1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
/// Fetch lifecycle states.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FetchState {
/// Initial state before any FETCH message is sent.
Idle,
/// FETCH has been sent; awaiting OK or ERROR.
Pending,
/// FETCH_OK received; data is being received on the stream.
Receiving,
/// Fetch has ended (error, cancel, FIN, or reset).
Done,
}
/// Errors that can occur during fetch state transitions.
#[derive(Debug, thiserror::Error, PartialEq, Eq)]
pub enum FetchError {
/// 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: FetchState,
/// The name of the event that was rejected.
event: String,
},
}
/// Pure state machine for a MoQT fetch request.
/// Transitions: Idle -> Pending -> Receiving -> Done.
pub struct FetchStateMachine {
state: FetchState,
}
impl Default for FetchStateMachine {
fn default() -> Self {
Self::new()
}
}
impl FetchStateMachine {
/// Creates a new state machine in the [`FetchState::Idle`] state.
pub fn new() -> Self {
Self { state: FetchState::Idle }
}
/// Returns the current state of the fetch request.
pub fn state(&self) -> FetchState {
self.state
}
/// Idle -> Pending (FETCH sent).
pub fn on_fetch_sent(&mut self) -> Result<(), FetchError> {
if self.state == FetchState::Idle {
self.state = FetchState::Pending;
Ok(())
} else {
Err(FetchError::InvalidTransition {
from: self.state,
event: "on_fetch_sent".to_string(),
})
}
}
/// Pending -> Receiving (FETCH_OK received).
pub fn on_fetch_ok(&mut self) -> Result<(), FetchError> {
if self.state == FetchState::Pending {
self.state = FetchState::Receiving;
Ok(())
} else {
Err(FetchError::InvalidTransition {
from: self.state,
event: "on_fetch_ok".to_string(),
})
}
}
/// Pending -> Done (REQUEST_ERROR received).
pub fn on_fetch_error(&mut self) -> Result<(), FetchError> {
if self.state == FetchState::Pending {
self.state = FetchState::Done;
Ok(())
} else {
Err(FetchError::InvalidTransition {
from: self.state,
event: "on_fetch_error".to_string(),
})
}
}
/// Pending|Receiving -> Done (FETCH_CANCEL sent).
pub fn on_fetch_cancel(&mut self) -> Result<(), FetchError> {
if self.state == FetchState::Pending || self.state == FetchState::Receiving {
self.state = FetchState::Done;
Ok(())
} else {
Err(FetchError::InvalidTransition {
from: self.state,
event: "on_fetch_cancel".to_string(),
})
}
}
/// Receiving -> Done (stream FIN received).
pub fn on_stream_fin(&mut self) -> Result<(), FetchError> {
if self.state == FetchState::Receiving {
self.state = FetchState::Done;
Ok(())
} else {
Err(FetchError::InvalidTransition {
from: self.state,
event: "on_stream_fin".to_string(),
})
}
}
/// Receiving -> Done (stream RESET received).
pub fn on_stream_reset(&mut self) -> Result<(), FetchError> {
if self.state == FetchState::Receiving {
self.state = FetchState::Done;
Ok(())
} else {
Err(FetchError::InvalidTransition {
from: self.state,
event: "on_stream_reset".to_string(),
})
}
}
}