/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF 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
   *
   *   http://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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  package org.apache.http.impl.nio.codecs;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.channels.ReadableByteChannel;
  
  import org.apache.http.ConnectionClosedException;
  import org.apache.http.impl.io.HttpTransportMetricsImpl;
  import org.apache.http.nio.FileContentDecoder;
  import org.apache.http.nio.reactor.SessionInputBuffer;
  import org.apache.http.util.Args;
  
  /**
   * Content decoder that cuts off after a defined number of bytes. This class
   * is used to receive content of HTTP messages where the end of the content
   * entity is determined by the value of the {@code Content-Length header}.
   * Entities transferred using this stream can be maximum {@link Long#MAX_VALUE}
   * long.
   * <p>
   * This decoder is optimized to transfer data directly from the underlying
   * I/O session's channel to a {@link FileChannel}, whenever
   * possible avoiding intermediate buffering in the session buffer.
   *
   * @since 4.0
   */
  public class LengthDelimitedDecoder extends AbstractContentDecoder
          implements FileContentDecoder {
  
      private final long contentLength;
  
      private long len;
  
      public LengthDelimitedDecoder(
              final ReadableByteChannel channel,
              final SessionInputBuffer buffer,
              final HttpTransportMetricsImpl metrics,
              final long contentLength) {
          super(channel, buffer, metrics);
          Args.notNegative(contentLength, "Content length");
          this.contentLength = contentLength;
      }
  
      @Override
      public int read(final ByteBuffer dst) throws IOException {
          Args.notNull(dst, "Byte buffer");
          if (isCompleted()) {
              return -1;
          }
          final int chunk = (int) Math.min((this.contentLength - this.len), Integer.MAX_VALUE);
  
          final int bytesRead;
          if (this.buffer.hasData()) {
              final int maxLen = Math.min(chunk, this.buffer.length());
              bytesRead = this.buffer.read(dst, maxLen);
          } else {
              bytesRead = readFromChannel(dst, chunk);
          }
          if (bytesRead == -1) {
              setCompleted();
              if (this.len < this.contentLength) {
                  throw new ConnectionClosedException(
                                  "Premature end of Content-Length delimited message body (expected: %,d; received: %,d)",
                                  contentLength, len);
              }
          }
          this.len += bytesRead;
          if (this.len >= this.contentLength) {
              setCompleted();
          }
          return isCompleted() && bytesRead == 0 ? -1 : bytesRead;
      }
 
     @Override
     public long transfer(
             final FileChannel dst,
             final long position,
             final long count) throws IOException {
 
         if (dst == null) {
             return 0;
         }
         if (isCompleted()) {
             return -1;
         }
 
         final int chunk = (int) Math.min((this.contentLength - this.len), Integer.MAX_VALUE);
 
         final long bytesRead;
         if (this.buffer.hasData()) {
             final int maxLen = Math.min(chunk, this.buffer.length());
             dst.position(position);
             bytesRead = this.buffer.read(dst, count < maxLen ? (int)count : maxLen);
         } else {
             if (this.channel.isOpen()) {
                 if (position > dst.size()) {
                     throw new IOException(String.format("Position past end of file [%,d > %,d]",
                                     position, dst.size()));
                 }
                 bytesRead = dst.transferFrom(this.channel, position, count < chunk ? count : chunk);
             } else {
                 bytesRead = -1;
             }
             if (bytesRead > 0) {
                 this.metrics.incrementBytesTransferred(bytesRead);
             }
         }
         if (bytesRead == -1) {
             setCompleted();
             if (this.len < this.contentLength) {
                 throw new ConnectionClosedException(
                                 "Premature end of Content-Length delimited message body (expected: %,d; received: %,d)",
                                 contentLength, len);
             }
         }
         this.len += bytesRead;
         if (this.len >= this.contentLength) {
             setCompleted();
         }
         return bytesRead;
     }
 
     @Override
     public String toString() {
         final StringBuilder sb = new StringBuilder();
         sb.append("[content length: ");
         sb.append(this.contentLength);
         sb.append("; pos: ");
         sb.append(this.len);
         sb.append("; completed: ");
         sb.append(this.completed);
         sb.append("]");
         return sb.toString();
     }
 }