OpenSSL::Cipher#update

static VALUE
ossl_cipher_update(int argc, VALUE *argv, VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    unsigned char *in;
    long in_len, out_len;
    VALUE data, str;

    rb_scan_args(argc, argv, "11", &data, &str);

    if (!RTEST(rb_attr_get(self, id_key_set)))
        ossl_raise(eCipherError, "key not set");

    StringValue(data);
    in = (unsigned char *)RSTRING_PTR(data);
    in_len = RSTRING_LEN(data);
    GetCipher(self, ctx);

    /*
     * As of OpenSSL 3.2, there is no reliable way to determine the required
     * output buffer size for arbitrary cipher modes.
     * https://github.com/openssl/openssl/issues/22628
     *
     * in_len+block_size is usually sufficient, but AES key wrap with padding
     * ciphers require in_len+15 even though they have a block size of 8 bytes.
     *
     * Using EVP_MAX_BLOCK_LENGTH (32) as a safe upper bound for ciphers
     * currently implemented in OpenSSL, but this can change in the future.
     */
    if (in_len > LONG_MAX - EVP_MAX_BLOCK_LENGTH) {
        ossl_raise(rb_eRangeError,
                   "data too big to make output buffer: %ld bytes", in_len);
    }
    out_len = in_len + EVP_MAX_BLOCK_LENGTH;

    if (NIL_P(str)) {
        str = rb_str_new(0, out_len);
    } else {
        StringValue(str);
        if ((long)rb_str_capacity(str) >= out_len)
            rb_str_modify(str);
        else
            rb_str_modify_expand(str, out_len - RSTRING_LEN(str));
    }

    if (!ossl_cipher_update_long(ctx, (unsigned char *)RSTRING_PTR(str), &out_len, in, in_len))
        ossl_raise(eCipherError, NULL);
    assert(out_len <= RSTRING_LEN(str));
    rb_str_set_len(str, out_len);

    return str;
}