Skip to main content

Access Control

Access Control is the component that allows a contract to implement role-based access control mechanisms. This is a lightweight version that doesn't allow enumerating role members except through off-chain means by accessing the contract event logs. Some applications may benefit from on-chain enumerability, for those cases see access-control-eunmerable[./access-control-enumerable.md].

Roles are referred to by their RoleId which is a 32-bytes. These should be exposed in the external API and be unique. The best way to achieve this is by using hash digests.

Roles can be used to represent a set of permissions. To restrict access to a function call, use ensure_caller_role:

    // need role    #[ink(message)]    pub fn func(&mut self) {        access_control::Impl::ensure_caller_role(self, ROLE_ID_XXX);
        // other logics    }

Roles can be granted and revoked dynamically via the grant_role and revoke_role functions. Each role has an associated admin role, and only accounts that have a role's admin role can call grant_role and revoke_role.

Dependency#

metis_access_control = { git = "https://github.com/patractlabs/metis", default-features = false }

Storage#

The storage contains the roles and admin_roles:

/// The Data of access control component#[cfg_attr(feature = "std", derive(::ink_storage::traits::StorageLayout))]#[derive(Debug, SpreadLayout)]pub struct Data<E>where    E: Env,{    /// the account - role relationship map    pub roles: StorageHashMap<(RoleId, E::AccountId), ()>,
    /// the admin role of a role    pub admin_roles: StorageHashMap<RoleId, RoleId>,}

To declare the storage:

    #[ink(storage)]    #[import(access_control)]    pub struct Contract {        access_control: access_control::Data<Contract>,
        // other modules    }

Mutable Messages#

grant_role#

Grants role to account. If account had not been already granted role, emits a RoleGranted event.

Requirements:

  • the caller must have role's admin role.
    fn grant_role(&mut self, role: RoleId, account: E::AccountId) {        // check the admin role        self.ensure_admin_role(role, Self::caller());
        self._setup_role(role, account);    }

revoke_role#

Revokes role from account. If account had been granted role, emits a RoleRevoked event.

Requirements:

  • the caller must have role's admin role.
    fn revoke_role(&mut self, role: RoleId, account: E::AccountId) {        let caller = Self::caller();
        // check the admin role        self.ensure_admin_role(role, caller.clone());
        // if has not role        self.get_mut()            .revoke_role(role, account.clone())            .expect("no has role");
        // emit if revoke role success        self.emit_event_role_revoked(role, account, caller);    }

renounce_role#

Revokes role from the calling account.

Roles are often managed via grant_role and revoke_role: this function's purpose is to provide a mechanism for accounts to lose their privileges if they are compromised (such as when a trusted device is misplaced).

If the calling account had been granted role, emits a RoleRevoked event.

Requirements:

  • the caller must be account.
    fn renounce_role(&mut self, role: RoleId, account: E::AccountId) {        let caller = Self::caller();
        // check the caller is account        assert!(caller == account, "account not caller");
        // if has not role        self.get_mut()            .revoke_role(role, account.clone())            .expect("no has role");
        // emit if revoke role success        self.emit_event_role_revoked(role, account, caller);    }

Immutable Message#

Use has_role and get_role_admin can to get the role releations of accounts.

has_role#

Returns true if account has been granted role.

    fn has_role(&self, role: RoleId, account: E::AccountId) -> bool {        self.get().has_role(role, account)    }

get_role_admin#

Returns the admin role that controls role. See {grant_role} and {revoke_role}.

To change a role's admin, use _set_role_admin.

    fn get_role_admin(&self, role: RoleId) -> Option<RoleId> {        self.get().admin_roles.get(&role).copied()    }

Internal Functions#

Use Apis to check and ensure account has role.

ensure_role#

Panic if owner is not an owner.

    fn ensure_role(&self, role: RoleId, account: E::AccountId) {        assert!(self.has_role(role, account), "role missing");    }

ensure_caller_role#

Panic if caller is not granted role.

    fn ensure_caller_role(&self, role: RoleId) {        self.ensure_role(role, Self::caller());    }

ensure_admin_role#

Panic error if account is missing the admin role of the role.

    fn ensure_admin_role(&self, role: RoleId, account: E::AccountId) {        match self.get_role_admin(role) {            Some(admin_role) => self.ensure_role(admin_role, account),            None => panic!("admin role missing"),        }    }

check_role#

Return error if account is missing role.

    fn check_role(&self, role: RoleId, account: E::AccountId) -> Result<()> {        if self.has_role(role, account) {            Ok(())        } else {            Err(Error::RoleNotFound)        }    }

check_admin_role#

Return error if account is missing the admin role of the role.

    fn check_admin_role(&self, role: RoleId, account: E::AccountId) -> Result<()> {        match self.get_role_admin(role) {            Some(admin_role) => self.check_role(admin_role, account),            None => Err(Error::AdminRoleNotFound),        }    }

Events#

RoleAdminChanged#

Emitted when new_admin_role is set as role's admin role, replacing previous_admin_role

  • will emit by call _set_role_admin.
    #[ink(event)]    #[metis(access_control)]    pub struct RoleAdminChanged {        #[ink(topic)]        pub role: RoleId,        #[ink(topic)]        pub previous_admin_role: Option<RoleId>,        #[ink(topic)]        pub new_admin_role: RoleId,    }

RoleGranted#

Emitted when account is granted role.

  • will emit by call _setup_role.
    #[ink(event)]    #[metis(access_control)]    pub struct RoleGranted {        #[ink(topic)]        pub role: RoleId,        #[ink(topic)]        pub account: AccountId,        #[ink(topic)]        pub sender: AccountId,    }

RoleRevoked#

Emitted when account is revoked role.

sender is the account that originated the contract call:

  • if using revoke_role, it is the admin role bearer
  • if using renounce_role, it is the role bearer (i.e. account)
    #[ink(event)]    #[metis(access_control)]    pub struct RoleRevoked {        #[ink(topic)]        pub role: RoleId,        #[ink(topic)]        pub account: AccountId,        #[ink(topic)]        pub sender: AccountId,    }

Usage Example#

To use the Access Control Component, First is import the access_control:

#![cfg_attr(not(feature = "std"), no_std)]
#[metis_lang::contract]pub mod example {    pub use access_control::{        Error,        Result,        RoleId,    };    use metis_access_control as access_control;    use metis_lang::{        import,        metis,    };
    #[ink(storage)]    #[import(access_control)]    pub struct Contract {        access_control: access_control::Data<Contract>,
        // other modules    }

Define the Event for access control:

    /// Emitted when `new_admin_role` is set as ``role``'s    /// admin role, replacing `previous_admin_role`    #[ink(event)]    #[metis(access_control)]    pub struct RoleAdminChanged {        #[ink(topic)]        pub role: RoleId,        #[ink(topic)]        pub previous_admin_role: Option<RoleId>,        #[ink(topic)]        pub new_admin_role: RoleId,    }
    /// Emitted when `account` is granted `role`.    ///    /// `sender` is the account that originated the contract call,    /// an admin role bearer except when using {_setupRole}.    #[ink(event)]    #[metis(access_control)]    pub struct RoleGranted {        #[ink(topic)]        pub role: RoleId,        #[ink(topic)]        pub account: AccountId,        #[ink(topic)]        pub sender: AccountId,    }
    /// Emitted when `account` is revoked `role`.    ///    /// `sender` is the account that originated the contract call:    ///   - if using `revoke_role`, it is the admin role bearer    ///   - if using `renounce_role`, it is the role bearer (i.e. `account`)    #[ink(event)]    #[metis(access_control)]    pub struct RoleRevoked {        #[ink(topic)]        pub role: RoleId,        #[ink(topic)]        pub account: AccountId,        #[ink(topic)]        pub sender: AccountId,    }

Impl the constructor of the contract:

    #[ink(constructor)]    pub fn new(        fliper: AccountId,        setter: AccountId,        admin: AccountId,    ) -> Self {        let mut instance = Self {            // Need add access_control module            access_control: access_control::Data::new(),        };
        // Use the `_setup_role` set the ROLEs        access_control::Impl::_setup_role(&mut instance, ROLE_ID_FLIPER, fliper);        access_control::Impl::_setup_role(&mut instance, ROLE_ID_SETTER, setter);        access_control::Impl::_setup_role(&mut instance, ROLE_ID_ADMIN, admin);
        // Use `_set_role_admin` set the role admin        access_control::Impl::_set_role_admin(            &mut instance,            ROLE_ID_FLIPER,            ROLE_ID_ADMIN,        );
        // create the default role        instance    }

WARNNING: In metis, access control not have a default admin role which be admin role of all roles, so we need defined the role releations in constructor.

In constructor, we can use _setup_role and _set_role_admin to set the role releations for contract.

Next, Add the message to control the role releations.

    /// Returns `true` if `account` has been granted `role`.    #[ink(message)]    pub fn has_role(&self, role: RoleId, account: AccountId) -> bool {        access_control::Impl::has_role(self, role, account)    }
    /// @dev Returns the admin role that controls `role`. See {grant_role} and    /// {revoke_role}.    ///    /// To change a role's admin, use {_setRoleAdmin}.    #[ink(message)]    pub fn get_role_admin(&self, role: RoleId) -> Option<RoleId> {        access_control::Impl::get_role_admin(self, role)    }
    /// @dev Grants `role` to `account`.    ///    /// If `account` had not been already granted `role`, emits a {RoleGranted}    /// event.    ///    /// Requirements:    ///    /// - the caller must have ``role``'s admin role.    #[ink(message)]    pub fn grant_role(&mut self, role: RoleId, account: AccountId) {        access_control::Impl::grant_role(self, role, account)    }
    /// @dev Revokes `role` from `account`.    ///    /// If `account` had been granted `role`, emits a {RoleRevoked} event.    ///    /// Requirements:    ///    /// - the caller must have ``role``'s admin role.    #[ink(message)]    pub fn revoke_role(&mut self, role: RoleId, account: AccountId) {        access_control::Impl::revoke_role(self, role, account)    }
    /// @dev Revokes `role` from the calling account.    ///    /// Roles are often managed via {grant_role} and {revoke_role}: this function's    /// purpose is to provide a mechanism for accounts to lose their privileges    /// if they are compromised (such as when a trusted device is misplaced).    ///    /// If the calling account had been granted `role`, emits a {RoleRevoked}    /// event.    ///    /// Requirements:    ///    /// - the caller must be `account`.    #[ink(message)]    pub fn renounce_role(&mut self, role: RoleId, account: AccountId) {        access_control::Impl::renounce_role(self, role, account)    }