void ERR_error_string_n(unsigned long e, char *buf, size_t len)
{
    char lsbuf[64], fsbuf[64], rsbuf[64];
    const char *ls, *fs, *rs;
    unsigned long l, f, r;

    if (len == 0)
        return;

    l = ERR_GET_LIB(e);
    f = ERR_GET_FUNC(e);
    r = ERR_GET_REASON(e);

    ls = ERR_lib_error_string(e);
    fs = ERR_func_error_string(e);
    rs = ERR_reason_error_string(e);

    if (ls == NULL)
        BIO_snprintf(lsbuf, sizeof(lsbuf), "lib(%lu)", l);
    if (fs == NULL)
        BIO_snprintf(fsbuf, sizeof(fsbuf), "func(%lu)", f);
    if (rs == NULL)
        BIO_snprintf(rsbuf, sizeof(rsbuf), "reason(%lu)", r);

    BIO_snprintf(buf, len, "error:%08lX:%s:%s:%s", e, ls ? ls : lsbuf,
                 fs ? fs : fsbuf, rs ? rs : rsbuf);
    if (strlen(buf) == len - 1) {
        /*
         * output may be truncated; make sure we always have 5
         * colon-separated fields, i.e. 4 colons ...
         */
#define NUM_COLONS 4
        if (len > NUM_COLONS) { /* ... if possible */
            int i;
            char *s = buf;

            for (i = 0; i < NUM_COLONS; i++) {
                char *colon = strchr(s, ':');
                if (colon == NULL || colon > &buf[len - 1] - NUM_COLONS + i) {
                    /*
                     * set colon no. i at last possible position (buf[len-1]
                     * is the terminating 0)
                     */
                    colon = &buf[len - 1] - NUM_COLONS + i;
                    *colon = ':';
                }
                s = colon + 1;
            }
        }
    }
}