Function decrypt_block 

pub fn decrypt_block<P, AccountId, IvkTag>(
    params: &P,
    block: Block,
    scanning_keys: &ScanningKeys<AccountId, IvkTag>,
) -> (BlockHeader, Vec<BatchResult<IvkTag>>)
where
    P: Parameters + Send + 'static,
    IvkTag: Copy + Send + 'static,

Decrypts a block with a set of ScanningKeys.

This is an inline, synchronous alternative to the batch decryption engine in the sync::decryptor module (available behind the sync-decryptor feature flag): it internally spins up batch runners to process the block, and discards them afterwards.

This is the first half of block scanning. Pass the result to scan_block for the second half.