CharacterEncoder.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.misc;

import java.io.InputStream;
import java.io.ByteArrayInputStream;
import java.io.OutputStream;
import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.io.IOException;
import java.nio.ByteBuffer;


/**
 * This class defines the encoding half of character encoders.
 * A character encoder is an algorithim for transforming 8 bit binary
 * data into text (generally 7 bit ASCII or 8 bit ISO-Latin-1 text)
 * for transmition over text channels such as e-mail and network news.
 *
 * The character encoders have been structured around a central theme
 * that, in general, the encoded text has the form:
 *
 * <pre>
 *      [Buffer Prefix]
 *      [Line Prefix][encoded data atoms][Line Suffix]
 *      [Buffer Suffix]
 * </pre>
 *
 * In the CharacterEncoder and CharacterDecoder classes, one complete
 * chunk of data is referred to as a <i>buffer</i>. Encoded buffers
 * are all text, and decoded buffers (sometimes just referred to as
 * buffers) are binary octets.
 *
 * To create a custom encoder, you must, at a minimum,  overide three
 * abstract methods in this class.
 * <DL>
 * <DD>bytesPerAtom which tells the encoder how many bytes to
 * send to encodeAtom
 * <DD>encodeAtom which encodes the bytes sent to it as text.
 * <DD>bytesPerLine which tells the encoder the maximum number of
 * bytes per line.
 * </DL>
 *
 * Several useful encoders have already been written and are
 * referenced in the See Also list below.
 *
 * @author      Chuck McManis
 * @see         CharacterDecoder;
 * @see         UCEncoder
 * @see         UUEncoder
 * @see         BASE64Encoder
 */
public abstract class CharacterEncoder {

    /** Stream that understands "printing" */
    protected PrintStream pStream;

    /** Return the number of bytes per atom of encoding */
    abstract protected int bytesPerAtom();

    /** Return the number of bytes that can be encoded per line */
    abstract protected int bytesPerLine();

    /**
     * Encode the prefix for the entire buffer. By default is simply
     * opens the PrintStream for use by the other functions.
     */
    protected void encodeBufferPrefix(OutputStream aStream) throws IOException {
        pStream = new PrintStream(aStream);
    }

    /**
     * Encode the suffix for the entire buffer.
     */
    protected void encodeBufferSuffix(OutputStream aStream) throws IOException {
    }

    /**
     * Encode the prefix that starts every output line.
     */
    protected void encodeLinePrefix(OutputStream aStream, int aLength)
    throws IOException {
    }

    /**
     * Encode the suffix that ends every output line. By default
     * this method just prints a <newline> into the output stream.
     */
    protected void encodeLineSuffix(OutputStream aStream) throws IOException {
        pStream.println();
    }

    /** Encode one "atom" of information into characters. */
    abstract protected void encodeAtom(OutputStream aStream, byte someBytes[],
                int anOffset, int aLength) throws IOException;

    /**
     * This method works around the bizarre semantics of BufferedInputStream's
     * read method.
     */
    protected int readFully(InputStream in, byte buffer[])
        throws java.io.IOException {
        for (int i = 0; i < buffer.length; i++) {
            int q = in.read();
            if (q == -1)
                return i;
            buffer[i] = (byte)q;
        }
        return buffer.length;
    }

    /**
     * Encode bytes from the input stream, and write them as text characters
     * to the output stream. This method will run until it exhausts the
     * input stream, but does not print the line suffix for a final
     * line that is shorter than bytesPerLine().
     */
    public void encode(InputStream inStream, OutputStream outStream)
        throws IOException {
        int     j;
        int     numBytes;
        byte    tmpbuffer[] = new byte[bytesPerLine()];

        encodeBufferPrefix(outStream);

        while (true) {
            numBytes = readFully(inStream, tmpbuffer);
            if (numBytes == 0) {
                break;
            }
            encodeLinePrefix(outStream, numBytes);
            for (j = 0; j < numBytes; j += bytesPerAtom()) {

                if ((j + bytesPerAtom()) <= numBytes) {
                    encodeAtom(outStream, tmpbuffer, j, bytesPerAtom());
                } else {
                    encodeAtom(outStream, tmpbuffer, j, (numBytes)- j);
                }
            }
            if (numBytes < bytesPerLine()) {
                break;
            } else {
                encodeLineSuffix(outStream);
            }
        }
        encodeBufferSuffix(outStream);
    }

    /**
     * Encode the buffer in <i>aBuffer</i> and write the encoded
     * result to the OutputStream <i>aStream</i>.
     */
    public void encode(byte aBuffer[], OutputStream aStream)
    throws IOException {
        ByteArrayInputStream inStream = new ByteArrayInputStream(aBuffer);
        encode(inStream, aStream);
    }

    /**
     * A 'streamless' version of encode that simply takes a buffer of
     * bytes and returns a string containing the encoded buffer.
     */
    public String encode(byte aBuffer[]) {
        ByteArrayOutputStream   outStream = new ByteArrayOutputStream();
        ByteArrayInputStream    inStream = new ByteArrayInputStream(aBuffer);
        String retVal = null;
        try {
            encode(inStream, outStream);
            // explicit ascii->unicode conversion
            retVal = outStream.toString("8859_1");
        } catch (Exception IOException) {
            // This should never happen.
            throw new Error("CharacterEncoder.encode internal error");
        }
        return (retVal);
    }

    /**
     * Return a byte array from the remaining bytes in this ByteBuffer.
     * <P>
     * The ByteBuffer's position will be advanced to ByteBuffer's limit.
     * <P>
     * To avoid an extra copy, the implementation will attempt to return the
     * byte array backing the ByteBuffer.  If this is not possible, a
     * new byte array will be created.
     */
    private byte [] getBytes(ByteBuffer bb) {
        /*
         * This should never return a BufferOverflowException, as we're
         * careful to allocate just the right amount.
         */
        byte [] buf = null;

        /*
         * If it has a usable backing byte buffer, use it.  Use only
         * if the array exactly represents the current ByteBuffer.
         */
        if (bb.hasArray()) {
            byte [] tmp = bb.array();
            if ((tmp.length == bb.capacity()) &&
                    (tmp.length == bb.remaining())) {
                buf = tmp;
                bb.position(bb.limit());
            }
        }

        if (buf == null) {
            /*
             * This class doesn't have a concept of encode(buf, len, off),
             * so if we have a partial buffer, we must reallocate
             * space.
             */
            buf = new byte[bb.remaining()];

            /*
             * position() automatically updated
             */
            bb.get(buf);
        }

        return buf;
    }

    /**
     * Encode the <i>aBuffer</i> ByteBuffer and write the encoded
     * result to the OutputStream <i>aStream</i>.
     * <P>
     * The ByteBuffer's position will be advanced to ByteBuffer's limit.
     */
    public void encode(ByteBuffer aBuffer, OutputStream aStream)
        throws IOException {
        byte [] buf = getBytes(aBuffer);
        encode(buf, aStream);
    }

    /**
     * A 'streamless' version of encode that simply takes a ByteBuffer
     * and returns a string containing the encoded buffer.
     * <P>
     * The ByteBuffer's position will be advanced to ByteBuffer's limit.
     */
    public String encode(ByteBuffer aBuffer) {
        byte [] buf = getBytes(aBuffer);
        return encode(buf);
    }

    /**
     * Encode bytes from the input stream, and write them as text characters
     * to the output stream. This method will run until it exhausts the
     * input stream. It differs from encode in that it will add the
     * line at the end of a final line that is shorter than bytesPerLine().
     */
    public void encodeBuffer(InputStream inStream, OutputStream outStream)
        throws IOException {
        int     j;
        int     numBytes;
        byte    tmpbuffer[] = new byte[bytesPerLine()];

        encodeBufferPrefix(outStream);

        while (true) {
            numBytes = readFully(inStream, tmpbuffer);
            if (numBytes == 0) {
                break;
            }
            encodeLinePrefix(outStream, numBytes);
            for (j = 0; j < numBytes; j += bytesPerAtom()) {
                if ((j + bytesPerAtom()) <= numBytes) {
                    encodeAtom(outStream, tmpbuffer, j, bytesPerAtom());
                } else {
                    encodeAtom(outStream, tmpbuffer, j, (numBytes)- j);
                }
            }
            encodeLineSuffix(outStream);
            if (numBytes < bytesPerLine()) {
                break;
            }
        }
        encodeBufferSuffix(outStream);
    }

    /**
     * Encode the buffer in <i>aBuffer</i> and write the encoded
     * result to the OutputStream <i>aStream</i>.
     */
    public void encodeBuffer(byte aBuffer[], OutputStream aStream)
    throws IOException {
        ByteArrayInputStream inStream = new ByteArrayInputStream(aBuffer);
        encodeBuffer(inStream, aStream);
    }

    /**
     * A 'streamless' version of encode that simply takes a buffer of
     * bytes and returns a string containing the encoded buffer.
     */
    public String encodeBuffer(byte aBuffer[]) {
        ByteArrayOutputStream   outStream = new ByteArrayOutputStream();
        ByteArrayInputStream    inStream = new ByteArrayInputStream(aBuffer);
        try {
            encodeBuffer(inStream, outStream);
        } catch (Exception IOException) {
            // This should never happen.
            throw new Error("CharacterEncoder.encodeBuffer internal error");
        }
        return (outStream.toString());
    }

    /**
     * Encode the <i>aBuffer</i> ByteBuffer and write the encoded
     * result to the OutputStream <i>aStream</i>.
     * <P>
     * The ByteBuffer's position will be advanced to ByteBuffer's limit.
     */
    public void encodeBuffer(ByteBuffer aBuffer, OutputStream aStream)
        throws IOException {
        byte [] buf = getBytes(aBuffer);
        encodeBuffer(buf, aStream);
    }

    /**
     * A 'streamless' version of encode that simply takes a ByteBuffer
     * and returns a string containing the encoded buffer.
     * <P>
     * The ByteBuffer's position will be advanced to ByteBuffer's limit.
     */
    public String encodeBuffer(ByteBuffer aBuffer) {
        byte [] buf = getBytes(aBuffer);
        return encodeBuffer(buf);
    }

}