imapfilter/imapfilter/request.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <time.h>

#include "config.h"
#include "imapfilter.h"
#include "data.h"


extern int sockpri, sockaux;
extern unsigned int options;
extern char charset[CHARSET_LEN];
extern unsigned int capspri, capsaux;

namesp_t nsppri, nspaux;        /* Primary and auxiliary namespace. */


#ifdef DEBUG
/*
 * Test/ping server.
 */
int
test(int *sock)
{
        return server_response(sock, imap_noop(sock));
}

#endif


/*
 * Check server's capabilities.
 */
int
check_capabilities(int *sock)
{
        if (sock == &sockpri)
                capspri = CAPABILITY_NONE;
        else
                capsaux = CAPABILITY_NONE;

        return capability_response(sock, imap_capability(sock));
}


/*
 * Get namespace of mail server's mailboxes.
 */
int
check_namespace(int *sock, namesp_t * nsp)
{
        unsigned int *caps;

        caps = (sock == &sockpri ? &capspri : &capsaux);
        nsp->prefix[0] = nsp->delim = '\0';

        if (!(options & OPTION_NAMESPACE) ||
            !(*caps & CAPABILITY_NAMESPACE))
                return 0;
        else
                return namespace_response(sock, imap_namespace(sock), nsp);
}


#ifdef SSL_TLS
/*
 * Begin TLS negotiation (STARTTLS).
 */
int
imf_starttls(int *sock)
{
        int r;

        r = server_response(sock, imap_starttls(sock));
        imf_ssl_init(sock, SSL_TLS_V1);

        return r;
}

#endif


/*
 * Login to server.
 */
int
login(int *sock, char *user, char *pass)
{
        return server_response(sock, imap_login(sock, user, pass));
}


/*
 * Check if a mailbox exists.
 */
int
check_mailbox(int *sock, char *mbox)
{
        return server_response(sock, imap_status(sock, mbox, "MESSAGES"));
}


/*
 * Open mailbox in read-write mode.
 */
int
select_mailbox(int *sock, char *mbox, namesp_t * nsp)
{
        int r;

        if (mailbox_status(sock, mbox, nsp) == -2)
                return -2;      /* No messages exist. No filters need to be
                                 * applied. */

        r = select_response(sock, imap_select(sock,
                apply_namespace(mbox, nsp->prefix,
                    nsp->delim)));

        log_info(LOG_MAILBOX, mbox);

        return r;
}


/*
 * Get mailbox's status.
 */
int
mailbox_status(int *sock, char *mbox, namesp_t * nsp)
{
        return status_response(sock, imap_status(sock,
                apply_namespace(mbox, nsp->prefix, nsp->delim),
                "MESSAGES RECENT UNSEEN"), mbox);
}


/*
 * Close examined/selected mailbox.
 */
int
close_mailbox(int *sock)
{
        return server_response(sock, imap_close(sock));
}


/*
 * Logout from server.
 */
int
logout(int *sock)
{
        return logout_response(sock, imap_logout(sock));
}


/*
 * Match and apply filters assigned to a mailbox.
 */
int
apply_filters(char *mbox, filter_t ** filters)
{
        int i;
        char *mesgs;

        for (i = 0; filters[i] != NULL; i++) {
                mesgs = NULL;

                if (match_filter(filters[i], &mesgs))
                        continue;

                log_info(LOG_FILTER, filters[i]->key);

                apply_action(mbox, mesgs, &(filters[i]->action.type),
                    filters[i]->action.raccount, filters[i]->action.destmbox,
                    &filters[i]->action.msgflags, filters[i]->action.args);

                xfree(mesgs);
        }

        return 0;
}


/*
 * Generate the search request by the masks of the filter and try to
 * match the generated filter.
 */
int
match_filter(filter_t * filter, char **mesgs)
{
        char *search;

        if (filter->mode == FILTER_MODE_OR)
                search = generate_filter_or(filter->masks, filter->masknum,
                    filter->masklen);
        else
                search = generate_filter_and(filter->masks, filter->masknum,
                    filter->masklen);

        search_response(&sockpri, imap_search(&sockpri, charset, search),
            mesgs);

        xfree(search);

        if (*mesgs == '\0')
                return 1;

        return 0;
}


/*
 * Empty the FIFO inventory.
 */
void
empty_fifo(mask_t ** mfifo)
{
        mfifo[0] = NULL;

        queue_fifo(NULL, NULL);
        dequeue_fifo(NULL);
}


/*
 * Add item to FIFO inventory.
 */
void
queue_fifo(mask_t ** mfifo, mask_t * mask)
{
        static unsigned int i;

        if (mfifo == NULL) {
                i = 0;
                return;
        }
        mfifo[i++] = mask;
        mfifo[i] = NULL;
}


/*
 * Get next item from FIFO inventory.
 */
mask_t *
dequeue_fifo(mask_t ** mfifo)
{
        static unsigned int j;

        if (mfifo == NULL) {
                j = 0;
                return NULL;
        }
        return mfifo[j++];
}


/*
 * Generate the filter search command from the masks, assuming that
 * masks are AND-ed.
 */
char *
generate_filter_and(mask_t * mask, unsigned int masknum,
    unsigned int masklen)
{
        const unsigned int searchbuf = masklen + masknum * 6 + 8;
        unsigned int len;
        char *search;
        mask_t *tmp;

        len = 0;

        search = (char *)xmalloc(sizeof(char) * searchbuf);
        search[0] = '\0';

        tmp = mask;
        if (tmp == NULL) {
                strncat(search, "ALL ", searchbuf - len - 1);
                len += 4;
        } else
                while ((tmp = tmp->next) != NULL) {
                        if (tmp->type != MASK_TYPE_OR) {
                                strncat(search, "ALL ", searchbuf - len - 1);
                                len += 4;
                                break;
                        }
                }

        tmp = NULL;
        while (mask != NULL) {
                tmp = mask;
                mask = mask->next;

                if (mask != NULL && mask->type == MASK_TYPE_OR) {
                        strncat(search, "OR (", searchbuf - len - 1);
                        len += 4;

                        strncat(search, tmp->body, searchbuf - len - 1);
                        len = strlen(search);
                        search[len] = ' ';
                        search[++len] = '\0';

                        search[len - 1] = ')';
                        search[len] = ' ';
                        search[++len] = '\0';

                        if (mask->next == NULL ||
                            mask->next->type != MASK_TYPE_OR) {
                                search[len] = '(';
                                search[++len] = '\0';
                                strncat(search, mask->body,
                                    searchbuf - len - 1);
                                len = strlen(search);
                                search[len] = ')';
                                search[++len] = ' ';
                                search[++len] = '\0';
                                mask = mask->next;
                        }
                } else {
                        strncat(search, tmp->body, searchbuf - len - 1);
                        len = strlen(search);
                        search[len] = ' ';
                        search[++len] = '\0';
                }
        }

        search[len - 1] = '\0';

        return search;
}


/*
 * Generate the filter search command from the masks, assuming that
 * masks are OR-ed.
 */
char *
generate_filter_or(mask_t * mask, unsigned int masknum,
    unsigned int masklen)
{
        const unsigned int searchbuf = masklen + masknum * 6 + 8;
        unsigned int len;
        char *search;
        mask_t **mfifo;         /* Mailbox FIFO queue. */
        mask_t *mf;             /* Mask returned from FIFO. */

        len = 0;

        search = (char *)xmalloc(sizeof(char) * searchbuf);
        mfifo = (mask_t **) xmalloc(sizeof(mask_t *) * (masknum + 1));

        search[0] = '\0';
        empty_fifo(mfifo);

        strncat(search, "ALL ", searchbuf - len - 1);
        len += 4;

        while (mask != NULL) {
                queue_fifo(mfifo, mask);
                mask = mask->next;

                while (mask != NULL && mask->type == MASK_TYPE_AND) {
                        queue_fifo(mfifo, mask);
                        mask = mask->next;
                }

                if (mask != NULL) {
                        if (len == 4 && search[0] == 'A') {
                                search[0] = '\0';
                                len = 0;
                        }
                        strncat(search, "OR ", searchbuf - len - 1);
                        len += 3;
                }
                if (search[0] != 'A') {
                        search[len] = '(';
                        search[++len] = '\0';
                }
                while ((mf = dequeue_fifo(mfifo)) != NULL) {
                        strncat(search, mf->body, searchbuf - len - 1);
                        len = strlen(search);
                        search[len] = ' ';
                        search[++len] = '\0';
                }

                if (strchr(search, '(')) {
                        search[len - 1] = ')';
                        search[len] = ' ';
                        search[++len] = '\0';
                }
                empty_fifo(mfifo);
        }

        search[len - 1] = '\0';

        xfree(mfifo);

        return search;
}


/*
 * Apply the appropriate action.
 */
int
apply_action(char *mbox, char *mesgs, unsigned int *type, account_t * raccount,
    char *destmbox, unsigned int *msgflags, char *args)
{
        unsigned int cnt;

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

        log_info(LOG_ACTION, type);
        log_info(LOG_DESTINATION_ACCOUNT, raccount->key);
        log_info(LOG_DESTINATION_MAILBOX, destmbox);

        cnt = count_messages(mesgs);

        switch (*type) {
        case FILTER_ACTION_DELETE:
                info("%d message%s deleted.\n", cnt, plural(cnt));
                action_delete(mesgs, args);
                break;
        case FILTER_ACTION_COPY:
                info("%d message%s copied from \"%s\" to mailbox \"%s\".\n",
                    cnt, plural(cnt), mbox, destmbox);
                action_copy(mbox, mesgs, apply_namespace(destmbox,
                        nsppri.prefix, nsppri.delim), args);
                break;
        case FILTER_ACTION_MOVE:
                info("%d message%s moved from \"%s\" to mailbox \"%s\".\n",
                    cnt, plural(cnt), mbox, destmbox);
                action_move(mbox, mesgs, apply_namespace(destmbox,
                        nsppri.prefix, nsppri.delim), args);
                break;
        case FILTER_ACTION_RCOPY:
                info("%d message%s copied from \"%s\" to mailbox "
                    "\"%s\" at account %s.\n", cnt, plural(cnt),
                    mbox, destmbox, raccount->key);
                action_rcopy(mbox, mesgs, raccount, destmbox, args);
                break;
        case FILTER_ACTION_RMOVE:
                info("%d message%s moved from \"%s\" to mailbox "
                    "\"%s\" at account %s.\n", cnt, plural(cnt),
                    mbox, destmbox, raccount->key);
                action_rmove(mbox, mesgs, raccount, destmbox, args);
                break;
        case FILTER_ACTION_FLAG_REPLACE:
        case FILTER_ACTION_FLAG_ADD:
        case FILTER_ACTION_FLAG_REMOVE:
                info("%d message%s flagged.\n", cnt, plural(cnt));
                action_flag(mesgs, type, msgflags, args);
                break;
        case FILTER_ACTION_LIST:
                info("%d message%s listed.\n", cnt, plural(cnt));
                action_list(mesgs, args);
                break;
        }

        if (*args == '\0')
                log_info(LOG_PREAMBLE, NULL);

        return 0;
}


/*
 * Delete messages and optionally list some of their headers.
 */
int
action_delete(char *mesgs, char *args)
{
        char *tok, *m, *mcp;

        action_list(mesgs, args);

        m = mcp = convert_messages(mesgs);

        tok = strtok_r(m, " ", &m);
        while (tok) {
                server_response(&sockpri, imap_store(&sockpri, tok,
                        STORE_FLAG_ADD, "\\Deleted"));

                tok = strtok_r(NULL, " ", &m);
        }

        if (options & OPTION_EXPUNGE)
                server_response(&sockpri, imap_expunge(&sockpri));

        xfree(mcp);

        return 0;
}


/*
 * Copy messages to specified mailbox.
 */
int
action_copy(char *mbox, char *mesgs, char *destmbox, char *args)
{
        int r;
        char *tok, *mcp, *m;
        char dm[2][MBOX_NAME_LEN];

        r = 0;
        tok = NULL;

        action_list(mesgs, args);

        if (strchr(destmbox, '@'))
                m = mcp = xstrdup(mesgs);
        else
                m = mcp = convert_messages(mesgs);

        xstrncpy(dm[0], destmbox, MBOX_NAME_LEN - 1);
        default_variables(mbox, dm[0]);
        current_date(dm[0]);
        tok = strtok_r(m, " ", &m);
        while (tok != NULL) {
                xstrncpy(dm[1], dm[0], MBOX_NAME_LEN - 1);
                message_date(tok, dm[1]);

                if ((r = copy_response(&sockpri, imap_copy(&sockpri, tok,
                                dm[1]))) == RESPONSE_TRYCREATE)
                        if (!server_response(&sockpri, imap_create(&sockpri,
                                    dm[1]))) {
                                if ((options & OPTION_SUBSCRIBE))
                                        server_response(&sockpri,
                                            imap_subscribe(&sockpri, dm[1]));
                                r = copy_response(&sockpri,
                                    imap_copy(&sockpri, tok, dm[1]));
                        }
                tok = strtok_r(NULL, " ", &m);
        }

        xfree(mcp);

        return r;
}


/*
 * Move messages to specified mailbox.
 */
int
action_move(char *mbox, char *mesgs, char *destmbox, char *args)
{
        if (!action_copy(mbox, mesgs, destmbox, args))
                action_delete(mesgs, "\0");

        return 0;
}


/*
 * Copy messages to the specified mailbox of another mail server.
 */
int
action_rcopy(char *mbox, char *mesgs, account_t * destacc, char *destmbox,
    char *args)
{
        int r, ta, tf;
        char *tok, *m, *mcp, *ndm;
        unsigned int n;
        char buf[RESPONSE_BUF * 2 + 1];
        char dm[3][MBOX_NAME_LEN];

        *dm[0] = *dm[1] = *dm[2] = '\0';

        if (init_connection(&sockaux, destacc->server, destacc->port,
                destacc->ssl))
                return ERROR_NETWORK;

        r = greeting_response(&sockaux);

#ifdef DEBUG
        test(&sockaux);
#endif

        if (r == RESPONSE_BYE || check_capabilities(&sockaux))
                return ERROR_NETWORK;

#ifdef SSL_TLS
        if (destacc->ssl == SSL_DISABLED && capsaux & CAPABILITY_STARTTLS)
                if (imf_starttls(&sockaux) == RESPONSE_OK)
                        check_capabilities(&sockaux);
#endif

        if (r != RESPONSE_PREAUTH) {
                if (destacc->passwdattr == PASSWORD_NONE) {
                        printf("Enter password for %s@%s: ", destacc->username,
                            destacc->server);
                        get_password(destacc->password, PASSWORD_LEN);
                        destacc->passwdattr = PASSWORD_PLAIN;
                }
#ifdef CRAM_MD5
                if (capsaux & CAPABILITY_AUTH_CRAM_MD5)
                        r = imf_cram_md5(&sockaux, destacc->username,
                            destacc->password);
                else
#endif
                        r = login(&sockaux, destacc->username,
                            destacc->password);

                if (r == RESPONSE_NO) {
                        error("username %s or password rejected at %s\n",
                            destacc->username, destacc->server);
                        return ERROR_NETWORK;
                }
        }
        check_namespace(&sockaux, &nspaux);

        m = mcp = xstrdup(mesgs);

        xstrncpy(dm[1], destmbox, MBOX_NAME_LEN - 1);
        current_date(dm[1]);

        tok = strtok_r(m, " ", &m);
        while (tok != NULL) {
                xstrncpy(dm[2], dm[1], MBOX_NAME_LEN - 1);
                message_date(tok, dm[2]);

                /* apply_namespace() returns a pointer to a static buffer. */
                ndm = apply_namespace(dm[2], nspaux.prefix, nspaux.delim);

                /* Check only if mailbox name is different from last one. */
                if (strncmp(dm[0], dm[2], strlen(dm[2]))) {
                        r = check_mailbox(&sockaux, ndm);
                        if (r == RESPONSE_NO) {
                                server_response(&sockaux,
                                    imap_create(&sockaux, ndm));
                                if ((options & OPTION_SUBSCRIBE))
                                        server_response(&sockaux,
                                            imap_subscribe(&sockaux, ndm));
                        }
                }
                xstrncpy(dm[0], dm[2], MBOX_NAME_LEN - 1);

                fetchsize_response(&sockpri, &n,
                    imap_fetch(&sockpri, tok, "RFC822.SIZE"));

                ta = imap_append(&sockaux, ndm, n);

                fetch_response(&sockpri, 0, 1, NULL);
                tf = imap_fetch(&sockpri, tok, "RFC822.HEADER");
                do {
                        r = fetch_response(&sockpri, tf, 0, buf);
                        socket_write(&sockaux, buf);
                } while (r == RESPONSE_NONE);

                socket_write(&sockaux, "\r\n");

                fetch_response(&sockpri, 0, 1, NULL);
                tf = imap_fetch(&sockpri, tok, "BODY[TEXT]");
                do {
                        r = fetch_response(&sockpri, tf, 0, buf);
                        if (r != RESPONSE_NULLBODY)
                                socket_write(&sockaux, buf);
                } while (r == RESPONSE_NONE);

                if (r != RESPONSE_NULLBODY)
                        socket_write(&sockaux, "\r\n\r\n");
                else
                        socket_write(&sockaux, "\r\n");

                append_response(&sockaux, ta);

                tok = strtok_r(NULL, " ", &m);
        }

        logout(&sockaux);

        action_list(mesgs, args);

        xfree(mcp);

        return 0;
}


/*
 * Move messages to the specified mailbox of another mail server.
 */
int
action_rmove(char *mbox, char *mesgs, account_t * destacc, char *destmbox,
    char *args)
{
        if (!action_rcopy(mbox, mesgs, destacc, destmbox, args))
                action_delete(mesgs, "\0");

        return 0;
}


/*
 * Flag messages by replacing, adding or removing specified flags.
 */
int
action_flag(char *mesgs, unsigned int *type, unsigned int *msgflags,
    char *args)
{
        unsigned int t;
        char s[STORE_FLAGS_BUF];
        char *tok, *m, *mcp;

        *s = 0;

        switch (*type) {
        case FILTER_ACTION_FLAG_ADD:
                t = STORE_FLAG_ADD;
                break;
        case FILTER_ACTION_FLAG_REMOVE:
                t = STORE_FLAG_REMOVE;
                break;
        default:
                t = STORE_FLAG_REPLACE;
        }

        if ((*msgflags != MESSAGE_FLAG_NONE)) {
                if ((*msgflags & MESSAGE_FLAG_SEEN))
                        strncat(s, "\\Seen ", STORE_FLAGS_BUF - strlen(s) - 1);
                if ((*msgflags & MESSAGE_FLAG_ANSWERED))
                        strncat(s, "\\Answered ",
                            STORE_FLAGS_BUF - strlen(s) - 1);
                if ((*msgflags & MESSAGE_FLAG_FLAGGED))
                        strncat(s, "\\Flagged ",
                            STORE_FLAGS_BUF - strlen(s) - 1);
                if ((*msgflags & MESSAGE_FLAG_DELETED))
                        strncat(s, "\\Deleted ",
                            STORE_FLAGS_BUF - strlen(s) - 1);
                if ((*msgflags & MESSAGE_FLAG_DRAFT))
                        strncat(s, "\\Draft", STORE_FLAGS_BUF - strlen(s) - 1);
                if ((s[strlen(s) - 1] == ' '))
                        s[strlen(s) - 1] = 0;
        }
        action_list(mesgs, args);

        m = mcp = convert_messages(mesgs);

        tok = strtok_r(m, " ", &m);
        while (tok != NULL) {
                server_response(&sockpri, imap_store(&sockpri, tok, t, s));

                tok = strtok_r(NULL, " ", &m);
        }

        if (options & OPTION_EXPUNGE)
                server_response(&sockpri, imap_expunge(&sockpri));

        xfree(mcp);

        return 0;
}

/*
 * List user selected headers of messages.
 */
int
action_list(char *mesgs, char *args)
{
        int r, t;
        char *tok, *mcp, *m;
        char s[ARGS_LEN + 27];
        char hdrs[RESPONSE_BUF * 2 + 1];

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

        m = mcp = xstrdup(mesgs);

        snprintf(s, ARGS_LEN + 27 - 1, "BODY.PEEK[HEADER.FIELDS (%s)]", args);

        tok = strtok_r(m, " ", &m);
        while (tok != NULL) {
                /* Reset internal fetch counter. */
                fetch_response(&sockpri, 0, 1, NULL);
                t = imap_fetch(&sockpri, tok, s);

                log_info(LOG_PREAMBLE, NULL);
                do {
                        r = fetch_response(&sockpri, t, 0, hdrs);

                        if (*hdrs != '\0') {
                                if (options & OPTION_HEADERS)
                                        info("%s\n", hdrs);
                                log_info(LOG_HEADER, hdrs);
                        }
                } while (r == RESPONSE_NONE);

                tok = strtok_r(NULL, " ", &m);
        }

        xfree(mcp);

        return 0;
}


/*
 * Count how many messages matched the filter.
 */
unsigned int
count_messages(char *mesgs)
{
        unsigned int cnt;
        char *c;

        cnt = 0;
        c = mesgs;

        while ((c = strchr(c, ' '))) {
                cnt++;
                c++;
        }

        return ++cnt;
}


/*
 * Convert messages with contiguous sequence number to the corresponding
 * number range, eg. 1 2 3 5 7 8 --> 1:3 5 7:8 and return a newly allocated
 * buffer with the results.
 */
char *
convert_messages(char *mesgs)
{
        int maxlen;
        unsigned int start, end, tmp;
        char *c, *cp, *tail;

        start = end = tmp = 0;
        maxlen = strlen(mesgs) + 1;
        tail = NULL;

        c = cp = xstrdup(mesgs);

        start = (unsigned int)strtoul(mesgs, &tail, 10);
        end = start;

        do {
                if (tail != NULL) {
                        tmp = (unsigned int)strtoul(tail, &tail, 10);
                        if (tmp == 0)
                                tail = NULL;
                }
                if (tmp == end + 1)
                        end++;
                else {
                        if (start == end) {
                                xstrncpy(c, ultostr(start, 10), maxlen);
                                c += strlen(c);
                        } else {
                                xstrncpy(c, ultostr(start, 10), maxlen - 1);
                                c += strlen(c);
                                *c = ':';
                                *++c = 0;
                                xstrncpy(c, ultostr(end, 10), maxlen);
                                c += strlen(c);
                        }

                        if (tail != NULL && c - cp < maxlen) {
                                *c = ' ';
                                *++c = 0;
                        }
                        start = end = tmp;
                }
        } while (tmp != 0);

        return cp;
}


/*
 * Substitute all occurences of the '@' character with the '%' character,
 * and any double '@' characters with a signle '@' character, returning the
 * number of replacements.
 */
int
substitute_date(char *str)
{
        int n;
        char *r, *w, *s;

        n = 0;

        s = xstrdup(str);

        for (r = s, w = str; *r != '\0'; r++, w++) {
                if (*r == '%') {
                        *w++ = '%';
                        *w = '%';
                } else if (*r == '@') {
                        if (*(r + 1) == '@') {
                                *w = *r++;
                        } else {
                                *w = '%';
                                n++;
                        }
                } else {
                        *w = *r;
                }
        }
        *w = '\0';

        xfree(s);

        return n;
}


/*
 * Format the destination mailbox according to the current date conversion
 * specifiers.
 */
void
current_date(char *destmbox)
{
        char s[MBOX_NAME_LEN];
        time_t te;
        struct tm *tl;

        if (!strchr(destmbox, '%'))
                return;

        te = time(NULL);
        tl = localtime(&te);

        if (strftime(s, MBOX_NAME_LEN - 1, destmbox, tl))
                xstrncpy(destmbox, s, MBOX_NAME_LEN - 1);
}


/*
 * Format the destination mailbox according to the message date conversion
 * specifiers.
 */
void
message_date(char *mesg, char *destmbox)
{
        unsigned int t;
        char s[MBOX_NAME_LEN];
        struct tm tl;
        char dbuf[RESPONSE_BUF + 1];

        if (!strchr(destmbox, '@'))
                return;

        substitute_date(destmbox);

        fetch_response(&sockpri, 0, 1, NULL);
        t = imap_fetch(&sockpri, mesg, "BODY.PEEK[HEADER.FIELDS (DATE)]");

        while (fetch_response(&sockpri, t, 0, dbuf) == RESPONSE_NONE);

        if (strptime(dbuf, "Date: %a, %d %b %Y %H:%M:%S", &tl) &&
            strftime(s, MBOX_NAME_LEN - 1, destmbox, &tl))
                xstrncpy(destmbox, s, MBOX_NAME_LEN - 1);
}


/*
 * Format the destination mailbox according to "default variables" specifiers.
 */
void
default_variables(char *mbox, char *destmbox)
{
        char *m, *r, *w, *s;

        if (!strchr(destmbox, '$'))
                return;

        s = xstrdup(destmbox);

        for (r = s, w = destmbox; *r != '\0';) {
                if (w - destmbox >= MBOX_NAME_LEN - 1)
                        break;
                if (*r == '$') {
                        switch (*(r + 1)) {
                        case '_':
                                if (w + strlen(mbox) - destmbox >
                                    MBOX_NAME_LEN - 1) {
                                        r += 2;
                                        break;
                                }
                                for (m = mbox; *m != '\0'; m++, w++)
                                        *w = *m;
                                r += 2;
                                break;
                        case '$':
                                *w++ = '$';
                                r += 2;
                                break;
                        default:
                                *w++ = *r++;
                                break;
                        }
                } else {
                        *w++ = *r++;
                }
        }
        *w = '\0';

        xfree(s);
}