Blueshift | Anchor Escrow

Take

We can now move to the take instruction, that lives in the take.rs and will perform these actions:

Close the escrow record, sending its rent lamports back to the maker.
Move Token A from the vault to the taker, then close the vault.
Move the agreed amount of Token B from the taker to the maker.

Accounts

The accounts needed in this context are:

taker: the user that accepts the terms of the maker and is making the exchange
maker: the user that initially set the terms
escrow: the account where all the terms of this exchange lives
mint_a: the token that the maker has deposited
mint_b: the token that the maker wants in exchange
vault: the token account associated with the escrow and mint_a that will send the tokens to the taker
taker_ata_a: the token account associated with the taker and mint_a that will receive the tokens from the vault
taker_ata_b: the token account associated with the taker and mint_b that will send the tokens to the maker
maker_ata_b: the token account associated with the maker and mint_b that will receive the tokens to the taker
associated_token_program: the associated token program used to create the associated token accounts
token_program: the token program used to CPI the transfer
system_program: the system program used to create the Escrow

And with all the constraint it will look something like this:

rust
#[derive(Accounts)]
pub struct Take<'info> {
  #[account(mut)]
  pub taker: Signer<'info>,
  #[account(mut)]
  pub maker: SystemAccount<'info>,
  #[account(
      mut,
      close = maker,
      seeds = [b"escrow", maker.key().as_ref(), escrow.seed.to_le_bytes().as_ref()],
      bump = escrow.bump,
      has_one = maker @ EscrowError::InvalidMaker,
      has_one = mint_a @ EscrowError::InvalidMintA,
      has_one = mint_b @ EscrowError::InvalidMintB,
  )]
  pub escrow: Box<Account<'info, Escrow>>,

  /// Token Accounts
  pub mint_a: Box<InterfaceAccount<'info, Mint>>,
  pub mint_b: Box<InterfaceAccount<'info, Mint>>,
  #[account(
      mut,
      associated_token::mint = mint_a,
      associated_token::authority = escrow,
      associated_token::token_program = token_program
  )]
  pub vault: Box<InterfaceAccount<'info, TokenAccount>>,
  #[account(
      init_if_needed,
      payer = taker,
      associated_token::mint = mint_a,
      associated_token::authority = taker,
      associated_token::token_program = token_program
  )]
  pub taker_ata_a: Box<InterfaceAccount<'info, TokenAccount>>,
  #[account(
      mut,
      associated_token::mint = mint_b,
      associated_token::authority = taker,
      associated_token::token_program = token_program
  )]
  pub taker_ata_b: Box<InterfaceAccount<'info, TokenAccount>>,
  #[account(
      init_if_needed,
      payer = taker,
      associated_token::mint = mint_b,
      associated_token::authority = maker,
      associated_token::token_program = token_program
  )]
  pub maker_ata_b: Box<InterfaceAccount<'info, TokenAccount>>,

  /// Programs
  pub associated_token_program: Program<'info, AssociatedToken>,
  pub token_program: Interface<'info, TokenInterface>,
  pub system_program: Program<'info, System>,
}

Logic

In the logic we then start by transferring the tokens from the taker_ata_b to the maker_ata_b; we then move onto transferring the tokens from the vault to the taker_ata_a before closing the now empty vault like this:

rust
impl<'info> Take<'info> {
    fn transfer_to_maker(&mut self) -> Result<()> {
        transfer_checked(
            CpiContext::new(
                self.token_program.to_account_info(),
                TransferChecked {
                    from: self.taker_ata_b.to_account_info(),
                    to: self.maker_ata_b.to_account_info(),
                    mint: self.mint_b.to_account_info(),
                    authority: self.taker.to_account_info(),
                },
            ),
            self.escrow.receive,
            self.mint_b.decimals,
        )?;

        Ok(())
    }

    fn withdraw_and_close_vault(&mut self) -> Result<()> {
        // Create the signer seeds for the Vault
        let signer_seeds: [&[&[u8]]; 1] = [&[
            b"escrow",
            self.maker.to_account_info().key.as_ref(),
            &self.escrow.seed.to_le_bytes()[..],
            &[self.escrow.bump],
        ]];

        // Transfer Token A (Vault -> Taker)
        transfer_checked(
            CpiContext::new_with_signer(
                self.token_program.to_account_info(),
                TransferChecked {
                    from: self.vault.to_account_info(),
                    to: self.taker_ata_a.to_account_info(),
                    mint: self.mint_a.to_account_info(),
                    authority: self.escrow.to_account_info(),
                },
                &signer_seeds,
            ),
            self.vault.amount,
            self.mint_a.decimals,
        )?;

        // Close the Vault
        close_account(CpiContext::new_with_signer(
            self.token_program.to_account_info(),
            CloseAccount {
                account: self.vault.to_account_info(),
                authority: self.escrow.to_account_info(),
                destination: self.maker.to_account_info(),
            },
            &signer_seeds,
        ))?;

        Ok(())
    }
}

We now create the handler function and this time luckily we don't need to perform any additional checks so it will look like this:

rust
pub fn handler(ctx: Context<Take>) -> Result<()> {
    // Transfer Token B to Maker
    ctx.accounts.transfer_to_maker()?;

    // Withdraw and close the Vault
    ctx.accounts.withdraw_and_close_vault()?;

    Ok(())
}