hexdigest

static VALUE
ossl_hmac_hexdigest(VALUE self)
{
    HMAC_CTX *ctx;
    unsigned char *buf;
    char *hexbuf;
    unsigned int buf_len;
    VALUE hexdigest;

    GetHMAC(self, ctx);
    hmac_final(ctx, &buf, &buf_len);
    if (string2hex(buf, buf_len, &hexbuf, NULL) != 2 * (int)buf_len) {
        OPENSSL_free(buf);
        ossl_raise(eHMACError, "Memory alloc error");
    }
    OPENSSL_free(buf);
    hexdigest = ossl_buf2str(hexbuf, 2 * buf_len);

    return hexdigest;
}