hexdigest

static VALUE
ossl_hmac_s_hexdigest(VALUE klass, VALUE digest, VALUE key, VALUE data)
{
    unsigned char *buf;
    char *hexbuf;
    unsigned int buf_len;
    VALUE hexdigest;

    StringValue(key);
    StringValue(data);

    buf = HMAC(GetDigestPtr(digest), RSTRING_PTR(key), RSTRING_LENINT(key),
               (unsigned char *)RSTRING_PTR(data), RSTRING_LEN(data), NULL, &buf_len);
    if (string2hex(buf, buf_len, &hexbuf, NULL) != 2 * (int)buf_len) {
        ossl_raise(eHMACError, "Cannot convert buf to hexbuf");
    }
    hexdigest = ossl_buf2str(hexbuf, 2 * buf_len);

    return hexdigest;
}