Anchor¶

typedef struct cardano_anchor_t cardano_anchor_t¶

An anchor is a pair of:

a URL to a JSON payload of metadata.
a hash of the contents of the metadata URL.

The on-chain rules will not check either the URL or the hash. Client applications should, however, perform the usual sanity checks when fetching content from the provided URL.

cardano_error_t cardano_anchor_new(const char *url, size_t url_size, const cardano_blake2b_hash_t *hash, cardano_anchor_t **anchor)¶

Creates and initializes a new instance of an anchor.

This function allocates and initializes a new instance of cardano_anchor_t, using the provided URL and associated hash. It returns an error code to indicate the success or failure of the operation.

Usage Example:

const char* url = "https://example.com/anchor";
size_t url_size = strlen(url);
cardano_blake2b_hash_t* hash = ...;  // Assume hash is initialized here
cardano_anchor_t* anchor = NULL;

// Attempt to create a new anchor
cardano_error_t result = cardano_anchor_new(url, url_size, hash, &anchor);

if (result == CARDANO_SUCCESS)
{
  // Use the anchor

  // Once done, ensure to clean up and release the anchor
  cardano_anchor_unref(&anchor);
}

cardano_blake2b_hash_unref(&hash);

Parameters:¶

const char *url¶: [in] A pointer to a character array containing the URL associated with the anchor.
size_t url_size¶: [in] The size of the URL character array in bytes.
const cardano_blake2b_hash_t *hash¶: [in] A pointer to cardano_blake2b_hash_t representing the hash associated with this anchor. The hash must be properly initialized before being passed to this function.
cardano_anchor_t **anchor¶: [out] On successful initialization, this will point to a newly created cardano_anchor_t object. This object represents a “strong reference” to the anchor, meaning that it is fully initialized and ready for use. The caller is responsible for managing the lifecycle of this object. Specifically, once the anchor is no longer needed, the caller must release it by calling cardano_anchor_unref.

Returns:¶

cardano_error_t indicating the outcome of the operation. Returns CARDANO_SUCCESS if the anchor was successfully created, or an appropriate error code indicating the failure reason.

cardano_error_t cardano_anchor_from_hash_hex(const char *url, size_t url_size, const char *hex, size_t hex_size, cardano_anchor_t **anchor)¶

Creates an anchor from a hexadecimal hash string.

This function constructs a cardano_anchor_t object by interpreting the provided hexadecimal string as a hash value. It returns an error code indicating the success or failure of the operation.

Usage Example:

const char* url = "https://example.com";
size_t url_size = strlen(url);
const char* hash_hex = "abcdef1234567890abcdef1234567890abcdef12...";
size_t hex_size = strlen(hash_hex);
cardano_anchor_t* anchor = NULL;

// Attempt to create a new anchor from a hexadecimal hash
cardano_error_t result = cardano_anchor_from_hash_hex(url, url_size, hash_hex, hex_size, &anchor);

if (result == CARDANO_SUCCESS)
{
  // Use the anchor

  // Once done, ensure to clean up and release the anchor
  cardano_anchor_unref(&anchor);
}

Parameters:¶

const char *url¶: [in] A pointer to a character array containing the URL associated with the anchor.
size_t url_size¶: [in] The size of the URL string in bytes.
const char *hex¶: [in] A pointer to a character array containing the hexadecimal representation of the hash.
size_t hex_size¶: [in] The size of the hexadecimal string in bytes.
cardano_anchor_t **anchor¶: [out] On successful initialization, this will point to a newly created cardano_anchor_t object. This object represents a “strong reference” to the anchor, meaning that it is fully initialized and ready for use. The caller is responsible for managing the lifecycle of this object, specifically, once the anchor is no longer needed, the caller must release it by calling cardano_anchor_unref.

Returns:¶

CARDANO_SUCCESS if the anchor was successfully created, or an appropriate error code indicating the reason for failure.

cardano_error_t cardano_anchor_from_hash_bytes(const char *url, size_t url_size, const byte_t *data, size_t data_size, cardano_anchor_t **anchor)¶

Creates an anchor from a byte array representing a hash.

This function constructs a cardano_anchor_t object by using the provided byte array as a hash value and associating it with a specified URL. It returns an error code indicating the success or failure of the operation.

Usage Example:

const char* url = "https://example.com";
size_t url_size = strlen(url);
const byte_t hash_data[] = { 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef ... };
size_t data_size = sizeof(hash_data);
cardano_anchor_t* anchor = NULL;

// Attempt to create a new anchor from byte array hash
cardano_error_t result = cardano_anchor_from_hash_bytes(url, url_size, hash_data, data_size, &anchor);

if (result == CARDANO_SUCCESS && anchor)
{
  // Use the anchor

  // Once done, ensure to clean up and release the anchor
  cardano_anchor_unref(&anchor);
}

Note

This function assumes that the byte array and URL are correctly formatted and valid. Malformed or incorrect input may lead to errors or undefined behavior.

Parameters:¶

const char *url¶: [in] A pointer to the character array containing the URL associated with the anchor.
size_t url_size¶: [in] The size of the URL string in bytes.
const byte_t *data¶: [in] A pointer to the byte array containing the hash data.
size_t data_size¶: [in] The size of the byte array in bytes.
cardano_anchor_t **anchor¶: [out] On successful initialization, this pointer is set to the newly created cardano_anchor_t object. This object represents a “strong reference” to the anchor, meaning that it is fully initialized and ready for use. The caller is responsible for managing the lifecycle of this object, specifically, once the anchor is no longer needed, the caller must release it by calling cardano_anchor_unref.

Returns:¶

CARDANO_SUCCESS if the anchor was successfully created, or an appropriate error code indicating the reason for failure.

cardano_error_t cardano_anchor_from_cbor(cardano_cbor_reader_t *reader, cardano_anchor_t **anchor)¶

Creates a anchor from a CBOR reader.

This function parses CBOR data using a provided cardano_cbor_reader_t and constructs a cardano_anchor_t object. It assumes that the CBOR reader is set up correctly and that the CBOR data corresponds to the structure expected for a anchor.

Usage Example:

cardano_cbor_reader_t* reader = cardano_cbor_reader_new(cbor_data, data_size);
cardano_anchor_t* anchor = NULL;

cardano_error_t result = cardano_anchor_from_cbor(reader, &anchor);

if (result == CARDANO_SUCCESS)
{
  // Use the anchor

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

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

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_anchor_t object by calling cardano_anchor_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 anchor data.
cardano_anchor_t **anchor¶: [out] A pointer to a pointer of cardano_anchor_t that will be set to the address of the newly created anchor object upon successful decoding.

Returns:¶

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

cardano_error_t cardano_anchor_to_cbor(const cardano_anchor_t *anchor, cardano_cbor_writer_t *writer)¶

Serializes a anchor into CBOR format using a CBOR writer.

This function serializes the given cardano_anchor_t object using a cardano_cbor_writer_t.

Usage Example:

cardano_anchor_t* anchor = ...;
cardano_cbor_writer_t* writer = cardano_cbor_writer_new();

if (writer)
{
  cardano_error_t result = cardano_anchor_to_cbor(anchor, 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_anchor_unref(&anchor);

Parameters:¶

const cardano_anchor_t *anchor¶: [in] A constant pointer to the cardano_anchor_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 anchor or writer is NULL, returns CARDANO_ERROR_POINTER_IS_NULL.

cardano_error_t cardano_anchor_to_cip116_json(const cardano_anchor_t *anchor, cardano_json_writer_t *writer)¶

Serializes an anchor to CIP-116 JSON.

The function writes the full JSON object, including the surrounding braces. Keys are written in the order: “url”, “data_hash”.

Parameters:¶

const cardano_anchor_t *anchor¶: [in] Pointer to a valid cardano_anchor_t.
cardano_json_writer_t *writer¶: [in] Pointer to a valid cardano_json_writer_t.

Returns:¶

CARDANO_SUCCESS On success. CARDANO_ERROR_POINTER_IS_NULL If anchor or writer is NULL. CARDANO_ERROR_MEMORY_ALLOCATION_FAILED If memory allocation fails. Other Any error propagated from nested writers.

cardano_blake2b_hash_t *cardano_anchor_get_hash(const cardano_anchor_t *anchor)¶

Retrieves the hash associated with a anchor.

This function provides access to the hash part of a cardano_anchor_t object. It returns a new reference to a cardano_blake2b_hash_t object representing the hash. This allows the hash to be used independently of the original anchor object. The reference count of the hash object is increased by one, making it the caller’s responsibility to release it by calling cardano_blake2b_hash_unref when it is no longer needed.

Usage Example:

cardano_anchor_t* original_anchor = cardano_anchor_new(...);
cardano_blake2b_hash_t* hash_anchor = cardano_anchor_get_hash(original_anchor);

if (hash_anchor)
{
  // Use the hash anchor

  // Once done, ensure to clean up and release the hash anchor
  cardano_blake2b_hash_unref(&hash_anchor);
}
// Release the original anchor after use
cardano_anchor_unref(&original_anchor);

Parameters:¶

const cardano_anchor_t *anchor¶: A constant pointer to the cardano_anchor_t object from which the hash is to be retrieved.

Returns:¶

A pointer to a new cardano_blake2b_hash_t object containing the hash. If the input anchor is NULL, returns NULL. The caller is responsible for managing the lifecycle of this object, including releasing it with cardano_blake2b_hash_unref.

size_t cardano_anchor_get_hash_bytes_size(const cardano_anchor_t *anchor)¶

Retrieves the size of the hash bytes stored in the anchor.

This function computes the size of the hash bytes stored within a cardano_anchor_t object. It is particularly useful for determining the buffer size needed to store the hash bytes when retrieving them via cardano_anchor_get_hash_bytes.

Usage Example:

cardano_anchor_t* anchor = cardano_anchor_new(...);
size_t hash_size = cardano_anchor_get_hash_bytes_size(anchor);

if (hash_size > 0)
{
  byte_t* hash_bytes = malloc(hash_size);
  if (hash_bytes)
  {
    // Proceed to get the hash bytes
  }
}
cardano_anchor_unref(&anchor);

Parameters:¶

const cardano_anchor_t *anchor¶: [in] A constant pointer to the cardano_anchor_t object from which the size of the hash bytes is to be retrieved.

Returns:¶

The size of the hash bytes. If the anchor is NULL the function returns zero.

const byte_t *cardano_anchor_get_hash_bytes(const cardano_anchor_t *anchor)¶

Retrieves the byte array representation of the hash from a anchor.

This function accesses the byte representation of the hash associated with a given cardano_anchor_t object. It provides a direct pointer to the internal byte array representing the hash, which should not be modified or freed by the caller.

Usage Example:

cardano_anchor_t* anchor = cardano_anchor_new(...);
const byte_t* hash_bytes = cardano_anchor_get_hash_bytes(anchor);

if (hash_bytes)
{
  // Use the hash bytes for operations like comparison or display
}

// Clean up the anchor object once done
cardano_anchor_unref(&anchor);

Parameters:¶

const cardano_anchor_t *anchor¶: A constant pointer to the cardano_anchor_t object from which the hash bytes are to be retrieved.

Returns:¶

A pointer to a constant byte array containing the hash data. If the input anchor is NULL, returns NULL. The data remains valid as long as the anchor object is not freed or modified.

size_t cardano_anchor_get_hash_hex_size(const cardano_anchor_t *anchor)¶

Retrieves the size needed for the hexadecimal string representation of the anchor’s hash.

This function calculates the size required to store the hexadecimal string representation of the hash associated with a cardano_anchor_t object. This size includes the space needed for the null-terminator.

Usage Example:

cardano_anchor_t* anchor = cardano_anchor_new(...);
size_t hex_size = cardano_anchor_get_hash_hex_size(anchor);
char* hex_string = malloc(hex_size);

if (hex_string)
{
  // Now use hex_string to get the hash or do other operations
  free(hex_string);
}

cardano_anchor_unref(&anchor);

Parameters:¶

const cardano_anchor_t *anchor¶: [in] A constant pointer to the cardano_anchor_t object whose hash size is to be determined.

Returns:¶

The size in bytes required to store the hexadecimal representation of the hash, including the null terminator.

const char *cardano_anchor_get_hash_hex(const cardano_anchor_t *anchor)¶

Retrieves the hexadecimal string representation of the hash from a anchor.

This function provides access to the hexadecimal (hex) string representation of the hash associated with a given cardano_anchor_t object. It returns a direct pointer to the internal hex string which should not be modified or freed by the caller.

Usage Example:

cardano_anchor_t* anchor = cardano_anchor_new(...);
const char* hash_hex = cardano_anchor_get_hash_hex(anchor);

if (hash_hex)
{
  // Use the hash hex for operations like logging, display, or comparison
}

// Clean up the anchor object once done
cardano_anchor_unref(&anchor);

Parameters:¶

const cardano_anchor_t *anchor¶: A constant pointer to the cardano_anchor_t object from which the hex string of the hash is to be retrieved. The object must not be NULL.

Returns:¶

A pointer to a constant character array containing the hex representation of the hash. If the input anchor is NULL, returns NULL. The data remains valid as long as the anchor object is not freed or modified.

size_t cardano_anchor_get_url_size(const cardano_anchor_t *anchor)¶

Retrieves the size of the URL string stored in the anchor.

This function calculates the size of the URL string, including the null terminator, associated with the provided cardano_anchor_t object. This size is necessary to allocate a buffer large enough to store the URL string.

Usage Example:

cardano_anchor_t* anchor = ...; // Assume this is initialized
size_t url_size = cardano_anchor_get_url_size(anchor);

if (url_size > 0)
{
  char* url = malloc(url_size); // Allocate space for the URL
  if (url)
  {
    // Further operations such as fetching the URL can be performed here
    free(url);
  }
}

Parameters:¶

const cardano_anchor_t *anchor¶: [in] A constant pointer to the cardano_anchor_t object from which the URL size is to be retrieved.

Returns:¶

The size in bytes of the URL string including the null terminator. If the anchor is NULL or if there is no URL assigned, returns 0.

const char *cardano_anchor_get_url(const cardano_anchor_t *anchor)¶

Retrieves the URL from an anchor.

This function returns the URL associated with a cardano_anchor_t object. The URL is returned as a pointer to a null-terminated string. This pointer points to internal memory managed by the anchor object, and therefore should not be modified or freed by the caller.

Usage Example:

cardano_anchor_t* anchor = ...; // Assume this is initialized
const char* url = cardano_anchor_get_url(anchor);

if (url)
{
  printf("Anchor URL: %s\n", url);
}
else
{
  printf("Failed to retrieve URL from anchor\n");
}

Parameters:¶

const cardano_anchor_t *anchor¶: [in] A constant pointer to the cardano_anchor_t object from which the URL is to be retrieved.

Returns:¶

A constant pointer to a null-terminated string containing the URL. If the anchor is NULL or if the anchor does not have a URL, returns NULL.

cardano_error_t cardano_anchor_set_url(cardano_anchor_t *anchor, const char *url, size_t url_size)¶

Sets the URL for an anchor.

This function assigns a new URL to an existing cardano_anchor_t object. The URL is specified as a character array and its size. The function copies the URL into the anchor object.

Usage Example:

cardano_anchor_t* anchor = ...;
const char* url = "https://example.com/new-anchor-url";
size_t url_size = strlen(url);

cardano_error_t result = cardano_anchor_set_url(anchor, url, url_size);

if (result == CARDANO_SUCCESS)
{
    // URL is successfully updated
}

cardano_anchor_unref(&anchor);

Parameters:¶

cardano_anchor_t *anchor¶: [inout] A pointer to the cardano_anchor_t object whose URL is to be set.
const char *url¶: [in] A pointer to a character array containing the new URL to be set for the anchor.
size_t url_size¶: [in] The size of the URL character array in bytes, excluding any null-terminator.

Returns:¶

CARDANO_SUCCESS if the URL was successfully set. Returns CARDANO_ERROR_POINTER_IS_NULL if any of the inputs are NULL, CARDANO_ERROR_INSUFFICIENT_BUFFER_SIZE if the URL size exceeds internal limits, or other error codes as appropriate for other failure reasons.

cardano_error_t cardano_anchor_set_hash(cardano_anchor_t *anchor, const cardano_blake2b_hash_t *hash)¶

Sets the hash for a anchor.

This function assigns a new hash to an existing cardano_anchor_t object. The hash represents the identifying data for the anchor.The function copies the provided hash into the anchor, so the original hash object may be modified or freed after this operation without affecting the anchor’s hash.

Usage Example:

cardano_anchor_t* anchor = ...;
cardano_blake2b_hash_t* new_hash = cardano_blake2b_compute_hash(...);

cardano_error_t result = cardano_anchor_set_hash(anchor, new_hash);

if (result == CARDANO_SUCCESS)
{
    // The hash was successfully set
}

// Clean up
cardano_anchor_unref(&anchor);
cardano_blake2b_hash_unref(&new_hash);

Parameters:¶

cardano_anchor_t *anchor¶: [inout] A pointer to the cardano_anchor_t object whose hash is to be set. This object must have been previously created and not yet freed.
const cardano_blake2b_hash_t *hash¶: [in] A pointer to a cardano_blake2b_hash_t object containing the new hash to be set. This parameter must not be NULL.

Returns:¶

A cardano_error_t value indicating the outcome of the operation. Returns CARDANO_SUCCESS if the hash was successfully set. If the anchor or hash is NULL, returns CARDANO_ERROR_POINTER_IS_NULL.

void cardano_anchor_unref(cardano_anchor_t **anchor)¶

Decrements the reference count of a anchor object.

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

Usage Example:

cardano_anchor_t* anchor = cardano_anchor_new();

// Perform operations with the anchor...

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

Note

After calling cardano_anchor_unref, the pointer to the cardano_anchor_t object will be set to NULL to prevent its reuse.

Parameters:¶

cardano_anchor_t **anchor¶: [inout] A pointer to the pointer of the anchor 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_anchor_ref(cardano_anchor_t *anchor)¶

Increases the reference count of the cardano_anchor_t object.

This function is used to manually increment the reference count of a anchor 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_anchor_unref.

Usage Example:

// Assuming anchor is a previously created anchor object

cardano_anchor_ref(anchor);

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

Note

Always ensure that for every call to cardano_anchor_ref there is a corresponding call to cardano_anchor_unref to prevent memory leaks.

Parameters:¶

cardano_anchor_t *anchor¶: A pointer to the anchor object whose reference count is to be incremented.

size_t cardano_anchor_refcount(const cardano_anchor_t *anchor)¶

Retrieves the current reference count of the cardano_anchor_t object.

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

Usage Example:

// Assuming anchor is a previously created anchor object

size_t ref_count = cardano_anchor_refcount(anchor);

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_anchor_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_anchor_t *anchor¶: A pointer to the anchor object whose reference count is queried. The object must not be NULL.

Returns:¶

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

void cardano_anchor_set_last_error(cardano_anchor_t *anchor, const char *message)¶

Sets the last error message for a given anchor object.

Records an error message in the anchor’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_anchor_t *anchor¶: [in] A pointer to the cardano_anchor_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 anchor’s last_error is set to an empty string, indicating no error.

const char *cardano_anchor_get_last_error(const cardano_anchor_t *anchor)¶

Retrieves the last error message recorded for a specific anchor.

This function returns a pointer to the null-terminated string containing the last error message set by cardano_anchor_set_last_error for the given anchor. 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_anchor_set_last_error for the same anchor, or until the anchor is deallocated.

Parameters:¶

const cardano_anchor_t *anchor¶: [in] A pointer to the cardano_anchor_t instance whose last error message is to be retrieved. If the anchor is NULL, the function returns a generic error message indicating the null anchor.

Returns:¶

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