TIER 1 · THE ACCOUNT MODEL · 3-type-cosplay

TYPE COSPLAY

Two account structs with identical layout but different meaning. Pass account B where A is expected: fields reinterpreted, authority fields become balances. Anchor fixes this with the 8-byte discriminator — raw Solana programs must roll their own.

seen in the wild

The reason Anchor prepends a type discriminator to every account — without it, bytes are just bytes.

rust · anchor

use anchor_lang::prelude::*;
use borsh::{BorshDeserialize, BorshSerialize};

declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");

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

    pub fn update_user(ctx: Context<UpdateUser>) -> ProgramResult {
        let user = User::try_from_slice(&ctx.accounts.user.data.borrow()).unwrap();
        if ctx.accounts.user.owner != ctx.program_id {
            return Err(ProgramError::IllegalOwner);
        }
        if user.authority != ctx.accounts.authority.key() {
            return Err(ProgramError::InvalidAccountData);
        }
        msg!("GM {}", user.authority);
        Ok(())
    }
}

#[derive(Accounts)]
pub struct UpdateUser<'info> {
    user: AccountInfo<'info>,
    authority: Signer<'info>,
}

#[derive(BorshSerialize, BorshDeserialize)]
pub struct User {
    authority: Pubkey,
}

#[derive(BorshSerialize, BorshDeserialize)]
pub struct Metadata {
    account: Pubkey,
}

[ UNLEASH THE PACK ]hunt this class ↗full program + testsgithub ↗

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