How to change account size

use {
  crate::{
      instruction::WhitelistInstruction,
      state::WhiteListData,
  },
  borsh::{BorshDeserialize, BorshSerialize},
  solana_program::{
      account_info::{next_account_info, AccountInfo},
      entrypoint::ProgramResult,
      msg,
      program::invoke_signed,
      program::invoke,
      program_error::ProgramError,
      pubkey::Pubkey,
      sysvar::Sysvar,
      sysvar::rent::Rent,
      system_instruction,
  },
  std::convert::TryInto,
};
 
pub fn process_instruction(
  _program_id: &Pubkey,
  accounts: &[AccountInfo],
  input: &[u8],
) -> ProgramResult {
  // Length = BOOL + VEC + Pubkey * n (n = number of keys)
  const INITIAL_ACCOUNT_LEN: usize = 1 + 4 + 0 ;
  msg!("input: {:?}", input);
 
  let instruction = WhitelistInstruction::try_from_slice(input)?;
 
  let accounts_iter = &mut accounts.iter();
 
  let funding_account = next_account_info(accounts_iter)?;
  let pda_account = next_account_info(accounts_iter)?;
  let system_program = next_account_info(accounts_iter)?;
 
  match instruction {
    WhitelistInstruction::Initialize => {
      msg!("Initialize");
 
      let (pda, pda_bump) = Pubkey::find_program_address(
          &[
            b"customaddress",
            &funding_account.key.to_bytes(),
          ],
          _program_id,
      );
 
      let signers_seeds: &[&[u8]; 3] = &[
          b"customaddress",
          &funding_account.key.to_bytes(),
          &[pda_bump],
      ];
 
      if pda.ne(&pda_account.key) {
          return Err(ProgramError::InvalidAccountData);
      }
 
      let lamports_required = Rent::get()?.minimum_balance(INITIAL_ACCOUNT_LEN);
      let create_pda_account_ix = system_instruction::create_account(
          &funding_account.key,
          &pda_account.key,
          lamports_required,
          INITIAL_ACCOUNT_LEN.try_into().unwrap(),
          &_program_id,
      );
 
      invoke_signed(
          &create_pda_account_ix,
          &[
              funding_account.clone(),
              pda_account.clone(),
              system_program.clone(),
          ],
          &[signers_seeds],
      )?;
 
      let mut pda_account_state = WhiteListData::try_from_slice(&pda_account.data.borrow())?;
 
      pda_account_state.is_initialized = true;
      pda_account_state.white_list = Vec::new();
      pda_account_state.serialize(&mut &mut pda_account.data.borrow_mut()[..])?;
      Ok(())
    }
    WhitelistInstruction::AddKey { key } => {
      msg!("AddKey");
 
      let mut pda_account_state = WhiteListData::try_from_slice(&pda_account.data.borrow())?;
 
      if !pda_account_state.is_initialized {
          return Err(ProgramError::InvalidAccountData);
      }
 
      let new_size = pda_account.data.borrow().len() + 32;
 
      let rent = Rent::get()?;
      let new_minimum_balance = rent.minimum_balance(new_size);
 
      let lamports_diff = new_minimum_balance.saturating_sub(pda_account.lamports());
      invoke(
          &system_instruction::transfer(funding_account.key, pda_account.key, lamports_diff),
          &[
              funding_account.clone(),
              pda_account.clone(),
              system_program.clone(),
          ],
      )?;
 
      pda_account.realloc(new_size, false)?;
 
      pda_account_state.white_list.push(key);
      pda_account_state.serialize(&mut &mut pda_account.data.borrow_mut()[..])?;
 
      Ok(())
    }
  }
}