SolanaのToken Programのソースコードを理解する

こんにちは。次世代システム研究室のL.W.です。

研究室のメンバーは「ソラナ（Solana）ブロックチェーン及び ソラナ上のトークンの発行について」を共有したことがあります。

今回はSolanaのトークンのソースコードを理解してみましたので、共有します。

参照になりましたら、ありがたいです。

 

1.基本的なデータストラクチャー

• System Program：新しいアカウントの作成（主に、lamports、owner、dataのspaceの初期化）、トークン（ネイティブトークンのSOL）の転送など
• BPF Loader Program：チェーン上でプログラムをデプロイ、アップグレード、実行など

pub struct Pubkey([u8; 32]);

// jsonファイルではプライベートキーを格納されています 
solana-keygen new --outfile 目的dir/ファイル名.json

---
Generating a new keypair

For added security, enter a BIP39 passphrase

NOTE! This passphrase improves security of the recovery seed phrase NOT the
keypair file itself, which is stored as insecure plain text

BIP39 Passphrase (empty for none): 

Wrote new keypair to solana-wallet/keypair.json
================================================================================
pubkey: 4wb4h4XExBm9hF2g3XqAuUE4T8NBErj1QJoFrN6uPNBu
================================================================================
Save this seed phrase and your BIP39 passphrase to recover your new keypair:
sister lucky weasel trouble mosquito bread system winter transfer crew lava page
================================================================================

/// Account information
#[derive(Clone)]
pub struct AccountInfo<'a> {
    /// Public key of the account
    pub key: &'a Pubkey,
    /// Was the transaction signed by this account's public key?
    pub is_signer: bool,
    /// Is the account writable?
    pub is_writable: bool,
    /// The lamports in the account.  Modifiable by programs.
    pub lamports: Rc<RefCell<&'a mut u64>>,
    /// The data held in this account.  Modifiable by programs.
    pub data: Rc<RefCell<&'a mut [u8]>>,
    /// Program that owns this account
    pub owner: &'a Pubkey,
    /// This account's data contains a loaded program (and is now read-only)
    pub executable: bool,
    /// The epoch at which this account will next owe rent
    pub rent_epoch: Epoch,
}

// solana rent <data size>
solana rent 165

-----
Rent per byte-year: 0.00000348 SOL
Rent per epoch: 0.000005583 SOL
Rent-exempt minimum: 0.00203928 SOL

1.3 AccountMeta

#[derive(Debug, Default, PartialEq, Eq, Clone, Serialize, Deserialize)]
pub struct AccountMeta {
    /// An account's public key.
    pub pubkey: Pubkey,
    /// True if an `Instruction` requires a `Transaction` signature matching `pubkey`.
    pub is_signer: bool,
    /// True if the account data or metadata may be mutated during program execution.
    pub is_writable: bool,
}

/**
 * Construct an InitializeMint instruction
 *
 * @param mint            Token mint account
 * @param decimals        Number of decimals in token account amounts
 * @param mintAuthority   Minting authority
 * @param freezeAuthority Optional authority that can freeze token accounts
 * @param programId       SPL Token program account
 *
 * @return Instruction to add to a transaction
 */
export function createInitializeMintInstruction(
    mint: PublicKey,
    decimals: number,
    mintAuthority: PublicKey,
    freezeAuthority: PublicKey | null,
    programId = TOKEN_PROGRAM_ID
): TransactionInstruction {
    const keys = [
        { pubkey: mint, isSigner: false, isWritable: true },
        { pubkey: SYSVAR_RENT_PUBKEY, isSigner: false, isWritable: false },
    ];

    const data = Buffer.alloc(initializeMintInstructionData.span);
    initializeMintInstructionData.encode(
        {
            instruction: TokenInstruction.InitializeMint,
            decimals,
            mintAuthority,
            freezeAuthorityOption: freezeAuthority ? 1 : 0,
            freezeAuthority: freezeAuthority || new PublicKey(0),
        },
        data
    );

    return new TransactionInstruction({ keys, programId, data });
}

2.Token Program

.
├── Cargo.lock
├── Cargo.toml
├── src
│   ├── entrypoint.rs
│   ├── error.rs
│   ├── instruction.rs
│   ├── lib.rs
│   ├── processsor.rs
│   ├── native_mint.rs
│   └── state.rs
├── inc
├── tests
└── Xargo.toml

entrypoint!(process_instruction);
fn process_instruction(
    program_id: &Pubkey,
    accounts: &[AccountInfo],
    instruction_data: &[u8],
) -> ProgramResult {
    if let Err(error) = Processor::process(program_id, accounts, instruction_data) {
        // catch the error so we can print it
        error.print::<TokenError>();
        return Err(error);
    }
    Ok(())
}

export enum TokenInstruction {
    InitializeMint = 0,
    InitializeAccount = 1,
    InitializeMultisig = 2,
    Transfer = 3,
    Approve = 4,
    Revoke = 5,
    SetAuthority = 6,
    MintTo = 7,
    Burn = 8,
    CloseAccount = 9,
    FreezeAccount = 10,
    ThawAccount = 11,
    TransferChecked = 12,
    ApproveChecked = 13,
    MintToChecked = 14,
    BurnChecked = 15,
    InitializeAccount2 = 16,
    SyncNative = 17,
    InitializeAccount3 = 18,
    InitializeMultisig2 = 19,
    InitializeMint2 = 20,
}

2.1Token Programでのデータストラクチャー

2.1.1mint account

/// Mint data.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq)]
pub struct Mint {
    /// Optional authority used to mint new tokens. The mint authority may only be provided during
    /// mint creation. If no mint authority is present then the mint has a fixed supply and no
    /// further tokens may be minted.
    pub mint_authority: COption<Pubkey>,
    /// Total supply of tokens.
    pub supply: u64,
    /// Number of base 10 digits to the right of the decimal place.
    pub decimals: u8,
    /// Is `true` if this structure has been initialized
    pub is_initialized: bool,
    /// Optional authority to freeze token accounts.
    pub freeze_authority: COption<Pubkey>,
}

2.1.2 token account

/// Account data.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq)]
pub struct Account {
    /// The mint associated with this account
    pub mint: Pubkey,
    /// The owner of this account.
    pub owner: Pubkey,
    /// The amount of tokens this account holds.
    pub amount: u64,
    /// If `delegate` is `Some` then `delegated_amount` represents
    /// the amount authorized by the delegate
    pub delegate: COption<Pubkey>,
    /// The account's state
    pub state: AccountState,
    /// If is_native.is_some, this is a native token, and the value logs the rent-exempt reserve. An
    /// Account is required to be rent-exempt, so the value is used by the Processor to ensure that
    /// wrapped SOL accounts do not drop below this threshold.
    pub is_native: COption<u64>,
    /// The amount delegated
    pub delegated_amount: u64,
    /// Optional authority to close the account.
    pub close_authority: COption<Pubkey>,
}

2.1.3 MultiSig account

/// Multisignature data.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq)]
pub struct Multisig {
    /// Number of signers required
    pub m: u8,
    /// Number of valid signers
    pub n: u8,
    /// Is `true` if this structure has been initialized
    pub is_initialized: bool,
    /// Signer public keys
    pub signers: [Pubkey; MAX_SIGNERS],
}

2.2 提供した機能

2.2.1 create mint

fn _process_initialize_mint(
    accounts: &[AccountInfo],
    decimals: u8,
    mint_authority: Pubkey,
    freeze_authority: COption<Pubkey>,
    rent_sysvar_account: bool,
) -> ProgramResult {
    let account_info_iter = &mut accounts.iter();
    let mint_info = next_account_info(account_info_iter)?;
    let mint_data_len = mint_info.data_len();
    let rent = if rent_sysvar_account {
        Rent::from_account_info(next_account_info(account_info_iter)?)?
    } else {
        Rent::get()?
    };

    let mut mint = Mint::unpack_unchecked(&mint_info.data.borrow())?;
    if mint.is_initialized {
        return Err(TokenError::AlreadyInUse.into());
    }

    if !rent.is_exempt(mint_info.lamports(), mint_data_len) {
        return Err(TokenError::NotRentExempt.into());
    }

    mint.mint_authority = COption::Some(mint_authority);
    mint.decimals = decimals;
    mint.is_initialized = true;
    mint.freeze_authority = freeze_authority;

    Mint::pack(mint, &mut mint_info.data.borrow_mut())?;

    Ok(())
}

2.2.2 create token account

fn _process_initialize_account(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        owner: Option<&Pubkey>,
        rent_sysvar_account: bool,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let new_account_info = next_account_info(account_info_iter)?;
        let mint_info = next_account_info(account_info_iter)?;
        let owner = if let Some(owner) = owner {
            owner
        } else {
            next_account_info(account_info_iter)?.key
        };
        let new_account_info_data_len = new_account_info.data_len();
        let rent = if rent_sysvar_account {
            Rent::from_account_info(next_account_info(account_info_iter)?)?
        } else {
            Rent::get()?
        };

        let mut account = Account::unpack_unchecked(&new_account_info.data.borrow())?;
        if account.is_initialized() {
            return Err(TokenError::AlreadyInUse.into());
        }

        if !rent.is_exempt(new_account_info.lamports(), new_account_info_data_len) {
            return Err(TokenError::NotRentExempt.into());
        }

        let is_native_mint = Self::cmp_pubkeys(mint_info.key, &crate::native_mint::id());
        if !is_native_mint {
            Self::check_account_owner(program_id, mint_info)?;
            let _ = Mint::unpack(&mint_info.data.borrow_mut())
                .map_err(|_| Into::<ProgramError>::into(TokenError::InvalidMint))?;
        }

        account.mint = *mint_info.key;
        account.owner = *owner;
        account.close_authority = COption::None;
        account.delegate = COption::None;
        account.delegated_amount = 0;
        account.state = AccountState::Initialized;
        if is_native_mint {
            let rent_exempt_reserve = rent.minimum_balance(new_account_info_data_len);
            account.is_native = COption::Some(rent_exempt_reserve);
            account.amount = new_account_info
                .lamports()
                .checked_sub(rent_exempt_reserve)
                .ok_or(TokenError::Overflow)?;
        } else {
            account.is_native = COption::None;
            account.amount = 0;
        };

        Account::pack(account, &mut new_account_info.data.borrow_mut())?;

        Ok(())
    }

2.2.3 create multisig account

fn _process_initialize_multisig(
        accounts: &[AccountInfo],
        m: u8,
        rent_sysvar_account: bool,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let multisig_info = next_account_info(account_info_iter)?;
        let multisig_info_data_len = multisig_info.data_len();
        let rent = if rent_sysvar_account {
            Rent::from_account_info(next_account_info(account_info_iter)?)?
        } else {
            Rent::get()?
        };

        let mut multisig = Multisig::unpack_unchecked(&multisig_info.data.borrow())?;
        if multisig.is_initialized {
            return Err(TokenError::AlreadyInUse.into());
        }

        if !rent.is_exempt(multisig_info.lamports(), multisig_info_data_len) {
            return Err(TokenError::NotRentExempt.into());
        }

        let signer_infos = account_info_iter.as_slice();
        multisig.m = m;
        multisig.n = signer_infos.len() as u8;
        if !is_valid_signer_index(multisig.n as usize) {
            return Err(TokenError::InvalidNumberOfProvidedSigners.into());
        }
        if !is_valid_signer_index(multisig.m as usize) {
            return Err(TokenError::InvalidNumberOfRequiredSigners.into());
        }
        for (i, signer_info) in signer_infos.iter().enumerate() {
            multisig.signers[i] = *signer_info.key;
        }
        multisig.is_initialized = true;

        Multisig::pack(multisig, &mut multisig_info.data.borrow_mut())?;

        Ok(())
    }

2.2.4 mint to

pub fn process_mint_to(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        amount: u64,
        expected_decimals: Option<u8>,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let mint_info = next_account_info(account_info_iter)?;
        let destination_account_info = next_account_info(account_info_iter)?;
        let owner_info = next_account_info(account_info_iter)?;

        let mut destination_account = Account::unpack(&destination_account_info.data.borrow())?;
        if destination_account.is_frozen() {
            return Err(TokenError::AccountFrozen.into());
        }

        if destination_account.is_native() {
            return Err(TokenError::NativeNotSupported.into());
        }
        if !Self::cmp_pubkeys(mint_info.key, &destination_account.mint) {
            return Err(TokenError::MintMismatch.into());
        }

        let mut mint = Mint::unpack(&mint_info.data.borrow())?;
        if let Some(expected_decimals) = expected_decimals {
            if expected_decimals != mint.decimals {
                return Err(TokenError::MintDecimalsMismatch.into());
            }
        }

        match mint.mint_authority {
            COption::Some(mint_authority) => Self::validate_owner(
                program_id,
                &mint_authority,
                owner_info,
                account_info_iter.as_slice(),
            )?,
            COption::None => return Err(TokenError::FixedSupply.into()),
        }

        if amount == 0 {
            Self::check_account_owner(program_id, mint_info)?;
            Self::check_account_owner(program_id, destination_account_info)?;
        }

        destination_account.amount = destination_account
            .amount
            .checked_add(amount)
            .ok_or(TokenError::Overflow)?;

        mint.supply = mint
            .supply
            .checked_add(amount)
            .ok_or(TokenError::Overflow)?;

        Account::pack(
            destination_account,
            &mut destination_account_info.data.borrow_mut(),
        )?;
        Mint::pack(mint, &mut mint_info.data.borrow_mut())?;

        Ok(())
    }

2.2.5 burn

pub fn process_burn(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        amount: u64,
        expected_decimals: Option<u8>,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();

        let source_account_info = next_account_info(account_info_iter)?;
        let mint_info = next_account_info(account_info_iter)?;
        let authority_info = next_account_info(account_info_iter)?;

        let mut source_account = Account::unpack(&source_account_info.data.borrow())?;
        let mut mint = Mint::unpack(&mint_info.data.borrow())?;

        if source_account.is_frozen() {
            return Err(TokenError::AccountFrozen.into());
        }
        if source_account.is_native() {
            return Err(TokenError::NativeNotSupported.into());
        }
        if source_account.amount < amount {
            return Err(TokenError::InsufficientFunds.into());
        }
        if !Self::cmp_pubkeys(mint_info.key, &source_account.mint) {
            return Err(TokenError::MintMismatch.into());
        }

        if let Some(expected_decimals) = expected_decimals {
            if expected_decimals != mint.decimals {
                return Err(TokenError::MintDecimalsMismatch.into());
            }
        }

        if !source_account.is_owned_by_system_program_or_incinerator() {
            match source_account.delegate {
                COption::Some(ref delegate) if Self::cmp_pubkeys(authority_info.key, delegate) => {
                    Self::validate_owner(
                        program_id,
                        delegate,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;

                    if source_account.delegated_amount < amount {
                        return Err(TokenError::InsufficientFunds.into());
                    }
                    source_account.delegated_amount = source_account
                        .delegated_amount
                        .checked_sub(amount)
                        .ok_or(TokenError::Overflow)?;
                    if source_account.delegated_amount == 0 {
                        source_account.delegate = COption::None;
                    }
                }
                _ => Self::validate_owner(
                    program_id,
                    &source_account.owner,
                    authority_info,
                    account_info_iter.as_slice(),
                )?,
            }
        }

        if amount == 0 {
            Self::check_account_owner(program_id, source_account_info)?;
            Self::check_account_owner(program_id, mint_info)?;
        }

        source_account.amount = source_account
            .amount
            .checked_sub(amount)
            .ok_or(TokenError::Overflow)?;
        mint.supply = mint
            .supply
            .checked_sub(amount)
            .ok_or(TokenError::Overflow)?;

        Account::pack(source_account, &mut source_account_info.data.borrow_mut())?;
        Mint::pack(mint, &mut mint_info.data.borrow_mut())?;

        Ok(())
    }

2.2.6 close

pub fn process_close_account(program_id: &Pubkey, accounts: &[AccountInfo]) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let source_account_info = next_account_info(account_info_iter)?;
        let destination_account_info = next_account_info(account_info_iter)?;
        let authority_info = next_account_info(account_info_iter)?;

        if Self::cmp_pubkeys(source_account_info.key, destination_account_info.key) {
            return Err(ProgramError::InvalidAccountData);
        }

        let source_account = Account::unpack(&source_account_info.data.borrow())?;
        if !source_account.is_native() && source_account.amount != 0 {
            return Err(TokenError::NonNativeHasBalance.into());
        }

        let authority = source_account
            .close_authority
            .unwrap_or(source_account.owner);
        if !source_account.is_owned_by_system_program_or_incinerator() {
            Self::validate_owner(
                program_id,
                &authority,
                authority_info,
                account_info_iter.as_slice(),
            )?;
        } else if !solana_program::incinerator::check_id(destination_account_info.key) {
            return Err(ProgramError::InvalidAccountData);
        }

        let destination_starting_lamports = destination_account_info.lamports();
        **destination_account_info.lamports.borrow_mut() = destination_starting_lamports
            .checked_add(source_account_info.lamports())
            .ok_or(TokenError::Overflow)?;

        **source_account_info.lamports.borrow_mut() = 0;
        delete_account(source_account_info)?;

        Ok(())
    }

2.2.7 freeze

pub fn process_toggle_freeze_account(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        freeze: bool,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let source_account_info = next_account_info(account_info_iter)?;
        let mint_info = next_account_info(account_info_iter)?;
        let authority_info = next_account_info(account_info_iter)?;

        let mut source_account = Account::unpack(&source_account_info.data.borrow())?;
        if freeze && source_account.is_frozen() || !freeze && !source_account.is_frozen() {
            return Err(TokenError::InvalidState.into());
        }
        if source_account.is_native() {
            return Err(TokenError::NativeNotSupported.into());
        }
        if !Self::cmp_pubkeys(mint_info.key, &source_account.mint) {
            return Err(TokenError::MintMismatch.into());
        }

        let mint = Mint::unpack(&mint_info.data.borrow_mut())?;
        match mint.freeze_authority {
            COption::Some(authority) => Self::validate_owner(
                program_id,
                &authority,
                authority_info,
                account_info_iter.as_slice(),
            ),
            COption::None => Err(TokenError::MintCannotFreeze.into()),
        }?;

        source_account.state = if freeze {
            AccountState::Frozen
        } else {
            AccountState::Initialized
        };

        Account::pack(source_account, &mut source_account_info.data.borrow_mut())?;

        Ok(())
    }

2.2.8 thaw

pub fn process_toggle_freeze_account(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        freeze: bool,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let source_account_info = next_account_info(account_info_iter)?;
        let mint_info = next_account_info(account_info_iter)?;
        let authority_info = next_account_info(account_info_iter)?;

        let mut source_account = Account::unpack(&source_account_info.data.borrow())?;
        if freeze && source_account.is_frozen() || !freeze && !source_account.is_frozen() {
            return Err(TokenError::InvalidState.into());
        }
        if source_account.is_native() {
            return Err(TokenError::NativeNotSupported.into());
        }
        if !Self::cmp_pubkeys(mint_info.key, &source_account.mint) {
            return Err(TokenError::MintMismatch.into());
        }

        let mint = Mint::unpack(&mint_info.data.borrow_mut())?;
        match mint.freeze_authority {
            COption::Some(authority) => Self::validate_owner(
                program_id,
                &authority,
                authority_info,
                account_info_iter.as_slice(),
            ),
            COption::None => Err(TokenError::MintCannotFreeze.into()),
        }?;

        source_account.state = if freeze {
            AccountState::Frozen
        } else {
            AccountState::Initialized
        };

        Account::pack(source_account, &mut source_account_info.data.borrow_mut())?;

        Ok(())
    }

2.2.9 set authority

pub fn process_set_authority(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        authority_type: AuthorityType,
        new_authority: COption<Pubkey>,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let account_info = next_account_info(account_info_iter)?;
        let authority_info = next_account_info(account_info_iter)?;

        if account_info.data_len() == Account::get_packed_len() {
            let mut account = Account::unpack(&account_info.data.borrow())?;

            if account.is_frozen() {
                return Err(TokenError::AccountFrozen.into());
            }

            match authority_type {
                AuthorityType::AccountOwner => {
                    Self::validate_owner(
                        program_id,
                        &account.owner,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;

                    if let COption::Some(authority) = new_authority {
                        account.owner = authority;
                    } else {
                        return Err(TokenError::InvalidInstruction.into());
                    }

                    account.delegate = COption::None;
                    account.delegated_amount = 0;

                    if account.is_native() {
                        account.close_authority = COption::None;
                    }
                }
                AuthorityType::CloseAccount => {
                    let authority = account.close_authority.unwrap_or(account.owner);
                    Self::validate_owner(
                        program_id,
                        &authority,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;
                    account.close_authority = new_authority;
                }
                _ => {
                    return Err(TokenError::AuthorityTypeNotSupported.into());
                }
            }
            Account::pack(account, &mut account_info.data.borrow_mut())?;
        } else if account_info.data_len() == Mint::get_packed_len() {
            let mut mint = Mint::unpack(&account_info.data.borrow())?;
            match authority_type {
                AuthorityType::MintTokens => {
                    // Once a mint's supply is fixed, it cannot be undone by setting a new
                    // mint_authority
                    let mint_authority = mint
                        .mint_authority
                        .ok_or(Into::<ProgramError>::into(TokenError::FixedSupply))?;
                    Self::validate_owner(
                        program_id,
                        &mint_authority,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;
                    mint.mint_authority = new_authority;
                }
                AuthorityType::FreezeAccount => {
                    // Once a mint's freeze authority is disabled, it cannot be re-enabled by
                    // setting a new freeze_authority
                    let freeze_authority = mint
                        .freeze_authority
                        .ok_or(Into::<ProgramError>::into(TokenError::MintCannotFreeze))?;
                    Self::validate_owner(
                        program_id,
                        &freeze_authority,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;
                    mint.freeze_authority = new_authority;
                }
                _ => {
                    return Err(TokenError::AuthorityTypeNotSupported.into());
                }
            }
            Mint::pack(mint, &mut account_info.data.borrow_mut())?;
        } else {
            return Err(ProgramError::InvalidArgument);
        }

        Ok(())
    }

2.2.10 delegate

pub fn process_approve(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        amount: u64,
        expected_decimals: Option<u8>,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();

        let source_account_info = next_account_info(account_info_iter)?;

        let expected_mint_info = if let Some(expected_decimals) = expected_decimals {
            Some((next_account_info(account_info_iter)?, expected_decimals))
        } else {
            None
        };
        let delegate_info = next_account_info(account_info_iter)?;
        let owner_info = next_account_info(account_info_iter)?;

        let mut source_account = Account::unpack(&source_account_info.data.borrow())?;

        if source_account.is_frozen() {
            return Err(TokenError::AccountFrozen.into());
        }

        if let Some((mint_info, expected_decimals)) = expected_mint_info {
            if !Self::cmp_pubkeys(mint_info.key, &source_account.mint) {
                return Err(TokenError::MintMismatch.into());
            }

            let mint = Mint::unpack(&mint_info.data.borrow_mut())?;
            if expected_decimals != mint.decimals {
                return Err(TokenError::MintDecimalsMismatch.into());
            }
        }

        Self::validate_owner(
            program_id,
            &source_account.owner,
            owner_info,
            account_info_iter.as_slice(),
        )?;

        source_account.delegate = COption::Some(*delegate_info.key);
        source_account.delegated_amount = amount;

        Account::pack(source_account, &mut source_account_info.data.borrow_mut())?;

        Ok(())
    }

pub fn process_revoke(program_id: &Pubkey, accounts: &[AccountInfo]) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let source_account_info = next_account_info(account_info_iter)?;

        let mut source_account = Account::unpack(&source_account_info.data.borrow())?;

        let owner_info = next_account_info(account_info_iter)?;

        if source_account.is_frozen() {
            return Err(TokenError::AccountFrozen.into());
        }

        Self::validate_owner(
            program_id,
            &source_account.owner,
            owner_info,
            account_info_iter.as_slice(),
        )?;

        source_account.delegate = COption::None;
        source_account.delegated_amount = 0;

        Account::pack(source_account, &mut source_account_info.data.borrow_mut())?;

        Ok(())
    }

    /// Processes a [SetAuthority](enum.TokenInstruction.html) instruction.
    pub fn process_set_authority(
        program_id: &Pubkey,
        accounts: &[AccountInfo],
        authority_type: AuthorityType,
        new_authority: COption<Pubkey>,
    ) -> ProgramResult {
        let account_info_iter = &mut accounts.iter();
        let account_info = next_account_info(account_info_iter)?;
        let authority_info = next_account_info(account_info_iter)?;

        if account_info.data_len() == Account::get_packed_len() {
            let mut account = Account::unpack(&account_info.data.borrow())?;

            if account.is_frozen() {
                return Err(TokenError::AccountFrozen.into());
            }

            match authority_type {
                AuthorityType::AccountOwner => {
                    Self::validate_owner(
                        program_id,
                        &account.owner,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;

                    if let COption::Some(authority) = new_authority {
                        account.owner = authority;
                    } else {
                        return Err(TokenError::InvalidInstruction.into());
                    }

                    account.delegate = COption::None;
                    account.delegated_amount = 0;

                    if account.is_native() {
                        account.close_authority = COption::None;
                    }
                }
                AuthorityType::CloseAccount => {
                    let authority = account.close_authority.unwrap_or(account.owner);
                    Self::validate_owner(
                        program_id,
                        &authority,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;
                    account.close_authority = new_authority;
                }
                _ => {
                    return Err(TokenError::AuthorityTypeNotSupported.into());
                }
            }
            Account::pack(account, &mut account_info.data.borrow_mut())?;
        } else if account_info.data_len() == Mint::get_packed_len() {
            let mut mint = Mint::unpack(&account_info.data.borrow())?;
            match authority_type {
                AuthorityType::MintTokens => {
                    // Once a mint's supply is fixed, it cannot be undone by setting a new
                    // mint_authority
                    let mint_authority = mint
                        .mint_authority
                        .ok_or(Into::<ProgramError>::into(TokenError::FixedSupply))?;
                    Self::validate_owner(
                        program_id,
                        &mint_authority,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;
                    mint.mint_authority = new_authority;
                }
                AuthorityType::FreezeAccount => {
                    // Once a mint's freeze authority is disabled, it cannot be re-enabled by
                    // setting a new freeze_authority
                    let freeze_authority = mint
                        .freeze_authority
                        .ok_or(Into::<ProgramError>::into(TokenError::MintCannotFreeze))?;
                    Self::validate_owner(
                        program_id,
                        &freeze_authority,
                        authority_info,
                        account_info_iter.as_slice(),
                    )?;
                    mint.freeze_authority = new_authority;
                }
                _ => {
                    return Err(TokenError::AuthorityTypeNotSupported.into());
                }
            }
            Mint::pack(mint, &mut account_info.data.borrow_mut())?;
        } else {
            return Err(ProgramError::InvalidArgument);
        }

        Ok(())
    }

3.まとめ

4.最後に