/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.handler.codec.spdy;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.util.internal.ObjectUtil;
  
  import java.nio.charset.StandardCharsets;
  
  import static io.netty.handler.codec.spdy.SpdyCodecUtil.getSignedInt;
  
  public class SpdyHeaderBlockRawDecoder extends SpdyHeaderBlockDecoder {
  
      private static final int LENGTH_FIELD_SIZE = 4;
  
      private final int maxHeaderSize;
  
      private State state;
  
      private ByteBuf cumulation;
  
      private int headerSize;
      private int numHeaders;
      private int length;
      private String name;
  
      private enum State {
          READ_NUM_HEADERS,
          READ_NAME_LENGTH,
          READ_NAME,
          SKIP_NAME,
          READ_VALUE_LENGTH,
          READ_VALUE,
          SKIP_VALUE,
          END_HEADER_BLOCK,
          ERROR
      }
  
      public SpdyHeaderBlockRawDecoder(SpdyVersion spdyVersion, int maxHeaderSize) {
          ObjectUtil.checkNotNull(spdyVersion, "spdyVersion");
          this.maxHeaderSize = maxHeaderSize;
          state = State.READ_NUM_HEADERS;
      }
  
      private static int readLengthField(ByteBuf buffer) {
          int length = getSignedInt(buffer, buffer.readerIndex());
          buffer.skipBytes(LENGTH_FIELD_SIZE);
          return length;
      }
  
      @Override
      void decode(ByteBufAllocator alloc, ByteBuf headerBlock, SpdyHeadersFrame frame) throws Exception {
          ObjectUtil.checkNotNull(headerBlock, "headerBlock");
          ObjectUtil.checkNotNull(frame, "frame");
  
          if (cumulation == null) {
              decodeHeaderBlock(headerBlock, frame);
              if (headerBlock.isReadable()) {
                  cumulation = alloc.buffer(headerBlock.readableBytes());
                  cumulation.writeBytes(headerBlock);
              }
          } else {
              cumulation.writeBytes(headerBlock);
              decodeHeaderBlock(cumulation, frame);
              if (cumulation.isReadable()) {
                  cumulation.discardReadBytes();
              } else {
                  releaseBuffer();
              }
          }
      }
  
      protected void decodeHeaderBlock(ByteBuf headerBlock, SpdyHeadersFrame frame) throws Exception {
          int skipLength;
          while (headerBlock.isReadable()) {
              switch(state) {
                  case READ_NUM_HEADERS:
                      if (headerBlock.readableBytes() < LENGTH_FIELD_SIZE) {
                          return;
                      }
  
                      numHeaders = readLengthField(headerBlock);
  
                      if (numHeaders < 0) {
                          state = State.ERROR;
                         frame.setInvalid();
                     } else if (numHeaders == 0) {
                         state = State.END_HEADER_BLOCK;
                     } else {
                         state = State.READ_NAME_LENGTH;
                     }
                     break;
 
                 case READ_NAME_LENGTH:
                     if (headerBlock.readableBytes() < LENGTH_FIELD_SIZE) {
                         return;
                     }
 
                     length = readLengthField(headerBlock);
 
                     // Recipients of a zero-length name must issue a stream error
                     if (length <= 0) {
                         state = State.ERROR;
                         frame.setInvalid();
                     } else if (length > maxHeaderSize || headerSize > maxHeaderSize - length) {
                         headerSize = maxHeaderSize + 1;
                         state = State.SKIP_NAME;
                         frame.setTruncated();
                     } else {
                         headerSize += length;
                         state = State.READ_NAME;
                     }
                     break;
 
                 case READ_NAME:
                     if (headerBlock.readableBytes() < length) {
                         return;
                     }
 
                     byte[] nameBytes = new byte[length];
                     headerBlock.readBytes(nameBytes);
                     name = new String(nameBytes, StandardCharsets.UTF_8);
 
                     // Check for identically named headers
                     if (frame.headers().contains(name)) {
                         state = State.ERROR;
                         frame.setInvalid();
                     } else {
                         state = State.READ_VALUE_LENGTH;
                     }
                     break;
 
                 case SKIP_NAME:
                     skipLength = Math.min(headerBlock.readableBytes(), length);
                     headerBlock.skipBytes(skipLength);
                     length -= skipLength;
 
                     if (length == 0) {
                         state = State.READ_VALUE_LENGTH;
                     }
                     break;
 
                 case READ_VALUE_LENGTH:
                     if (headerBlock.readableBytes() < LENGTH_FIELD_SIZE) {
                         return;
                     }
 
                     length = readLengthField(headerBlock);
 
                     // Recipients of illegal value fields must issue a stream error
                     if (length < 0) {
                         state = State.ERROR;
                         frame.setInvalid();
                     } else if (length == 0) {
                         if (!frame.isTruncated()) {
                             // SPDY/3 allows zero-length (empty) header values
                             frame.headers().add(name, "");
                         }
 
                         name = null;
                         if (--numHeaders == 0) {
                             state = State.END_HEADER_BLOCK;
                         } else {
                             state = State.READ_NAME_LENGTH;
                         }
 
                     } else if (length > maxHeaderSize || headerSize > maxHeaderSize - length) {
                         headerSize = maxHeaderSize + 1;
                         name = null;
                         state = State.SKIP_VALUE;
                         frame.setTruncated();
                     } else {
                         headerSize += length;
                         state = State.READ_VALUE;
                     }
                     break;
 
                 case READ_VALUE:
                     if (headerBlock.readableBytes() < length) {
                         return;
                     }
 
                     byte[] valueBytes = new byte[length];
                     headerBlock.readBytes(valueBytes);
 
                     // Add Name/Value pair to headers
                     int index = 0;
                     int offset = 0;
 
                     // Value must not start with a NULL character
                     if (valueBytes[0] == (byte) 0) {
                         state = State.ERROR;
                         frame.setInvalid();
                         break;
                     }
 
                     while (index < length) {
                         while (index < valueBytes.length && valueBytes[index] != (byte) 0) {
                             index ++;
                         }
                         if (index < valueBytes.length) {
                             // Received NULL character
                             if (index + 1 == valueBytes.length || valueBytes[index + 1] == (byte) 0) {
                                 // Value field ended with a NULL character or
                                 // received multiple, in-sequence NULL characters.
                                 // Recipients of illegal value fields must issue a stream error
                                 state = State.ERROR;
                                 frame.setInvalid();
                                 break;
                             }
                         }
                         String value = new String(valueBytes, offset, index - offset, StandardCharsets.UTF_8);
 
                         try {
                             frame.headers().add(name, value);
                         } catch (IllegalArgumentException e) {
                             // Name contains NULL or non-ascii characters
                             state = State.ERROR;
                             frame.setInvalid();
                             break;
                         }
                         index ++;
                         offset = index;
                     }
 
                     name = null;
 
                     // If we broke out of the add header loop, break here
                     if (state == State.ERROR) {
                         break;
                     }
 
                     if (--numHeaders == 0) {
                         state = State.END_HEADER_BLOCK;
                     } else {
                         state = State.READ_NAME_LENGTH;
                     }
                     break;
 
                 case SKIP_VALUE:
                     skipLength = Math.min(headerBlock.readableBytes(), length);
                     headerBlock.skipBytes(skipLength);
                     length -= skipLength;
 
                     if (length == 0) {
                         if (--numHeaders == 0) {
                             state = State.END_HEADER_BLOCK;
                         } else {
                             state = State.READ_NAME_LENGTH;
                         }
                     }
                     break;
 
                 case END_HEADER_BLOCK:
                     state = State.ERROR;
                     frame.setInvalid();
                     break;
 
                 case ERROR:
                     headerBlock.skipBytes(headerBlock.readableBytes());
                     return;
 
                 default:
                     throw new Error("Shouldn't reach here.");
             }
         }
     }
 
     @Override
     void endHeaderBlock(SpdyHeadersFrame frame) throws Exception {
         if (state != State.END_HEADER_BLOCK) {
             frame.setInvalid();
         }
 
         releaseBuffer();
 
         // Initialize header block decoding fields
         headerSize = 0;
         name = null;
         state = State.READ_NUM_HEADERS;
     }
 
     @Override
     void end() {
         releaseBuffer();
     }
 
     private void releaseBuffer() {
         if (cumulation != null) {
             cumulation.release();
             cumulation = null;
         }
     }
 }