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/// Subscription lifecycle states.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SubscriptionState {
/// Initial state before any SUBSCRIBE message is sent.
Idle,
/// SUBSCRIBE has been sent; awaiting OK or ERROR.
Subscribing,
/// Subscription is accepted and data may be flowing.
Active,
/// Subscription has ended (error, unsubscribe, or publish done).
Done,
}
/// Errors that can occur during subscription state transitions.
#[derive(Debug, thiserror::Error, PartialEq, Eq)]
pub enum SubscriptionError {
/// An event was received that is not valid for the current state.
#[error("invalid transition from {from:?} on event {event}")]
InvalidTransition {
/// The state the machine was in when the invalid event arrived.
from: SubscriptionState,
/// The name of the event that was rejected.
event: String,
},
}
/// Pure state machine for a MoQT subscription.
/// Transitions: Idle -> Subscribing -> Active -> Done.
pub struct SubscriptionStateMachine {
state: SubscriptionState,
}
impl Default for SubscriptionStateMachine {
fn default() -> Self {
Self::new()
}
}
impl SubscriptionStateMachine {
/// Creates a new state machine in the [`SubscriptionState::Idle`] state.
pub fn new() -> Self {
Self { state: SubscriptionState::Idle }
}
/// Returns the current state of the subscription.
pub fn state(&self) -> SubscriptionState {
self.state
}
/// Idle -> Subscribing (SUBSCRIBE sent).
pub fn on_subscribe_sent(&mut self) -> Result<(), SubscriptionError> {
if self.state == SubscriptionState::Idle {
self.state = SubscriptionState::Subscribing;
Ok(())
} else {
Err(SubscriptionError::InvalidTransition {
from: self.state,
event: "on_subscribe_sent".to_string(),
})
}
}
/// Subscribing -> Active (SUBSCRIBE_OK received).
pub fn on_subscribe_ok(&mut self) -> Result<(), SubscriptionError> {
if self.state == SubscriptionState::Subscribing {
self.state = SubscriptionState::Active;
Ok(())
} else {
Err(SubscriptionError::InvalidTransition {
from: self.state,
event: "on_subscribe_ok".to_string(),
})
}
}
/// Subscribing -> Done (REQUEST_ERROR received).
pub fn on_subscribe_error(&mut self) -> Result<(), SubscriptionError> {
if self.state == SubscriptionState::Subscribing {
self.state = SubscriptionState::Done;
Ok(())
} else {
Err(SubscriptionError::InvalidTransition {
from: self.state,
event: "on_subscribe_error".to_string(),
})
}
}
/// Active -> Done (UNSUBSCRIBE sent).
pub fn on_unsubscribe(&mut self) -> Result<(), SubscriptionError> {
if self.state == SubscriptionState::Active {
self.state = SubscriptionState::Done;
Ok(())
} else {
Err(SubscriptionError::InvalidTransition {
from: self.state,
event: "on_unsubscribe".to_string(),
})
}
}
/// Active -> Active (SUBSCRIBE_UPDATE received -- self-transition).
pub fn on_subscribe_update(&mut self) -> Result<(), SubscriptionError> {
if self.state == SubscriptionState::Active {
Ok(())
} else {
Err(SubscriptionError::InvalidTransition {
from: self.state,
event: "on_subscribe_update".to_string(),
})
}
}
/// Active -> Done (PUBLISH_DONE received).
pub fn on_publish_done(&mut self) -> Result<(), SubscriptionError> {
if self.state == SubscriptionState::Active {
self.state = SubscriptionState::Done;
Ok(())
} else {
Err(SubscriptionError::InvalidTransition {
from: self.state,
event: "on_publish_done".to_string(),
})
}
}
}