ToNetASCIIOutputStream.java

/*
 * 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.net.io;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * This class wraps an output stream, replacing all singly occurring <LF> (linefeed) characters with <CR><LF> (carriage return followed by
 * linefeed), which is the NETASCII standard for representing a newline. You would use this class to implement ASCII file transfers requiring conversion to
 * NETASCII.
 */

public final class ToNetASCIIOutputStream extends FilterOutputStream {
    private boolean lastWasCR;

    /**
     * Creates a ToNetASCIIOutputStream instance that wraps an existing OutputStream.
     *
     * @param output The OutputStream to wrap.
     */
    public ToNetASCIIOutputStream(final OutputStream output) {
        super(output);
        lastWasCR = false;
    }

    /**
     * Writes a byte array to the stream.
     *
     * @param buffer The byte array to write.
     * @throws IOException If an error occurs while writing to the underlying stream.
     */
    @Override
    public synchronized void write(final byte buffer[]) throws IOException {
        write(buffer, 0, buffer.length);
    }

    /**
     * Writes a number of bytes from a byte array to the stream starting from a given offset.
     *
     * @param buffer The byte array to write.
     * @param offset The offset into the array at which to start copying data.
     * @param length The number of bytes to write.
     * @throws IOException If an error occurs while writing to the underlying stream.
     */
    @Override
    public synchronized void write(final byte buffer[], int offset, int length) throws IOException {
        while (length-- > 0) {
            write(buffer[offset++]);
        }
    }

    /**
     * Writes a byte to the stream. Note that a call to this method may result in multiple writes to the underlying input stream in order to convert naked
     * newlines to NETASCII line separators. This is transparent to the programmer and is only mentioned for completeness.
     *
     * @param ch The byte to write.
     * @throws IOException If an error occurs while writing to the underlying stream.
     */
    @Override
    public synchronized void write(final int ch) throws IOException {
        switch (ch) {
        case '\r':
            lastWasCR = true;
            out.write('\r');
            return;
        case '\n':
            if (!lastWasCR) {
                out.write('\r');
            }
            //$FALL-THROUGH$
        default:
            lastWasCR = false;
            out.write(ch);
        }
    }

}