// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library fuchsia.update;

/// The Manager protocol is used by a client that wishes to either check for an
/// update, or follow the status of ongoing updates.
///
/// The Manager provides a mechanism for checking for updates via the
/// [`Manager.CheckNow`] message.
@discoverable
protocol Manager {
    /// Immediately check for an update, and optionally track the state and
    /// progress of that update check.
    ///
    /// + request `options` Options for how this request should be performed.
    ///                     E.g. What kind of entity initiated this request?
    ///                     E.g. Is monitoring an existing update check that
    ///                          is already in process an acceptable
    ///                          alternative?
    ///
    /// + request `monitor` An interface on which to receive the status events
    ///                     for this update check.  The monitor is only valid
    ///                     for this single update check, after that it will
    ///                     not receive any more notifications and will be
    ///                     closed.
    ///
    /// * error If an update check cannot be started, an error will be returned.
    ///         The [`Monitor`], if provided, will not receive any notifications.
    CheckNow(resource struct {
        options CheckOptions;
        monitor client_end:<Monitor, optional>;
    }) -> (struct {}) error CheckNotStartedReason;

    /// Performs any pending reboot of the system into an updated OS, if an
    /// update has been staged for the next system startup.
    ///
    /// Should be used when the platform is configured to let the product drive
    /// reboot scheduling. If this method is called when the platform is not
    /// configured to let the product drive reboot scheduling, no reboot will
    /// occur, and the system will reboot on its own after an update.
    ///
    /// In product-driven reboot configurations, the platform still contains a
    /// backstop for post-update reboots. This means that if an update
    /// is installed but the system has not rebooted before the backstop
    /// duration occurs, the update system will automatically reboot the
    /// system as a security measure. To avoid hitting this backstop,
    /// products which desire control over reboot timing should call this
    /// method roughly daily.
    ///
    /// - response `rebooting` true if the system is rebooting, false if no
    ///                        update was pending reboot.
    PerformPendingReboot() -> (struct {
        rebooting bool;
    });
};

/// Configuration options for an update check.
type CheckOptions = table {
    /// Who or what initiated this update attempt.  This is taken as input to
    /// Policy, and may influence how the update check is performed.
    ///
    /// **This is a required field.**
    1: initiator Initiator;

    /// If an update check is already in progress, it's acceptable to instead
    /// attach a Monitor to that in-progress update instead of failing this
    /// request to check for updates.  This may convert situations that would
    /// have resulted in the ALREADY_IN_PROGRESS to be treated as non-error
    /// cases.
    2: allow_attaching_to_existing_update_check bool;
};

/// Who or what initiated the update check.
type Initiator = strict enum {
    /// The update check was initiated by an interactive user, or the user is
    /// otherwise blocked and waiting for the result of this update check.  This
    /// SHOULD only be used when there is a UI element or flow that a user has
    /// interacted with which has initiated this update check.
    USER = 1;

    /// The update check was initiated by a service, not a user-facing aspect
    /// of the system.
    SERVICE = 2;
};

/// Monitors a single update check.
///
/// Clients interested in receiving progress information for an update check
/// should implement this protocol and provide the client end to
/// [`Manager.CheckNow`].
protocol Monitor {
    /// Receives a status update for this update check.
    ///
    /// This request will be called for all state changes, skipping none.
    /// However, message delivery is throttled by the rate at which the
    /// implementation acknowledges the messages.
    ///
    /// The throttled delivery doesn't impact the underlying state of the
    /// [`Manager`].  It does not wait for any acknowledgements before it moves
    /// on to the next state in its state machine.  The [`Manager`] will simply
    /// queue up the states for the [`Monitor`] implementation to receive.
    ///
    /// During the installing_update state, the [`Manager`] may, at its
    /// discretion, collapse redundant information like the fraction completed,
    /// in the event that the [`Monitor`] implementation is not responding to
    /// the `OnState()` requests in a timely manner.
    ///
    /// + request `state` The new state of the update check.
    /// - response        The implementation is ready to receive the next
    ///                   [`State`] from the [`Manager`].
    OnState(struct {
        state State;
    }) -> ();
};

/// The set of states that a [`Monitor`] can receive during an update check.
///
/// An update check ends when it enters a terminal state, denoted below as the
/// states on the right-hand side of the diagram with no arrows leading out of
/// them.
///
/// # State Machine Diagram
///
/// ```
///     +----------------------+     +---------------------------------+
///     | checking_for_updates |---->|    error_checking_for_update    |
///     +----------------------+     +---------------------------------+
///                |
///                |                 +---------------------------------+
///                +---------------->|       no_update_available       |
///                |                 +---------------------------------+
///                |
///                |                 +---------------------------------+
///                +---------------->| installation_deferred_by_policy |
///                |                 +---------------------------------+
///                v
///     +----------------------+     +---------------------------------+
///     |  installing_update   |---->|       installation_error        |
///     +----------------------+     +---------------------------------+
///                |
///                |                 +---------------------------------+
///                +---------------->|       waiting_for_reboot        |
///                                  +---------------------------------+
/// ```
type State = strict union {

    /// The Manager is currently checking for an update.
    ///
    /// Next states:
    /// * `installing_update` update is available and allowed by policy
    /// * `error_checking_for_update` on error
    /// * `update_deferred_by_policy` update is available but deferred by policy
    1: checking_for_updates CheckingForUpdatesData;

    /// The Manager encountered an error while checking for the existence of a
    /// a new update.
    ///
    /// **This is a terminal state**
    ///
    2: error_checking_for_update ErrorCheckingForUpdateData;

    /// There is not update available at this time.
    ///
    /// **This is a terminal state**
    ///
    3: no_update_available NoUpdateAvailableData;

    /// The Manager has found an available update but is not acting on it at
    /// this time due to policy restrictions.
    ///
    /// **This is a terminal state**
    ///
    4: installation_deferred_by_policy InstallationDeferredData;

    /// The Manager is installing the available update.
    ///
    /// Next states:
    /// * `waiting_for_reboot` on success
    /// * `installation_error` on error
    5: installing_update InstallingData;

    /// The update has been installed, and the device is waiting to be rebooted.
    ///
    /// Next states:
    /// * (none, the device reboots)
    ///
    /// **This is a terminal state**
    ///
    6: waiting_for_reboot InstallingData;

    /// The Manager encountered an update in the installation of the update.
    ///
    /// **This is a terminal state**
    ///
    7: installation_error InstallationErrorData;
};

/// This is the set of data associated with `checking_for_updates`.
/// (currently none)
type CheckingForUpdatesData = table {};

/// This is the set of data associated with the `error_checking_for_update`
/// state.
/// (currently none)
type ErrorCheckingForUpdateData = table {};

/// This is the set of data associated with the `no_update_available` state.
/// (currently none)
type NoUpdateAvailableData = table {};

/// This is the set of data associated with the
/// `installation_deferred_by_policy` state.
type InstallationDeferredData = table {
    1: update UpdateInfo;
    2: deferral_reason InstallationDeferralReason;
};

/// This is the set of data associated with the states involved with installing
/// an update:
/// * `installing_update`
/// * `waiting_for_reboot`
type InstallingData = table {
    1: update UpdateInfo;
    2: installation_progress InstallationProgress;
};

/// This is the set of data associated with the `installation_error` state.
/// (currently none)
type InstallationErrorData = table {
    1: update UpdateInfo;
    2: installation_progress InstallationProgress;
};

/// This describes the update that is available to be installed.
type UpdateInfo = table {
    /// A string that describes the version that is available.  This may be
    /// either a semantic version (A.B.C.D) or an opaque hash.  Clients MUST
    /// not attempt to inspect this value, it is for display purposes only.
    1: version_available string:MAX_VERSION_STRING_SIZE;

    /// The total number of bytes that may be downloaded to apply this update.
    2: download_size uint64;
};

/// This is the maximum length of a version string that will be returned by the
/// protocol
const MAX_VERSION_STRING_SIZE uint32 = 128;

/// This describes the progress installing the update that has been made so far.
type InstallationProgress = table {
    /// The fraction [0-1.0f] of the installation that has been completed.
    1: fraction_completed float32;
};

/// This is the set of values that are returned by an request to immediately
/// check for an update.
type CheckNotStartedReason = strict enum {

    /// There was an internal error in starting the update check.  The client
    /// is not expected to be able to do something meaningful about this error,
    /// except to try again later (after an appropriate delay and back-off in
    /// the event of multiple errors.
    INTERNAL = 1;

    /// If there are required arguments or options (or option values in
    /// conflict), provided via the CheckOptions table to CheckNow, this error
    /// will be returned.
    INVALID_OPTIONS = 2;

    /// There was already another update check in progress when this request was
    /// made.  A new update check will not be started.
    ALREADY_IN_PROGRESS = 3;

    /// The update check was not started, because too many requests to check for
    /// updates have been made by clients in a short period of time.
    ///
    /// **NOTE:** Clients MUST NOT attempt to cause background update checks to
    /// happen at a more frequent rate than the fuchsia.update.Manager will do
    /// them.
    ///
    /// If a client attempts to abuse this, it will be throttled.
    THROTTLED = 4;
};

/// This is the set of values that are provided when an update installation
/// is deferred.
type InstallationDeferralReason = flexible enum {

    /// The update was not installed because the currently booted system is not
    /// committed. Consumers are encouraged to use the [`CommitStatusProvider`]
    /// to determine when to retry the update check such that the update will
    /// be installed.
    CURRENT_SYSTEM_NOT_COMMITTED = 1;
};