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
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
use crate::{ack, packet::number::PacketNumber};
use core::ops::RangeInclusive;
pub type AckRange = RangeInclusive<PacketNumber>;
#[derive(Clone, Debug, Default)]
pub struct Set {
/// A stable ack-eliciting transmission
///
/// In this case, "stable" means the oldest transmission that
/// hasn't been acked by the peer.
///
/// This transmission is stored to ensure the packet number ranges
/// are always either removed or declared lost. Without it,
/// the TX packet number would be a moving target
/// and packet number ranges would never be removed.
stable: Option<Transmission>,
/// The latest ack-eliciting transmission
latest: Option<Transmission>,
}
impl Set {
/// Called when an ACK frame is bundled with an ack eliciting packet
#[inline]
pub fn on_transmit(&mut self, transmission: Transmission) {
self.latest = Some(transmission);
// only set the stable transmission if it's not set
if self.stable.is_none() {
self.stable = Some(transmission);
}
}
/// Called when a set of packets was acknowledged or lost
#[inline]
pub fn on_update<A: ack::Set>(&mut self, ack_set: &A) -> Option<AckRange> {
if let Some(ack_range) = self
.latest
.as_ref()
.and_then(|transmission| transmission.ack_range(ack_set))
{
// the latest was either ACKed or lost so there is nothing pending
self.stable = None;
self.latest = None;
return Some(ack_range);
}
if let Some(ack_range) = self
.stable
.as_ref()
.and_then(|transmission| transmission.ack_range(ack_set))
{
// assign the latest transmission to stable
self.stable = self.latest;
return Some(ack_range);
}
None
}
/// Returns `true` if there are no pending ack-eliciting transmissions
/// Only used by tests
#[cfg(test)]
pub fn is_empty(&self) -> bool {
self.stable.is_none() && self.latest.is_none()
}
}
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd)]
pub struct Transmission {
pub sent_in_packet: PacketNumber,
pub largest_received_packet_number_acked: PacketNumber,
}
impl Transmission {
/// Called when a set of packets was acknowledged or lost
#[inline]
pub fn ack_range<A: ack::Set>(&self, ack_set: &A) -> Option<AckRange> {
//= https://www.rfc-editor.org/rfc/rfc9000#section-13.2.4
//# When a packet containing an ACK frame is acknowledged, the receiver can stop
//# acknowledging packets less than or equal to the Largest Acknowledged
//# field in the sent ACK frame.
if ack_set.contains(self.sent_in_packet) {
// create a range from 0..=largest
let pn_zero = self
.largest_received_packet_number_acked
.space()
.new_packet_number(Default::default());
Some(pn_zero..=self.largest_received_packet_number_acked)
} else {
None
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::ack::testing::transmissions_iter;
/// This test is meant to simulate an immediate ACK rate from a peer
#[test]
fn latest_ack_test() {
let mut set = Set::default();
assert!(set.is_empty());
let mut transmissions = transmissions_iter();
for transmission_count in 0..10 {
let stable = transmissions.next().unwrap();
set.on_transmit(stable);
// simulate a few transmissions before ACKing
let mut latest = stable;
for _ in 0..transmission_count {
latest = transmissions.next().unwrap();
set.on_transmit(latest);
}
// ACKing `latest` simulates an immediate ACK from peer
assert_eq!(
set.on_update(&latest.sent_in_packet).unwrap().end(),
&latest.largest_received_packet_number_acked
);
// ACKing the latest removes all items
assert!(set.is_empty());
}
}
/// This test is meant to simulate a delayed ACK rate from a peer
#[test]
fn stable_ack_test() {
let mut set = Set::default();
assert!(set.is_empty());
let mut transmissions = transmissions_iter();
// create an initial transmission
let mut stable = transmissions.next().unwrap();
set.on_transmit(stable);
for transmission_count in 0..10 {
// simulate a few transmissions before ACKing
let mut latest = stable;
for _ in 0..transmission_count {
latest = transmissions.next().unwrap();
set.on_transmit(latest);
}
// ACKing `stable` simulates a delayed ACK from peer
assert_eq!(
set.on_update(&stable.sent_in_packet).unwrap().end(),
&stable.largest_received_packet_number_acked
);
// on update latest is moved into stable
stable = latest;
// if there weren't any transmissions between, the set
// should be empty
if transmission_count == 0 {
assert!(set.is_empty());
set.on_transmit(stable);
}
}
}
#[test]
#[cfg_attr(miri, ignore)] // miri is unable to read the file system
fn size_of_snapshots() {
use core::mem::size_of;
use insta::assert_debug_snapshot;
assert_debug_snapshot!("Transmission", size_of::<Transmission>());
assert_debug_snapshot!("Set", size_of::<Set>());
}
}