Trait sc_client_api::backend::Backend

pub trait Backend<Block: BlockT>: AuxStore + Send + Sync {
    type BlockImportOperation: BlockImportOperation<Block, State = Self::State>;
    type Blockchain: BlockchainBackend<Block>;
    type State: StateBackend<HashFor<Block>> + Send + AsTrieBackend<HashFor<Block>, TrieBackendStorage = <Self::State as StateBackend<HashFor<Block>>>::TrieBackendStorage>;
    type OffchainStorage: OffchainStorage;

    // Required methods
    fn begin_operation(&self) -> Result<Self::BlockImportOperation>;
    fn begin_state_operation(
        &self,
        operation: &mut Self::BlockImportOperation,
        block: Block::Hash
    ) -> Result<()>;
    fn commit_operation(
        &self,
        transaction: Self::BlockImportOperation
    ) -> Result<()>;
    fn finalize_block(
        &self,
        hash: Block::Hash,
        justification: Option<Justification>
    ) -> Result<()>;
    fn append_justification(
        &self,
        hash: Block::Hash,
        justification: Justification
    ) -> Result<()>;
    fn blockchain(&self) -> &Self::Blockchain;
    fn usage_info(&self) -> Option<UsageInfo>;
    fn offchain_storage(&self) -> Option<Self::OffchainStorage>;
    fn pin_block(&self, hash: Block::Hash) -> Result<()>;
    fn unpin_block(&self, hash: Block::Hash);
    fn state_at(&self, hash: Block::Hash) -> Result<Self::State>;
    fn revert(
        &self,
        n: NumberFor<Block>,
        revert_finalized: bool
    ) -> Result<(NumberFor<Block>, HashSet<Block::Hash>)>;
    fn remove_leaf_block(&self, hash: Block::Hash) -> Result<()>;
    fn get_import_lock(&self) -> &RwLock<()>;
    fn requires_full_sync(&self) -> bool;

    // Provided methods
    fn have_state_at(&self, hash: Block::Hash, _number: NumberFor<Block>) -> bool { ... }
    fn insert_aux<'a, 'b: 'a, 'c: 'a, I: IntoIterator<Item = &'a (&'c [u8], &'c [u8])>, D: IntoIterator<Item = &'a &'b [u8]>>(
        &self,
        insert: I,
        delete: D
    ) -> Result<()> { ... }
    fn get_aux(&self, key: &[u8]) -> Result<Option<Vec<u8>>> { ... }
}

Client backend.

Manages the data layer.

State Pruning

While an object from state_at is alive, the state should not be pruned. The backend should internally reference-count its state objects.

The same applies for live BlockImportOperations: while an import operation building on a parent P is alive, the state for P should not be pruned.

Block Pruning

Users can pin blocks in memory by calling pin_block. When a block would be pruned, its value is kept in an in-memory cache until it is unpinned via unpin_block.

While a block is pinned, its state is also preserved.

The backend should internally reference count the number of pin / unpin calls.

Required Associated Types

type BlockImportOperation: BlockImportOperation<Block, State = Self::State>

Associated block insertion operation type.

type Blockchain: BlockchainBackend<Block>

Associated blockchain backend type.

type State: StateBackend<HashFor<Block>> + Send + AsTrieBackend<HashFor<Block>, TrieBackendStorage = <Self::State as StateBackend<HashFor<Block>>>::TrieBackendStorage>

Associated state backend type.

type OffchainStorage: OffchainStorage

Offchain workers local storage.

Required Methods

fn begin_operation(&self) -> Result<Self::BlockImportOperation>

Begin a new block insertion transaction with given parent block id.

When constructing the genesis, this is called with all-zero hash.

fn begin_state_operation( &self, operation: &mut Self::BlockImportOperation, block: Block::Hash ) -> Result<()>

Note an operation to contain state transition.

fn commit_operation(&self, transaction: Self::BlockImportOperation) -> Result<()>

Commit block insertion.

fn finalize_block( &self, hash: Block::Hash, justification: Option<Justification> ) -> Result<()>

Finalize block with given hash.

This should only be called if the parent of the given block has been finalized.

fn append_justification( &self, hash: Block::Hash, justification: Justification ) -> Result<()>

Append justification to the block with the given hash.

This should only be called for blocks that are already finalized.

fn blockchain(&self) -> &Self::Blockchain

Returns reference to blockchain backend.

fn usage_info(&self) -> Option<UsageInfo>

Returns current usage statistics.

fn offchain_storage(&self) -> Option<Self::OffchainStorage>

Returns a handle to offchain storage.

fn pin_block(&self, hash: Block::Hash) -> Result<()>

Pin the block to keep body, justification and state available after pruning. Number of pins are reference counted. Users need to make sure to perform one call to Self::unpin_block per call to Self::pin_block.

fn unpin_block(&self, hash: Block::Hash)

Unpin the block to allow pruning.

fn state_at(&self, hash: Block::Hash) -> Result<Self::State>

Returns state backend with post-state of given block.

fn revert( &self, n: NumberFor<Block>, revert_finalized: bool ) -> Result<(NumberFor<Block>, HashSet<Block::Hash>)>

Attempts to revert the chain by n blocks. If revert_finalized is set it will attempt to revert past any finalized block, this is unsafe and can potentially leave the node in an inconsistent state. All blocks higher than the best block are also reverted and not counting towards n.

Returns the number of blocks that were successfully reverted and the list of finalized blocks that has been reverted.

fn remove_leaf_block(&self, hash: Block::Hash) -> Result<()>

Discard non-best, unfinalized leaf block.

fn get_import_lock(&self) -> &RwLock<()>

Gain access to the import lock around this backend.

Note Backend isn’t expected to acquire the lock by itself ever. Rather the using components should acquire and hold the lock whenever they do something that the import of a block would interfere with, e.g. importing a new block or calculating the best head.

fn requires_full_sync(&self) -> bool

Tells whether the backend requires full-sync mode.

Provided Methods

fn have_state_at(&self, hash: Block::Hash, _number: NumberFor<Block>) -> bool

Returns true if state for given block is available.

fn insert_aux<'a, 'b: 'a, 'c: 'a, I: IntoIterator<Item = &'a (&'c [u8], &'c [u8])>, D: IntoIterator<Item = &'a &'b [u8]>>( &self, insert: I, delete: D ) -> Result<()>

Insert auxiliary data into key-value store.

fn get_aux(&self, key: &[u8]) -> Result<Option<Vec<u8>>>

Query auxiliary data from key-value store.

Implementors

impl<Block: BlockT> Backend<Block> for Backend<Block>where Block::Hash: Ord,

type BlockImportOperation = BlockImportOperation<Block>

type Blockchain = Blockchain<Block>

type State = TrieBackend<MemoryDB<<<Block as Block>::Header as Header>::Hashing, HashKey<<<Block as Block>::Header as Header>::Hashing>, Vec<u8, Global>>, <<Block as Block>::Header as Header>::Hashing, LocalTrieCache<<<Block as Block>::Header as Header>::Hashing>>

type OffchainStorage = InMemOffchainStorage