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   /*
    * Copyright 2013 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.buffer.ByteBufUtil;
  import io.netty.buffer.Unpooled;
  import io.netty.util.internal.ObjectUtil;
  
  import java.util.Set;
  
  import static io.netty.handler.codec.spdy.SpdyCodecUtil.SPDY_MAX_NV_LENGTH;
  
  public class SpdyHeaderBlockRawEncoder extends SpdyHeaderBlockEncoder {
  
      private final int version;
  
      public SpdyHeaderBlockRawEncoder(SpdyVersion version) {
          this.version = ObjectUtil.checkNotNull(version, "version").getVersion();
      }
  
      private static void setLengthField(ByteBuf buffer, int writerIndex, int length) {
          buffer.setInt(writerIndex, length);
      }
  
      private static void writeLengthField(ByteBuf buffer, int length) {
          buffer.writeInt(length);
      }
  
      @Override
      public ByteBuf encode(ByteBufAllocator alloc, SpdyHeadersFrame frame) throws Exception {
          Set<CharSequence> names = frame.headers().names();
          int numHeaders = names.size();
          if (numHeaders == 0) {
              return Unpooled.EMPTY_BUFFER;
          }
          if (numHeaders > SPDY_MAX_NV_LENGTH) {
              throw new IllegalArgumentException(
                      "header block contains too many headers");
          }
          ByteBuf headerBlock = alloc.heapBuffer();
          writeLengthField(headerBlock, numHeaders);
          for (CharSequence name: names) {
              writeLengthField(headerBlock, name.length());
              ByteBufUtil.writeAscii(headerBlock, name);
              int savedIndex = headerBlock.writerIndex();
              int valueLength = 0;
              writeLengthField(headerBlock, valueLength);
              for (CharSequence value: frame.headers().getAll(name)) {
                  int length = value.length();
                  if (length > 0) {
                      ByteBufUtil.writeAscii(headerBlock, value);
                      headerBlock.writeByte(0);
                      valueLength += length + 1;
                  }
              }
              if (valueLength != 0) {
                  valueLength --;
              }
              if (valueLength > SPDY_MAX_NV_LENGTH) {
                  throw new IllegalArgumentException(
                          "header exceeds allowable length: " + name);
              }
              if (valueLength > 0) {
                  setLengthField(headerBlock, savedIndex, valueLength);
                  headerBlock.writerIndex(headerBlock.writerIndex() - 1);
              }
          }
          return headerBlock;
      }
  
      @Override
      void end() {
      }
  }