/*
    * 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.ChannelPipeline;
  import io.netty.util.AsciiString;
  
  /**
   * Decodes {@link ByteBuf}s into {@link HttpRequest}s and {@link HttpContent}s.
   *
   * <h3>Parameters that prevents excessive memory consumption</h3>
   * <table border="1">
   * <tr>
   * <th>Name</th><th>Meaning</th>
   * </tr>
   * <tr>
   * <td>{@code maxInitialLineLength}</td>
   * <td>The maximum length of the initial line (e.g. {@code "GET / HTTP/1.0"})
   *     If the length of the initial line exceeds this value, a
   *     {@link TooLongHttpLineException} will be raised.</td>
   * </tr>
   * <tr>
   * <td>{@code maxHeaderSize}</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>The maximum length of the content or each chunk.  If the content length
   *     exceeds this value, the transfer encoding of the decoded request will be
   *     converted to 'chunked' and the content will be split into multiple
   *     {@link HttpContent}s.  If the transfer encoding of the HTTP request is
   *     'chunked' already, each chunk will be split into smaller chunks if the
   *     length of the chunk exceeds this value.  If you prefer not to handle
   *     {@link HttpContent}s in your handler, insert {@link HttpObjectAggregator}
   *     after this decoder in the {@link ChannelPipeline}.</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>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 class HttpRequestDecoder extends HttpObjectDecoder {
  
      private static final AsciiString Accept = AsciiString.cached("Accept");
      private static final AsciiString Host = AsciiString.cached("Host");
      private static final AsciiString Connection = AsciiString.cached("Connection");
      private static final AsciiString ContentType = AsciiString.cached("Content-Type");
      private static final AsciiString ContentLength = AsciiString.cached("Content-Length");
  
      private static final int GET_AS_INT = 'G' | 'E' << 8 | 'T' << 16;
     private static final int POST_AS_INT = 'P' | 'O' << 8 | 'S' << 16 | 'T' << 24;
     private static final long HTTP_1_1_AS_LONG = 'H' | 'T' << 8 | 'T' << 16 | 'P' << 24 | (long) '/' << 32 |
             (long) '1' << 40 | (long) '.' << 48 | (long) '1' << 56;
 
     private static final long HTTP_1_0_AS_LONG = 'H' | 'T' << 8 | 'T' << 16 | 'P' << 24 | (long) '/' << 32 |
             (long) '1' << 40 | (long) '.' << 48 | (long) '0' << 56;
 
     private static final int HOST_AS_INT = 'H' | 'o' << 8 | 's' << 16 | 't' << 24;
 
     private static final long CONNECTION_AS_LONG_0 = 'C' | 'o' << 8 | 'n' << 16 | 'n' << 24 |
             (long) 'e' << 32 | (long) 'c' << 40 | (long) 't' << 48 | (long) 'i' << 56;
 
     private static final short CONNECTION_AS_SHORT_1 = 'o' | 'n' << 8;
 
     private static final long CONTENT_AS_LONG = 'C' | 'o' << 8 | 'n' << 16 | 't' << 24 |
             (long) 'e' << 32 | (long) 'n' << 40 | (long) 't' << 48 | (long) '-' << 56;
 
     private static final int TYPE_AS_INT = 'T' | 'y' << 8 | 'p' << 16 | 'e' << 24;
 
     private static final long LENGTH_AS_LONG = 'L' | 'e' << 8 | 'n' << 16 | 'g' << 24 |
             (long) 't' << 32 | (long) 'h' << 40;
 
     private static final long ACCEPT_AS_LONG = 'A' | 'c' << 8 | 'c' << 16 | 'e' << 24 |
             (long) 'p' << 32 | (long) 't' << 40;
 
     /**
      * Creates a new instance with the default
      * {@code maxInitialLineLength (4096)}, {@code maxHeaderSize (8192)}, and
      * {@code maxChunkSize (8192)}.
      */
     public HttpRequestDecoder() {
     }
 
     /**
      * Creates a new instance with the specified parameters.
      */
     public HttpRequestDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize) {
         this(new HttpDecoderConfig()
                 .setMaxInitialLineLength(maxInitialLineLength)
                 .setMaxHeaderSize(maxHeaderSize)
                 .setMaxChunkSize(maxChunkSize));
     }
 
     /**
      * @deprecated Prefer the {@link #HttpRequestDecoder(HttpDecoderConfig)} constructor,
      * to always have header validation enabled.
      */
     @Deprecated
     public HttpRequestDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean validateHeaders) {
         super(maxInitialLineLength, maxHeaderSize, maxChunkSize, DEFAULT_CHUNKED_SUPPORTED, validateHeaders);
     }
 
     /**
      * @deprecated Prefer the {@link #HttpRequestDecoder(HttpDecoderConfig)} constructor,
      * to always have header validation enabled.
      */
     @Deprecated
     public HttpRequestDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean validateHeaders,
             int initialBufferSize) {
         super(maxInitialLineLength, maxHeaderSize, maxChunkSize, DEFAULT_CHUNKED_SUPPORTED, validateHeaders,
               initialBufferSize);
     }
 
     /**
      * @deprecated Prefer the {@link #HttpRequestDecoder(HttpDecoderConfig)} constructor,
      * to always have header validation enabled.
      */
     @Deprecated
     public HttpRequestDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean validateHeaders,
             int initialBufferSize, boolean allowDuplicateContentLengths) {
         super(maxInitialLineLength, maxHeaderSize, maxChunkSize, DEFAULT_CHUNKED_SUPPORTED, validateHeaders,
               initialBufferSize, allowDuplicateContentLengths);
     }
 
     /**
      * @deprecated Prefer the {@link #HttpRequestDecoder(HttpDecoderConfig)} constructor,
      * to always have header validation enabled.
      */
     @Deprecated
     public HttpRequestDecoder(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean validateHeaders,
             int initialBufferSize, boolean allowDuplicateContentLengths, boolean allowPartialChunks) {
         super(maxInitialLineLength, maxHeaderSize, maxChunkSize, DEFAULT_CHUNKED_SUPPORTED, validateHeaders,
               initialBufferSize, allowDuplicateContentLengths, allowPartialChunks);
     }
 
     /**
      * Creates a new instance with the specified configuration.
      */
     public HttpRequestDecoder(HttpDecoderConfig config) {
         super(config);
     }
 
     @Override
     protected HttpMessage createMessage(String[] initialLine) throws Exception {
         return new DefaultHttpRequest(
                 HttpVersion.valueOf(initialLine[2]),
                 HttpMethod.valueOf(initialLine[0]), initialLine[1], headersFactory);
     }
 
     @Override
     protected AsciiString splitHeaderName(final byte[] sb, final int start, final int length) {
         final byte firstChar = sb[start];
         if (firstChar == 'H') {
             if (length == 4 && isHost(sb, start)) {
                 return Host;
             }
         } else if (firstChar == 'A') {
             if (length == 6 && isAccept(sb, start)) {
                 return Accept;
             }
         } else if (firstChar == 'C') {
             if (length == 10) {
                 if (isConnection(sb, start)) {
                     return Connection;
                 }
             } else if (length == 12) {
                 if (isContentType(sb, start)) {
                     return ContentType;
                 }
             } else if (length == 14) {
                 if (isContentLength(sb, start)) {
                     return ContentLength;
                 }
             }
         }
         return super.splitHeaderName(sb, start, length);
     }
 
     private static boolean isAccept(byte[] sb, int start) {
         final long maybeAccept = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16 |
                 sb[start + 3] << 24 |
                 (long) sb[start + 4] << 32 |
                 (long) sb[start + 5] << 40;
         return maybeAccept == ACCEPT_AS_LONG;
     }
 
     private static boolean isHost(byte[] sb, int start) {
         final int maybeHost = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16 |
                 sb[start + 3] << 24;
         return maybeHost == HOST_AS_INT;
     }
 
     private static boolean isConnection(byte[] sb, int start) {
         final long maybeConnecti = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16 |
                 sb[start + 3] << 24 |
                 (long) sb[start + 4] << 32 |
                 (long) sb[start + 5] << 40 |
                 (long) sb[start + 6] << 48 |
                 (long) sb[start + 7] << 56;
         if (maybeConnecti != CONNECTION_AS_LONG_0) {
             return false;
         }
         final short maybeOn = (short) (sb[start + 8] | sb[start + 9] << 8);
         return maybeOn == CONNECTION_AS_SHORT_1;
     }
 
     private static boolean isContentType(byte[] sb, int start) {
         final long maybeContent = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16 |
                 sb[start + 3] << 24 |
                 (long) sb[start + 4] << 32 |
                 (long) sb[start + 5] << 40 |
                 (long) sb[start + 6] << 48 |
                 (long) sb[start + 7] << 56;
         if (maybeContent != CONTENT_AS_LONG) {
             return false;
         }
         final int maybeType = sb[start + 8] |
                 sb[start + 9] << 8 |
                 sb[start + 10] << 16 |
                 sb[start + 11] << 24;
         return maybeType == TYPE_AS_INT;
     }
 
     private static boolean isContentLength(byte[] sb, int start) {
         final long maybeContent = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16 |
                 sb[start + 3] << 24 |
                 (long) sb[start + 4] << 32 |
                 (long) sb[start + 5] << 40 |
                 (long) sb[start + 6] << 48 |
                 (long) sb[start + 7] << 56;
         if (maybeContent != CONTENT_AS_LONG) {
             return false;
         }
         final long maybeLength = sb[start + 8] |
                 sb[start + 9] << 8 |
                 sb[start + 10] << 16 |
                 sb[start + 11] << 24 |
                 (long) sb[start + 12] << 32 |
                 (long) sb[start + 13] << 40;
         return maybeLength == LENGTH_AS_LONG;
     }
 
     private static boolean isGetMethod(final byte[] sb, int start) {
         final int maybeGet = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16;
         return maybeGet == GET_AS_INT;
     }
 
     private static boolean isPostMethod(final byte[] sb, int start) {
         final int maybePost = sb[start] |
                 sb[start + 1] << 8 |
                 sb[start + 2] << 16 |
                 sb[start + 3] << 24;
         return maybePost == POST_AS_INT;
     }
 
     @Override
     protected String splitFirstWordInitialLine(final byte[] sb, final int start, final int length) {
         if (length == 3) {
             if (isGetMethod(sb, start)) {
                 return HttpMethod.GET.name();
             }
         } else if (length == 4) {
             if (isPostMethod(sb, start)) {
                 return HttpMethod.POST.name();
             }
         }
         return super.splitFirstWordInitialLine(sb, start, length);
     }
 
     @Override
     protected String splitThirdWordInitialLine(final byte[] sb, final int start, final int length) {
         if (length == 8) {
             final long maybeHttp1_x = sb[start] |
                     sb[start + 1] << 8 |
                     sb[start + 2] << 16 |
                     sb[start + 3] << 24 |
                     (long) sb[start + 4] << 32 |
                     (long) sb[start + 5] << 40 |
                     (long) sb[start + 6] << 48 |
                     (long) sb[start + 7] << 56;
             if (maybeHttp1_x == HTTP_1_1_AS_LONG) {
                 return HttpVersion.HTTP_1_1_STRING;
             } else if (maybeHttp1_x == HTTP_1_0_AS_LONG) {
                 return HttpVersion.HTTP_1_0_STRING;
             }
         }
         return super.splitThirdWordInitialLine(sb, start, length);
     }
 
     @Override
     protected HttpMessage createInvalidMessage() {
         return new DefaultFullHttpRequest(HttpVersion.HTTP_1_0, HttpMethod.GET, "/bad-request",
                 Unpooled.buffer(0), headersFactory, trailersFactory);
     }
 
     @Override
     protected boolean isDecodingRequest() {
         return true;
     }
 
     @Override
     protected boolean isContentAlwaysEmpty(final HttpMessage msg) {
         // fast-path to save expensive O(n) checks; users can override createMessage
         // and extends DefaultHttpRequest making implementing HttpResponse:
         // this is why we cannot use instanceof DefaultHttpRequest here :(
         if (msg.getClass() == DefaultHttpRequest.class) {
             return false;
         }
         return super.isContentAlwaysEmpty(msg);
     }
 }