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A NIO SMTP server API written in Java
There is a newer version: 1.0.6
/***********************************************************************
 * Copyright (c) 2000-2006 The Apache Software Foundation.             *
 * All rights reserved.                                                *
 * ------------------------------------------------------------------- *
 * Licensed 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.mailster.smtp.util;

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

/**
 * Removes the dot-stuffing happening during the SMTP message
 * transfer.
 */
public class DotUnstuffingInputStream extends FilterInputStream {

    /**
     * An array to hold the last two bytes read off the stream.
     * This allows the stream to detect '\r\n' sequences even
     * when they occur across read boundaries.
     */
    protected int[] last = {-1, -1};

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

    /**
     * Read through the stream, checking for '\r\n.'
     *
     * @return the byte read from the stream
     */
    @Override
    public int read() throws IOException {
        var b = in.read();
        if (b == '.' && last[0] == '\r' && last[1] == '\n') {
            //skip this '.' because it should have been stuffed
            b = in.read();
        }
        last[0] = last[1];
        last[1] = b;
        return b;
    }

    /**
     * Read through the stream, checking for '\r\n.'
     *
     * @param b   the byte array into which the bytes will be read
     * @param off the offset into the byte array where the bytes will be inserted
     * @param len the maximum number of bytes to be read off the stream
     * @return the number of bytes read
     */
    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if (len == 0) {
            return 0;
        } else if ((off < 0) || (off > b.length) || (len < 0) || ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        }

        var c = read();
        if (c == -1) {
            return -1;
        }
        b[off] = (byte) c;

        var i = 1;

        for (; i < len; i++) {
            c = read();
            if (c == -1) {
                break;
            }
            b[off + i] = (byte) c;
        }

        return i;
    }

    @Override
    public void close() throws IOException {
        in.close();
    }
}