to chunked encoding unless the entire stream
   * is a single header.
   */
  @UnstableApi
  @Sharable
  public class Http2StreamFrameToHttpObjectCodec extends MessageToMessageCodec<Http2StreamFrame, HttpObject> {
  
      private static final AttributeKey<HttpScheme> SCHEME_ATTR_KEY =
          AttributeKey.valueOf(HttpScheme.class, "STREAMFRAMECODEC_SCHEME");
  
      private final boolean isServer;
      private final boolean validateHeaders;
  
      public Http2StreamFrameToHttpObjectCodec(final boolean isServer,
                                               final boolean validateHeaders) {
          this.isServer = isServer;
          this.validateHeaders = validateHeaders;
      }
  
      public Http2StreamFrameToHttpObjectCodec(final boolean isServer) {
          this(isServer, true);
      }
  
      @Override
      public boolean acceptInboundMessage(Object msg) throws Exception {
          return msg instanceof Http2HeadersFrame || msg instanceof Http2DataFrame;
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, Http2StreamFrame frame, List<Object> out) throws Exception {
          if (frame instanceof Http2HeadersFrame) {
              Http2HeadersFrame headersFrame = (Http2HeadersFrame) frame;
              Http2Headers headers = headersFrame.headers();
              Http2FrameStream stream = headersFrame.stream();
              int id = stream == null ? 0 : stream.id();
  
              final CharSequence status = headers.status();
  
              // 1xx response (excluding 101) is a special case where Http2HeadersFrame#isEndStream=false
              // but we need to decode it as a FullHttpResponse to play nice with HttpObjectAggregator.
              if (null != status && isInformationalResponseHeaderFrame(status)) {
                  final FullHttpMessage fullMsg = newFullMessage(id, headers, ctx.alloc());
                  out.add(fullMsg);
                 return;
             }
 
             if (headersFrame.isEndStream()) {
                 if (headers.method() == null && status == null) {
                     LastHttpContent last = new DefaultLastHttpContent(Unpooled.EMPTY_BUFFER, validateHeaders);
                     HttpConversionUtil.addHttp2ToHttpHeaders(id, headers, last.trailingHeaders(),
                                                              HttpVersion.HTTP_1_1, true, true);
                     out.add(last);
                 } else {
                     FullHttpMessage full = newFullMessage(id, headers, ctx.alloc());
                     out.add(full);
                 }
             } else {
                 HttpMessage req = newMessage(id, headers);
                 if ((status == null || !isContentAlwaysEmpty(status)) && !HttpUtil.isContentLengthSet(req)) {
                     req.headers().add(HttpHeaderNames.TRANSFER_ENCODING, HttpHeaderValues.CHUNKED);
                 }
                 out.add(req);
             }
         } else if (frame instanceof Http2DataFrame) {
             Http2DataFrame dataFrame = (Http2DataFrame) frame;
             if (dataFrame.isEndStream()) {
                 out.add(new DefaultLastHttpContent(dataFrame.content().retain(), validateHeaders));
             } else {
                 out.add(new DefaultHttpContent(dataFrame.content().retain()));
             }
         }
     }
 
     private void encodeLastContent(LastHttpContent last, List<Object> out) {
         boolean needFiller = !(last instanceof FullHttpMessage) && last.trailingHeaders().isEmpty();
         if (last.content().isReadable() || needFiller) {
             out.add(new DefaultHttp2DataFrame(last.content().retain(), last.trailingHeaders().isEmpty()));
         }
         if (!last.trailingHeaders().isEmpty()) {
             Http2Headers headers = HttpConversionUtil.toHttp2Headers(last.trailingHeaders(), validateHeaders);
             out.add(new DefaultHttp2HeadersFrame(headers, true));
         }
     }
 
     /**
      * Encode from an {@link HttpObject} to an {@link Http2StreamFrame}. This method will
      * be called for each written message that can be handled by this encoder.
      *
      * NOTE: 100-Continue responses that are NOT {@link FullHttpResponse} will be rejected.
      *
      * @param ctx           the {@link ChannelHandlerContext} which this handler belongs to
      * @param obj           the {@link HttpObject} message to encode
      * @param out           the {@link List} into which the encoded msg should be added
      *                      needs to do some kind of aggregation
      * @throws Exception    is thrown if an error occurs
      */
     @Override
     protected void encode(ChannelHandlerContext ctx, HttpObject obj, List<Object> out) throws Exception {
         // 1xx (excluding 101) is typically a FullHttpResponse, but the decoded
         // Http2HeadersFrame should not be marked as endStream=true
         if (obj instanceof HttpResponse) {
             final HttpResponse res = (HttpResponse) obj;
             final HttpResponseStatus status = res.status();
             final int code = status.code();
             final HttpStatusClass statusClass = status.codeClass();
             // An informational response using a 1xx status code other than 101 is
             // transmitted as a HEADERS frame
             if (statusClass == HttpStatusClass.INFORMATIONAL && code != 101) {
                 if (res instanceof FullHttpResponse) {
                     final Http2Headers headers = toHttp2Headers(ctx, res);
                     out.add(new DefaultHttp2HeadersFrame(headers, false));
                     return;
                 } else {
                     throw new EncoderException(status + " must be a FullHttpResponse");
                 }
             }
         }
 
         if (obj instanceof HttpMessage) {
             Http2Headers headers = toHttp2Headers(ctx, (HttpMessage) obj);
             boolean noMoreFrames = false;
             if (obj instanceof FullHttpMessage) {
                 FullHttpMessage full = (FullHttpMessage) obj;
                 noMoreFrames = !full.content().isReadable() && full.trailingHeaders().isEmpty();
             }
 
             out.add(new DefaultHttp2HeadersFrame(headers, noMoreFrames));
         }
 
         if (obj instanceof LastHttpContent) {
             LastHttpContent last = (LastHttpContent) obj;
             encodeLastContent(last, out);
         } else if (obj instanceof HttpContent) {
             HttpContent cont = (HttpContent) obj;
             out.add(new DefaultHttp2DataFrame(cont.content().retain(), false));
         }
     }
 
     private Http2Headers toHttp2Headers(final ChannelHandlerContext ctx, final HttpMessage msg) {
         if (msg instanceof HttpRequest) {
             msg.headers().set(
                     HttpConversionUtil.ExtensionHeaderNames.SCHEME.text(),
                     connectionScheme(ctx));
         }
 
         return HttpConversionUtil.toHttp2Headers(msg, validateHeaders);
     }
 
     private HttpMessage newMessage(final int id,
                                    final Http2Headers headers) throws Http2Exception {
         return isServer ?
                 HttpConversionUtil.toHttpRequest(id, headers, validateHeaders) :
                 HttpConversionUtil.toHttpResponse(id, headers, validateHeaders);
     }
 
     private FullHttpMessage newFullMessage(final int id,
                                            final Http2Headers headers,
                                            final ByteBufAllocator alloc) throws Http2Exception {
         return isServer ?
                 HttpConversionUtil.toFullHttpRequest(id, headers, alloc, validateHeaders) :
                 HttpConversionUtil.toFullHttpResponse(id, headers, alloc, validateHeaders);
     }
 
     @Override
     public void handlerAdded(final ChannelHandlerContext ctx) throws Exception {
         super.handlerAdded(ctx);
 
         // this handler is typically used on an Http2StreamChannel. At this
         // stage, ssl handshake should've been established. checking for the
         // presence of SslHandler in the parent's channel pipeline to
         // determine the HTTP scheme should suffice, even for the case where
         // SniHandler is used.
         final Attribute<HttpScheme> schemeAttribute = connectionSchemeAttribute(ctx);
         if (schemeAttribute.get() == null) {
             final HttpScheme scheme = isSsl(ctx) ? HttpScheme.HTTPS : HttpScheme.HTTP;
             schemeAttribute.set(scheme);
         }
     }
 
     protected boolean isSsl(final ChannelHandlerContext ctx) {
         final Channel connChannel = connectionChannel(ctx);
         return null != connChannel.pipeline().get(SslHandler.class);
     }
 
     private static HttpScheme connectionScheme(ChannelHandlerContext ctx) {
         final HttpScheme scheme = connectionSchemeAttribute(ctx).get();
         return scheme == null ? HttpScheme.HTTP : scheme;
     }
 
     private static Attribute<HttpScheme> connectionSchemeAttribute(ChannelHandlerContext ctx) {
         final Channel ch = connectionChannel(ctx);
         return ch.attr(SCHEME_ATTR_KEY);
     }
 
     private static Channel connectionChannel(ChannelHandlerContext ctx) {
         final Channel ch = ctx.channel();
         return ch instanceof Http2StreamChannel ? ch.parent() : ch;
     }
 
     /**
      *    An informational response using a 1xx status code other than 101 is
      *    transmitted as a HEADERS frame
      */
     private static boolean isInformationalResponseHeaderFrame(CharSequence status) {
         if (status.length() == 3) {
             char char0 = status.charAt(0);
             char char1 = status.charAt(1);
             char char2 = status.charAt(2);
             return char0 == '1'
                 && char1 >= '0' && char1 <= '9'
                 && char2 >= '0' && char2 <= '9' && char2 != '1';
         }
         return false;
     }
 
     /*
      * https://datatracker.ietf.org/doc/html/rfc9113#section-8.1.1
      * '204' or '304' responses contain no content
      */
     private static boolean isContentAlwaysEmpty(CharSequence status) {
         if (status.length() == 3) {
             char char0 = status.charAt(0);
             char char1 = status.charAt(1);
             char char2 = status.charAt(2);
             return (char0 == '2' || char0 == '3')
                 && char1 == '0'
                 && char2 == '4';
         }
         return false;
     }
 }