Sub Transaction¶

typedef struct cardano_sub_transaction_t cardano_sub_transaction_t¶

A sub transaction is a transaction nested inside a top-level transaction.

Sub transactions allow several parties to compose intents that are validated and applied atomically as part of a single top-level transaction. Each sub transaction carries its own body, its own witness set and, optionally, its own auxiliary data.

On the wire a sub transaction is a three element array of the form [sub_transaction_body, transaction_witness_set, auxiliary_data / null]. Unlike the top-level mempool encoding, a sub transaction carries no validity flag, and absent auxiliary data is encoded as a CBOR null.

cardano_error_t cardano_sub_transaction_new(cardano_sub_transaction_body_t *body, cardano_witness_set_t *witness_set, cardano_auxiliary_data_t *auxiliary_data, cardano_sub_transaction_t **sub_transaction)¶

Creates and initializes a new Cardano sub transaction.

This function allocates and initializes a new instance of a cardano_sub_transaction_t object, which represents a Cardano sub transaction consisting of a sub transaction body, witness set, and optional auxiliary data.

Usage Example:

cardano_sub_transaction_body_t* body = ...; // Assume body is initialized
cardano_witness_set_t* witness_set = ...; // Assume witness set is initialized
cardano_auxiliary_data_t* auxiliary_data = ...; // Optional: can be NULL if no auxiliary data is present
cardano_sub_transaction_t* sub_transaction = NULL;

cardano_error_t result = cardano_sub_transaction_new(body, witness_set, auxiliary_data, &sub_transaction);

if (result == CARDANO_SUCCESS)
{
  // Use the sub transaction

  // Once done, ensure to clean up and release the sub transaction
  cardano_sub_transaction_unref(&sub_transaction);
}
else
{
  printf("Failed to create sub transaction: %s\n", cardano_error_to_string(result));
}

Parameters:¶

cardano_sub_transaction_body_t *body¶

[in] A pointer to an initialized cardano_sub_transaction_body_t object that represents the sub transaction body. This parameter is required and must not be NULL.

cardano_witness_set_t *witness_set¶

[in] A pointer to an initialized cardano_witness_set_t object that contains the witness data for the sub transaction. This parameter is required and must not be NULL.

cardano_auxiliary_data_t *auxiliary_data¶

[in] An optional pointer to a cardano_auxiliary_data_t object representing any auxiliary data associated with the sub transaction. This parameter can be NULL if no auxiliary data is provided.

cardano_sub_transaction_t **sub_transaction¶

[out] On successful creation, this will point to a newly created cardano_sub_transaction_t object. The caller is responsible for managing the lifecycle of this object. Specifically, once the sub transaction is no longer needed, the caller must release it by calling cardano_sub_transaction_unref.

Returns:¶

cardano_error_t indicating the outcome of the operation. Returns CARDANO_SUCCESS if the sub transaction was successfully created, or an appropriate error code indicating the failure reason, such as CARDANO_ERROR_POINTER_IS_NULL if required inputs (body or witness_set) are NULL.

cardano_error_t cardano_sub_transaction_from_cbor(cardano_cbor_reader_t *reader, cardano_sub_transaction_t **sub_transaction)¶

Creates a cardano_sub_transaction_t from a CBOR reader.

This function parses CBOR data using a provided cardano_cbor_reader_t and constructs a cardano_sub_transaction_t object. The CBOR data must be a three element array of the form [sub_transaction_body, transaction_witness_set, auxiliary_data / null]; arrays with any other number of elements are rejected.

Usage Example:

cardano_cbor_reader_t* reader = cardano_cbor_reader_new(cbor_data, data_size);
cardano_sub_transaction_t* sub_transaction = NULL;

cardano_error_t result = cardano_sub_transaction_from_cbor(reader, &sub_transaction);

if (result == CARDANO_SUCCESS)
{
  // Use the sub transaction

  // Once done, ensure to clean up and release the sub transaction
  cardano_sub_transaction_unref(&sub_transaction);
}
else
{
  const char* error = cardano_cbor_reader_get_last_error(reader);
  printf("Failed to decode sub transaction: %s\n", error);
}

cardano_cbor_reader_unref(&reader); // Cleanup the CBOR reader

Remark

In Cardano, transactions are encoded in CBOR, but CBOR allows multiple valid ways to encode the same data. The Cardano blockchain does not enforce a canonical transaction representation, meaning that if you decode a sub transaction from CBOR and then re-encode it, the resulting encoding could be different. This would change the sub transaction id and invalidate any existing signatures. To prevent this, when a sub transaction object is created using cardano_sub_transaction_from_cbor, it caches the original CBOR representation internally. When cardano_sub_transaction_to_cbor is called, it will output the cached CBOR. If the cached CBOR representation is not needed, the client can call cardano_sub_transaction_clear_cbor_cache after the object has been created.

Note

If the function fails, the last error can be retrieved by calling cardano_cbor_reader_get_last_error with the reader. The caller is responsible for freeing the created cardano_sub_transaction_t object by calling cardano_sub_transaction_unref when it is no longer needed.

Parameters:¶

cardano_cbor_reader_t *reader¶

[in] A pointer to an initialized cardano_cbor_reader_t that is ready to read the CBOR-encoded data.

cardano_sub_transaction_t **sub_transaction¶

[out] A pointer to a pointer of cardano_sub_transaction_t that will be set to the address of the newly created sub transaction object upon successful decoding.

Returns:¶

A cardano_error_t value indicating the outcome of the operation. Returns CARDANO_SUCCESS if the sub transaction was successfully created, or an appropriate error code if an error occurred.

cardano_error_t cardano_sub_transaction_to_cbor(const cardano_sub_transaction_t *sub_transaction, cardano_cbor_writer_t *writer)¶

Serializes a sub transaction into CBOR format using a CBOR writer.

This function serializes the given cardano_sub_transaction_t object using a cardano_cbor_writer_t. The sub transaction is written as a three element array of the form [sub_transaction_body, transaction_witness_set, auxiliary_data / null]. If the sub transaction has no auxiliary data, a CBOR null is written in its place.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...;
cardano_cbor_writer_t* writer = cardano_cbor_writer_new();

if (writer)
{
  cardano_error_t result = cardano_sub_transaction_to_cbor(sub_transaction, writer);

  if (result == CARDANO_SUCCESS)
  {
    // Use the writer's buffer containing the serialized data
  }
  else
  {
    const char* error_message = cardano_cbor_writer_get_last_error(writer);
    printf("Serialization failed: %s\n", error_message);
  }

  cardano_cbor_writer_unref(&writer);
}

cardano_sub_transaction_unref(&sub_transaction);

Remark

In Cardano, transactions are encoded in CBOR, but CBOR allows multiple valid ways to encode the same data. The Cardano blockchain does not enforce a canonical transaction representation, meaning that if you decode a sub transaction from CBOR and then re-encode it, the resulting encoding could be different. This would change the sub transaction id and invalidate any existing signatures. To prevent this, when a sub transaction object is created using cardano_sub_transaction_from_cbor, it caches the original CBOR representation internally. When cardano_sub_transaction_to_cbor is called, it will output the cached CBOR. If the cached CBOR representation is not needed, the client can call cardano_sub_transaction_clear_cbor_cache after the object has been created.

Parameters:¶

const cardano_sub_transaction_t *sub_transaction¶

[in] A constant pointer to the cardano_sub_transaction_t object that is to be serialized.

cardano_cbor_writer_t *writer¶

[out] A pointer to a cardano_cbor_writer_t where the CBOR serialized data will be written. The writer must already be initialized and ready to accept the data.

Returns:¶

Returns CARDANO_SUCCESS if the serialization is successful. If the sub_transaction or writer is NULL, returns CARDANO_ERROR_POINTER_IS_NULL.

cardano_sub_transaction_body_t *cardano_sub_transaction_get_body(cardano_sub_transaction_t *sub_transaction)¶

Retrieves the sub transaction body from a sub transaction object.

This function extracts the sub transaction body (cardano_sub_transaction_body_t) from a given cardano_sub_transaction_t object. The sub transaction body contains the essential elements of the sub transaction, such as inputs, outputs, and more.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is already initialized
cardano_sub_transaction_body_t* body = cardano_sub_transaction_get_body(sub_transaction);

if (body != NULL)
{
  // Use the sub transaction body

  // Clean up the body reference when done
  cardano_sub_transaction_body_unref(&body);
}
else
{
  printf("Failed to retrieve sub transaction body.\n");
}

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[in] A pointer to an initialized cardano_sub_transaction_t object.

Returns:¶

A pointer to the cardano_sub_transaction_body_t object representing the body of the sub transaction. The returned body is a new reference, and the caller is responsible for managing its lifecycle. Once the body is no longer needed, the caller must release it by calling cardano_sub_transaction_body_unref. If the input sub transaction pointer is NULL, this function returns NULL.

cardano_error_t cardano_sub_transaction_set_body(cardano_sub_transaction_t *sub_transaction, cardano_sub_transaction_body_t *body)¶

Sets the sub transaction body for a sub transaction.

This function allows replacing or setting the body for a given cardano_sub_transaction_t object. The sub transaction body encapsulates inputs, outputs, and other transaction-level data.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is already initialized
cardano_sub_transaction_body_t* new_body = ...; // Assume new_body is already initialized

cardano_error_t result = cardano_sub_transaction_set_body(sub_transaction, new_body);
if (result == CARDANO_SUCCESS)
{
  printf("Sub transaction body set successfully.\n");
}
else
{
  printf("Failed to set sub transaction body.\n");
}

Note

The reference count of the sub transaction body will be incremented by this function, so the caller retains ownership of the body object and is responsible for releasing it when it is no longer needed.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[inout] A pointer to an initialized cardano_sub_transaction_t object in which the body will be set.

cardano_sub_transaction_body_t *body¶

[in] A pointer to an initialized cardano_sub_transaction_body_t object representing the new sub transaction body.

Returns:¶

cardano_error_t indicating the outcome of the operation. Returns CARDANO_SUCCESS if the body was successfully set, or an appropriate error code such as CARDANO_ERROR_POINTER_IS_NULL if the sub transaction or body pointers are NULL.

cardano_witness_set_t *cardano_sub_transaction_get_witness_set(cardano_sub_transaction_t *sub_transaction)¶

Retrieves the witness set associated with a sub transaction.

This function returns the witness set from the given cardano_sub_transaction_t object. The witness set contains cryptographic signatures, public keys, and other necessary information required to verify the sub transaction.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume initialized
cardano_witness_set_t* witness_set = cardano_sub_transaction_get_witness_set(sub_transaction);

if (witness_set != NULL)
{
  // Use the witness set

  // Cleanup the witness set once done
  cardano_witness_set_unref(&witness_set);
}

Note

The returned witness set is a “strong reference” and must be unref’d by the caller once it’s no longer needed.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[in] A pointer to an initialized cardano_sub_transaction_t object.

Returns:¶

A pointer to a cardano_witness_set_t object representing the witness set. This function returns a new reference to the witness set, and the caller is responsible for managing its lifecycle by calling cardano_witness_set_unref when it is no longer needed.

cardano_error_t cardano_sub_transaction_set_witness_set(cardano_sub_transaction_t *sub_transaction, cardano_witness_set_t *witness_set)¶

Sets the witness set for a sub transaction.

This function assigns a witness set to the specified cardano_sub_transaction_t object. A witness set contains the cryptographic signatures and other witness data needed to validate the sub transaction on the Cardano blockchain.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is already initialized
cardano_witness_set_t* witness_set = ...; // Assume witness_set is already initialized

cardano_error_t result = cardano_sub_transaction_set_witness_set(sub_transaction, witness_set);
if (result == CARDANO_SUCCESS)
{
  printf("Witness set successfully added to the sub transaction.\n");
}
else
{
  printf("Failed to set witness set: %s\n", cardano_error_to_string(result));
}

// Clean up when no longer needed
cardano_witness_set_unref(&witness_set);
cardano_sub_transaction_unref(&sub_transaction);

Note

This function increases the reference count of the witness_set object, meaning the caller retains ownership of the witness set and must release it by calling cardano_witness_set_unref when it is no longer needed.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[inout] A pointer to an initialized cardano_sub_transaction_t object to which the witness set will be added. This parameter must not be NULL.

cardano_witness_set_t *witness_set¶

[in] A pointer to an initialized cardano_witness_set_t object representing the witness data. This parameter must not be NULL.

Returns:¶

cardano_error_t indicating the outcome of the operation. Returns CARDANO_SUCCESS if the witness set was successfully added to the sub transaction, or an appropriate error code if any of the input pointers (sub_transaction or witness_set) is NULL, such as CARDANO_ERROR_POINTER_IS_NULL.

cardano_auxiliary_data_t *cardano_sub_transaction_get_auxiliary_data(cardano_sub_transaction_t *sub_transaction)¶

Retrieves the auxiliary data from a sub transaction.

This function fetches the auxiliary data associated with a given cardano_sub_transaction_t object.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is already initialized
cardano_auxiliary_data_t* aux_data = cardano_sub_transaction_get_auxiliary_data(sub_transaction);

if (aux_data != NULL)
{
  // Process the auxiliary data
  cardano_auxiliary_data_unref(&aux_data); // Clean up when done
}
else
{
  printf("No auxiliary data found in the sub transaction.\n");
}

// Clean up the sub transaction when no longer needed
cardano_sub_transaction_unref(&sub_transaction);

Note

Auxiliary data is optional in a sub transaction and may not always be present. Therefore, it is important to check the return value for NULL before dereferencing it.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[in] A pointer to an initialized cardano_sub_transaction_t object. This parameter must not be NULL.

Returns:¶

A pointer to a cardano_auxiliary_data_t object representing the auxiliary data in the sub transaction. If the sub transaction does not contain auxiliary data, the function will return NULL. The returned object is a new reference, and the caller is responsible for managing its lifecycle. Specifically, the caller must release the object by calling cardano_auxiliary_data_unref when it is no longer needed.

cardano_error_t cardano_sub_transaction_set_auxiliary_data(cardano_sub_transaction_t *sub_transaction, cardano_auxiliary_data_t *auxiliary_data)¶

Sets the auxiliary data for a sub transaction.

This function assigns auxiliary data to the specified cardano_sub_transaction_t object. Auxiliary data typically contains additional metadata associated with the sub transaction.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is initialized
cardano_auxiliary_data_t* aux_data = ...; // Assume auxiliary_data is initialized

cardano_error_t result = cardano_sub_transaction_set_auxiliary_data(sub_transaction, aux_data);
if (result == CARDANO_SUCCESS)
{
  printf("Auxiliary data successfully set for the sub transaction.\n");
}
else
{
  printf("Failed to set auxiliary data: %s\n", cardano_error_to_string(result));
}

// Clean up resources
cardano_auxiliary_data_unref(&aux_data);
cardano_sub_transaction_unref(&sub_transaction);

Remark

A sub transaction without auxiliary data is serialized with a CBOR null in place of the auxiliary data element.

Note

This function increases the reference count of the auxiliary_data object. The caller retains ownership of the auxiliary data and must release it by calling cardano_auxiliary_data_unref when it is no longer needed.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[inout] A pointer to an initialized cardano_sub_transaction_t object where the auxiliary data will be set. This parameter must not be NULL.

cardano_auxiliary_data_t *auxiliary_data¶

[in] A pointer to an initialized cardano_auxiliary_data_t object representing the auxiliary data to be included in the sub transaction. This parameter can be NULL to unset the auxiliary data in the sub transaction.

Returns:¶

cardano_error_t indicating the outcome of the operation. Returns CARDANO_SUCCESS if the auxiliary data was successfully set. Returns CARDANO_ERROR_POINTER_IS_NULL if the sub_transaction is NULL.

cardano_blake2b_hash_t *cardano_sub_transaction_get_id(cardano_sub_transaction_t *sub_transaction)¶

Retrieves the sub transaction ID (hash) from a sub transaction.

This function computes and returns the unique identifier (ID) for the specified cardano_sub_transaction_t object. The sub transaction ID is the blake2b-256 hash of the sub transaction body, following the same convention as the top-level transaction ID.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is already initialized
cardano_blake2b_hash_t* sub_tx_id = cardano_sub_transaction_get_id(sub_transaction);

if (sub_tx_id != NULL)
{
  // Use the sub transaction ID for reference or verification

  // Clean up when done
  cardano_blake2b_hash_unref(&sub_tx_id);
}
else
{
  printf("Failed to retrieve the sub transaction ID.\n");
}

// Clean up resources
cardano_sub_transaction_unref(&sub_transaction);

Note

The sub transaction ID is the primary reference used to identify and track a sub transaction within its enclosing top-level transaction.

Note

The hash is computed on the first call and cached inside the sub transaction; subsequent calls return a new reference to the cached hash. The cache is invalidated by cardano_sub_transaction_set_body and cardano_sub_transaction_clear_cbor_cache.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[in] A pointer to an initialized cardano_sub_transaction_t object. This parameter must not be NULL.

Returns:¶

A pointer to a cardano_blake2b_hash_t object representing the sub transaction ID (hash). The returned object is a new reference, and the caller is responsible for managing its lifecycle. Specifically, the caller must release the object by calling cardano_blake2b_hash_unref when it is no longer needed. If the sub_transaction is NULL, the function returns NULL.

void cardano_sub_transaction_clear_cbor_cache(cardano_sub_transaction_t *sub_transaction)¶

Clears the cached CBOR representation from a sub transaction.

This function removes the internally cached CBOR data from a cardano_sub_transaction_t object. It is useful when you have modified the sub transaction after it was created from CBOR using cardano_sub_transaction_from_cbor and you want to ensure that the next serialization reflects the current state of the sub transaction, rather than using the original cached CBOR.

Usage Example:

// Assume sub_transaction was created using cardano_sub_transaction_from_cbor
cardano_sub_transaction_t* sub_transaction = ...;

// Modify the sub transaction as needed

// Clear the CBOR cache to ensure serialization uses the updated sub transaction
cardano_sub_transaction_clear_cbor_cache(sub_transaction);

// Serialize the sub transaction to CBOR
cardano_cbor_writer_t* writer = cardano_cbor_writer_new();

cardano_error_t result = cardano_sub_transaction_to_cbor(sub_transaction, writer);

if (result == CARDANO_SUCCESS)
{
  // Process the CBOR data as needed
}
else
{
  const char* error_message = cardano_cbor_writer_get_last_error(writer);
  printf("Serialization failed: %s\n", error_message);
}

// Clean up resources
cardano_cbor_writer_unref(&writer);
cardano_sub_transaction_unref(&sub_transaction);

Note

After calling this function, subsequent calls to cardano_sub_transaction_to_cbor will serialize the sub transaction using the standard encoding as defined in CIP-21, rather than reusing the original cached CBOR.

Warning

Clearing the CBOR cache may change the binary representation of the sub transaction when serialized, which can alter the sub transaction id and invalidate any existing signatures. Use this function with caution, especially if the sub transaction has already been signed or if preserving the exact CBOR encoding is important for your application.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[inout] A pointer to an initialized cardano_sub_transaction_t object from which the CBOR cache will be cleared.

void cardano_sub_transaction_unref(cardano_sub_transaction_t **sub_transaction)¶

Decrements the reference count of a cardano_sub_transaction_t object.

This function is responsible for managing the lifecycle of a cardano_sub_transaction_t object by decreasing its reference count. When the reference count reaches zero, the sub transaction is finalized; its associated resources are released, and its memory is deallocated.

Usage Example:

cardano_sub_transaction_t* sub_transaction = ...; // Assume sub transaction is already initialized

// Perform operations with the sub transaction...

cardano_sub_transaction_unref(&sub_transaction);
// At this point, sub_transaction is NULL and cannot be used.

Note

After calling cardano_sub_transaction_unref, the pointer to the cardano_sub_transaction_t object will be set to NULL to prevent its reuse.

Parameters:¶

cardano_sub_transaction_t **sub_transaction¶

[inout] A pointer to the pointer of the sub transaction object. This double indirection allows the function to set the caller’s pointer to NULL, avoiding dangling pointer issues after the object has been freed.

void cardano_sub_transaction_ref(cardano_sub_transaction_t *sub_transaction)¶

Increases the reference count of the cardano_sub_transaction_t object.

This function is used to manually increment the reference count of an cardano_sub_transaction_t object, indicating that another part of the code has taken ownership of it. This ensures the object remains allocated and valid until all owners have released their reference by calling cardano_sub_transaction_unref.

Usage Example:

// Assuming sub_transaction is a previously created sub transaction object

cardano_sub_transaction_ref(sub_transaction);

// Now sub_transaction can be safely used elsewhere without worrying about premature deallocation

Note

Always ensure that for every call to cardano_sub_transaction_ref there is a corresponding call to cardano_sub_transaction_unref to prevent memory leaks.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

A pointer to the cardano_sub_transaction_t object whose reference count is to be incremented.

size_t cardano_sub_transaction_refcount(const cardano_sub_transaction_t *sub_transaction)¶

Retrieves the current reference count of the cardano_sub_transaction_t object.

This function returns the number of active references to an cardano_sub_transaction_t object. It’s useful for debugging purposes or managing the lifecycle of the object in complex scenarios.

Usage Example:

// Assuming sub_transaction is a previously created sub transaction object

size_t ref_count = cardano_sub_transaction_refcount(sub_transaction);

printf("Reference count: %zu\n", ref_count);

Warning

This function does not account for transitive references. A transitive reference occurs when an object holds a reference to another object, rather than directly to the cardano_sub_transaction_t. As such, the reported count may not fully represent the total number of conceptual references in cases where such transitive relationships exist.

Parameters:¶

const cardano_sub_transaction_t *sub_transaction¶

A pointer to the cardano_sub_transaction_t object whose reference count is queried. The object must not be NULL.

Returns:¶

The number of active references to the specified cardano_sub_transaction_t object. If the object is properly managed (i.e., every cardano_sub_transaction_ref call is matched with a cardano_sub_transaction_unref call), this count should reach zero right before the object is deallocated.

void cardano_sub_transaction_set_last_error(cardano_sub_transaction_t *sub_transaction, const char *message)¶

Sets the last error message for a given cardano_sub_transaction_t object.

Records an error message in the sub transaction’s last_error buffer, overwriting any existing message. This is useful for storing descriptive error information that can be later retrieved. The message is truncated if it exceeds the buffer’s capacity.

Note

The error message is limited to 1023 characters, including the null terminator, due to the fixed size of the last_error buffer.

Parameters:¶

cardano_sub_transaction_t *sub_transaction¶

[in] A pointer to the cardano_sub_transaction_t instance whose last error message is to be set. If NULL, the function does nothing.

const char *message¶

[in] A null-terminated string containing the error message. If NULL, the sub transaction’s last_error is set to an empty string, indicating no error.

const char *cardano_sub_transaction_get_last_error(const cardano_sub_transaction_t *sub_transaction)¶

Retrieves the last error message recorded for a specific sub transaction.

This function returns a pointer to the null-terminated string containing the last error message set by cardano_sub_transaction_set_last_error for the given sub transaction. If no error message has been set, or if the last_error buffer was explicitly cleared, an empty string is returned, indicating no error.

Note

The returned string points to internal storage within the object and must not be modified by the caller. The string remains valid until the next call to cardano_sub_transaction_set_last_error for the same sub transaction, or until the sub transaction is deallocated.

Parameters:¶

const cardano_sub_transaction_t *sub_transaction¶

[in] A pointer to the cardano_sub_transaction_t instance whose last error message is to be retrieved. If the sub transaction is NULL, the function returns a generic error message indicating the null sub transaction.

Returns:¶

A pointer to a null-terminated string containing the last error message for the specified sub transaction. If the sub transaction is NULL, “Object is NULL.” is returned to indicate the error.