Module sc_light::fetcher::cht

Canonical hash trie definitions and helper functions.

Each CHT is a trie mapping block numbers to canonical hash. One is generated for every SIZE blocks, allowing us to discard those blocks in favor of the trie root. When the “ancient” blocks need to be accessed, we simply request an inclusion proof of a specific block number against the trie with the root hash. A correct proof implies that the claimed block is identical to the one we discarded.

Functions

block_to_cht_number

Convert a block number to a CHT number. Returns None for block_num == 0, Some otherwise.

build_proof

Build CHT-based header proof.

check_proof

Check CHT-based header proof.

check_proof_on_proving_backend

Check CHT-based header proof on pre-created proving backend.

compute_root

Compute a CHT root from an iterator of block hashes. Fails if shorter than SIZE items. The items are assumed to proceed sequentially from start_number(cht_num). Discards the trie’s nodes.

decode_cht_value

Convert CHT value into block header hash.

encode_cht_key

Convert header number into CHT key.

end_number

Get the ending block of a given CHT.

for_each_cht_group

Group ordered blocks by CHT number and call functor with blocks of each group.

is_build_required

Returns Some(cht_number) if CHT is need to be built when the block with given number is canonized.

max_cht_number

Returns Some(max_cht_number) if CHT has ever been built given maximal canonical block number.

size

Gets default CHT size.

start_number

Get the starting block of a given CHT. CHT 0 includes block 1…SIZE, CHT 1 includes block SIZE + 1 … 2SIZE More generally: CHT N includes block (1 + NSIZE)…((N+1)*SIZE). This is because the genesis hash is assumed to be known and including it would be redundant.