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/*
 * @(#)LineInputStream.java   1.7 03/01/07
 */



package com.sun.xml.messaging.saaj.packaging.mime.util;

import java.io.*;

/**
 * This class is to support reading CRLF terminated lines that
 * contain only US-ASCII characters from an input stream. Provides
 * functionality that is similar to the deprecated 
 * <code>DataInputStream.readLine()</code>. Expected use is to read
 * lines as String objects from a RFC822 stream.
 *
 * It is implemented as a FilterInputStream, so one can just wrap 
 * this class around any input stream and read bytes from this filter.
 * 
 * @author John Mani
 */

public final class LineInputStream extends FilterInputStream {

    private char[] lineBuffer = null; // reusable byte buffer

    public LineInputStream(InputStream in) {
	super(in);
    }

    /**
     * Read a line containing only ASCII characters from the input 
     * stream. A line is terminated by a CR or NL or CR-NL sequence.
     * A common error is a CR-CR-NL sequence, which will also terminate
     * a line.
     * The line terminator is not returned as part of the returned 
     * String. Returns null if no data is available. <p>
     *
     * This class is similar to the deprecated 
     * <code>DataInputStream.readLine()</code>
     *
     * @return line.
     *
     * @throws IOException if an I/O error occurs.
     */
    public String readLine() throws IOException {
	InputStream in = this.in;
	char[] buf = lineBuffer;

	if (buf == null)
	    buf = lineBuffer = new char[128];

	int c1;
	int room = buf.length;
	int offset = 0;

	while ((c1 = in.read()) != -1) {
	    if (c1 == '\n') // Got NL, outa here.
		break;
	    else if (c1 == '\r') {
		// Got CR, is the next char NL ?
		int c2 = in.read();
		if (c2 == '\r')		// discard extraneous CR
		    c2 = in.read();
		if (c2 != '\n') {
		    // If not NL, push it back
		    if (!(in instanceof PushbackInputStream))
			in = this.in = new PushbackInputStream(in);
		    ((PushbackInputStream)in).unread(c2);
		}
		break; // outa here.
	    }

	    // Not CR, NL or CR-NL ...
	    // .. Insert the byte into our byte buffer
	    if (--room < 0) { // No room, need to grow.
		buf = new char[offset + 128];
		room = buf.length - offset - 1;
		System.arraycopy(lineBuffer, 0, buf, 0, offset);
		lineBuffer = buf;
	    }
	    buf[offset++] = (char)c1;
	}

	if ((c1 == -1) && (offset == 0))
	    return null;
	
	return String.copyValueOf(buf, 0, offset);
    }
}
