Token Transfer I - Implementing process_instruction

In this lesson, we will take a look at how we can invoke another project to transfer tokens.

Here is the template you should be using for this project.

Here is the changes we have made to lib.rs in this video:

solana_program::entrypoint!(process_instruction);
pub fn process_instruction(
    program_id: &Pubkey,
    accounts: &[AccountInfo],
    _instruction_data: &[u8],
) -> ProgramResult {
    // Create an iterator to safely reference accounts in the slice
    let account_info_iter = &mut accounts.iter();

    // As part of the program specification the instruction gives:
    let source_info = next_account_info(account_info_iter)?; // 1.
    let mint_info = next_account_info(account_info_iter)?; // 2.
    let destination_info = next_account_info(account_info_iter)?; // 3.
    let authority_info = next_account_info(account_info_iter)?; // 4.
    let token_program_info = next_account_info(account_info_iter)?; // 5.

    // In order to transfer from the source account, owned by the program-derived
    // address, we must have the correct address and seeds.
    let (expected_authority, bump_seed) = Pubkey::find_program_address(&[b"authority"], program_id);
    if expected_authority != *authority_info.key {
        return Err(ProgramError::InvalidSeeds);
    }

    // The program transfers everything out of its account, so extract that from
    // the account data.
    let source_account = Account::unpack(&source_info.try_borrow_data()?)?;
    let amount = source_account.amount;

    // The program uses `transfer_checked`, which requires the number of decimals
    // in the mint, so extract that from the account data too.
    let mint = Mint::unpack(&mint_info.try_borrow_data()?)?;
    let decimals = mint.decimals;

    // Invoke the transfer
    msg!("Attempting to transfer {} tokens", amount);
    invoke_signed(
        &transfer_checked(
            token_program_info.key,
            source_info.key,
            mint_info.key,
            destination_info.key,
            authority_info.key,
            &[], // no multisig allowed
            amount,
            decimals,
        )
        .unwrap(),
        &[
            source_info.clone(),
            mint_info.clone(),
            destination_info.clone(),
            authority_info.clone(),
            token_program_info.clone(), // not required, but better for clarity
        ],
        &[&[b"authority", &[bump_seed]]],
    )
}