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Trie API

Here we provide a specification of trie API. After this NEP is merged, the cases where our current implementation does not follow the specification are considered to be bugs that need to be fixed.

storage_write(key_len: u64, key_ptr: u64, value_len: u64, value_ptr: u64, register_id: u64) -> u64

Writes key-value into storage.

Normal operation​
  • If key is not in use it inserts the key-value pair and does not modify the register;
  • If key is in use it inserts the key-value and copies the old value into the register_id.
Returns​
  • If key was not used returns 0;
  • If key was used returns 1.
Panics​
  • If key_len + key_ptr or value_len + value_ptr exceeds the memory container or points to an unused register it panics with MemoryAccessViolation. (When we say that something panics with the given error we mean that we use Wasmer API to create this error and terminate the execution of VM. For mocks of the host that would only cause a non-name panic.)
  • If returning the preempted value into the registers exceed the memory container it panics with MemoryAccessViolation;
Current bugs​
  • External::storage_set trait can return an error which is then converted to a generic non-descriptive StorageUpdateError, here however the actual implementation does not return error at all, see;
  • Does not return into the registers.
storage_read(key_len: u64, key_ptr: u64, register_id: u64) -> u64

Reads the value stored under the given key.

Normal operation​
  • If key is used copies the content of the value into the register_id, even if the content is zero bytes;
  • If key is not present then does not modify the register.
Returns​
  • If key was not present returns 0;
  • If key was present returns 1.
Panics​
  • If key_len + key_ptr exceeds the memory container or points to an unused register it panics with MemoryAccessViolation;
  • If returning the preempted value into the registers exceed the memory container it panics with MemoryAccessViolation;
Current bugs​
  • This function currently does not exist.
storage_remove(key_len: u64, key_ptr: u64, register_id: u64) -> u64

Removes the value stored under the given key.

Normal operation​

Very similar to storage_read:

  • If key is used, removes the key-value from the trie and copies the content of the value into the register_id, even if the content is zero bytes.
  • If key is not present then does not modify the register.
Returns​
  • If key was not present returns 0;
  • If key was present returns 1.
Panics​
  • If key_len + key_ptr exceeds the memory container or points to an unused register it panics with MemoryAccessViolation;
  • If the registers exceed the memory limit panics with MemoryAccessViolation;
  • If returning the preempted value into the registers exceed the memory container it panics with MemoryAccessViolation;
Current bugs​
  • Does not return into the registers.
storage_has_key(key_len: u64, key_ptr: u64) -> u64

Checks if there is a key-value pair.

Normal operation​
  • If key is used returns 1, even if the value is zero bytes;
  • Otherwise returns 0.
Panics​
  • If key_len + key_ptr exceeds the memory container it panics with MemoryAccessViolation;
storage_iter_prefix(prefix_len: u64, prefix_ptr: u64) -> u64

DEPRECATED, calling it will result result in HostError::Deprecated error. Creates an iterator object inside the host. Returns the identifier that uniquely differentiates the given iterator from other iterators that can be simultaneously created.

Normal operation​
  • It iterates over the keys that have the provided prefix. The order of iteration is defined by the lexicographic order of the bytes in the keys. If there are no keys, it creates an empty iterator, see below on empty iterators;
Panics​
  • If prefix_len + prefix_ptr exceeds the memory container it panics with MemoryAccessViolation;
storage_iter_range(start_len: u64, start_ptr: u64, end_len: u64, end_ptr: u64) -> u64

DEPRECATED, calling it will result result in HostError::Deprecated error. Similarly to storage_iter_prefix creates an iterator object inside the host.

Normal operation​

Unless lexicographically start < end, it creates an empty iterator. Iterates over all key-values such that keys are between start and end, where start is inclusive and end is exclusive.

Note, this definition allows for start or end keys to not actually exist on the given trie.

Panics:​
  • If start_len + start_ptr or end_len + end_ptr exceeds the memory container or points to an unused register it panics with MemoryAccessViolation;
storage_iter_next(iterator_id: u64, key_register_id: u64, value_register_id: u64) -> u64

DEPRECATED, calling it will result result in HostError::Deprecated error. Advances iterator and saves the next key and value in the register.

Normal operation​
  • If iterator is not empty (after calling next it points to a key-value), copies the key into key_register_id and value into value_register_id and returns 1;
  • If iterator is empty returns 0.

This allows us to iterate over the keys that have zero bytes stored in values.

Panics​
  • If key_register_id == value_register_id panics with MemoryAccessViolation;
  • If the registers exceed the memory limit panics with MemoryAccessViolation;
  • If iterator_id does not correspond to an existing iterator panics with InvalidIteratorId
  • If between the creation of the iterator and calling storage_iter_next any modification to storage was done through storage_write or storage_remove the iterator is invalidated and the error message is IteratorWasInvalidated.
Current bugs​
  • Not implemented, currently we have storage_iter_next and data_read + DATA_TYPE_STORAGE_ITER that together fulfill the purpose, but have unspecified behavior.