Adding a new constructor

Implementing a new constructor on the struct helps you enforce all invariants, length checks, zero-padding, and the discriminator before the account ever touches chain storage.

Start by validating inputs. The slice you receive for description can be any length, so check it before you allocate. If the caller tries to pass more than MAX_DESC_LEN bytes, return ProgramError::InvalidInstructionData; failing early protects the program from buffer overruns and wasted compute.

Next, pad the description to a constant-size buffer. Allocate a zero-filled [u8; MAX_DESC_LEN], then copy the caller’s bytes into the front of that array. This single copy satisfies two invariants: the array’s length never changes, which keeps the account’s on-chain size fixed, and the unused bytes remain deterministic zeros, which helps later diff-based audits.

With validation and padding complete, build the struct. Like so:

src/poll.rs

impl Poll {
    pub const SIZE: usize = {...};

    pub fn new(
        creator: Pubkey,
        start_slot: u64,
        end_slot: u64,
        description: &[u8],
        options_cnt: u8,
    ) -> Result<Self, ProgramError> {
        let description_len = description.len();

        if description_len > MAX_DESC_LEN {
            return Err(ProgramError::InvalidInstructionData);
        }

        // Allocate a zero-filled array whose size never changes
        let mut padded_description = [0u8; MAX_DESC_LEN];

        //Copy the user-supplied bytes into the front of that array
        padded_description[..description_len].copy_from_slice(description);

        Ok(Self {
            discriminator: POLL_DISCRIMINATOR,
            poll_creator: creator,
            desc_len: description_len as u8,
            poll_description: padded_description,
            start_slot,
            end_slot,
            poll_stage: PollStage::Open,
            options_count: options_cnt,
        })
    }

    pub fn assert_valid(&self) -> Result<(), ProgramError> {...}
}

Repeat the formula for PollOption and VoteRecord. With these constructors in place, every account your program touches is type-safe and size-accurate.

Adding a new constructor

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