sendmail/aux/rfc2047.c

/*
 * rfc2047.c -- decode RFC-2047 header format
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#ifndef lint
static char sccsi2[] = "%W% (Sun) %G%";
#endif

/*
 * Copyright (c) 1997-1998 Richard Coleman
 * All rights reserved.
 *
 * Permission is hereby granted, without written agreement and without
 * license or royalty fees, to use, copy, modify, and distribute this
 * software and to distribute modified versions of this software for any
 * purpose, provided that the above copyright notice and the following two
 * paragraphs appear in all copies of this software.
 *
 * In no event shall Richard Coleman be liable to any party for direct,
 * indirect, special, incidental, or consequential damages arising out of
 * the use of this software and its documentation, even if Richard Coleman
 * has been advised of the possibility of such damage.
 *
 * Richard Coleman specifically disclaims any warranties, including, but
 * not limited to, the implied warranties of merchantability and fitness
 * for a particular purpose.  The software provided hereunder is on an "as
 * is" basis, and Richard Coleman has no obligation to provide maintenance,
 * support, updates, enhancements, or modifications.
 */

/*
 * Parts of this code were derived from metamail, which is ...
 *
 * Copyright (c) 1991 Bell Communications Research, Inc. (Bellcore)
 *
 * Permission to use, copy, modify, and distribute this material
 * for any purpose and without fee is hereby granted, provided
 * that the above copyright notice and this permission notice
 * appear in all copies, and that the name of Bellcore not be
 * used in advertising or publicity pertaining to this
 * material without the specific, prior written permission
 * of an authorized representative of Bellcore.  BELLCORE
 * MAKES NO REPRESENTATIONS ABOUT THE ACCURACY OR SUITABILITY
 * OF THIS MATERIAL FOR ANY PURPOSE.  IT IS PROVIDED "AS IS",
 * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES.
 */

/*
 * Copyright (c) 1998, by Sun Microsystems, Inc.
 * All rights reserved.
 */

#include <string.h>

typedef int bool;

#define FALSE   0
#define TRUE    1

static signed char hexindex[] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    0,   1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
};

static signed char index_64[128] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
    -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
    -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1
};

#define char64(c) (((unsigned char) (c) > 127) ? -1 : \
    index_64[(unsigned char) (c)])

static int
unqp(unsigned char byte1, unsigned char byte2)
{
    if (hexindex[byte1] == -1 || hexindex[byte2] == -1)
        return (-1);
    return (hexindex[byte1] << 4 | hexindex[byte2]);
}

/* Check if character is linear whitespace */
#define is_lws(c)  ((c) == ' ' || (c) == '\t' || (c) == '\n')

/*
 * Decode the string as a RFC-2047 header field
 */

bool
decode_rfc2047(char *str, char *dst, char *charset)
{
    char *p, *q, *pp;
    char *startofmime, *endofmime;
    int c, quoted_printable;
    bool encoding_found = FALSE;    /* did we decode anything?    */
    bool between_encodings = FALSE; /* are we between two encodings?  */
    bool equals_pending = FALSE;    /* is there a '=' pending?    */
    int whitespace = 0; /* how much whitespace between encodings? */

    if (str == NULL)
        return (FALSE);

    /*
     * Do a quick and dirty check for the '=' character.
     * This should quickly eliminate many cases.
     */
    if (!strchr(str, '='))
        return (FALSE);

    for (p = str, q = dst; *p; p++) {
        /*
         * If we had an '=' character pending from
         * last iteration, then add it first.
         */
        if (equals_pending) {
            *q++ = '=';
            equals_pending = FALSE;
            between_encodings = FALSE; /* we added non-WS text */
        }

        if (*p != '=') {
            /* count linear whitespace while between encodings */
            if (between_encodings && is_lws(*p))
                whitespace++;
            else
                between_encodings = FALSE; /* non-WS added */
            *q++ = *p;
            continue;
        }

        equals_pending = TRUE;  /* we have a '=' pending */

        /* Check for initial =? */
        if (*p == '=' && p[1] && p[1] == '?' && p[2]) {
            startofmime = p + 2;

            /* Scan ahead for the next '?' character */
            for (pp = startofmime; *pp && *pp != '?'; pp++)
                ;

            if (!*pp)
                continue;

            strncpy(charset, startofmime, pp - startofmime);
            charset[pp - startofmime] = '\0';

            startofmime = pp + 1;

            /* Check for valid encoding type */
            if (*startofmime != 'B' && *startofmime != 'b' &&
                *startofmime != 'Q' && *startofmime != 'q')
                continue;

            /* Is encoding quoted printable or base64? */
            quoted_printable = (*startofmime == 'Q' ||
                        *startofmime == 'q');
            startofmime++;

            /* Check for next '?' character */
            if (*startofmime != '?')
                continue;
            startofmime++;

            /*
             * Scan ahead for the ending ?=
             *
             * While doing this, we will also check if encoded
             * word has any embedded linear whitespace.
             */
            endofmime = NULL;
            for (pp = startofmime; *pp && *(pp+1); pp++) {
                if (is_lws(*pp))
                    break;
                else if (*pp == '?' && pp[1] == '=') {
                    endofmime = pp;
                    break;
                }
            }
            if (is_lws(*pp) || endofmime == NULL)
                continue;

            /*
             * We've found an encoded word, so we can drop
             * the '=' that was pending
             */
            equals_pending = FALSE;

            /*
             * If we are between two encoded words separated only
             * by linear whitespace, then we ignore the whitespace.
             * We will roll back the buffer the number of whitespace
             * characters we've seen since last encoded word.
             */
            if (between_encodings)
                q -= whitespace;

            /* Now decode the text */
            if (quoted_printable) {
                for (pp = startofmime; pp < endofmime; pp++) {
                    if (*pp == '=') {
                        c = unqp(pp[1], pp[2]);
                        if (c == -1)
                            continue;
                        if (c != 0)
                            *q++ = c;
                        pp += 2;
                    } else if (*pp == '_')
                        *q++ = ' ';
                    else
                        *q++ = *pp;
                }
            } else {
                /* base64 */
                int c1, c2, c3, c4;

                pp = startofmime;
                while (pp < endofmime) {
                    /* 6 + 2 bits */
                    while ((pp < endofmime) &&
                        ((c1 = char64(*pp)) == -1)) {
                        pp++;
                    }
                    if (pp < endofmime)
                        pp++;
                    while ((pp < endofmime) &&
                        ((c2 = char64(*pp)) == -1)) {
                        pp++;
                    }
                    if (pp < endofmime && c1 != -1 &&
                                c2 != -1) {
                        *q++ = (c1 << 2) | (c2 >> 4);
                        pp++;
                    }
                    /* 4 + 4 bits */
                    while ((pp < endofmime) &&
                        ((c3 = char64(*pp)) == -1)) {
                        pp++;
                    }
                    if (pp < endofmime && c2 != -1 &&
                                c3 != -1) {
                        *q++ = ((c2 & 0xF) << 4) |
                                (c3 >> 2);
                        pp++;
                    }
                    /* 2 + 6 bits */
                    while ((pp < endofmime) &&
                        ((c4 = char64(*pp)) == -1)) {
                        pp++;
                    }
                    if (pp < endofmime && c3 != -1 &&
                                c4 != -1) {
                        *q++ = ((c3 & 0x3) << 6) | (c4);
                        pp++;
                    }
                }
            }

            /*
             * Now that we are done decoding this particular
             * encoded word, advance string to trailing '='.
             */
            p = endofmime + 1;

            encoding_found = TRUE;   /* found (>= 1) encoded word */
            between_encodings = TRUE; /* just decoded something   */
            whitespace = 0; /* re-initialize amount of whitespace */
        }
    }

    /* If an equals was pending at end of string, add it now. */
    if (equals_pending)
        *q++ = '=';
    *q = '\0';

    return (encoding_found);
}