src/main/java/org/apache/commons/codec/net/QuotedPrintableCodec.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.codec.net;

import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.StandardCharsets;
import java.nio.charset.UnsupportedCharsetException;
import java.util.BitSet;

import org.apache.commons.codec.BinaryDecoder;
import org.apache.commons.codec.BinaryEncoder;
import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.EncoderException;
import org.apache.commons.codec.StringDecoder;
import org.apache.commons.codec.StringEncoder;
import org.apache.commons.codec.binary.StringUtils;

/**
 * Codec for the Quoted-Printable section of <a href="http://www.ietf.org/rfc/rfc1521.txt">RFC 1521</a>.
 * <p>
 * The Quoted-Printable encoding is intended to represent data that largely consists of octets that correspond to
 * printable characters in the ASCII character set. It encodes the data in such a way that the resulting octets are
 * unlikely to be modified by mail transport. If the data being encoded are mostly ASCII text, the encoded form of the
 * data remains largely recognizable by humans. A body which is entirely ASCII may also be encoded in Quoted-Printable
 * to ensure the integrity of the data should the message pass through a character- translating, and/or line-wrapping
 * gateway.
 * </p>
 * <p>
 * Note:
 * </p>
 * <p>
 * Depending on the selected {@code strict} parameter, this class will implement a different set of rules of the
 * quoted-printable spec:
 * </p>
 * <ul>
 *   <li>{@code strict=false}: only rules #1 and #2 are implemented</li>
 *   <li>{@code strict=true}: all rules #1 through #5 are implemented</li>
 * </ul>
 * <p>
 * Originally, this class only supported the non-strict mode, but the codec in this partial form could already be used
 * for certain applications that do not require quoted-printable line formatting (rules #3, #4, #5), for instance
 * Q codec. The strict mode has been added in 1.10.
 * </p>
 * <p>
 * This class is immutable and thread-safe.
 * </p>
 *
 * @see <a href="http://www.ietf.org/rfc/rfc1521.txt">RFC 1521 MIME (Multipurpose Internet Mail Extensions) Part One:
 *          Mechanisms for Specifying and Describing the Format of Internet Message Bodies </a>
 *
 * @since 1.3
 */
public class QuotedPrintableCodec implements BinaryEncoder, BinaryDecoder, StringEncoder, StringDecoder {
    /**
     * The default Charset used for string decoding and encoding.
     */
    private final Charset charset;

    /**
     * Indicates whether soft line breaks shall be used during encoding (rule #3-5).
     */
    private final boolean strict;

    /**
     * BitSet of printable characters as defined in RFC 1521.
     */
    private static final BitSet PRINTABLE_CHARS = new BitSet(256);

    private static final byte ESCAPE_CHAR = '=';

    private static final byte TAB = 9;

    private static final byte SPACE = 32;

    private static final byte CR = 13;

    private static final byte LF = 10;

    /**
     * Safe line length for quoted printable encoded text.
     */
    private static final int SAFE_LENGTH = 73;

    // Static initializer for printable chars collection
    static {
        // alpha characters
        for (int i = 33; i <= 60; i++) {
            PRINTABLE_CHARS.set(i);
        }
        for (int i = 62; i <= 126; i++) {
            PRINTABLE_CHARS.set(i);
        }
        PRINTABLE_CHARS.set(TAB);
        PRINTABLE_CHARS.set(SPACE);
    }

    /**
     * Default constructor, assumes default Charset of {@link StandardCharsets#UTF_8}
     */
    public QuotedPrintableCodec() {
        this(StandardCharsets.UTF_8, false);
    }

    /**
     * Constructor which allows for the selection of the strict mode.
     *
     * @param strict
     *            if {@code true}, soft line breaks will be used
     * @since 1.10
     */
    public QuotedPrintableCodec(final boolean strict) {
        this(StandardCharsets.UTF_8, strict);
    }

    /**
     * Constructor which allows for the selection of a default Charset.
     *
     * @param charset
     *            the default string Charset to use.
     * @since 1.7
     */
    public QuotedPrintableCodec(final Charset charset) {
        this(charset, false);
    }

    /**
     * Constructor which allows for the selection of a default Charset and strict mode.
     *
     * @param charset
     *            the default string Charset to use.
     * @param strict
     *            if {@code true}, soft line breaks will be used
     * @since 1.10
     */
    public QuotedPrintableCodec(final Charset charset, final boolean strict) {
        this.charset = charset;
        this.strict = strict;
    }

    /**
     * Constructor which allows for the selection of a default Charset.
     *
     * @param charsetName
     *            the default string Charset to use.
     * @throws UnsupportedCharsetException
     *             If no support for the named Charset is available
     *             in this instance of the Java virtual machine
     * @throws IllegalArgumentException
     *             If the given charsetName is null
     * @throws IllegalCharsetNameException
     *             If the given Charset name is illegal
     *
     * @since 1.7 throws UnsupportedCharsetException if the named Charset is unavailable
     */
    public QuotedPrintableCodec(final String charsetName)
            throws IllegalCharsetNameException, IllegalArgumentException, UnsupportedCharsetException {
        this(Charset.forName(charsetName), false);
    }

    /**
     * Encodes byte into its quoted-printable representation.
     *
     * @param b
     *            byte to encode
     * @param buffer
     *            the buffer to write to
     * @return The number of bytes written to the {@code buffer}
     */
    private static final int encodeQuotedPrintable(final int b, final ByteArrayOutputStream buffer) {
        buffer.write(ESCAPE_CHAR);
        final char hex1 = Utils.hexDigit(b >> 4);
        final char hex2 = Utils.hexDigit(b);
        buffer.write(hex1);
        buffer.write(hex2);
        return 3;
    }

    /**
     * Return the byte at position {@code index} of the byte array and
     * make sure it is unsigned.
     *
     * @param index
     *            position in the array
     * @param bytes
     *            the byte array
     * @return the unsigned octet at position {@code index} from the array
     */
    private static int getUnsignedOctet(final int index, final byte[] bytes) {
        int b = bytes[index];
        if (b < 0) {
            b = 256 + b;
        }
        return b;
    }

    /**
     * Write a byte to the buffer.
     *
     * @param b
     *            byte to write
     * @param encode
     *            indicates whether the octet shall be encoded
     * @param buffer
     *            the buffer to write to
     * @return the number of bytes that have been written to the buffer
     */
    private static int encodeByte(final int b, final boolean encode,
                                  final ByteArrayOutputStream buffer) {
        if (encode) {
            return encodeQuotedPrintable(b, buffer);
        }
        buffer.write(b);
        return 1;
    }

    /**
     * Checks whether the given byte is whitespace.
     *
     * @param b
     *            byte to be checked
     * @return {@code true} if the byte is either a space or tab character
     */
    private static boolean isWhitespace(final int b) {
        return b == SPACE || b == TAB;
    }

    /**
     * Encodes an array of bytes into an array of quoted-printable 7-bit characters. Unsafe characters are escaped.
     * <p>
     * This function implements a subset of quoted-printable encoding specification (rule #1 and rule #2) as defined in
     * RFC 1521 and is suitable for encoding binary data and unformatted text.
     *
     * @param printable
     *            bitset of characters deemed quoted-printable
     * @param bytes
     *            array of bytes to be encoded
     * @return array of bytes containing quoted-printable data
     */
    public static final byte[] encodeQuotedPrintable(final BitSet printable, final byte[] bytes) {
        return encodeQuotedPrintable(printable, bytes, false);
    }

    /**
     * Encodes an array of bytes into an array of quoted-printable 7-bit characters. Unsafe characters are escaped.
     * <p>
     * Depending on the selection of the {@code strict} parameter, this function either implements the full ruleset
     * or only a subset of quoted-printable encoding specification (rule #1 and rule #2) as defined in
     * RFC 1521 and is suitable for encoding binary data and unformatted text.
     *
     * @param printable
     *            bitset of characters deemed quoted-printable
     * @param bytes
     *            array of bytes to be encoded
     * @param strict
     *            if {@code true} the full ruleset is used, otherwise only rule #1 and rule #2
     * @return array of bytes containing quoted-printable data
     * @since 1.10
     */
    public static final byte[] encodeQuotedPrintable(BitSet printable, final byte[] bytes, final boolean strict) {
        if (bytes == null) {
            return null;
        }
        if (printable == null) {
            printable = PRINTABLE_CHARS;
        }
        final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        final int bytesLength = bytes.length;

        if (strict) {
            int pos = 1;
            // encode up to buffer.length - 3, the last three octets will be treated
            // separately for simplification of note #3
            for (int i = 0; i < bytesLength - 3; i++) {
                final int b = getUnsignedOctet(i, bytes);
                if (pos < SAFE_LENGTH) {
                    // up to this length it is safe to add any byte, encoded or not
                    pos += encodeByte(b, !printable.get(b), buffer);
                } else {
                    // rule #3: whitespace at the end of a line *must* be encoded
                    encodeByte(b, !printable.get(b) || isWhitespace(b), buffer);

                    // rule #5: soft line break
                    buffer.write(ESCAPE_CHAR);
                    buffer.write(CR);
                    buffer.write(LF);
                    pos = 1;
                }
            }

            // rule #3: whitespace at the end of a line *must* be encoded
            // if we would do a soft break line after this octet, encode whitespace
            int b = getUnsignedOctet(bytesLength - 3, bytes);
            boolean encode = !printable.get(b) || (isWhitespace(b) && pos > SAFE_LENGTH - 5);
            pos += encodeByte(b, encode, buffer);

            // note #3: '=' *must not* be the ultimate or penultimate character
            // simplification: if < 6 bytes left, do a soft line break as we may need
            //                 exactly 6 bytes space for the last 2 bytes
            if (pos > SAFE_LENGTH - 2) {
                buffer.write(ESCAPE_CHAR);
                buffer.write(CR);
                buffer.write(LF);
            }
            for (int i = bytesLength - 2; i < bytesLength; i++) {
                b = getUnsignedOctet(i, bytes);
                // rule #3: trailing whitespace shall be encoded
                encode = !printable.get(b) || (i > bytesLength - 2 && isWhitespace(b));
                encodeByte(b, encode, buffer);
            }
        } else {
            for (final byte c : bytes) {
                int b = c;
                if (b < 0) {
                    b = 256 + b;
                }
                if (printable.get(b)) {
                    buffer.write(b);
                } else {
                    encodeQuotedPrintable(b, buffer);
                }
            }
        }
        return buffer.toByteArray();
    }

    /**
     * Decodes an array quoted-printable characters into an array of original bytes. Escaped characters are converted
     * back to their original representation.
     * <p>
     * This function fully implements the quoted-printable encoding specification (rule #1 through rule #5) as
     * defined in RFC 1521.
     *
     * @param bytes
     *            array of quoted-printable characters
     * @return array of original bytes
     * @throws DecoderException
     *             Thrown if quoted-printable decoding is unsuccessful
     */
    public static final byte[] decodeQuotedPrintable(final byte[] bytes) throws DecoderException {
        if (bytes == null) {
            return null;
        }
        final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        for (int i = 0; i < bytes.length; i++) {
            final int b = bytes[i];
            if (b == ESCAPE_CHAR) {
                try {
                    // if the next octet is a CR we have found a soft line break
                    if (bytes[++i] == CR) {
                        continue;
                    }
                    final int u = Utils.digit16(bytes[i]);
                    final int l = Utils.digit16(bytes[++i]);
                    buffer.write((char) ((u << 4) + l));
                } catch (final ArrayIndexOutOfBoundsException e) {
                    throw new DecoderException("Invalid quoted-printable encoding", e);
                }
            } else if (b != CR && b != LF) {
                // every other octet is appended except for CR & LF
                buffer.write(b);
            }
        }
        return buffer.toByteArray();
    }

    /**
     * Encodes an array of bytes into an array of quoted-printable 7-bit characters. Unsafe characters are escaped.
     * <p>
     * Depending on the selection of the {@code strict} parameter, this function either implements the full ruleset
     * or only a subset of quoted-printable encoding specification (rule #1 and rule #2) as defined in
     * RFC 1521 and is suitable for encoding binary data and unformatted text.
     *
     * @param bytes
     *            array of bytes to be encoded
     * @return array of bytes containing quoted-printable data
     */
    @Override
    public byte[] encode(final byte[] bytes) {
        return encodeQuotedPrintable(PRINTABLE_CHARS, bytes, strict);
    }

    /**
     * Decodes an array of quoted-printable characters into an array of original bytes. Escaped characters are converted
     * back to their original representation.
     * <p>
     * This function fully implements the quoted-printable encoding specification (rule #1 through rule #5) as
     * defined in RFC 1521.
     *
     * @param bytes
     *            array of quoted-printable characters
     * @return array of original bytes
     * @throws DecoderException
     *             Thrown if quoted-printable decoding is unsuccessful
     */
    @Override
    public byte[] decode(final byte[] bytes) throws DecoderException {
        return decodeQuotedPrintable(bytes);
    }

    /**
     * Encodes a string into its quoted-printable form using the default string Charset. Unsafe characters are escaped.
     * <p>
     * Depending on the selection of the {@code strict} parameter, this function either implements the full ruleset
     * or only a subset of quoted-printable encoding specification (rule #1 and rule #2) as defined in
     * RFC 1521 and is suitable for encoding binary data and unformatted text.
     *
     * @param sourceStr
     *            string to convert to quoted-printable form
     * @return quoted-printable string
     * @throws EncoderException
     *             Thrown if quoted-printable encoding is unsuccessful
     *
     * @see #getCharset()
     */
    @Override
    public String encode(final String sourceStr) throws EncoderException {
        return this.encode(sourceStr, getCharset());
    }

    /**
     * Decodes a quoted-printable string into its original form using the specified string Charset. Escaped characters
     * are converted back to their original representation.
     *
     * @param sourceStr
     *            quoted-printable string to convert into its original form
     * @param sourceCharset
     *            the original string Charset
     * @return original string
     * @throws DecoderException
     *             Thrown if quoted-printable decoding is unsuccessful
     * @since 1.7
     */
    public String decode(final String sourceStr, final Charset sourceCharset) throws DecoderException {
        if (sourceStr == null) {
            return null;
        }
        return new String(this.decode(StringUtils.getBytesUsAscii(sourceStr)), sourceCharset);
    }

    /**
     * Decodes a quoted-printable string into its original form using the specified string Charset. Escaped characters
     * are converted back to their original representation.
     *
     * @param sourceStr
     *            quoted-printable string to convert into its original form
     * @param sourceCharset
     *            the original string Charset
     * @return original string
     * @throws DecoderException
     *             Thrown if quoted-printable decoding is unsuccessful
     * @throws UnsupportedEncodingException
     *             Thrown if Charset is not supported
     */
    public String decode(final String sourceStr, final String sourceCharset)
            throws DecoderException, UnsupportedEncodingException {
        if (sourceStr == null) {
            return null;
        }
        return new String(decode(StringUtils.getBytesUsAscii(sourceStr)), sourceCharset);
    }

    /**
     * Decodes a quoted-printable string into its original form using the default string Charset. Escaped characters are
     * converted back to their original representation.
     *
     * @param sourceStr
     *            quoted-printable string to convert into its original form
     * @return original string
     * @throws DecoderException
     *             Thrown if quoted-printable decoding is unsuccessful. Thrown if Charset is not supported.
     * @see #getCharset()
     */
    @Override
    public String decode(final String sourceStr) throws DecoderException {
        return this.decode(sourceStr, this.getCharset());
    }

    /**
     * Encodes an object into its quoted-printable safe form. Unsafe characters are escaped.
     *
     * @param obj
     *            string to convert to a quoted-printable form
     * @return quoted-printable object
     * @throws EncoderException
     *             Thrown if quoted-printable encoding is not applicable to objects of this type or if encoding is
     *             unsuccessful
     */
    @Override
    public Object encode(final Object obj) throws EncoderException {
        if (obj == null) {
            return null;
        } else if (obj instanceof byte[]) {
            return encode((byte[]) obj);
        } else if (obj instanceof String) {
            return encode((String) obj);
        } else {
            throw new EncoderException("Objects of type " +
                  obj.getClass().getName() +
                  " cannot be quoted-printable encoded");
        }
    }

    /**
     * Decodes a quoted-printable object into its original form. Escaped characters are converted back to their original
     * representation.
     *
     * @param obj
     *            quoted-printable object to convert into its original form
     * @return original object
     * @throws DecoderException
     *             Thrown if the argument is not a {@code String} or {@code byte[]}. Thrown if a failure
     *             condition is encountered during the decode process.
     */
    @Override
    public Object decode(final Object obj) throws DecoderException {
        if (obj == null) {
            return null;
        } else if (obj instanceof byte[]) {
            return decode((byte[]) obj);
        } else if (obj instanceof String) {
            return decode((String) obj);
        } else {
            throw new DecoderException("Objects of type " +
                  obj.getClass().getName() +
                  " cannot be quoted-printable decoded");
        }
    }

    /**
     * Gets the default Charset name used for string decoding and encoding.
     *
     * @return the default Charset name
     * @since 1.7
     */
    public Charset getCharset() {
        return this.charset;
    }

    /**
     * Gets the default Charset name used for string decoding and encoding.
     *
     * @return the default Charset name
     */
    public String getDefaultCharset() {
        return this.charset.name();
    }

    /**
     * Encodes a string into its quoted-printable form using the specified Charset. Unsafe characters are escaped.
     * <p>
     * Depending on the selection of the {@code strict} parameter, this function either implements the full ruleset
     * or only a subset of quoted-printable encoding specification (rule #1 and rule #2) as defined in
     * RFC 1521 and is suitable for encoding binary data and unformatted text.
     *
     * @param sourceStr
     *            string to convert to quoted-printable form
     * @param sourceCharset
     *            the Charset for sourceStr
     * @return quoted-printable string
     * @since 1.7
     */
    public String encode(final String sourceStr, final Charset sourceCharset) {
        if (sourceStr == null) {
            return null;
        }
        return StringUtils.newStringUsAscii(this.encode(sourceStr.getBytes(sourceCharset)));
    }

    /**
     * Encodes a string into its quoted-printable form using the specified Charset. Unsafe characters are escaped.
     * <p>
     * Depending on the selection of the {@code strict} parameter, this function either implements the full ruleset
     * or only a subset of quoted-printable encoding specification (rule #1 and rule #2) as defined in
     * RFC 1521 and is suitable for encoding binary data and unformatted text.
     *
     * @param sourceStr
     *            string to convert to quoted-printable form
     * @param sourceCharset
     *            the Charset for sourceStr
     * @return quoted-printable string
     * @throws UnsupportedEncodingException
     *             Thrown if the Charset is not supported
     */
    public String encode(final String sourceStr, final String sourceCharset) throws UnsupportedEncodingException {
        if (sourceStr == null) {
            return null;
        }
        return StringUtils.newStringUsAscii(encode(sourceStr.getBytes(sourceCharset)));
    }
}