/*
    * 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:
    *
    *   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;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.FileRegion;
  import io.netty.handler.codec.EncoderException;
  import io.netty.handler.codec.MessageToMessageEncoder;
  import io.netty.util.CharsetUtil;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.concurrent.PromiseCombiner;
  import io.netty.util.internal.StringUtil;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map.Entry;
  
  import static io.netty.buffer.Unpooled.directBuffer;
  import static io.netty.buffer.Unpooled.unreleasableBuffer;
  import static io.netty.handler.codec.http.HttpConstants.CR;
  import static io.netty.handler.codec.http.HttpConstants.LF;
  
  /**
   * Encodes an {@link HttpMessage} or an {@link HttpContent} into
   * a {@link ByteBuf}.
   *
   * <h3>Extensibility</h3>
   *
   * Please note that this encoder is designed to be extended to implement
   * a protocol derived from HTTP, such as
   * <a href="https://en.wikipedia.org/wiki/Real_Time_Streaming_Protocol">RTSP</a> and
   * <a href="https://en.wikipedia.org/wiki/Internet_Content_Adaptation_Protocol">ICAP</a>.
   * To implement the encoder of such a derived protocol, extend this class and
   * implement all abstract methods properly.
   */
  public abstract class HttpObjectEncoder<H extends HttpMessage> extends MessageToMessageEncoder<Object> {
  
      // this is a constant to decide when it is appropriate to copy the data content into the header buffer
      private static final int COPY_CONTENT_THRESHOLD = 128;
      static final int CRLF_SHORT = (CR << 8) | LF;
      private static final int ZERO_CRLF_MEDIUM = ('0' << 16) | CRLF_SHORT;
      private static final byte[] ZERO_CRLF_CRLF = { '0', CR, LF, CR, LF };
      private static final ByteBuf CRLF_BUF = unreleasableBuffer(
              directBuffer(2).writeByte(CR).writeByte(LF)).asReadOnly();
      private static final ByteBuf ZERO_CRLF_CRLF_BUF = unreleasableBuffer(
              directBuffer(ZERO_CRLF_CRLF.length).writeBytes(ZERO_CRLF_CRLF)).asReadOnly();
      private static final float HEADERS_WEIGHT_NEW = 1 / 5f;
      private static final float HEADERS_WEIGHT_HISTORICAL = 1 - HEADERS_WEIGHT_NEW;
      private static final float TRAILERS_WEIGHT_NEW = HEADERS_WEIGHT_NEW;
      private static final float TRAILERS_WEIGHT_HISTORICAL = HEADERS_WEIGHT_HISTORICAL;
  
      private static final int ST_INIT = 0;
      private static final int ST_CONTENT_NON_CHUNK = 1;
      private static final int ST_CONTENT_CHUNK = 2;
      private static final int ST_CONTENT_ALWAYS_EMPTY = 3;
  
      @SuppressWarnings("RedundantFieldInitialization")
      private int state = ST_INIT;
  
      /**
       * Used to calculate an exponential moving average of the encoded size of the initial line and the headers for
       * a guess for future buffer allocations.
       */
      private float headersEncodedSizeAccumulator = 256;
  
      /**
       * Used to calculate an exponential moving average of the encoded size of the trailers for
       * a guess for future buffer allocations.
       */
      private float trailersEncodedSizeAccumulator = 256;
  
      private final List<Object> out = new ArrayList<Object>();
  
      private static boolean checkContentState(int state) {
          return state == ST_CONTENT_CHUNK || state == ST_CONTENT_NON_CHUNK || state == ST_CONTENT_ALWAYS_EMPTY;
      }
  
      @Override
      public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
          try {
              if (acceptOutboundMessage(msg)) {
                 encode(ctx, msg, out);
                 if (out.isEmpty()) {
                     throw new EncoderException(
                             StringUtil.simpleClassName(this) + " must produce at least one message.");
                 }
             } else {
                 ctx.write(msg, promise);
             }
         } catch (EncoderException e) {
             throw e;
         } catch (Throwable t) {
             throw new EncoderException(t);
         } finally {
             writeOutList(ctx, out, promise);
         }
     }
 
     private static void writeOutList(ChannelHandlerContext ctx, List<Object> out, ChannelPromise promise) {
         final int size = out.size();
         try {
             if (size == 1) {
                 ctx.write(out.get(0), promise);
             } else if (size > 1) {
                 // Check if we can use a voidPromise for our extra writes to reduce GC-Pressure
                 // See https://github.com/netty/netty/issues/2525
                 if (promise == ctx.voidPromise()) {
                     writeVoidPromise(ctx, out);
                 } else {
                     writePromiseCombiner(ctx, out, promise);
                 }
             }
         } finally {
             out.clear();
         }
     }
 
     private static void writeVoidPromise(ChannelHandlerContext ctx, List<Object> out) {
         final ChannelPromise voidPromise = ctx.voidPromise();
         for (int i = 0; i < out.size(); i++) {
             ctx.write(out.get(i), voidPromise);
         }
     }
 
     private static void writePromiseCombiner(ChannelHandlerContext ctx, List<Object> out, ChannelPromise promise) {
         final PromiseCombiner combiner = new PromiseCombiner(ctx.executor());
         for (int i = 0; i < out.size(); i++) {
             combiner.add(ctx.write(out.get(i)));
         }
         combiner.finish(promise);
     }
 
     @Override
     @SuppressWarnings("ConditionCoveredByFurtherCondition")
     protected void encode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {
         // fast-path for common idiom that doesn't require class-checks
         if (msg == Unpooled.EMPTY_BUFFER) {
             out.add(Unpooled.EMPTY_BUFFER);
             return;
         }
         // The reason why we perform instanceof checks in this order,
         // by duplicating some code and without relying on ReferenceCountUtil::release as a generic release
         // mechanism, is https://bugs.openjdk.org/browse/JDK-8180450.
         // https://github.com/netty/netty/issues/12708 contains more detail re how the previous version of this
         // code was interacting with the JIT instanceof optimizations.
         if (msg instanceof FullHttpMessage) {
             encodeFullHttpMessage(ctx, msg, out);
             return;
         }
         if (msg instanceof HttpMessage) {
             final H m;
             try {
                 m = (H) msg;
             } catch (Exception rethrow) {
                 ReferenceCountUtil.release(msg);
                 throw rethrow;
             }
             if (m instanceof LastHttpContent) {
                 encodeHttpMessageLastContent(ctx, m, out);
             } else if (m instanceof HttpContent) {
                 encodeHttpMessageNotLastContent(ctx, m, out);
             } else {
                 encodeJustHttpMessage(ctx, m, out);
             }
         } else {
             encodeNotHttpMessageContentTypes(ctx, msg, out);
         }
     }
 
     private void encodeJustHttpMessage(ChannelHandlerContext ctx, H m, List<Object> out) throws Exception {
         assert !(m instanceof HttpContent);
         try {
             if (state != ST_INIT) {
                 throwUnexpectedMessageTypeEx(m, state);
             }
             final ByteBuf buf = encodeInitHttpMessage(ctx, m);
 
             assert checkContentState(state);
 
             out.add(buf);
         } finally {
             ReferenceCountUtil.release(m);
         }
     }
 
     private void encodeByteBufHttpContent(int state, ChannelHandlerContext ctx, ByteBuf buf, ByteBuf content,
                                           HttpHeaders trailingHeaders, List<Object> out) {
         switch (state) {
             case ST_CONTENT_NON_CHUNK:
                 if (encodeContentNonChunk(out, buf, content)) {
                     break;
                 }
                 // fall-through!
             case ST_CONTENT_ALWAYS_EMPTY:
                 // We allocated a buffer so add it now.
                 out.add(buf);
                 break;
             case ST_CONTENT_CHUNK:
                 // We allocated a buffer so add it now.
                 out.add(buf);
                 encodeChunkedHttpContent(ctx, content, trailingHeaders, out);
                 break;
             default:
                 throw new Error();
         }
     }
 
     private void encodeHttpMessageNotLastContent(ChannelHandlerContext ctx, H m, List<Object> out) throws Exception {
         assert m instanceof HttpContent;
         assert !(m instanceof LastHttpContent);
         final HttpContent httpContent = (HttpContent) m;
         try {
             if (state != ST_INIT) {
                 throwUnexpectedMessageTypeEx(m, state);
             }
             final ByteBuf buf = encodeInitHttpMessage(ctx, m);
 
             assert checkContentState(state);
 
             encodeByteBufHttpContent(state, ctx, buf, httpContent.content(), null, out);
         } finally {
             httpContent.release();
         }
     }
 
     private void encodeHttpMessageLastContent(ChannelHandlerContext ctx, H m, List<Object> out) throws Exception {
         assert m instanceof LastHttpContent;
         final LastHttpContent httpContent = (LastHttpContent) m;
         try {
             if (state != ST_INIT) {
                 throwUnexpectedMessageTypeEx(m, state);
             }
             final ByteBuf buf = encodeInitHttpMessage(ctx, m);
 
             assert checkContentState(state);
 
             encodeByteBufHttpContent(state, ctx, buf, httpContent.content(), httpContent.trailingHeaders(), out);
 
             state = ST_INIT;
         } finally {
             httpContent.release();
         }
     }
     @SuppressWarnings("ConditionCoveredByFurtherCondition")
     private void encodeNotHttpMessageContentTypes(ChannelHandlerContext ctx, Object msg, List<Object> out) {
         assert !(msg instanceof HttpMessage);
         if (state == ST_INIT) {
             try {
                 if (msg instanceof ByteBuf && bypassEncoderIfEmpty((ByteBuf) msg, out)) {
                     return;
                 }
                 throwUnexpectedMessageTypeEx(msg, ST_INIT);
             } finally {
                 ReferenceCountUtil.release(msg);
             }
         }
         if (msg == LastHttpContent.EMPTY_LAST_CONTENT) {
             state = encodeEmptyLastHttpContent(state, out);
             return;
         }
         if (msg instanceof LastHttpContent) {
             encodeLastHttpContent(ctx, (LastHttpContent) msg, out);
             return;
         }
         if (msg instanceof HttpContent) {
             encodeHttpContent(ctx, (HttpContent) msg, out);
             return;
         }
         if (msg instanceof ByteBuf) {
             encodeByteBufContent(ctx, (ByteBuf) msg, out);
             return;
         }
         if (msg instanceof FileRegion) {
             encodeFileRegionContent(ctx, (FileRegion) msg, out);
             return;
         }
         try {
             throwUnexpectedMessageTypeEx(msg, state);
         } finally {
             ReferenceCountUtil.release(msg);
         }
     }
 
     private void encodeFullHttpMessage(ChannelHandlerContext ctx, Object o, List<Object> out)
             throws Exception {
         assert o instanceof FullHttpMessage;
         final FullHttpMessage msg = (FullHttpMessage) o;
         try {
             if (state != ST_INIT) {
                 throwUnexpectedMessageTypeEx(o, state);
             }
 
             final H m = (H) o;
 
             final int state = isContentAlwaysEmpty(m) ? ST_CONTENT_ALWAYS_EMPTY :
                     HttpUtil.isTransferEncodingChunked(m) ? ST_CONTENT_CHUNK : ST_CONTENT_NON_CHUNK;
 
             ByteBuf content = msg.content();
 
             final boolean accountForContentSize = content.readableBytes() > 0 &&
                                         state == ST_CONTENT_NON_CHUNK &&
                                         // try embed the content if less or equals than
                                         // the biggest of ~12.5% of the header estimated size and COPY_DATA_THRESHOLD:
                                         // it limits a wrong estimation to waste too much memory
                                         content.readableBytes() <=
                                         Math.max(COPY_CONTENT_THRESHOLD, ((int) headersEncodedSizeAccumulator) / 8);
 
             final int headersAndContentSize = (int) headersEncodedSizeAccumulator +
                                                   (accountForContentSize? content.readableBytes() : 0);
             final ByteBuf buf = ctx.alloc().buffer(headersAndContentSize);
 
             encodeInitialLine(buf, m);
 
             sanitizeHeadersBeforeEncode(m, state == ST_CONTENT_ALWAYS_EMPTY);
 
             encodeHeaders(m.headers(), buf);
             ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
 
             // don't consider the copyContent case here: the statistics is just related the headers
             headersEncodedSizeAccumulator = HEADERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
                     HEADERS_WEIGHT_HISTORICAL * headersEncodedSizeAccumulator;
 
             encodeByteBufHttpContent(state, ctx, buf, content, msg.trailingHeaders(), out);
         } finally {
             msg.release();
         }
     }
 
     private static boolean encodeContentNonChunk(List<Object> out, ByteBuf buf, ByteBuf content) {
         final int contentLength = content.readableBytes();
         if (contentLength > 0) {
             if (buf.maxFastWritableBytes() >= contentLength) {
                 // merge into other buffer for performance reasons
                 buf.writeBytes(content);
                 out.add(buf);
             } else {
                 out.add(buf);
                 out.add(content.retain());
             }
             return true;
         }
         return false;
     }
 
     private static void throwUnexpectedMessageTypeEx(Object msg, int state) {
         throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg)
                 + ", state: " + state);
     }
 
     private void encodeFileRegionContent(ChannelHandlerContext ctx, FileRegion msg, List<Object> out) {
         try {
             assert state != ST_INIT;
             switch (state) {
                 case ST_CONTENT_NON_CHUNK:
                     if (msg.count() > 0) {
                         out.add(msg.retain());
                         break;
                     }
 
                     // fall-through!
                 case ST_CONTENT_ALWAYS_EMPTY:
                     // Need to produce some output otherwise an
                     // IllegalStateException will be thrown as we did not write anything
                     // Its ok to just write an EMPTY_BUFFER as if there are reference count issues these will be
                     // propagated as the caller of the encode(...) method will release the original
                     // buffer.
                     // Writing an empty buffer will not actually write anything on the wire, so if there is a user
                     // error with msg it will not be visible externally
                     out.add(Unpooled.EMPTY_BUFFER);
                     break;
                 case ST_CONTENT_CHUNK:
                     encodedChunkedFileRegionContent(ctx, msg, out);
                     break;
                 default:
                     throw new Error();
             }
         } finally {
             msg.release();
         }
     }
 
     // Bypass the encoder in case of an empty buffer, so that the following idiom works:
     //
     //     ch.write(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
     //
     // See https://github.com/netty/netty/issues/2983 for more information.
     private static boolean bypassEncoderIfEmpty(ByteBuf msg, List<Object> out) {
         if (!msg.isReadable()) {
             out.add(msg.retain());
             return true;
         }
         return false;
     }
 
     private void encodeByteBufContent(ChannelHandlerContext ctx, ByteBuf content, List<Object> out) {
         try {
             assert state != ST_INIT;
             if (bypassEncoderIfEmpty(content, out)) {
                 return;
             }
             encodeByteBufAndTrailers(state, ctx, out, content, null);
         } finally {
             content.release();
         }
     }
 
     private static int encodeEmptyLastHttpContent(int state, List<Object> out) {
         assert state != ST_INIT;
 
         switch (state) {
             case ST_CONTENT_NON_CHUNK:
             case ST_CONTENT_ALWAYS_EMPTY:
                 out.add(Unpooled.EMPTY_BUFFER);
                 break;
             case ST_CONTENT_CHUNK:
                 out.add(ZERO_CRLF_CRLF_BUF.duplicate());
                 break;
             default:
                 throw new Error();
         }
         return ST_INIT;
     }
 
     private void encodeLastHttpContent(ChannelHandlerContext ctx, LastHttpContent msg, List<Object> out) {
         assert state != ST_INIT;
         assert !(msg instanceof HttpMessage);
         try {
             encodeByteBufAndTrailers(state, ctx, out, msg.content(), msg.trailingHeaders());
             state = ST_INIT;
         } finally {
             msg.release();
         }
     }
 
     private void encodeHttpContent(ChannelHandlerContext ctx, HttpContent msg, List<Object> out) {
         assert state != ST_INIT;
         assert !(msg instanceof HttpMessage);
         assert !(msg instanceof LastHttpContent);
         try {
             this.encodeByteBufAndTrailers(state, ctx, out, msg.content(), null);
         } finally {
             msg.release();
         }
     }
 
     private void encodeByteBufAndTrailers(int state, ChannelHandlerContext ctx, List<Object> out, ByteBuf content,
                                           HttpHeaders trailingHeaders) {
         switch (state) {
             case ST_CONTENT_NON_CHUNK:
                 if (content.isReadable()) {
                     out.add(content.retain());
                     break;
                 }
                 // fall-through!
             case ST_CONTENT_ALWAYS_EMPTY:
                 out.add(Unpooled.EMPTY_BUFFER);
                 break;
             case ST_CONTENT_CHUNK:
                 encodeChunkedHttpContent(ctx, content, trailingHeaders, out);
                 break;
             default:
                 throw new Error();
         }
     }
 
     private void encodeChunkedHttpContent(ChannelHandlerContext ctx, ByteBuf content, HttpHeaders trailingHeaders,
                                           List<Object> out) {
         final int contentLength = content.readableBytes();
         if (contentLength > 0) {
             addEncodedLengthHex(ctx, contentLength, out);
             out.add(content.retain());
             out.add(CRLF_BUF.duplicate());
         }
         if (trailingHeaders != null) {
             encodeTrailingHeaders(ctx, trailingHeaders, out);
         } else if (contentLength == 0) {
             // Need to produce some output otherwise an
             // IllegalStateException will be thrown
             out.add(content.retain());
         }
     }
 
     private void encodeTrailingHeaders(ChannelHandlerContext ctx, HttpHeaders trailingHeaders, List<Object> out) {
         if (trailingHeaders.isEmpty()) {
             out.add(ZERO_CRLF_CRLF_BUF.duplicate());
         } else {
             ByteBuf buf = ctx.alloc().buffer((int) trailersEncodedSizeAccumulator);
             ByteBufUtil.writeMediumBE(buf, ZERO_CRLF_MEDIUM);
             encodeHeaders(trailingHeaders, buf);
             ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
             trailersEncodedSizeAccumulator = TRAILERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
                     TRAILERS_WEIGHT_HISTORICAL * trailersEncodedSizeAccumulator;
             out.add(buf);
         }
     }
 
     private ByteBuf encodeInitHttpMessage(ChannelHandlerContext ctx, H m) throws Exception {
         assert state == ST_INIT;
 
         ByteBuf buf = ctx.alloc().buffer((int) headersEncodedSizeAccumulator);
         // Encode the message.
         encodeInitialLine(buf, m);
         state = isContentAlwaysEmpty(m) ? ST_CONTENT_ALWAYS_EMPTY :
                 HttpUtil.isTransferEncodingChunked(m) ? ST_CONTENT_CHUNK : ST_CONTENT_NON_CHUNK;
 
         sanitizeHeadersBeforeEncode(m, state == ST_CONTENT_ALWAYS_EMPTY);
 
         encodeHeaders(m.headers(), buf);
         ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
 
         headersEncodedSizeAccumulator = HEADERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
                 HEADERS_WEIGHT_HISTORICAL * headersEncodedSizeAccumulator;
         return buf;
     }
 
     /**
      * Encode the {@link HttpHeaders} into a {@link ByteBuf}.
      */
     protected void encodeHeaders(HttpHeaders headers, ByteBuf buf) {
         Iterator<Entry<CharSequence, CharSequence>> iter = headers.iteratorCharSequence();
         while (iter.hasNext()) {
             Entry<CharSequence, CharSequence> header = iter.next();
             HttpHeadersEncoder.encoderHeader(header.getKey(), header.getValue(), buf);
         }
     }
 
     private static void encodedChunkedFileRegionContent(ChannelHandlerContext ctx, FileRegion msg, List<Object> out) {
         final long contentLength = msg.count();
         if (contentLength > 0) {
             addEncodedLengthHex(ctx, contentLength, out);
             out.add(msg.retain());
             out.add(CRLF_BUF.duplicate());
         } else if (contentLength == 0) {
             // Need to produce some output otherwise an
             // IllegalStateException will be thrown
             out.add(msg.retain());
         }
     }
 
     private static void addEncodedLengthHex(ChannelHandlerContext ctx, long contentLength, List<Object> out) {
         String lengthHex = Long.toHexString(contentLength);
         ByteBuf buf = ctx.alloc().buffer(lengthHex.length() + 2);
         buf.writeCharSequence(lengthHex, CharsetUtil.US_ASCII);
         ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
         out.add(buf);
     }
 
     /**
      * Allows to sanitize headers of the message before encoding these.
      */
     protected void sanitizeHeadersBeforeEncode(@SuppressWarnings("unused") H msg, boolean isAlwaysEmpty) {
         // noop
     }
 
     /**
      * Determine whether a message has a content or not. Some message may have headers indicating
      * a content without having an actual content, e.g the response to an HEAD or CONNECT request.
      *
      * @param msg the message to test
      * @return {@code true} to signal the message has no content
      */
     protected boolean isContentAlwaysEmpty(@SuppressWarnings("unused") H msg) {
         return false;
     }
 
     @Override
     @SuppressWarnings("ConditionCoveredByFurtherCondition")
     public boolean acceptOutboundMessage(Object msg) throws Exception {
         return msg == Unpooled.EMPTY_BUFFER ||
                 msg == LastHttpContent.EMPTY_LAST_CONTENT ||
                 msg instanceof FullHttpMessage ||
                 msg instanceof HttpMessage ||
                 msg instanceof LastHttpContent ||
                 msg instanceof HttpContent ||
                 msg instanceof ByteBuf || msg instanceof FileRegion;
     }
 
     /**
      * Add some additional overhead to the buffer. The rational is that it is better to slightly over allocate and waste
      * some memory, rather than under allocate and require a resize/copy.
      *
      * @param readableBytes The readable bytes in the buffer.
      * @return The {@code readableBytes} with some additional padding.
      */
     private static int padSizeForAccumulation(int readableBytes) {
         return (readableBytes << 2) / 3;
     }
 
     @Deprecated
     protected static void encodeAscii(String s, ByteBuf buf) {
         buf.writeCharSequence(s, CharsetUtil.US_ASCII);
     }
 
     protected abstract void encodeInitialLine(ByteBuf buf, H message) throws Exception;
 }