code: /*
   * 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.
   */
  package org.apache.commons.io.input;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.Reader;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.Charset;
  import java.nio.charset.CharsetEncoder;
  import java.nio.charset.CoderResult;
  
  /**
   * {@link InputStream} implementation that reads a character stream from a {@link Reader}
   * and transforms it to a byte stream using a specified charset encoding. The stream
   * is transformed using a {@link CharsetEncoder} object, guaranteeing that all charset
   * encodings supported by the JRE are handled correctly. In particular for charsets such as
   * UTF-16, the implementation ensures that one and only one byte order marker
   * is produced.
   * <p>
   * Since in general it is not possible to predict the number of characters to be read from the
   * {@link Reader} to satisfy a read request on the {@link ReaderInputStream}, all reads from
   * the {@link Reader} are buffered. There is therefore no well defined correlation
   * between the current position of the {@link Reader} and that of the {@link ReaderInputStream}.
   * This also implies that in general there is no need to wrap the underlying {@link Reader}
   * in a {@link java.io.BufferedReader}.
   * <p>
   * {@link ReaderInputStream} implements the inverse transformation of {@link java.io.InputStreamReader};
   * in the following example, reading from <tt>in2</tt> would return the same byte
   * sequence as reading from <tt>in</tt> (provided that the initial byte sequence is legal
   * with respect to the charset encoding):
   * <pre>
   * InputStream in = ...
   * Charset cs = ...
   * InputStreamReader reader = new InputStreamReader(in, cs);
   * ReaderInputStream in2 = new ReaderInputStream(reader, cs);</pre>
   * {@link ReaderInputStream} implements the same transformation as {@link java.io.OutputStreamWriter},
   * except that the control flow is reversed: both classes transform a character stream
   * into a byte stream, but {@link java.io.OutputStreamWriter} pushes data to the underlying stream,
   * while {@link ReaderInputStream} pulls it from the underlying stream.
   * <p>
   * Note that while there are use cases where there is no alternative to using
   * this class, very often the need to use this class is an indication of a flaw
   * in the design of the code. This class is typically used in situations where an existing
   * API only accepts an {@link InputStream}, but where the most natural way to produce the data
   * is as a character stream, i.e. by providing a {@link Reader} instance. An example of a situation
   * where this problem may appear is when implementing the {@link javax.activation.DataSource}
   * interface from the Java Activation Framework.
   * <p>
   * Given the fact that the {@link Reader} class doesn't provide any way to predict whether the next
   * read operation will block or not, it is not possible to provide a meaningful
   * implementation of the {@link InputStream#available()} method. A call to this method
   * will always return 0. Also, this class doesn't support {@link InputStream#mark(int)}.
   * <p>
   * Instances of {@link ReaderInputStream} are not thread safe.
   * 
   * @see org.apache.commons.io.output.WriterOutputStream
   * 
   * @author <a href="mailto:veithen@apache.org">Andreas Veithen</a>
   * @since Commons IO 2.0
   */
  public class ReaderInputStream extends InputStream {
      private static final int DEFAULT_BUFFER_SIZE = 1024;
  
      private final Reader reader;
      private final CharsetEncoder encoder;
  
      /**
       * CharBuffer used as input for the decoder. It should be reasonably
       * large as we read data from the underlying Reader into this buffer.
       */
      private final CharBuffer encoderIn;
  
      /**
       * ByteBuffer used as output for the decoder. This buffer can be small
       * as it is only used to transfer data from the decoder to the
       * buffer provided by the caller.
       */
      private final ByteBuffer encoderOut = ByteBuffer.allocate(128);
  
      private CoderResult lastCoderResult;
      private boolean endOfInput;
  
      /**
       * Construct a new {@link ReaderInputStream}.
       * 
       * @param reader the target {@link Reader}
       * @param charset the charset encoding
       * @param bufferSize the size of the input buffer in number of characters
       */
      public ReaderInputStream(Reader reader, Charset charset, int bufferSize) {
          this.reader = reader;
          encoder = charset.newEncoder();
          encoderIn = CharBuffer.allocate(bufferSize);
          encoderIn.flip();
      }
  
      /**
       * Construct a new {@link ReaderInputStream} with a default input buffer size of
       * 1024 characters.
       * 
       * @param reader the target {@link Reader}
       * @param charset the charset encoding
       */
      public ReaderInputStream(Reader reader, Charset charset) {
          this(reader, charset, DEFAULT_BUFFER_SIZE);
      }
  
      /**
       * Construct a new {@link ReaderInputStream}.
       * 
       * @param reader the target {@link Reader}
       * @param charsetName the name of the charset encoding
       * @param bufferSize the size of the input buffer in number of characters
       */
      public ReaderInputStream(Reader reader, String charsetName, int bufferSize) {
          this(reader, Charset.forName(charsetName), bufferSize);
      }
  
      /**
       * Construct a new {@link ReaderInputStream} with a default input buffer size of
       * 1024 characters.
       * 
       * @param reader the target {@link Reader}
       * @param charsetName the name of the charset encoding
       */
      public ReaderInputStream(Reader reader, String charsetName) {
          this(reader, charsetName, DEFAULT_BUFFER_SIZE);
      }
  
      /**
       * Construct a new {@link ReaderInputStream} that uses the default character encoding
       * with a default input buffer size of 1024 characters.
       * 
       * @param reader the target {@link Reader}
       */
      public ReaderInputStream(Reader reader) {
          this(reader, Charset.defaultCharset());
      }
  
      /**
       * Read the specified number of bytes into an array.
       * 
       * @param b the byte array to read into
       * @param off the offset to start reading bytes into
       * @param len the number of bytes to read
       * @return the number of bytes read or <code>-1</code>
       *         if the end of the stream has been reached
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int read(byte[] b, int off, int len) throws IOException {
          int read = 0;
          while (len > 0) {
              if (encoderOut.position() > 0) {
                  encoderOut.flip();
                  int c = Math.min(encoderOut.remaining(), len);
                  encoderOut.get(b, off, c);
                  off += c;
                  len -= c;
                  read += c;
                  encoderOut.compact();
              } else {
                  if (!endOfInput && (lastCoderResult == null || lastCoderResult.isUnderflow())) {
                      encoderIn.compact();
                      int position = encoderIn.position();
                      // We don't use Reader#read(CharBuffer) here because it is more efficient
                      // to write directly to the underlying char array (the default implementation
                      // copies data to a temporary char array).
                      int c = reader.read(encoderIn.array(), position, encoderIn.remaining());
                      if (c == -1) {
                          endOfInput = true;
                      } else {
                          encoderIn.position(position+c);
                      }
                      encoderIn.flip();
                  }
                  lastCoderResult = encoder.encode(encoderIn, encoderOut, endOfInput);
                  if (endOfInput && encoderOut.position() == 0) {
                      break;
                  }
              }
          }
          return read == 0 && endOfInput ? -1 : read;
      }
  
      /**
       * Read the specified number of bytes into an array.
       * 
       * @param b the byte array to read into
       * @return the number of bytes read or <code>-1</code>
       *         if the end of the stream has been reached
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int read(byte[] b) throws IOException {
          return read(b, 0, b.length);
      }
  
      /**
       * Read a single byte.
       *
       * @return either the byte read or <code>-1</code> if the end of the stream
       *         has been reached
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int read() throws IOException {
          byte[] b = new byte[1];
          return read(b) == -1 ? -1 : b[0] & 0xFF;
      }
  
      /**
       * Close the stream. This method will cause the underlying {@link Reader}
       * to be closed.
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void close() throws IOException {
          reader.close();
      }
  }
  