[nmh] / sbr / encode_rfc2047.c

/* encode_rfc2047.c -- encode message headers using RFC 2047 encoding.
 *
 * This code is Copyright (c) 2002, by the authors of nmh.  See the
 * COPYRIGHT file in the root directory of the nmh distribution for
 * complete copyright information.
 */

#include "h/mh.h"
#include "error.h"
#include "h/mhparse.h"
#include "h/addrsbr.h"
#include "h/utils.h"
#include "base64.h"
#include "unquote.h"

/*
 * List of headers that contain addresses and as a result require special
 * handling
 */

static char *address_headers[] = {
    "To",
    "From",
    "cc",
    "Bcc",
    "Reply-To",
    "Sender",
    "Resent-To",
    "Resent-From",
    "Resent-cc",
    "Resent-Bcc",
    "Resent-Reply-To",
    "Resent-Sender",
    NULL,
};

/*
 * Macros we use for parsing headers
 */

#define is_fws(c) (c == '\t' || c == ' ' || c == '\n')

#define qphrasevalid(c) ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || \
                         (c >= 'a' && c <= 'z') || \
                         c == '!' || c == '*' || c == '+' || c == '-' || \
                         c == '/' || c == '=' || c == '_')
#define qpspecial(c) (c < ' ' || c == '=' || c == '?' || c == '_')

#define base64len(n) ((((n) + 2) / 3 ) * 4)     /* String len to base64 len */
#define strbase64(n) ((n) / 4 * 3)              /* Chars that fit in base64 */

#define ENCODELINELIMIT 76

static void unfold_header(char **, int);
static int field_encode_address(const char *, char **, int, const char *);
static int field_encode_quoted(const char *, char **, const char *, int,
                               int, int);
static int field_encode_base64(const char *, char **, const char *);
static int scanstring(const char *, int *, int *, int *);
static int utf8len(const char *);
static int pref_encoding(int, int, int);

/*
 * Encode a message header using RFC 2047 encoding.  We make the assumption
 * that all characters < 128 are ASCII and as a consequence don't need any
 * encoding.
 */

int
encode_rfc2047(const char *name, char **value, int encoding,
               const char *charset)
{
    int i, asciicount = 0, eightbitcount = 0, qpspecialcount = 0;
    char *p;

    /*
     * First, check to see if we even need to encode the header
     */

    for (p = *value; *p != '\0'; p++) {
        if (isascii((unsigned char) *p)) {
            asciicount++;
            if (qpspecial((unsigned char) *p))
                qpspecialcount++;
        } else
            eightbitcount++;
    }

    if (eightbitcount == 0)
        return 0;

    /*
     * Some rules from RFC 2047:
     *
     * - Encoded words cannot be more than 75 characters long
     * - Multiple "long" encoded words must be on new lines.
     *
     * Also, we're not permitted to encode email addresses, so
     * we need to actually _parse_ email addresses and only encode
     * the right bits.  
     */

    /*
     * If charset was NULL, then get the value from the locale.  But
     * we reject it if it returns US-ASCII
     */

    if (charset == NULL)
        charset = write_charset_8bit();

    if (strcasecmp(charset, "US-ASCII") == 0) {
        inform("Cannot use US-ASCII with 8 bit characters in header");
        return 1;
    }

    /*
     * If we have an address header, then we need to parse the addresses
     * and only encode the names or comments.  Otherwise, handle it normally.
     */

    for (i = 0; address_headers[i]; i++) {
        if (strcasecmp(name, address_headers[i]) == 0)
            return field_encode_address(name, value, encoding, charset);
    }

    /*
     * On the encoding we choose, and the specifics of encoding:
     *
     * - If a specified encoding is passed in, we use that.
     * - Otherwise, pick which encoding is shorter.
     *
     * We don't quite handle continuation right here, but it should be
     * pretty close.
     */

    if (encoding == CE_UNKNOWN)
        encoding = pref_encoding(asciicount, qpspecialcount, eightbitcount);

    unfold_header(value, asciicount + eightbitcount);

    switch (encoding) {

    case CE_BASE64:
        return field_encode_base64(name, value, charset);

    case CE_QUOTED:
        return field_encode_quoted(name, value, charset, asciicount,
                                   eightbitcount + qpspecialcount, 0);

    default:
        inform("Internal error: unknown RFC-2047 encoding type");
        return 1;
    }
}

/*
 * Encode our specified header (or field) using quoted-printable
 */

static int
field_encode_quoted(const char *name, char **value, const char *charset,
                    int ascii, int encoded, int phraserules)
{
    int prefixlen = name ? strlen(name) + 2: 0, outlen = 0, column;
    int charsetlen = strlen(charset), utf8;
    char *output = NULL, *p, *q = NULL;

    /*
     * Right now we just encode the whole thing.  Maybe later on we'll
     * only encode things on a per-atom basis.
     */

    p = *value;

    column = prefixlen + 2;     /* Header name plus ": " */

    utf8 = strcasecmp(charset, "UTF-8") == 0;

    bool newline = true;
    while (*p != '\0') {
        /*
         * Start a new line, if it's time
         */
        if (newline) {
            /*
             * If it's the start of the header, we don't need to pad it
             *
             * The length of the output string is ...
             * =?charset?Q?...?=  so that's 7+strlen(charset) + 2 for \n NUL
             *
             * plus 1 for every ASCII character and 3 for every eight bit
             * or special character (eight bit characters are written as =XX).
             *
             */

            int tokenlen;

            outlen += 9 + charsetlen + ascii + 3 * encoded;

            /*
             * If output is set, then we're continuing the header.  Otherwise
             * do the initial allocation.
             */

            if (output) {
                int curlen = q - output, i;
                outlen += prefixlen + 1;        /* Header plus \n ": " */
                output = mh_xrealloc(output, outlen);
                q = output + curlen;
                *q++ = '?';
                *q++ = '=';
                *q++ = '\n';
                for (i = 0; i < prefixlen; i++)
                    *q++ = ' ';
            } else {
                /*
                 * A bit of a hack here; the header can contain multiple
                 * spaces (probably at least one) until we get to the
                 * actual text.  Copy until we get to a non-space.
                 */
                output = mh_xmalloc(outlen);
                q = output;
                while (is_fws(*p))
                    *q++ = *p++;
            }

            tokenlen = snprintf(q, outlen - (q - output), "=?%s?Q?", charset);
            q += tokenlen;
            column = prefixlen + tokenlen;
            newline = false;
        }

        /*
         * Process each character, encoding if necessary
         *
         * Note that we have a different set of rules if we're processing
         * RFC 5322 'phrase' (something you'd see in an address header).
         */

        column++;

        if (*p == ' ') {
            *q++ = '_';
            ascii--;
        } else if (isascii((unsigned char) *p) &&
                   (phraserules ? qphrasevalid((unsigned char) *p) :
                                        !qpspecial((unsigned char) *p))) {
            *q++ = *p;
            ascii--;
        } else {
            snprintf(q, outlen - (q - output), "=%02X", (unsigned char) *p);
            q += 3;
            column += 2;        /* column already incremented by 1 above */
            encoded--;
        }

        p++;

        /*
         * We're not allowed more than ENCODELINELIMIT characters per line,
         * so reserve some room for the final ?=.
         *
         * If prefixlen == 0, we haven't been passed in a header name, so
         * don't ever wrap the field (we're likely doing an address).
         */

        if (prefixlen == 0)
            continue;

        if (column >= ENCODELINELIMIT - 2) {
            newline = true;
        } else if (utf8) {
            /*
             * Okay, this is a bit weird, but to explain a bit more ...
             *
             * RFC 2047 prohibits the splitting of multibyte characters
             * across encoded words.  Right now we only handle the case
             * of UTF-8, the most common multibyte encoding.
             *
             * p is now pointing at the next input character.  If we're
             * using UTF-8 _and_ we'd go over ENCODELINELIMIT given the
             * length of the complete character, then trigger a newline
             * now.  Note that we check the length * 3 since we have to
             * allow for the encoded output.
             */
            if (column + (utf8len(p) * 3) > ENCODELINELIMIT - 2) {
                newline = true;
            }
        }
    }

    if (q == NULL) {
        /* This should never happen, but just in case.  Found by
           clang static analyzer. */
        inform("null output encoding for %s, continuing...", *value);
        return 1;
    }
    *q++ = '?';
    *q++ = '=';

    if (prefixlen)
        *q++ = '\n';

    *q = '\0';

    free(*value);

    *value = output;

    return 0;
}

/*
 * Encode our specified header (or field) using base64.
 *
 * This is a little easier since every character gets encoded, we can
 * calculate the line wrap up front.
 */

static int
field_encode_base64(const char *name, char **value, const char *charset)
{
    int prefixlen = name ? strlen(name) + 2 : 0, charsetlen = strlen(charset);
    int outlen = 0, numencode, curlen;
    char *output = NULL, *p = *value, *q = NULL, *linestart = NULL;

    /*
     * Skip over any leading white space.
     */

    while (*p == ' ' || *p == '\t')
        p++;

    /*
     * If we had a zero-length prefix, then just encode the whole field
     * as-is, without line wrapping.  Note that in addition to the encoding
     *
     * The added length we need is =? + charset + ?B? ... ?=
     *
     * That's 7 + strlen(charset) + 2 (for \n NUL).
     */

    while (prefixlen && ((base64len(strlen(p)) + 7 + charsetlen +
                          prefixlen) > ENCODELINELIMIT)) {

        /*
         * Our very first time, don't pad the line in the front
         *
         * Note ENCODELINELIMIT is + 2 because of \n \0
         */


        if (! output) {
            outlen += ENCODELINELIMIT + 2;
            output = q = mh_xmalloc(outlen);
            linestart = q - prefixlen;  /* Yes, this is intentional */
        } else {
            int curstart = linestart - output;
            curlen = q - output;

            outlen += ENCODELINELIMIT + 2;
            output = mh_xrealloc(output, outlen);
            q = output + curlen;
            linestart = output + curstart;
        }

        /*
         * We should have enough space now, so prepend the encoding markers
         * and character set information.  The leading space is intentional.
         */

        q += snprintf(q, outlen - (q - output), " =?%s?B?", charset);

        /*
         * Find out how much room we have left on the line and see how
         * many characters we can stuff in.  The start of our line
         * is marked by "linestart", so use that to figure out how
         * many characters are left out of ENCODELINELIMIT.  Reserve
         * 2 characters for the end markers and calculate how many
         * characters we can fit into that space given the base64
         * encoding expansion.
         */

        numencode = strbase64(ENCODELINELIMIT - (q - linestart) - 2);

        if (numencode <= 0) {
            inform("Internal error: tried to encode %d characters "
                   "in base64", numencode);
            return 1;
        }

        /*
         * RFC 2047 prohibits spanning multibyte characters across tokens.
         * Right now we only check for UTF-8.
         *
         * So note the key here ... we want to make sure the character BEYOND
         * our last character is not a continuation byte.  If it's the start
         * of a new multibyte character or a single-byte character, that's ok.
         */

        if (strcasecmp(charset, "UTF-8") == 0) {
            /*
             * p points to the start of our current buffer, so p + numencode
             * is one past the last character to encode
             */

            while (numencode > 0 && ((*(p + numencode) & 0xc0) == 0x80))
                numencode--;

            if (numencode == 0) {
                inform("Internal error: could not find start of "
                       "UTF-8 character when base64 encoding header");
                return 1;
            }
        }

        if (writeBase64raw((unsigned char *) p, numencode,
                           (unsigned char *) q) != OK) {
            inform("Internal error: base64 encoding of header failed");
            return 1;
        }

        p += numencode;
        q += base64len(numencode);

        /*
         * This will point us at the beginning of the new line (trust me).
         */

        linestart = q + 3;

        /*
         * What's going on here?  Well, we know we're continuing to the next
         * line, so we want to add continuation padding.  We also add the
         * trailing marker for the RFC 2047 token at this time as well.
         * This uses a trick of snprintf(); we tell it to print a zero-length
         * string, but pad it out to prefixlen - 1 characters; that ends
         * up always printing out the requested number of spaces.  We use
         * prefixlen - 1 because we always add a space on the starting
         * token marker; this makes things work out correctly for the first
         * line, which should have a space between the ':' and the start
         * of the token.
         *
         * It's okay if you don't follow all of that.
         */

        q += snprintf(q, outlen - (q - output), "?=\n%*s", prefixlen - 1, "");
    }

    /*
     * We're here if there is either no prefix, or we can fit it in less
     * than ENCODELINELIMIT characters.  Encode the whole thing.
     */

    outlen += prefixlen + 9 + charsetlen + base64len(strlen(p));
    curlen = q - output;

    output = mh_xrealloc(output, outlen);
    q = output + curlen;

    q += snprintf(q, outlen - (q - output), "%s=?%s?B?",
                  prefixlen ? " " : "", charset);

    if (writeBase64raw((unsigned char *) p, strlen(p),
                       (unsigned char *) q) != OK) {
        inform("Internal error: base64 encoding of header failed");
        return 1;
    }

    strcat(q, "?=");

    if (prefixlen)
        strcat(q, "\n");

    free(*value);

    *value = output;

    return 0;
}

/*
 * Calculate the length of a UTF-8 character.
 *
 * If it's not a UTF-8 character (or we're in the middle of a multibyte
 * character) then simply return 0.
 */

static int
utf8len(const char *p)
{
    int len = 1;

    if (*p == '\0')
        return 0;

    if (isascii((unsigned char) *p) || (((unsigned char) *p) & 0xc0) == 0x80)
        return 0;

    p++;
    while ((((unsigned char) *p++) & 0xc0) == 0x80)
        len++;

    return len;
}

/*
 * "Unfold" a header, making it a single line (without continuation)
 *
 * We cheat a bit here; we never make the string longer, so using the
 * original length here is fine.
 */

static void
unfold_header(char **value, int len)
{
    char *str = mh_xmalloc(len + 1);
    char *p = str, *q = *value;

    while (*q != '\0') {
        if (*q == '\n') {
            /*
             * When we get a newline, skip to the next non-whitespace
             * character and add a space to replace all of the whitespace
             *
             * This has the side effect of stripping off the final newline
             * for the header; we put it back in the encoding routine.
             */
            while (is_fws(*q))
                q++;
            if (*q == '\0')
                break;

            *p++ = ' ';
        } else {
            *p++ = *q++;
        }
    }

    *p = '\0';

    free(*value);
    *value = str;
}

/*
 * Decode a header containing addresses.  This means we have to parse
 * each address and only encode the display-name or comment field.
 */

static int
field_encode_address(const char *name, char **value, int encoding,
                     const char *charset)
{
    int prefixlen = strlen(name) + 2, column = prefixlen, groupflag;
    int asciichars;
    int specialchars;
    int eightbitchars;
    bool reformat = false;
    bool errflag = false;
    size_t len;
    char *mp, *cp = NULL, *output = NULL;
    char *tmpbuf = NULL;
    size_t tmpbufsize = 0;
    struct mailname *mn;
    char errbuf[BUFSIZ];

    /*
     * Because these are addresses, we need to handle them individually.
     *
     * Break them down and process them one by one.  This means we have to
     * rewrite the whole header, but that's unavoidable.
     */

    /*
     * The output headers always have to start with a space first; this
     * is just the way the API works right now.
     */

    output = add(" ", output);

    for (groupflag = 0; (mp = getname(*value)); ) {
        if ((mn = getm(mp, NULL, 0, errbuf, sizeof(errbuf))) == NULL) {
            inform("%s: %s", errbuf, mp);
            errflag = true;
            continue;
        }

        reformat = false;

        /*
         * We only care if the phrase (m_pers) or any trailing comment
         * (m_note) have 8-bit characters.  If doing q-p, we also need
         * to encode anything marked as qspecial().  Unquote it first
         * so the specialchars count is right.
         */

        if (! mn->m_pers)
            goto check_note;

        if ((len = strlen(mn->m_pers)) + 1 > tmpbufsize) {
            tmpbuf = mh_xrealloc(tmpbuf, tmpbufsize = len + 1);
        }

        unquote_string(mn->m_pers, tmpbuf);

        if (scanstring(tmpbuf, &asciichars, &eightbitchars,
                       &specialchars)) {
            /*
             * If we have 8-bit characters, encode it.
             */

            if (encoding == CE_UNKNOWN)
                encoding = pref_encoding(asciichars, specialchars,
                                         eightbitchars);

            /*
             * This is okay, because the output of unquote_string will be either
             * equal or shorter than the original.
             */

            strcpy(mn->m_pers, tmpbuf);

            switch (encoding) {

            case CE_BASE64:
                if (field_encode_base64(NULL, &mn->m_pers, charset)) {
                    errflag = true;
                    goto out;
                }
                break;

            case CE_QUOTED:
                if (field_encode_quoted(NULL, &mn->m_pers, charset, asciichars,
                                        eightbitchars + specialchars, 1)) {
                    errflag = true;
                    goto out;
                }
                break;

            default:
                inform("Internal error: unknown RFC-2047 encoding type");
                errflag = true;
                goto out;
            }

            reformat = true;
        }

        check_note:

        /*
         * The "note" field is generally a comment at the end of the address,
         * at least as how it's implemented here.  Notes are always surrounded
         * by parenthesis (since they're comments).  Strip them out and
         * then put them back when we format the final field, but they do
         * not get encoded.
         */

        if (! mn->m_note)
            goto do_reformat;

        if ((len = strlen(mn->m_note)) + 1 > tmpbufsize) {
            tmpbuf = mh_xrealloc(tmpbuf, tmpbufsize = len + 1);
        }

        if (mn->m_note[0] != '(' || mn->m_note[len - 1] != ')') {
            inform("Internal error: Invalid note field \"%s\"",
                   mn->m_note);
            errflag = true;
            goto out;
        }

        strncpy(tmpbuf, mn->m_note + 1, len - 1);
        tmpbuf[len - 2] = '\0';

        if (scanstring(tmpbuf, &asciichars, &eightbitchars,
                       &specialchars)) {
            /*
             * If we have 8-bit characters, encode it.
             */

            if (encoding == CE_UNKNOWN)
                encoding = pref_encoding(asciichars, specialchars,
                                         eightbitchars);

            switch (encoding) {

            case CE_BASE64:
                if (field_encode_base64(NULL, &tmpbuf, charset)) {
                    errflag = true;
                    goto out;
                }
                break;

            case CE_QUOTED:
                if (field_encode_quoted(NULL, &tmpbuf, charset, asciichars,
                                        eightbitchars + specialchars, 1)) {
                    errflag = true;
                    goto out;
                }
                break;

            default:
                inform("Internal error: unknown RFC-2047 encoding type");
                errflag = true;
                goto out;
            }

            reformat = true;

            /*
             * Make sure the size of tmpbuf is correct (it always gets
             * reallocated in the above functions).
             */

            tmpbufsize = strlen(tmpbuf) + 1;

            /*
             * Put the note field back surrounded by parenthesis.
             */

            mn->m_note = mh_xrealloc(mn->m_note, tmpbufsize + 2);

            snprintf(mn->m_note, tmpbufsize + 2, "(%s)", tmpbuf);
        }

do_reformat:

        /*
         * So, some explanation is in order.
         *
         * We know we need to rewrite at least one address in the header,
         * otherwise we wouldn't be here.  If we had to reformat this
         * particular address, then run it through adrformat().  Otherwise
         * we can use m_text directly.
         */

        /*
         * If we were in a group but are no longer, make sure we add a
         * semicolon (which needs to be FIRST, as it needs to be at the end
         * of the last address).
         */

        if (groupflag && ! mn->m_ingrp) {
            output = add(";", output);
            column++;
        }

        groupflag = mn->m_ingrp;

        if (mn->m_gname) {
            cp = mh_xstrdup(mn->m_gname);
        }

        if (reformat) {
            cp = add(adrformat(mn), cp);
        } else {
            cp = add(mn->m_text, cp);
        }

        len = strlen(cp);

        /*
         * If we're not at the beginning of the line, add a command and
         * either a space or a newline.
         */

        if (column != prefixlen) {
            if (len + column + 2 > OUTPUTLINELEN) {

                if ((size_t) (prefixlen + 3) < tmpbufsize)
                    tmpbuf = mh_xrealloc(tmpbuf, tmpbufsize = prefixlen + 3);

                snprintf(tmpbuf, tmpbufsize, ",\n%*s", column = prefixlen, "");
                output = add(tmpbuf, output);
            } else {
                output = add(", ", output);
                column += 2;
            }
        }

        /*
         * Finally add the address
         */

        output = add(cp, output);
        column += len;
        free(cp);
        cp = NULL;
    }

    /*
     * Just in case we're at the end of a list
     */

    if (groupflag) {
        output = add(";", output);
    }

    output = add("\n", output);

    free(*value);
    *value = output;
    output = NULL;

out:
    free(tmpbuf);
    free(output);

    return errflag;
}

/*
 * Scan a string, check for characters that need to be encoded
 */

static int
scanstring(const char *string, int *asciilen, int *eightbitchars,
           int *specialchars)
{
    *asciilen = 0;
    *eightbitchars = 0;
    *specialchars = 0;

    for (; *string != '\0'; string++) {
        if ((isascii((unsigned char) *string))) {
            (*asciilen)++;
            /*
             * So, a space is not a valid phrase character, but we're counting
             * an exception here, because in q-p a space can be directly
             * encoded as an underscore.
             */
            if (!qphrasevalid((unsigned char) *string) && *string != ' ')
                (*specialchars)++;
        } else {
            (*eightbitchars)++;
        }
    }

    return *eightbitchars > 0;
}

/*
 * This function is to be used to decide which encoding algorithm we should
 * use if one is not given.  Basically, we pick whichever one is the shorter
 * of the two.
 *
 * Arguments are:
 *
 * ascii        - Number of ASCII characters in to-be-encoded string.
 * specials     - Number of ASCII characters in to-be-encoded string that
 *                still require encoding under quoted-printable.  Note that
 *                these are included in the "ascii" total.
 * eightbit     - Eight-bit characters in the to-be-encoded string.
 *
 * Returns one of CE_BASE64 or CE_QUOTED.
 */

static int
pref_encoding(int ascii, int specials, int eightbits)
{
    /*
     * The length of the q-p encoding is:
     *
     * ascii - specials + (specials + eightbits) * 3.
     *
     * The length of the base64 encoding is:
     *
     * base64len(ascii + eightbits)     (See macro for details)
     */

    return base64len(ascii + eightbits) < (ascii - specials +
                        (specials + eightbits) * 3) ? CE_BASE64 : CE_QUOTED;
}