path: root/libjava/java/io/BufferedReader.java

/* BufferedReader.java
   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 
     Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.
 
GNU Classpath is distributed in the hope that it will be useful, but
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General Public License for more details.

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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
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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terms of your choice, provided that you also meet, for each linked
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package java.io;

/* Written using "Java Class Libraries", 2nd edition, plus online
 * API docs for JDK 1.2 beta from http://www.javasoft.com.
 * Status:  Believed complete and correct.
 */

/**
 * This subclass of <code>FilterReader</code> buffers input from an 
 * underlying implementation to provide a possibly more efficient read
 * mechanism.  It maintains the buffer and buffer state in instance 
 * variables that are available to subclasses.  The default buffer size
 * of 8192 chars can be overridden by the creator of the stream.
 * <p>
 * This class also implements mark/reset functionality.  It is capable
 * of remembering any number of input chars, to the limits of
 * system memory or the size of <code>Integer.MAX_VALUE</code>
 *
 * @author Per Bothner <bothner@cygnus.com>
 * @author Aaron M. Renn <arenn@urbanophile.com>
 */
public class BufferedReader extends Reader
{
  Reader in;
  char[] buffer;
  /* Index of current read position.  Must be >= 0 and <= limit. */
  /* There is a special case where pos may be equal to limit+1; this
   * is used as an indicator that a readLine was done with a '\r' was
   * the very last char in the buffer.  Since we don't want to read-ahead
   * and potentially block, we set pos this way to indicate the situation
   * and deal with it later.  Doing it this way rather than having a
   * separate boolean field to indicate the condition has the advantage
   * that it is self-clearing on things like mark/reset.
   */
  int pos;
  /* Limit of valid data in buffer.  Must be >= pos and <= buffer.length. */
  /* This can be < pos in the one special case described above. */
  int limit;

  /* The value -1 means there is no mark, or the mark has been invalidated.
     Otherwise, markPos is the index in the buffer of the marked position.
     Must be >= 0 and <= pos.
     Note we do not explicitly store the read-limit.
     The implicit read-limit is (buffer.length - markPos), which is
     guaranteed to be >= the read-limit requested in the call to mark. */
  int markPos = -1;

  // The JCL book specifies the default buffer size as 8K characters.
  // This is package-private because it is used by LineNumberReader.
  static final int DEFAULT_BUFFER_SIZE = 8192;

  /**
    * Create a new <code>BufferedReader</code> that will read from the 
    * specified subordinate stream with a default buffer size of 8192 chars.
    *
    * @param in The subordinate stream to read from
    */
  public BufferedReader(Reader in)
  {
    this(in, DEFAULT_BUFFER_SIZE);
  }

  /**
   * Create a new <code>BufferedReader</code> that will read from the 
   * specified subordinate stream with a buffer size that is specified by the 
   * caller.
   *
   * @param in The subordinate stream to read from
   * @param size The buffer size to use
   */
  public BufferedReader(Reader in, int size)
  {
    super(in.lock);
    this.in = in;
    buffer = new char[size];
  }

  /**
   * This method closes the underlying stream and frees any associated
   * resources.
   *
   * @exception IOException If an error occurs
   */
  public void close() throws IOException
  {
    synchronized (lock)
      {
	if (in != null)
	  in.close();
	in = null;
	buffer = null;
      }
  }

  /**
   * Returns <code>true</code> to indicate that this class supports mark/reset 
   * functionality.
   *
   * @return <code>true</code>
   */
  public boolean markSupported()
  {
    return true;
  }

  /**
   * Mark a position in the input to which the stream can be
   * "reset" by calling the <code>reset()</code> method.  The parameter
   * <code>readLimit</code> is the number of chars that can be read from the 
   * stream after setting the mark before the mark becomes invalid.  For
   * example, if <code>mark()</code> is called with a read limit of 10, then 
   * when 11 chars of data are read from the stream before the 
   * <code>reset()</code> method is called, then the mark is invalid and the 
   * stream object instance is not required to remember the mark.
   * <p>
   * Note that the number of chars that can be remembered by this method
   * can be greater than the size of the internal read buffer.  It is also
   * not dependent on the subordinate stream supporting mark/reset
   * functionality.
   *
   * @param readLimit The number of chars that can be read before the mark 
   *        becomes invalid
   *
   * @exception IOException If an error occurs
   */
  public void mark(int readLimit) throws IOException
  {
    if (readLimit < 0)
      throw new IllegalArgumentException();

    synchronized (lock)
      {
	checkStatus();
	// In this method we need to be aware of the special case where
	// pos + 1 == limit.  This indicates that a '\r' was the last char
	// in the buffer during a readLine.  We'll want to maintain that
	// condition after we shift things around and if a larger buffer is
	// needed to track readLimit, we'll have to make it one element
	// larger to ensure we don't invalidate the mark too early, if the
	// char following the '\r' is NOT a '\n'.  This is ok because, per
	// the spec, we are not required to invalidate when passing readLimit.
	//
	// Note that if 'pos > limit', then doing 'limit -= pos' will cause
	// limit to be negative.  This is the only way limit will be < 0.

	if (pos + readLimit > limit)
	  {
	    char[] old_buffer = buffer;
	    int extraBuffSpace = 0;
	    if (pos > limit)
	      extraBuffSpace = 1;
	    if (readLimit + extraBuffSpace > limit)
	      buffer = new char[readLimit + extraBuffSpace];
	    limit -= pos;
	    if (limit >= 0)
	      {
	        System.arraycopy(old_buffer, pos, buffer, 0, limit);
	        pos = 0;
	      }
	  }

	if (limit < 0)
	  {
	    // Maintain the relationship of 'pos > limit'.
	    pos = 1;
	    limit = markPos = 0;
	  }
	else
	  markPos = pos;
	// Now pos + readLimit <= buffer.length. thus if we need to read
	// beyond buffer.length, then we are allowed to invalidate markPos.
      }
  }

  /**
   * Reset the stream to the point where the <code>mark()</code> method
   * was called.  Any chars that were read after the mark point was set will
   * be re-read during subsequent reads.
   * <p>
   * This method will throw an IOException if the number of chars read from
   * the stream since the call to <code>mark()</code> exceeds the mark limit
   * passed when establishing the mark.
   *
   * @exception IOException If an error occurs;
   */
  public void reset() throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	if (markPos < 0)
	  throw new IOException("mark never set or invalidated");

	// Need to handle the extremely unlikely case where a readLine was
	// done with a '\r' as the last char in the buffer; which was then
	// immediately followed by a mark and a reset with NO intervening
	// read of any sort.  In that case, setting pos to markPos would
	// lose that info and a subsequent read would thus not skip a '\n'
	// (if one exists).  The value of limit in this rare case is zero.
	// We can assume that if limit is zero for other reasons, then
	// pos is already set to zero and doesn't need to be readjusted.
	if (limit > 0)
	  pos = markPos;
      }
  }

  /**
   * This method determines whether or not a stream is ready to be read.  If
   * this method returns <code>false</code> then this stream could (but is
   * not guaranteed to) block on the next read attempt.
   *
   * @return <code>true</code> if this stream is ready to be read, 
   * <code>false</code> otherwise
   *
   * @exception IOException If an error occurs
   */
  public boolean ready() throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	return pos < limit || in.ready();
      }
  }

  /**
   * This method read chars from a stream and stores them into a caller
   * supplied buffer.  It starts storing the data at index 
   * <code>offset</code> into
   * the buffer and attempts to read <code>len</code> chars.  This method can
   * return before reading the number of chars requested.  The actual number
   * of chars read is returned as an int.  A -1 is returned to indicate the
   * end of the stream.
   * <p>
   * This method will block until some data can be read.
   *
   * @param buf The array into which the chars read should be stored
   * @param offset The offset into the array to start storing chars
   * @param count The requested number of chars to read
   *
   * @return The actual number of chars read, or -1 if end of stream.
   *
   * @exception IOException If an error occurs.
   */
  public int read(char[] buf, int offset, int count) throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	// Once again, we need to handle the special case of a readLine
	// that has a '\r' at the end of the buffer.  In this case, we'll
	// need to skip a '\n' if it is the next char to be read.
	// This special case is indicated by 'pos > limit'.
	boolean retAtEndOfBuffer = false;

	int avail = limit - pos;
	if (count > avail)
	  {
	    if (avail > 0)
	      count = avail;
	    else // pos >= limit
	      {
		if (limit == buffer.length)
		  markPos = -1; // read too far - invalidate the mark.
		if (pos > limit)
		  {
		    // Set a boolean and make pos == limit to simplify things.
		    retAtEndOfBuffer = true;
		    --pos;
		  }
		if (markPos < 0)
		  {
		    // Optimization:  can read directly into buf.
		    if (count >= buffer.length && !retAtEndOfBuffer)
		      return in.read(buf, offset, count);
		    pos = limit = 0;
		  }
		avail = in.read(buffer, limit, buffer.length - limit);
		if (retAtEndOfBuffer && avail > 0 && buffer[limit] == '\n')
		  {
		    --avail;
		    limit++;
		  }
		if (avail < count)
		  {
		    if (avail <= 0)
		      return avail;
		    count = avail;
		  }
		limit += avail;
	      }
	  }
	System.arraycopy(buffer, pos, buf, offset, count);
	pos += count;
	return count;
      }
  }

  /* Read more data into the buffer.  Update pos and limit appropriately.
     Assumes pos==limit initially.  May invalidate the mark if read too much.
     Return number of chars read (never 0), or -1 on eof. */
  private int fill() throws IOException
  {
    checkStatus();
    // Handle the special case of a readLine that has a '\r' at the end of
    // the buffer.  In this case, we'll need to skip a '\n' if it is the
    // next char to be read.  This special case is indicated by 'pos > limit'.
    boolean retAtEndOfBuffer = false;
    if (pos > limit)
      {
        retAtEndOfBuffer = true;
	--pos;
      }

    if (markPos >= 0 && limit == buffer.length)
      markPos = -1;
    if (markPos < 0)
      pos = limit = 0;
    int count = in.read(buffer, limit, buffer.length - limit);
    if (count > 0)
      limit += count;

    if (retAtEndOfBuffer && buffer[pos] == '\n')
      {
	--count;
	// If the mark was set to the location of the \n, then we
	// must change it to fully pretend that the \n does not
	// exist.
	if (markPos == pos)
	  ++markPos;
	++pos;
      }

    return count;
  }
  
  public int read() throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	if (pos >= limit && fill () <= 0)
	  return -1;
	return buffer[pos++];
      }
  }

  /* Return the end of the line starting at this.pos and ending at limit.
   * The index returns is *before* any line terminators, or limit
   * if no line terminators were found.
   */
  private int lineEnd(int limit)
  {
    int i = pos;
    for (; i < limit; i++)
      {
	char ch = buffer[i];
	if (ch == '\n' || ch == '\r')
	  break;
      }
    return i;
  }

  /**
   * This method reads a single line of text from the input stream, returning
   * it as a <code>String</code>.  A line is terminated by "\n", a "\r", or
   * an "\r\n" sequence.  The system dependent line separator is not used.
   * The line termination characters are not returned in the resulting
   * <code>String</code>.
   * 
   * @return The line of text read, or <code>null</code> if end of stream.
   * 
   * @exception IOException If an error occurs
   */
  public String readLine() throws IOException
  {
    checkStatus();
    // Handle the special case where a previous readLine (with no intervening
    // reads/skips) had a '\r' at the end of the buffer.
    // In this case, we'll need to skip a '\n' if it's the next char to be read.
    // This special case is indicated by 'pos > limit'.
    if (pos > limit)
      {
	int ch = read();
	if (ch < 0)
	  return null;
	if (ch != '\n')
	  --pos;
      }
    int i = lineEnd(limit);
    if (i < limit)
      {
	String str = new String(buffer, pos, i - pos);
	pos = i + 1;
	// If the last char in the buffer is a '\r', we must remember
	// to check if the next char to be read after the buffer is refilled
	// is a '\n'.  If so, skip it.  To indicate this condition, we set pos
	// to be limit + 1, which normally is never possible.
	if (buffer[i] == '\r')
	  if (pos == limit || buffer[pos] == '\n')
	    pos++;
	return str;
      }
    StringBuffer sbuf = new StringBuffer(200);
    sbuf.append(buffer, pos, i - pos);
    pos = i;
    // We only want to return null when no characters were read before
    // EOF.  So we must keep track of this separately.  Otherwise we
    // would treat an empty `sbuf' as an EOF condition, which is wrong
    // when there is just a newline.
    boolean eof = false;
    for (;;)
      {
	int ch = read();
	if (ch < 0)
	  {
	    eof = true;
	    break;
	  }
	if (ch == '\n' || ch == '\r')
	  {
	    // Check here if a '\r' was the last char in the buffer; if so,
	    // mark it as in the comment above to indicate future reads
	    // should skip a newline that is the next char read after
	    // refilling the buffer.
	    if (ch == '\r')
	      if (pos == limit || buffer[pos] == '\n')
	        pos++;
	    break;
	  }
	i = lineEnd(limit);
	sbuf.append(buffer, pos - 1, i - (pos - 1));
	pos = i;
      }
    return (sbuf.length() == 0 && eof) ? null : sbuf.toString();
  }

  /**
   * This method skips the specified number of chars in the stream.  It
   * returns the actual number of chars skipped, which may be less than the
   * requested amount.
   * <p>
   * This method first discards chars in the buffer, then calls the
   * <code>skip</code> method on the underlying stream to skip the 
   * remaining chars.
   *
   * @param numChars The requested number of chars to skip
   *
   * @return The actual number of chars skipped.
   *
   * @exception IOException If an error occurs
   */
  public long skip(long count) throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	if (count <= 0)
	  return 0;
	// Yet again, we need to handle the special case of a readLine
	// that has a '\r' at the end of the buffer.  In this case, we need
	// to ignore a '\n' if it is the next char to be read.
	// This special case is indicated by 'pos > limit' (i.e. avail < 0).
	// To simplify things, if we're dealing with the special case for
	// readLine, just read the next char (since the fill method will
	// skip the '\n' for us).  By doing this, we'll have to back up pos.
	// That's easier than trying to keep track of whether we've skipped
	// one element or not.
	int ch;
	if (pos > limit)
	  if ((ch = read()) < 0)
	    return 0;
	  else
	    --pos; 

	int avail = limit - pos;

	if (count < avail)
	  {
	    pos += count;
	    return count;
	  }

	pos = limit;
	long todo = count - avail;
	if (todo > buffer.length)
	  {
	    markPos = -1;
	    todo -= in.skip(todo);
	  }
	else
	  {
	    while (todo > 0)
	      {
		avail = fill();
		if (avail <= 0)
		  break;
		if (avail > todo)
		  avail = (int) todo;
		pos += avail;
		todo -= avail;
	      }
	  }
	return count - todo;
      }
  }
  
  private void checkStatus() throws IOException
  {
    if (in == null)
      throw new IOException("Stream closed");
  }  
}