How do you calculate the canopy length for the Merkle tree account?

Question

Keep getting CanopyLengthMismatch error

How do you calculate the canopy length?

Answer 1

The canopy length will be 32 * the canopy size you want.

A tree of depth 14 and a canopy size of 7 will mean you need to allocate 7*32 bytes more to the account.

The number 32 is the size of each node of the tree.

Answer 2

The canopy length is the number of levels, from the max_depth, you want to cache. Get it's size by multiplying the canopy levels by 32.

// calculate additional bytes to pass by multiplying the number of levels by 32
let canopy_size = canopy_levels * 32;

// calculate merkle tree account size by passing canopy_size as additional bytes
let merkle_tree_account_size: usize =
        CONCURRENT_MERKLE_TREE_HEADER_SIZE_V1 + merkle_tree_account_size + canopy_size as usize;

// create account 
let merkle_tree_account = system_instruction::create_account(
        &input.payer.pubkey(),
        &input.merkle_tree.pubkey(),
        lamports,
        u64::try_from(merkle_tree_account_size).unwrap(),
        &spl_account_compression::id(),
    );

Source: https://github.com/solana-labs/solana-program-library/blob/45764e6737cc7101fad13708ed76e13d8827aa8f/account-compression/programs/account-compression/src/canopy.rs#LL28C24-L28C24