Anchor Realloc PDA

Question

I am trying to write a program that: a) Creates an account (state) if one does not already exist b) Reallocs as needed for changed state

Error

Error: Account allocation failed: RPC response error -32002: Transaction simulation failed: This account may not be used to pay transaction fees
There was a problem deploying: Output { status: ExitStatus(unix_wait_status(256)), stdout: "", stderr: "" }.

Code

#[program]
pub mod todo {
    use super::*;

    pub fn create_and_realloc(ctx: Context<CreateAndRealloc>, replacing_tasks: Vec<Task>) -> Result<()> {
        let tasks = &mut ctx.accounts.tasks;

        // If length of tasks is not equal to the length of replacing_tasks, then
        // reallocate the tasks account.
        if tasks.0.len() != replacing_tasks.len() {
            let new_len = 8 + Task::INIT_SPACE * replacing_tasks.len();

            let rent = Rent::get()?;
            let new_minimum_balance = rent.minimum_balance(new_len);

            let tasks_account_info = tasks.to_account_info();

            let user = &ctx.accounts.user;
            let system_program = ctx.accounts.system_program.to_account_info();

            let lamports_diff = new_minimum_balance.saturating_sub(tasks_account_info.lamports());

            // The below commented-out has the same error.
            // anchor_lang::solana_program::program::invoke_signed(
            //     &anchor_lang::solana_program::system_instruction::transfer(
            //         user.key,
            //         tasks_account_info.key,
            //         lamports_diff,
            //     ),
            //     &[
            //         user.to_account_info().clone(),
            //         tasks_account_info.clone(),
            //         system_program.clone(),
            //     ],
            //     &[&[b"tasks"]],
            // )?;

            let cpi_context = CpiContext::new(
                system_program,
                anchor_lang::system_program::Transfer {
                    from: user.to_account_info().clone(),
                    to: tasks_account_info.clone(),
                },
            );
            anchor_lang::system_program::transfer(cpi_context, lamports_diff)?;

            tasks_account_info.realloc(new_len, true)?;
        }

        tasks.0 = replacing_tasks;

        Ok(())
    }
}

#[derive(Accounts)]
#[instruction(replacing_tasks: Vec<Task>)]
pub struct CreateAndRealloc<'info> {
    #[account(init_if_needed, space = 8 + replacing_tasks.len() * Task::INIT_SPACE, payer = user, seeds = [b"tasks"], bump)]
    pub tasks: Account<'info, Tasks>,
    #[account(mut)]
    pub user: Signer<'info>,
    pub system_program: Program<'info, System>,
}

#[account]
#[derive(Debug)]
pub struct Tasks(Vec<Task>);

#[derive(Debug, AnchorSerialize, AnchorDeserialize, Clone, InitSpace)]
pub struct Task {
    pub id: u32,
    /// The name of the task truncated to 32 characters.
    #[max_len(32)]
    pub name: String,
    pub completed: bool,
}

What I originally wanted to do was mark the tasks PDA as init_if_needed, mut, and realloc, but those are incompatible.

---

Question

How can one (within one instruction handler) init a PDA if needed, transfer lamports to the account, and realloc its size?

Answer 1

i think what you are looking for is this:

#[derive(Accounts)]
#[instruction(len: u16)]
pub struct IncreaseAccoutSize<'info> {

#[account(mut, 
    realloc = len as usize, 
    realloc::zero = true, 
    realloc::payer=signer)]
    pub data_holder: Account<'info, DataHolderNoZeroCopy>,
    #[account(mut)]
    pub signer: Signer<'info>,
    #[account(address = system_program::ID)]
    pub system_program: Program<'info, System>,
}

Here is an example with different ways to work with big accounts: https://github.com/solana-developers/anchor-zero-copy-example/blob/main/programs/zero-copy/src/lib.rs

The error you are getting indicates that you are using a PDA where there should be a system program account. Try substracting and adding lamports like here: beta.solpg.io/tutorials/tiny-adventure-two line 60

Answer 2

Turns out the issue was not restarting the test validator with --reset. All of the following work:

// 1 - Explicit CPI
let cpi_context = CpiContext::new(
    system_program,
    anchor_lang::system_program::Transfer {
        from: user.to_account_info().clone(),
        to: tasks_account_info.clone(),
    },
);
anchor_lang::system_program::transfer(cpi_context, lamports_diff)?;
// 2 - invoke
anchor_lang::solana_program::program::invoke(
    &anchor_lang::solana_program::system_instruction::transfer(
        user.key,
        tasks_account_info.key,
        lamports_diff,
    ),
    &[
        user.to_account_info().clone(),
        tasks_account_info.clone(),
        system_program.clone(),
    ],
)?;
// 3 - Lamport mutation
let lamports_diff = new_minimum_balance.saturating_sub(tasks_account_info.lamports());
**ctx
    .accounts
    .user
    .to_account_info()
    .try_borrow_mut_lamports()? -= lamports_diff;
**tasks_account_info.try_borrow_mut_lamports()? += lamports_diff;

---

I found this out because after changing my test to use skipPreflight: true, the same error appeared, and it did not even try to run the instruction.