Solana PDA

• tags: Solana, Solana 101: 2. Anchor

What is Program Derived Address(PDA)?¹

A Program Derived Address is simply an account owned by the program, but has no private key. Instead it’s signature is obtained by a set of seeds and a bump (a nonce which makes sure it’s off curve). “Generating” a Program Address is different from “creating” it.

• Generating One can generate a PDA using Pubkey::find_program_address in Rust or PublicKey.findProgramAddressSync in JavaScript;
• Creating a PDA essentially means to initialize the address with space and set the state to it.

#+end_quote

How to Generate a PDA?

In frontend by using @solana/web3.js:

import * as web3 from "@solana/web3.js";
import { Buffer } from 'buffer';

const keypair = await connectWallet();
const programId = "Cj9VjDrohXuz914FNbaTMmEqYXkLkJKZn9FCq4UGGGwr";
const [pda, dump] = web3.PublicKey.findProgramAddressSync(
  [
    Buffer.from("seed1"),
    keypair.publicKey,
  ],
  new web3.PublicKey(programId),
);

Summary:

1. Seeds can be used to distinguish different purpose of PDA for one program;
2. Multipe items of bump shall be returned, but the first dump is called “canonical bump”;
3. bump is needed when to use PDA sign tx on chain via program.

How the PDA be Created By a Program?²

1. Change the owner of PDA to the specific program by AccountInfo.assign;
2. Transfer some lamports from funding account to the PDA to pay the rent;
3. Allocate data space by AccountInfo.realloc.

   // Assessing required lamports and creating transaction instruction
      let lamports_required = Rent::get()?.minimum_balance(ACCOUNT_DATA_LEN);
      let create_pda_account_ix = system_instruction::create_account(
          &funding_account.key,
          &pda_account.key,
          lamports_required,
          ACCOUNT_DATA_LEN.try_into().unwrap(),
          &program_id,
      );
      // Invoking the instruction but with PDAs as additional signer
      invoke_signed(
          &create_pda_account_ix,
          &[
              funding_account.clone(),
              pda_account.clone(),
              system_program.clone(),
          ],
          &[signers_seeds],
      )?;
   

How the PDA be Created By anchor?³

By using #[account(init)] macro attribute:

#[account]
pub struct UserStats {
    level: u16,
    name: String,
    bump: u8,
}

// validation struct
#[derive(Accounts)]
pub struct CreateUserStats<'info> {
    #[account(mut)]
    pub user: Signer<'info>,
    // space: 8 discriminator + 2 level + 4 name length + 200 name + 1 bump
    #[account(
        init,
        payer = user,
        space = 8 + 2 + 4 + 200 + 1, seeds = [b"user-stats", user.key().as_ref()], bump
    )]
    pub user_stats: Account<'info, UserStats>,
    pub system_program: Program<'info, System>,
}