/*
 * CRLFInputStream.java
 * Copyright (C) 2002 The Free Software Foundation
 * 
 * This file is part of GNU inetlib, a library.
 * 
 * GNU inetlib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * GNU inetlib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Linking this library statically or dynamically with other modules is
 * making a combined work based on this library.  Thus, the terms and
 * conditions of the GNU General Public License cover the whole
 * combination.
 *
 * As a special exception, the copyright holders of this library give you
 * permission to link this library with independent modules to produce an
 * executable, regardless of the license terms of these independent
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obliged to do so.  If you do not wish to do so, delete this
 * exception statement from your version.
 */

package gnu.inet.util;

import java.io.FilterInputStream;
import java.io.InputStream;
import java.io.IOException;

/**
 * An input stream that filters out CR/LF pairs into LFs.
 *
 * @author <a href="mailto:dog@gnu.org">Chris Burdess</a>
 */
public class CRLFInputStream
  extends FilterInputStream
{

  /**
   * The CR octet.
   */
  public static final int CR = 13;

  /**
   * The LF octet.
   */
  public static final int LF = 10;

  /**
   * Buffer.
   */
  protected int buf = -1;

  /**
   * Buffer at time of mark.
   */
  protected int markBuf = -1;

  /**
   * Constructs a CR/LF input stream connected to the specified input
   * stream.
   */
  public CRLFInputStream(InputStream in)
  {
    super(in);
  }

  /**
   * Reads the next byte of data from this input stream.
   * Returns -1 if the end of the stream has been reached.
   * @exception IOException if an I/O error occurs
   */
  public int read()
    throws IOException
  {
    int c;
    if (buf != -1)
      {
        c = buf;
        buf = -1;
        return c;
      }
    else
      {
        c = super.read();
        if (c == CR)
          {
            buf = super.read();
            if (buf == LF)
              {
                c = buf;
                buf = -1;
              }
          }
      }
    return c;
  }
  
  /**
   * Reads up to b.length bytes of data from this input stream into
   * an array of bytes.
   * Returns -1 if the end of the stream has been reached.
   * @exception IOException if an I/O error occurs
   */
  public int read(byte[] b)
    throws IOException
  {
    return read(b, 0, b.length);
  }

  /**
   * Reads up to len bytes of data from this input stream into an
   * array of bytes, starting at the specified offset.
   * Returns -1 if the end of the stream has been reached.
   * @exception IOException if an I/O error occurs
   */
  public int read(byte[] b, int off, int len)
    throws IOException
  {
    int shift = 0;
    if (buf != -1)
      {
        // Push buf onto start of byte array
        b[off] = (byte) buf;
        off++;
        len--;
        buf = -1;
        shift++;
      }
    int l = super.read(b, off, len);
    l = removeCRLF(b, off - shift, l + shift);
    return l;
  }

  /**
   * Indicates whether this stream supports the mark and reset methods.
   */
  public boolean markSupported()
  {
    return in.markSupported();
  }

  /**
   * Marks the current position in this stream.
   */
  public void mark(int readlimit)
  {
    in.mark(readlimit + 1);
    markBuf = buf;
  }

  /**
   * Repositions this stream to the position at the time the mark method was
   * called.
   */
  public void reset()
    throws IOException
  {
    in.reset();
    buf = markBuf;
  }

  private int removeCRLF(byte[] b, int off, int len) throws IOException
  {
    int end = off + len;
    int i = off;
    // The first loop prevents unnecessary copying when there are no CR in the buffer.
    for (; i < end; i++)
      {
        if (b[i] == CR) break;
      }
    for (int j = i; i < end; i++, j++) {
        if (b[i] == CR)
          {
            if (i + 1 == end)
              {
                // This is the last byte, look ahead for LF
                buf = in.read();
                if (buf == LF) {
                    // LF found, substitute for the CR
                    b[j] = (byte)buf;
                    buf = -1;
                    break;
                }
                // Not a LF drop through and use the CR
              }
            else if (b[i + 1] == LF)
              {
                // Skip the CR and only save the LF
                i++;
                len--;
              }
          }
        b[j] = b[i];
      }
    return len;
  }

}