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A fork of a fork (!) of SubEtha, an easy-to-use server-side SMTP library for Java.
There is a newer version: 7.1.3
/****************************************************************
 * 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.subethamail.smtp.internal.io;

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

/**
 * A Filter for use with SMTP or other protocols in which lines must end with
 * CRLF. Converts every "isolated" occourency of \r or \n with \r\n
 *
 * RFC 2821 #2.3.7 mandates that line termination is CRLF, and that CR and LF
 * must not be transmitted except in that pairing. If we get a naked LF, convert
 * to CRLF.
 *
 */
class CRLFOutputStream extends FilterOutputStream {

    /**
     * Counter for number of last (0A or 0D).
     */
    protected int statusLast;

    protected final static int LAST_WAS_OTHER = 0;

    protected final static int LAST_WAS_CR = 1;

    protected final static int LAST_WAS_LF = 2;

    protected boolean startOfLine = true;

    /**
     * Constructor that wraps an OutputStream.
     *
     * @param out
     *            the OutputStream to be wrapped
     */
    CRLFOutputStream(OutputStream out) {
        super(out);
        this.statusLast = LAST_WAS_LF; // we already assume a CRLF at beginning
                                       // (otherwise TOP would not work
                                       // correctly
                                       // !)
    }

    /**
     * Writes a byte to the stream Fixes any naked CR or LF to the RFC 2821
     * mandated CFLF pairing.
     *
     * @param b
     *            the byte to write
     *
     * @throws IOException
     *             if an error occurs writing the byte
     */
    @Override
    public void write(int b) throws IOException {
        switch (b) {
        case '\r':
            this.out.write('\r');
            this.out.write('\n');
            this.startOfLine = true;
            this.statusLast = LAST_WAS_CR;
            break;
        case '\n':
            if (this.statusLast != LAST_WAS_CR) {
                this.out.write('\r');
                this.out.write('\n');
                this.startOfLine = true;
            }
            this.statusLast = LAST_WAS_LF;
            break;
        default:
            // we're no longer at the start of a line
            this.out.write(b);
            this.startOfLine = false;
            this.statusLast = LAST_WAS_OTHER;
            break;
        }
    }

    /**
     * Provides an extension point for ExtraDotOutputStream to be able to add
     * dots at the beginning of new lines.
     *
     * @see java.io.FilterOutputStream#write(byte[], int, int)
     */
    protected void writeChunk(byte buffer[], int offset, int length) throws IOException {
        this.out.write(buffer, offset, length);
    }

    /**
     * @see java.io.FilterOutputStream#write(byte[], int, int)
     */
    @Override
    public synchronized void write(byte buffer[], int offset, int length) throws IOException {
        /* optimized */
        int lineStart = offset;
        for (int i = offset; i < length + offset; i++) {
            switch (buffer[i]) {
            case '\r':
                // CR case. Write down the last line
                // and position the new lineStart at the next char
                this.writeChunk(buffer, lineStart, i - lineStart);
                this.out.write('\r');
                this.out.write('\n');
                this.startOfLine = true;
                lineStart = i + 1;
                this.statusLast = LAST_WAS_CR;
                break;
            case '\n':
                if (this.statusLast != LAST_WAS_CR) {
                    this.writeChunk(buffer, lineStart, i - lineStart);
                    this.out.write('\r');
                    this.out.write('\n');
                    this.startOfLine = true;
                }
                lineStart = i + 1;
                this.statusLast = LAST_WAS_LF;
                break;
            default:
                this.statusLast = LAST_WAS_OTHER;
            }
        }
        if (length + offset > lineStart) {
            this.writeChunk(buffer, lineStart, length + offset - lineStart);
            this.startOfLine = false;
        }
    }

    /**
     * Ensure that the stream is CRLF terminated.
     *
     * @throws IOException
     *             if an error occurs writing the byte
     */
    void checkCRLFTerminator() throws IOException {
        if (this.statusLast == LAST_WAS_OTHER) {
            this.out.write('\r');
            this.out.write('\n');
            this.statusLast = LAST_WAS_CR;
        }
    }
}