/*
    * 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.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPipeline;
  import io.netty.handler.codec.ByteToMessageDecoder;
  import io.netty.handler.codec.DecoderResult;
  import io.netty.handler.codec.PrematureChannelClosureException;
  import io.netty.handler.codec.TooLongFrameException;
  import io.netty.util.AsciiString;
  import io.netty.util.ByteProcessor;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.SystemPropertyUtil;
  
  import java.util.List;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * Decodes {@link ByteBuf}s into {@link HttpMessage}s and
   * {@link HttpContent}s.
   *
   * <h3>Parameters that prevents excessive memory consumption</h3>
   * <table border="1">
   * <tr>
   * <th>Name</th><th>Default value</th><th>Meaning</th>
   * </tr>
   * <tr>
   * <td>{@code maxInitialLineLength}</td>
   * <td>{@value #DEFAULT_MAX_INITIAL_LINE_LENGTH}</td>
   * <td>The maximum length of the initial line
   *     (e.g. {@code "GET / HTTP/1.0"} or {@code "HTTP/1.0 200 OK"})
   *     If the length of the initial line exceeds this value, a
   *     {@link TooLongHttpLineException} will be raised.</td>
   * </tr>
   * <tr>
   * <td>{@code maxHeaderSize}</td>
   * <td>{@value #DEFAULT_MAX_HEADER_SIZE}</td>
   * <td>The maximum length of all headers.  If the sum of the length of each
   *     header exceeds this value, a {@link TooLongHttpHeaderException} will be raised.</td>
   * </tr>
   * <tr>
   * <td>{@code maxChunkSize}</td>
   * <td>{@value #DEFAULT_MAX_CHUNK_SIZE}</td>
   * <td>The maximum length of the content or each chunk.  If the content length
   *     (or the length of each chunk) exceeds this value, the content or chunk
   *     will be split into multiple {@link HttpContent}s whose length is
   *     {@code maxChunkSize} at maximum.</td>
   * </tr>
   * </table>
   *
   * <h3>Parameters that control parsing behavior</h3>
   * <table border="1">
   * <tr>
   * <th>Name</th><th>Default value</th><th>Meaning</th>
   * </tr>
   * <tr>
   * <td>{@code allowDuplicateContentLengths}</td>
   * <td>{@value #DEFAULT_ALLOW_DUPLICATE_CONTENT_LENGTHS}</td>
   * <td>When set to {@code false}, will reject any messages that contain multiple Content-Length header fields.
   *     When set to {@code true}, will allow multiple Content-Length headers only if they are all the same decimal value.
   *     The duplicated field-values will be replaced with a single valid Content-Length field.
   *     See <a href="https://tools.ietf.org/html/rfc7230#section-3.3.2">RFC 7230, Section 3.3.2</a>.</td>
   * </tr>
   * <tr>
   * <td>{@code allowPartialChunks}</td>
   * <td>{@value #DEFAULT_ALLOW_PARTIAL_CHUNKS}</td>
   * <td>If the length of a chunk exceeds the {@link ByteBuf}s readable bytes and {@code allowPartialChunks}
   *     is set to {@code true}, the chunk will be split into multiple {@link HttpContent}s.
   *     Otherwise, if the chunk size does not exceed {@code maxChunkSize} and {@code allowPartialChunks}
   *     is set to {@code false}, the {@link ByteBuf} is not decoded into an {@link HttpContent} until
   *     the readable bytes are greater or equal to the chunk size.</td>
   * </tr>
   * </table>
   *
   * <h3>Chunked Content</h3>
   *
   * If the content of an HTTP message is greater than {@code maxChunkSize} or
   * the transfer encoding of the HTTP message is 'chunked', this decoder
   * generates one {@link HttpMessage} instance and its following
   * {@link HttpContent}s per single HTTP message to avoid excessive memory
   * consumption. For example, the following HTTP message:
  * <pre>
  * GET / HTTP/1.1
  * Transfer-Encoding: chunked
  *
  * 1a
  * abcdefghijklmnopqrstuvwxyz
  * 10
  * 1234567890abcdef
  * 0
  * Content-MD5: ...
  * <i>[blank line]</i>
  * </pre>
  * triggers {@link HttpRequestDecoder} to generate 3 objects:
  * <ol>
  * <li>An {@link HttpRequest},</li>
  * <li>The first {@link HttpContent} whose content is {@code 'abcdefghijklmnopqrstuvwxyz'},</li>
  * <li>The second {@link LastHttpContent} whose content is {@code '1234567890abcdef'}, which marks
  * the end of the content.</li>
  * </ol>
  *
  * If you prefer not to handle {@link HttpContent}s by yourself for your
  * convenience, insert {@link HttpObjectAggregator} after this decoder in the
  * {@link ChannelPipeline}.  However, please note that your server might not
  * be as memory efficient as without the aggregator.
  *
  * <h3>Extensibility</h3>
  *
  * Please note that this decoder 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 decoder of such a derived protocol, extend this class and
  * implement all abstract methods properly.
  *
  * <h3>Header Validation</h3>
  *
  * It is recommended to always enable header validation.
  * <p>
  * Without header validation, your system can become vulnerable to
  * <a href="https://cwe.mitre.org/data/definitions/113.html">
  *     CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')
  * </a>.
  * <p>
  * This recommendation stands even when both peers in the HTTP exchange are trusted,
  * as it helps with defence-in-depth.
  */
 public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
     public static final int DEFAULT_MAX_INITIAL_LINE_LENGTH = 4096;
     public static final int DEFAULT_MAX_HEADER_SIZE = 8192;
     public static final boolean DEFAULT_CHUNKED_SUPPORTED = true;
     public static final boolean DEFAULT_ALLOW_PARTIAL_CHUNKS = true;
     public static final int DEFAULT_MAX_CHUNK_SIZE = 8192;
     public static final boolean DEFAULT_VALIDATE_HEADERS = true;
     public static final int DEFAULT_INITIAL_BUFFER_SIZE = 128;
     public static final boolean DEFAULT_ALLOW_DUPLICATE_CONTENT_LENGTHS = false;
     public static final boolean DEFAULT_STRICT_LINE_PARSING =
             SystemPropertyUtil.getBoolean("io.netty.handler.codec.http.defaultStrictLineParsing", true);
 
     private static final Runnable THROW_INVALID_CHUNK_EXTENSION = new Runnable() {
         @Override
         public void run() {
             throw new InvalidChunkExtensionException();
         }
     };
 
     private static final Runnable THROW_INVALID_LINE_SEPARATOR = new Runnable() {
         @Override
         public void run() {
             throw new InvalidLineSeparatorException();
         }
     };
 
     private final int maxChunkSize;
     private final boolean chunkedSupported;
     private final boolean allowPartialChunks;
     /**
      * This field is no longer used. It is only kept around for backwards compatibility purpose.
      */
     @Deprecated
     protected final boolean validateHeaders;
     protected final HttpHeadersFactory headersFactory;
     protected final HttpHeadersFactory trailersFactory;
     private final boolean allowDuplicateContentLengths;
     private final ByteBuf parserScratchBuffer;
     private final Runnable defaultStrictCRLFCheck;
     private final HeaderParser headerParser;
     private final LineParser lineParser;
 
     private HttpMessage message;
     private long chunkSize;
     private long contentLength = Long.MIN_VALUE;
     private boolean chunked;
     private boolean isSwitchingToNonHttp1Protocol;
 
     private final AtomicBoolean resetRequested = new AtomicBoolean();
 
     // These will be updated by splitHeader(...)
     private AsciiString name;
     private String value;
     private LastHttpContent trailer;
 
     @Override
     protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception {
         try {
             parserScratchBuffer.release();
         } finally {
             super.handlerRemoved0(ctx);
         }
     }
 
     /**
      * The internal state of {@link HttpObjectDecoder}.
      * <em>Internal use only</em>.
      */
     private enum State {
         SKIP_CONTROL_CHARS,
         READ_INITIAL,
         READ_HEADER,
         READ_VARIABLE_LENGTH_CONTENT,
         READ_FIXED_LENGTH_CONTENT,
         READ_CHUNK_SIZE,
         READ_CHUNKED_CONTENT,
         READ_CHUNK_DELIMITER,
         READ_CHUNK_FOOTER,
         BAD_MESSAGE,
         UPGRADED
     }
 
     private State currentState = State.SKIP_CONTROL_CHARS;
 
     /**
      * Creates a new instance with the default
      * {@code maxInitialLineLength (4096)}, {@code maxHeaderSize (8192)}, and
      * {@code maxChunkSize (8192)}.
      */
     protected HttpObjectDecoder() {
         this(new HttpDecoderConfig());
     }
 
     /**
      * Creates a new instance with the specified parameters.
      *
      * @deprecated Use {@link #HttpObjectDecoder(HttpDecoderConfig)} instead.
      */
     @Deprecated
     protected HttpObjectDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean chunkedSupported) {
         this(new HttpDecoderConfig()
                 .setMaxInitialLineLength(maxInitialLineLength)
                 .setMaxHeaderSize(maxHeaderSize)
                 .setMaxChunkSize(maxChunkSize)
                 .setChunkedSupported(chunkedSupported));
     }
 
     /**
      * Creates a new instance with the specified parameters.
      *
      * @deprecated Use {@link #HttpObjectDecoder(HttpDecoderConfig)} instead.
      */
     @Deprecated
     protected HttpObjectDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
             boolean chunkedSupported, boolean validateHeaders) {
         this(new HttpDecoderConfig()
                 .setMaxInitialLineLength(maxInitialLineLength)
                 .setMaxHeaderSize(maxHeaderSize)
                 .setMaxChunkSize(maxChunkSize)
                 .setChunkedSupported(chunkedSupported)
                 .setValidateHeaders(validateHeaders));
     }
 
     /**
      * Creates a new instance with the specified parameters.
      *
      * @deprecated Use {@link #HttpObjectDecoder(HttpDecoderConfig)} instead.
      */
     @Deprecated
     protected HttpObjectDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
             boolean chunkedSupported, boolean validateHeaders, int initialBufferSize) {
         this(new HttpDecoderConfig()
                 .setMaxInitialLineLength(maxInitialLineLength)
                 .setMaxHeaderSize(maxHeaderSize)
                 .setMaxChunkSize(maxChunkSize)
                 .setChunkedSupported(chunkedSupported)
                 .setValidateHeaders(validateHeaders)
                 .setInitialBufferSize(initialBufferSize));
     }
 
     /**
      * Creates a new instance with the specified parameters.
      *
      * @deprecated Use {@link #HttpObjectDecoder(HttpDecoderConfig)} instead.
      */
     @Deprecated
     protected HttpObjectDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
             boolean chunkedSupported, boolean validateHeaders, int initialBufferSize,
             boolean allowDuplicateContentLengths) {
         this(new HttpDecoderConfig()
                 .setMaxInitialLineLength(maxInitialLineLength)
                 .setMaxHeaderSize(maxHeaderSize)
                 .setMaxChunkSize(maxChunkSize)
                 .setChunkedSupported(chunkedSupported)
                 .setValidateHeaders(validateHeaders)
                 .setInitialBufferSize(initialBufferSize)
                 .setAllowDuplicateContentLengths(allowDuplicateContentLengths));
     }
 
     /**
      * Creates a new instance with the specified parameters.
      *
      * @deprecated Use {@link #HttpObjectDecoder(HttpDecoderConfig)} instead.
      */
     @Deprecated
     protected HttpObjectDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
             boolean chunkedSupported, boolean validateHeaders, int initialBufferSize,
             boolean allowDuplicateContentLengths, boolean allowPartialChunks) {
         this(new HttpDecoderConfig()
                 .setMaxInitialLineLength(maxInitialLineLength)
                 .setMaxHeaderSize(maxHeaderSize)
                 .setMaxChunkSize(maxChunkSize)
                 .setChunkedSupported(chunkedSupported)
                 .setValidateHeaders(validateHeaders)
                 .setInitialBufferSize(initialBufferSize)
                 .setAllowDuplicateContentLengths(allowDuplicateContentLengths)
                 .setAllowPartialChunks(allowPartialChunks));
     }
 
     /**
      * Creates a new instance with the specified configuration.
      */
     protected HttpObjectDecoder(HttpDecoderConfig config) {
         checkNotNull(config, "config");
 
         parserScratchBuffer = Unpooled.buffer(config.getInitialBufferSize());
         defaultStrictCRLFCheck = config.isStrictLineParsing() ? THROW_INVALID_LINE_SEPARATOR : null;
         lineParser = new LineParser(parserScratchBuffer, config.getMaxInitialLineLength());
         headerParser = new HeaderParser(parserScratchBuffer, config.getMaxHeaderSize());
         maxChunkSize = config.getMaxChunkSize();
         chunkedSupported = config.isChunkedSupported();
         headersFactory = config.getHeadersFactory();
         trailersFactory = config.getTrailersFactory();
         validateHeaders = isValidating(headersFactory);
         allowDuplicateContentLengths = config.isAllowDuplicateContentLengths();
         allowPartialChunks = config.isAllowPartialChunks();
     }
 
     protected boolean isValidating(HttpHeadersFactory headersFactory) {
         if (headersFactory instanceof DefaultHttpHeadersFactory) {
             DefaultHttpHeadersFactory builder = (DefaultHttpHeadersFactory) headersFactory;
             return builder.isValidatingHeaderNames() || builder.isValidatingHeaderValues();
         }
         return true; // We can't actually tell in this case, but we assume some validation is taking place.
     }
 
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf buffer, List<Object> out) throws Exception {
         if (resetRequested.get()) {
             resetNow();
         }
 
         switch (currentState) {
         case SKIP_CONTROL_CHARS:
             // Fall-through
         case READ_INITIAL: try {
             ByteBuf line = lineParser.parse(buffer, defaultStrictCRLFCheck);
             if (line == null) {
                 return;
             }
             final String[] initialLine = splitInitialLine(line);
             assert initialLine.length == 3 : "initialLine::length must be 3";
 
             message = createMessage(initialLine);
             currentState = State.READ_HEADER;
             // fall-through
         } catch (Exception e) {
             out.add(invalidMessage(message, buffer, e));
             return;
         }
         case READ_HEADER: try {
             State nextState = readHeaders(buffer);
             if (nextState == null) {
                 return;
             }
             currentState = nextState;
             switch (nextState) {
             case SKIP_CONTROL_CHARS:
                 // fast-path
                 // No content is expected.
                 addCurrentMessage(out);
                 out.add(LastHttpContent.EMPTY_LAST_CONTENT);
                 resetNow();
                 return;
             case READ_CHUNK_SIZE:
                 if (!chunkedSupported) {
                     throw new IllegalArgumentException("Chunked messages not supported");
                 }
                 // Chunked encoding - generate HttpMessage first.  HttpChunks will follow.
                 addCurrentMessage(out);
                 return;
             default:
                 /*
                  * RFC 7230, 3.3.3 (https://tools.ietf.org/html/rfc7230#section-3.3.3) states that if a
                  * request does not have either a transfer-encoding or a content-length header then the message body
                  * length is 0. However, for a response the body length is the number of octets received prior to the
                  * server closing the connection. So we treat this as variable length chunked encoding.
                  */
                 if (contentLength == 0 || contentLength == -1 && isDecodingRequest()) {
                     addCurrentMessage(out);
                     out.add(LastHttpContent.EMPTY_LAST_CONTENT);
                     resetNow();
                     return;
                 }
 
                 assert nextState == State.READ_FIXED_LENGTH_CONTENT ||
                         nextState == State.READ_VARIABLE_LENGTH_CONTENT;
 
                 addCurrentMessage(out);
 
                 if (nextState == State.READ_FIXED_LENGTH_CONTENT) {
                     // chunkSize will be decreased as the READ_FIXED_LENGTH_CONTENT state reads data chunk by chunk.
                     chunkSize = contentLength;
                 }
 
                 // We return here, this forces decode to be called again where we will decode the content
                 return;
             }
         } catch (Exception e) {
             out.add(invalidMessage(message, buffer, e));
             return;
         }
         case READ_VARIABLE_LENGTH_CONTENT: {
             // Keep reading data as a chunk until the end of connection is reached.
             int toRead = Math.min(buffer.readableBytes(), maxChunkSize);
             if (toRead > 0) {
                 ByteBuf content = buffer.readRetainedSlice(toRead);
                 out.add(new DefaultHttpContent(content));
             }
             return;
         }
         case READ_FIXED_LENGTH_CONTENT: {
             int readLimit = buffer.readableBytes();
 
             // Check if the buffer is readable first as we use the readable byte count
             // to create the HttpChunk. This is needed as otherwise we may end up with
             // create an HttpChunk instance that contains an empty buffer and so is
             // handled like it is the last HttpChunk.
             //
             // See https://github.com/netty/netty/issues/433
             if (readLimit == 0) {
                 return;
             }
 
             int toRead = Math.min(readLimit, maxChunkSize);
             if (toRead > chunkSize) {
                 toRead = (int) chunkSize;
             }
             ByteBuf content = buffer.readRetainedSlice(toRead);
             chunkSize -= toRead;
 
             if (chunkSize == 0) {
                 // Read all content.
                 out.add(new DefaultLastHttpContent(content, trailersFactory));
                 resetNow();
             } else {
                 out.add(new DefaultHttpContent(content));
             }
             return;
         }
         /*
          * Everything else after this point takes care of reading chunked content. Basically, read chunk size,
          * read chunk, read and ignore the CRLF and repeat until 0
          */
         case READ_CHUNK_SIZE: try {
             ByteBuf line = lineParser.parse(buffer, THROW_INVALID_CHUNK_EXTENSION);
             if (line == null) {
                 return;
             }
             int chunkSize = getChunkSize(line.array(), line.arrayOffset() + line.readerIndex(), line.readableBytes());
             this.chunkSize = chunkSize;
             if (chunkSize == 0) {
                 currentState = State.READ_CHUNK_FOOTER;
                 return;
             }
             currentState = State.READ_CHUNKED_CONTENT;
             // fall-through
         } catch (Exception e) {
             out.add(invalidChunk(buffer, e));
             return;
         }
         case READ_CHUNKED_CONTENT: {
             assert chunkSize <= Integer.MAX_VALUE;
             int toRead = Math.min((int) chunkSize, maxChunkSize);
             if (!allowPartialChunks && buffer.readableBytes() < toRead) {
                 return;
             }
             toRead = Math.min(toRead, buffer.readableBytes());
             if (toRead == 0) {
                 return;
             }
             HttpContent chunk = new DefaultHttpContent(buffer.readRetainedSlice(toRead));
             chunkSize -= toRead;
 
             out.add(chunk);
 
             if (chunkSize != 0) {
                 return;
             }
             currentState = State.READ_CHUNK_DELIMITER;
             // fall-through
         }
         case READ_CHUNK_DELIMITER: {
             if (buffer.readableBytes() >= 2) {
                 int rIdx = buffer.readerIndex();
                 if (buffer.getByte(rIdx) == HttpConstants.CR &&
                         buffer.getByte(rIdx + 1) == HttpConstants.LF) {
                     buffer.skipBytes(2);
                     currentState = State.READ_CHUNK_SIZE;
                 } else {
                     out.add(invalidChunk(buffer, new InvalidChunkTerminationException()));
                 }
             }
             return;
         }
         case READ_CHUNK_FOOTER: try {
             LastHttpContent trailer = readTrailingHeaders(buffer);
             if (trailer == null) {
                 return;
             }
             out.add(trailer);
             resetNow();
             return;
         } catch (Exception e) {
             out.add(invalidChunk(buffer, e));
             return;
         }
         case BAD_MESSAGE: {
             // Keep discarding until disconnection.
             buffer.skipBytes(buffer.readableBytes());
             break;
         }
         case UPGRADED: {
             int readableBytes = buffer.readableBytes();
             if (readableBytes > 0) {
                 // Keep on consuming as otherwise we may trigger an DecoderException,
                 // other handler will replace this codec with the upgraded protocol codec to
                 // take the traffic over at some point then.
                 // See https://github.com/netty/netty/issues/2173
                 out.add(buffer.readBytes(readableBytes));
             }
             break;
         }
         default:
             break;
         }
     }
 
     @Override
     protected void decodeLast(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
         super.decodeLast(ctx, in, out);
 
         if (resetRequested.get()) {
             // If a reset was requested by decodeLast() we need to do it now otherwise we may produce a
             // LastHttpContent while there was already one.
             resetNow();
         }
 
         // Handle the last unfinished message.
         switch (currentState) {
             case READ_VARIABLE_LENGTH_CONTENT:
                 if (!chunked && !in.isReadable()) {
                     // End of connection.
                     out.add(LastHttpContent.EMPTY_LAST_CONTENT);
                     resetNow();
                 }
                 return;
             case READ_HEADER:
                 // If we are still in the state of reading headers we need to create a new invalid message that
                 // signals that the connection was closed before we received the headers.
                 out.add(invalidMessage(message, Unpooled.EMPTY_BUFFER,
                         new PrematureChannelClosureException("Connection closed before received headers")));
                 resetNow();
                 return;
             case READ_CHUNK_DELIMITER: // fall-trough
             case READ_CHUNK_FOOTER: // fall-trough
             case READ_CHUNKED_CONTENT: // fall-trough
             case READ_CHUNK_SIZE: // fall-trough
             case READ_FIXED_LENGTH_CONTENT:
                 // Check if the closure of the connection signifies the end of the content.
                 boolean prematureClosure;
                 if (isDecodingRequest() || chunked) {
                     // The last request did not wait for a response.
                     prematureClosure = true;
                 } else {
                     // Compare the length of the received content and the 'Content-Length' header.
                     // If the 'Content-Length' header is absent, the length of the content is determined by the end of
                     // the connection, so it is perfectly fine.
                     prematureClosure = contentLength > 0;
                 }
                 if (!prematureClosure) {
                     out.add(LastHttpContent.EMPTY_LAST_CONTENT);
                 }
                 resetNow();
                 return;
             case SKIP_CONTROL_CHARS: // fall-trough
             case READ_INITIAL:// fall-trough
             case BAD_MESSAGE: // fall-trough
             case UPGRADED: // fall-trough
                 // Do nothing
                 break;
             default:
                 throw new IllegalStateException("Unhandled state " + currentState);
         }
     }
 
     @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
         if (evt instanceof HttpExpectationFailedEvent) {
             switch (currentState) {
             case READ_FIXED_LENGTH_CONTENT:
             case READ_VARIABLE_LENGTH_CONTENT:
             case READ_CHUNK_SIZE:
                 reset();
                 break;
             default:
                 break;
             }
         }
         super.userEventTriggered(ctx, evt);
     }
 
     private void addCurrentMessage(List<Object> out) {
         HttpMessage message = this.message;
         assert message != null;
         this.message = null;
         out.add(message);
     }
 
     protected boolean isContentAlwaysEmpty(HttpMessage msg) {
         if (msg instanceof HttpResponse) {
             HttpResponse res = (HttpResponse) msg;
             final HttpResponseStatus status = res.status();
             final int code = status.code();
             final HttpStatusClass statusClass = status.codeClass();
 
             // Correctly handle return codes of 1xx.
             //
             // See:
             //     - https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html Section 4.4
             //     - https://github.com/netty/netty/issues/222
             if (statusClass == HttpStatusClass.INFORMATIONAL) {
                 // One exception: Hixie 76 websocket handshake response
                 return !(code == 101 && !res.headers().contains(HttpHeaderNames.SEC_WEBSOCKET_ACCEPT)
                          && res.headers().contains(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET, true));
             }
 
             switch (code) {
             case 204: case 304:
                 return true;
             default:
                 return false;
             }
         }
         return false;
     }
 
     /**
      * Returns true if the server switched to a different protocol than HTTP/1.0 or HTTP/1.1, e.g. HTTP/2 or Websocket.
      * Returns false if the upgrade happened in a different layer, e.g. upgrade from HTTP/1.1 to HTTP/1.1 over TLS.
      */
     protected boolean isSwitchingToNonHttp1Protocol(HttpResponse msg) {
         if (msg.status().code() != HttpResponseStatus.SWITCHING_PROTOCOLS.code()) {
             return false;
         }
         String newProtocol = msg.headers().get(HttpHeaderNames.UPGRADE);
         return newProtocol == null ||
                 !newProtocol.contains(HttpVersion.HTTP_1_0.text()) &&
                 !newProtocol.contains(HttpVersion.HTTP_1_1.text());
     }
 
     /**
      * Resets the state of the decoder so that it is ready to decode a new message.
      * This method is useful for handling a rejected request with {@code Expect: 100-continue} header.
      */
     public void reset() {
         resetRequested.lazySet(true);
     }
 
     private void resetNow() {
         message = null;
         name = null;
         value = null;
         contentLength = Long.MIN_VALUE;
         chunked = false;
         lineParser.reset();
         headerParser.reset();
         trailer = null;
         if (isSwitchingToNonHttp1Protocol) {
             isSwitchingToNonHttp1Protocol = false;
             currentState = State.UPGRADED;
             return;
         }
 
         resetRequested.lazySet(false);
         currentState = State.SKIP_CONTROL_CHARS;
     }
 
     private HttpMessage invalidMessage(HttpMessage current, ByteBuf in, Exception cause) {
         currentState = State.BAD_MESSAGE;
         message = null;
         trailer = null;
 
         // Advance the readerIndex so that ByteToMessageDecoder does not complain
         // when we produced an invalid message without consuming anything.
         in.skipBytes(in.readableBytes());
 
         if (current == null) {
             current = createInvalidMessage();
         }
         current.setDecoderResult(DecoderResult.failure(cause));
 
         return current;
     }
 
     private HttpContent invalidChunk(ByteBuf in, Exception cause) {
         currentState = State.BAD_MESSAGE;
         message = null;
         trailer = null;
 
         // Advance the readerIndex so that ByteToMessageDecoder does not complain
         // when we produced an invalid message without consuming anything.
         in.skipBytes(in.readableBytes());
 
         HttpContent chunk = new DefaultLastHttpContent(Unpooled.EMPTY_BUFFER);
         chunk.setDecoderResult(DecoderResult.failure(cause));
         return chunk;
     }
 
     private State readHeaders(ByteBuf buffer) {
         final HttpMessage message = this.message;
         final HttpHeaders headers = message.headers();
 
         final HeaderParser headerParser = this.headerParser;
 
         ByteBuf line = headerParser.parse(buffer, defaultStrictCRLFCheck);
         if (line == null) {
             return null;
         }
         int lineLength = line.readableBytes();
         while (lineLength > 0) {
             final byte[] lineContent = line.array();
             final int startLine = line.arrayOffset() + line.readerIndex();
             final byte firstChar = lineContent[startLine];
             if (name != null && (firstChar == ' ' || firstChar == '\t')) {
                 //please do not make one line from below code
                 //as it breaks +XX:OptimizeStringConcat optimization
                 String trimmedLine = langAsciiString(lineContent, startLine, lineLength).trim();
                 String valueStr = value;
                 value = valueStr + ' ' + trimmedLine;
             } else {
                 if (name != null) {
                     headers.add(name, value);
                 }
                 splitHeader(lineContent, startLine, lineLength);
             }
 
             line = headerParser.parse(buffer, defaultStrictCRLFCheck);
             if (line == null) {
                 return null;
             }
             lineLength = line.readableBytes();
         }
 
         // Add the last header.
         if (name != null) {
             headers.add(name, value);
         }
 
         // reset name and value fields
         name = null;
         value = null;
 
         // Done parsing initial line and headers. Set decoder result.
         HttpMessageDecoderResult decoderResult = new HttpMessageDecoderResult(lineParser.size, headerParser.size);
         message.setDecoderResult(decoderResult);
 
         List<String> contentLengthFields = headers.getAll(HttpHeaderNames.CONTENT_LENGTH);
         if (!contentLengthFields.isEmpty()) {
             HttpVersion version = message.protocolVersion();
             boolean isHttp10OrEarlier = version.majorVersion() < 1 || (version.majorVersion() == 1
                     && version.minorVersion() == 0);
             // Guard against multiple Content-Length headers as stated in
             // https://tools.ietf.org/html/rfc7230#section-3.3.2:
             contentLength = HttpUtil.normalizeAndGetContentLength(contentLengthFields,
                     isHttp10OrEarlier, allowDuplicateContentLengths);
             if (contentLength != -1) {
                 String lengthValue = contentLengthFields.get(0).trim();
                 if (contentLengthFields.size() > 1 || // don't unnecessarily re-order headers
                         !lengthValue.equals(Long.toString(contentLength))) {
                     headers.set(HttpHeaderNames.CONTENT_LENGTH, contentLength);
                 }
             }
         } else {
             // We know the content length if it's a Web Socket message even if
             // Content-Length header is missing.
             contentLength = HttpUtil.getWebSocketContentLength(message);
         }
         if (!isDecodingRequest() && message instanceof HttpResponse) {
             HttpResponse res = (HttpResponse) message;
             this.isSwitchingToNonHttp1Protocol = isSwitchingToNonHttp1Protocol(res);
         }
         if (isContentAlwaysEmpty(message)) {
             HttpUtil.setTransferEncodingChunked(message, false);
             return State.SKIP_CONTROL_CHARS;
         }
         if (HttpUtil.isTransferEncodingChunked(message)) {
             this.chunked = true;
             if (!contentLengthFields.isEmpty() && message.protocolVersion() == HttpVersion.HTTP_1_1) {
                 handleTransferEncodingChunkedWithContentLength(message);
             }
             return State.READ_CHUNK_SIZE;
         }
         if (contentLength >= 0) {
             return State.READ_FIXED_LENGTH_CONTENT;
         }
         return State.READ_VARIABLE_LENGTH_CONTENT;
     }
 
     /**
      * Invoked when a message with both a "Transfer-Encoding: chunked" and a "Content-Length" header field is detected.
      * The default behavior is to <i>remove</i> the Content-Length field, but this method could be overridden
      * to change the behavior (to, e.g., throw an exception and produce an invalid message).
      * <p>
      * See: https://tools.ietf.org/html/rfc7230#section-3.3.3
      * <pre>
      *     If a message is received with both a Transfer-Encoding and a
      *     Content-Length header field, the Transfer-Encoding overrides the
      *     Content-Length.  Such a message might indicate an attempt to
      *     perform request smuggling (Section 9.5) or response splitting
      *     (Section 9.4) and ought to be handled as an error.  A sender MUST
      *     remove the received Content-Length field prior to forwarding such
      *     a message downstream.
      * </pre>
      * Also see:
      * https://github.com/apache/tomcat/blob/b693d7c1981fa7f51e58bc8c8e72e3fe80b7b773/
      * java/org/apache/coyote/http11/Http11Processor.java#L747-L755
      * https://github.com/nginx/nginx/blob/0ad4393e30c119d250415cb769e3d8bc8dce5186/
      * src/http/ngx_http_request.c#L1946-L1953
      */
     protected void handleTransferEncodingChunkedWithContentLength(HttpMessage message) {
         message.headers().remove(HttpHeaderNames.CONTENT_LENGTH);
         contentLength = Long.MIN_VALUE;
     }
 
     private LastHttpContent readTrailingHeaders(ByteBuf buffer) {
         final HeaderParser headerParser = this.headerParser;
         ByteBuf line = headerParser.parse(buffer, defaultStrictCRLFCheck);
         if (line == null) {
             return null;
         }
         LastHttpContent trailer = this.trailer;
         int lineLength = line.readableBytes();
         if (lineLength == 0 && trailer == null) {
             // We have received the empty line which signals the trailer is complete and did not parse any trailers
             // before. Just return an empty last content to reduce allocations.
             return LastHttpContent.EMPTY_LAST_CONTENT;
         }
 
         CharSequence lastHeader = null;
         if (trailer == null) {
             trailer = this.trailer = new DefaultLastHttpContent(Unpooled.EMPTY_BUFFER, trailersFactory);
         }
         while (lineLength > 0) {
             final byte[] lineContent = line.array();
             final int startLine = line.arrayOffset() + line.readerIndex();
             final byte firstChar = lineContent[startLine];
             if (lastHeader != null && (firstChar == ' ' || firstChar == '\t')) {
                 List<String> current = trailer.trailingHeaders().getAll(lastHeader);
                 if (!current.isEmpty()) {
                     int lastPos = current.size() - 1;
                     //please do not make one line from below code
                     //as it breaks +XX:OptimizeStringConcat optimization
                     String lineTrimmed = langAsciiString(lineContent, startLine, line.readableBytes()).trim();
                     String currentLastPos = current.get(lastPos);
                     current.set(lastPos, currentLastPos + lineTrimmed);
                 }
             } else {
                 splitHeader(lineContent, startLine, lineLength);
                 AsciiString headerName = name;
                 if (!HttpHeaderNames.CONTENT_LENGTH.contentEqualsIgnoreCase(headerName) &&
                         !HttpHeaderNames.TRANSFER_ENCODING.contentEqualsIgnoreCase(headerName) &&
                         !HttpHeaderNames.TRAILER.contentEqualsIgnoreCase(headerName)) {
                     trailer.trailingHeaders().add(headerName, value);
                 }
                 lastHeader = name;
                 // reset name and value fields
                 name = null;
                 value = null;
             }
             line = headerParser.parse(buffer, defaultStrictCRLFCheck);
             if (line == null) {
                 return null;
             }
             lineLength = line.readableBytes();
         }
 
         this.trailer = null;
         return trailer;
     }
 
     protected abstract boolean isDecodingRequest();
     protected abstract HttpMessage createMessage(String[] initialLine) throws Exception;
     protected abstract HttpMessage createInvalidMessage();
 
     /**
      * It skips any whitespace char and return the number of skipped bytes.
      */
     private static int skipWhiteSpaces(byte[] hex, int start, int length) {
         for (int i = 0; i < length; i++) {
             if (!isWhitespace(hex[start + i])) {
                 return i;
             }
         }
         return length;
     }
 
     private static int getChunkSize(byte[] hex, int start, int length) {
         // trim the leading bytes if white spaces, if any
         final int skipped = skipWhiteSpaces(hex, start, length);
         if (skipped == length) {
             // empty case
             throw new NumberFormatException();
         }
         start += skipped;
         length -= skipped;
         int result = 0;
         for (int i = 0; i < length; i++) {
             final int digit = StringUtil.decodeHexNibble(hex[start + i]);
             if (digit == -1) {
                 // uncommon path
                 final byte b = hex[start + i];
                 if (b == ';' || isControlOrWhitespaceAsciiChar(b)) {
                     if (i == 0) {
                         // empty case
                         throw new NumberFormatException("Empty chunk size");
                     }
                     return result;
                 }
                 // non-hex char fail-fast path
                 throw new NumberFormatException("Invalid character in chunk size");
             }
             result *= 16;
             result += digit;
             if (result < 0) {
                 throw new NumberFormatException("Chunk size overflow: " + result);
             }
         }
         return result;
     }
 
     private String[] splitInitialLine(ByteBuf asciiBuffer) {
         final byte[] asciiBytes = asciiBuffer.array();
 
         final int arrayOffset = asciiBuffer.arrayOffset();
 
         final int startContent = arrayOffset + asciiBuffer.readerIndex();
 
         final int end = startContent + asciiBuffer.readableBytes();
 
         byte lastByte = asciiBytes[end - 1];
         if (isControlOrWhitespaceAsciiChar(lastByte)) {
             if (isDecodingRequest() || !isOWS(lastByte)) {
                 // There should no extra control or whitespace char in case of a request.
                 // In case of a response there might be a SP if there is no reason-phrase given.
                 // See
                 //  - https://datatracker.ietf.org/doc/html/rfc2616#section-5.1
                 //  - https://datatracker.ietf.org/doc/html/rfc9112#name-status-line
                 throw new IllegalArgumentException(
                         "Illegal character in request line: 0x" + Integer.toHexString(lastByte));
             }
         }
 
         final int aStart = findNonSPLenient(asciiBytes, startContent, end);
         final int aEnd = findSPLenient(asciiBytes, aStart, end);
 
         final int bStart = findNonSPLenient(asciiBytes, aEnd, end);
         final int bEnd = findSPLenient(asciiBytes, bStart, end);
 
         final int cStart = findNonSPLenient(asciiBytes, bEnd, end);
         final int cEnd = findEndOfString(asciiBytes, Math.max(cStart - 1, startContent), end);
 
         return new String[]{
                 splitFirstWordInitialLine(asciiBytes, aStart, aEnd - aStart),
                 splitSecondWordInitialLine(asciiBytes, bStart, bEnd - bStart),
                 cStart < cEnd ? splitThirdWordInitialLine(asciiBytes, cStart, cEnd - cStart) : StringUtil.EMPTY_STRING};
     }
 
     protected String splitFirstWordInitialLine(final byte[] asciiContent, int start, int length) {
         return langAsciiString(asciiContent, start, length);
     }
 
     protected String splitSecondWordInitialLine(final byte[] asciiContent, int start, int length) {
         return langAsciiString(asciiContent, start, length);
     }
 
     protected String splitThirdWordInitialLine(final byte[] asciiContent, int start, int length) {
         return langAsciiString(asciiContent, start, length);
     }
 
     /**
      * This method shouldn't exist: look at https://bugs.openjdk.org/browse/JDK-8295496 for more context
      */
     private static String langAsciiString(final byte[] asciiContent, int start, int length) {
         if (length == 0) {
             return StringUtil.EMPTY_STRING;
         }
         // DON'T REMOVE: it helps JIT to use a simpler intrinsic stub for System::arrayCopy based on the call-site
         if (start == 0) {
             if (length == asciiContent.length) {
                 return new String(asciiContent, 0, 0, asciiContent.length);
             }
             return new String(asciiContent, 0, 0, length);
         }
         return new String(asciiContent, 0, start, length);
     }
 
     private void splitHeader(byte[] line, int start, int length) {
         final int end = start + length;
         int nameEnd;
         final int nameStart = start;
         // hoist this load out of the loop, because it won't change!
         final boolean isDecodingRequest = isDecodingRequest();
         for (nameEnd = nameStart; nameEnd < end; nameEnd ++) {
             byte ch = line[nameEnd];
             // https://tools.ietf.org/html/rfc7230#section-3.2.4
             //
             // No whitespace is allowed between the header field-name and colon. In
             // the past, differences in the handling of such whitespace have led to
             // security vulnerabilities in request routing and response handling. A
             // server MUST reject any received request message that contains
             // whitespace between a header field-name and colon with a response code
             // of 400 (Bad Request). A proxy MUST remove any such whitespace from a
             // response message before forwarding the message downstream.
             if (ch == ':' ||
                     // In case of decoding a request we will just continue processing and header validation
                     // is done in the DefaultHttpHeaders implementation.
                     //
                     // In the case of decoding a response we will "skip" the whitespace.
                     (!isDecodingRequest && isOWS(ch))) {
                 break;
             }
         }
 
         if (nameEnd == end) {
             // There was no colon present at all.
             throw new IllegalArgumentException("No colon found");
         }
         int colonEnd;
         for (colonEnd = nameEnd; colonEnd < end; colonEnd ++) {
             if (line[colonEnd] == ':') {
                 colonEnd ++;
                 break;
             }
         }
         name = splitHeaderName(line, nameStart, nameEnd - nameStart);
         final int valueStart = findNonWhitespace(line, colonEnd, end);
         if (valueStart == end) {
             value = StringUtil.EMPTY_STRING;
         } else {
             final int valueEnd = findEndOfString(line, start, end);
             // no need to make uses of the ByteBuf's toString ASCII method here, and risk to get JIT confused
             value = langAsciiString(line, valueStart, valueEnd - valueStart);
         }
     }
 
     protected AsciiString splitHeaderName(byte[] sb, int start, int length) {
         return new AsciiString(sb, start, length, true);
     }
 
     private static int findNonSPLenient(byte[] sb, int offset, int end) {
         for (int result = offset; result < end; ++result) {
             byte c = sb[result];
             // See https://tools.ietf.org/html/rfc7230#section-3.5
             if (isSPLenient(c)) {
                 continue;
             }
             if (isWhitespace(c)) {
                 // Any other whitespace delimiter is invalid
                 throw new IllegalArgumentException("Invalid separator");
             }
             return result;
         }
         return end;
     }
 
     private static int findSPLenient(byte[] sb, int offset, int end) {
         for (int result = offset; result < end; ++result) {
             if (isSPLenient(sb[result])) {
                 return result;
             }
         }
         return end;
     }
 
     private static final boolean[] SP_LENIENT_BYTES;
     private static final boolean[] LATIN_WHITESPACE;
 
     static {
         // See https://tools.ietf.org/html/rfc7230#section-3.5
         SP_LENIENT_BYTES = new boolean[256];
         SP_LENIENT_BYTES[128 + ' '] = true;
         SP_LENIENT_BYTES[128 + 0x09] = true;
         SP_LENIENT_BYTES[128 + 0x0B] = true;
         SP_LENIENT_BYTES[128 + 0x0C] = true;
         SP_LENIENT_BYTES[128 + 0x0D] = true;
         // TO SAVE PERFORMING Character::isWhitespace ceremony
         LATIN_WHITESPACE = new boolean[256];
         for (byte b = Byte.MIN_VALUE; b < Byte.MAX_VALUE; b++) {
             LATIN_WHITESPACE[128 + b] = Character.isWhitespace(b);
         }
     }
 
     private static boolean isSPLenient(byte c) {
         // See https://tools.ietf.org/html/rfc7230#section-3.5
         return SP_LENIENT_BYTES[c + 128];
     }
 
     private static boolean isWhitespace(byte b) {
         return LATIN_WHITESPACE[b + 128];
     }
 
     private static int findNonWhitespace(byte[] sb, int offset, int end) {
         for (int result = offset; result < end; ++result) {
             byte c = sb[result];
             if (!isWhitespace(c)) {
                 return result;
             } else if (!isOWS(c)) {
                 // Only OWS is supported for whitespace
                 throw new IllegalArgumentException("Invalid separator, only a single space or horizontal tab allowed," +
                         " but received a '" + c + "' (0x" + Integer.toHexString(c) + ")");
             }
         }
         return end;
     }
 
     private static int findEndOfString(byte[] sb, int start, int end) {
         for (int result = end - 1; result > start; --result) {
             if (!isOWS(sb[result])) {
                 return result + 1;
             }
         }
         return 0;
     }
 
     private static boolean isOWS(byte ch) {
         return ch == ' ' || ch == 0x09;
     }
 
     private static class HeaderParser {
         protected final ByteBuf seq;
         protected final int maxLength;
         int size;
 
         HeaderParser(ByteBuf seq, int maxLength) {
             this.seq = seq;
             this.maxLength = maxLength;
         }
 
         public ByteBuf parse(ByteBuf buffer, Runnable strictCRLFCheck) {
             final int readableBytes = buffer.readableBytes();
             final int readerIndex = buffer.readerIndex();
             final int maxBodySize = maxLength - size;
             assert maxBodySize >= 0;
             // adding 2 to account for both CR (if present) and LF
             // don't remove 2L: it's key to cover maxLength = Integer.MAX_VALUE
             final long maxBodySizeWithCRLF = maxBodySize + 2L;
             final int toProcess = (int) Math.min(maxBodySizeWithCRLF, readableBytes);
             final int toIndexExclusive = readerIndex + toProcess;
             assert toIndexExclusive >= readerIndex;
             final int indexOfLf = buffer.indexOf(readerIndex, toIndexExclusive, HttpConstants.LF);
             if (indexOfLf == -1) {
                 if (readableBytes > maxBodySize) {
                     // TODO: Respond with Bad Request and discard the traffic
                     //    or close the connection.
                     //       No need to notify the upstream handlers - just log.
                     //       If decoding a response, just throw an exception.
                     throw newException(maxLength);
                 }
                 return null;
             }
             final int endOfSeqIncluded;
             if (indexOfLf > readerIndex && buffer.getByte(indexOfLf - 1) == HttpConstants.CR) {
                 // Drop CR if we had a CRLF pair
                 endOfSeqIncluded = indexOfLf - 1;
             } else {
                 if (strictCRLFCheck != null) {
                     strictCRLFCheck.run();
                 }
                 endOfSeqIncluded = indexOfLf;
             }
             final int newSize = endOfSeqIncluded - readerIndex;
             if (newSize == 0) {
                 seq.clear();
                 buffer.readerIndex(indexOfLf + 1);
                 return seq;
             }
             int size = this.size + newSize;
             if (size > maxLength) {
                 throw newException(maxLength);
             }
             this.size = size;
             seq.clear();
             seq.writeBytes(buffer, readerIndex, newSize);
             buffer.readerIndex(indexOfLf + 1);
             return seq;
         }
 
         public void reset() {
             size = 0;
         }
 
         protected TooLongFrameException newException(int maxLength) {
             return new TooLongHttpHeaderException("HTTP header is larger than " + maxLength + " bytes.");
         }
     }
 
     private final class LineParser extends HeaderParser {
 
         LineParser(ByteBuf seq, int maxLength) {
             super(seq, maxLength);
         }
 
         @Override
         public ByteBuf parse(ByteBuf buffer, Runnable strictCRLFCheck) {
             // Suppress a warning because HeaderParser.reset() is supposed to be called
             reset();
             final int readableBytes = buffer.readableBytes();
             if (readableBytes == 0) {
                 return null;
             }
             if (currentState == State.SKIP_CONTROL_CHARS &&
                     skipControlChars(buffer, readableBytes, buffer.readerIndex())) {
                 return null;
             }
             return super.parse(buffer, strictCRLFCheck);
         }
 
         private boolean skipControlChars(ByteBuf buffer, int readableBytes, int readerIndex) {
             assert currentState == State.SKIP_CONTROL_CHARS;
             final int maxToSkip = Math.min(maxLength, readableBytes);
             final int firstNonControlIndex = buffer.forEachByte(readerIndex, maxToSkip, SKIP_CONTROL_CHARS_BYTES);
             if (firstNonControlIndex == -1) {
                 buffer.skipBytes(maxToSkip);
                 if (readableBytes > maxLength) {
                     throw newException(maxLength);
                 }
                 return true;
             }
             // from now on we don't care about control chars
             buffer.readerIndex(firstNonControlIndex);
             currentState = State.READ_INITIAL;
             return false;
         }
 
         @Override
         protected TooLongFrameException newException(int maxLength) {
             return new TooLongHttpLineException("An HTTP line is larger than " + maxLength + " bytes.");
         }
     }
 
     private static final boolean[] ISO_CONTROL_OR_WHITESPACE;
 
     static {
         ISO_CONTROL_OR_WHITESPACE = new boolean[256];
         for (byte b = Byte.MIN_VALUE; b < Byte.MAX_VALUE; b++) {
             ISO_CONTROL_OR_WHITESPACE[128 + b] = Character.isISOControl(b) || isWhitespace(b);
         }
     }
 
     private static final ByteProcessor SKIP_CONTROL_CHARS_BYTES = new ByteProcessor() {
 
         @Override
         public boolean process(byte value) {
             return ISO_CONTROL_OR_WHITESPACE[128 + value];
         }
     };
 
     private static boolean isControlOrWhitespaceAsciiChar(byte b) {
         return ISO_CONTROL_OR_WHITESPACE[128 + b];
     }
 }