k-9/src/com/fsck/k9/mail/internet/DecoderUtil.java

package com.fsck.k9.mail.internet;

import android.util.Log;
import com.fsck.k9.K9;
import com.fsck.k9.mail.Message;
import com.fsck.k9.mail.MessagingException;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import org.apache.james.mime4j.decoder.Base64InputStream;
import org.apache.james.mime4j.decoder.QuotedPrintableInputStream;
import org.apache.james.mime4j.util.CharsetUtil;


/**
 * Static methods for decoding strings, byte arrays and encoded words.
 *
 * This class is copied from the org.apache.james.mime4j.decoder.DecoderUtil class.  It's modified here in order to
 * decode emoji characters in the Subject headers.  The method to decode emoji depends on the MimeMessage class because
 * it has to be determined with the sender address, the mailer and so on.
 */
public class DecoderUtil
{
    /**
     * Decodes an encoded word encoded with the 'B' encoding (described in
     * RFC 2047) found in a header field body.
     *
     * @param encodedWord the encoded word to decode.
     * @param charset the Java charset to use.
     * @return the decoded string.
     */
    private static String decodeB(String encodedWord, String charset)
    {
        byte[] bytes;
        try
        {
            bytes = encodedWord.getBytes("US-ASCII");
        }
        catch (UnsupportedEncodingException e)
        {
            return null;
        }

        Base64InputStream is = new Base64InputStream(new ByteArrayInputStream(bytes));
        try
        {
            return MimeUtility.readToString(is, charset);
        }
        catch (IOException e)
        {
            return null;
        }
    }

    /**
     * Decodes an encoded word encoded with the 'Q' encoding (described in
     * RFC 2047) found in a header field body.
     *
     * @param encodedWord the encoded word to decode.
     * @param charset the Java charset to use.
     * @return the decoded string.
     */
    private static String decodeQ(String encodedWord, String charset)
    {

        /*
         * Replace _ with =20
         */
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < encodedWord.length(); i++)
        {
            char c = encodedWord.charAt(i);
            if (c == '_')
            {
                sb.append("=20");
            }
            else
            {
                sb.append(c);
            }
        }

        byte[] bytes;
        try
        {
            bytes = encodedWord.getBytes("US-ASCII");
        }
        catch (UnsupportedEncodingException e)
        {
            return null;
        }

        QuotedPrintableInputStream is = new QuotedPrintableInputStream(new ByteArrayInputStream(bytes));
        try
        {
            return MimeUtility.readToString(is, charset);
        }
        catch (IOException e)
        {
            return null;
        }
    }

    /**
     * Decodes a string containing encoded words as defined by RFC 2047.
     * Encoded words in have the form
     * =?charset?enc?Encoded word?= where enc is either 'Q' or 'q' for
     * quoted-printable and 'B' or 'b' for Base64.
     *
     * ANDROID:  COPIED FROM A NEWER VERSION OF MIME4J
     *
     * @param body the string to decode.
     * @param message the message which has the string.
     * @return the decoded string.
     */
    public static String decodeEncodedWords(String body, Message message)
    {

        // ANDROID:  Most strings will not include "=?" so a quick test can prevent unneeded
        // object creation.  This could also be handled via lazy creation of the StringBuilder.
        if (body.indexOf("=?") == -1)
        {
            return body;
        }

        int previousEnd = 0;
        boolean previousWasEncoded = false;

        StringBuilder sb = new StringBuilder();

        while (true)
        {
            int begin = body.indexOf("=?", previousEnd);

            // ANDROID:  The mime4j original version has an error here.  It gets confused if
            // the encoded string begins with an '=' (just after "?Q?").  This patch seeks forward
            // to find the two '?' in the "header", before looking for the final "?=".
            int endScan = begin + 2;
            if (begin != -1)
            {
                int qm1 = body.indexOf('?', endScan + 2);
                int qm2 = body.indexOf('?', qm1 + 1);
                if (qm2 != -1)
                {
                    endScan = qm2 + 1;
                }
            }

            int end = begin == -1 ? -1 : body.indexOf("?=", endScan);
            if (end == -1)
            {
                if (previousEnd == 0)
                    return body;

                sb.append(body.substring(previousEnd));
                return sb.toString();
            }
            end += 2;

            String sep = body.substring(previousEnd, begin);

            String decoded = decodeEncodedWord(body, begin, end, message);
            if (decoded == null)
            {
                sb.append(sep);
                sb.append(body.substring(begin, end));
            }
            else
            {
                if (!previousWasEncoded || !CharsetUtil.isWhitespace(sep))
                {
                    sb.append(sep);
                }
                sb.append(decoded);
            }

            previousEnd = end;
            previousWasEncoded = decoded != null;
        }
    }

    // return null on error
    private static String decodeEncodedWord(String body, int begin, int end, Message message)
    {
        int qm1 = body.indexOf('?', begin + 2);
        if (qm1 == end - 2)
            return null;

        int qm2 = body.indexOf('?', qm1 + 1);
        if (qm2 == end - 2)
            return null;

        String mimeCharset = body.substring(begin + 2, qm1);
        String encoding = body.substring(qm1 + 1, qm2);
        String encodedText = body.substring(qm2 + 1, end - 2);

        String charset;
        try
        {
            charset = MimeUtility.fixupCharset(mimeCharset, message);
        }
        catch (MessagingException e)
        {
            return null;
        }

        if (encodedText.length() == 0)
        {
            Log.w(K9.LOG_TAG, "Missing encoded text in encoded word: '" + body.substring(begin, end) + "'");
            return null;
        }

        if (encoding.equalsIgnoreCase("Q"))
        {
            return DecoderUtil.decodeQ(encodedText, charset);
        }
        else if (encoding.equalsIgnoreCase("B"))
        {
            return DecoderUtil.decodeB(encodedText, charset);
        }
        else
        {
            Log.w(K9.LOG_TAG, "Warning: Unknown encoding in encoded word '" + body.substring(begin, end) + "'");
            return null;
        }
    }
}