1 // Copyright 2013 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "quiche/quic/core/quic_received_packet_manager.h"
6
7 #include <algorithm>
8 #include <limits>
9 #include <utility>
10
11 #include "quiche/quic/core/congestion_control/rtt_stats.h"
12 #include "quiche/quic/core/crypto/crypto_protocol.h"
13 #include "quiche/quic/core/quic_config.h"
14 #include "quiche/quic/core/quic_connection_stats.h"
15 #include "quiche/quic/core/quic_types.h"
16 #include "quiche/quic/platform/api/quic_bug_tracker.h"
17 #include "quiche/quic/platform/api/quic_flag_utils.h"
18 #include "quiche/quic/platform/api/quic_flags.h"
19 #include "quiche/quic/platform/api/quic_logging.h"
20
21 namespace quic {
22
23 namespace {
24
25 // The maximum number of packets to ack immediately after a missing packet for
26 // fast retransmission to kick in at the sender. This limit is created to
27 // reduce the number of acks sent that have no benefit for fast retransmission.
28 // Set to the number of nacks needed for fast retransmit plus one for protection
29 // against an ack loss
30 const size_t kMaxPacketsAfterNewMissing = 4;
31
32 // One eighth RTT delay when doing ack decimation.
33 const float kShortAckDecimationDelay = 0.125;
34 } // namespace
35
QuicReceivedPacketManager()36 QuicReceivedPacketManager::QuicReceivedPacketManager()
37 : QuicReceivedPacketManager(nullptr) {}
38
QuicReceivedPacketManager(QuicConnectionStats * stats)39 QuicReceivedPacketManager::QuicReceivedPacketManager(QuicConnectionStats* stats)
40 : ack_frame_updated_(false),
41 max_ack_ranges_(0),
42 time_largest_observed_(QuicTime::Zero()),
43 save_timestamps_(false),
44 save_timestamps_for_in_order_packets_(false),
45 stats_(stats),
46 num_retransmittable_packets_received_since_last_ack_sent_(0),
47 min_received_before_ack_decimation_(kMinReceivedBeforeAckDecimation),
48 ack_frequency_(kDefaultRetransmittablePacketsBeforeAck),
49 ack_decimation_delay_(kAckDecimationDelay),
50 unlimited_ack_decimation_(false),
51 one_immediate_ack_(false),
52 ignore_order_(false),
53 local_max_ack_delay_(
54 QuicTime::Delta::FromMilliseconds(kDefaultDelayedAckTimeMs)),
55 ack_timeout_(QuicTime::Zero()),
56 time_of_previous_received_packet_(QuicTime::Zero()),
57 was_last_packet_missing_(false),
58 last_ack_frequency_frame_sequence_number_(-1) {}
59
~QuicReceivedPacketManager()60 QuicReceivedPacketManager::~QuicReceivedPacketManager() {}
61
SetFromConfig(const QuicConfig & config,Perspective perspective)62 void QuicReceivedPacketManager::SetFromConfig(const QuicConfig& config,
63 Perspective perspective) {
64 if (config.HasClientSentConnectionOption(kAKD3, perspective)) {
65 ack_decimation_delay_ = kShortAckDecimationDelay;
66 }
67 if (config.HasClientSentConnectionOption(kAKDU, perspective)) {
68 unlimited_ack_decimation_ = true;
69 }
70 if (config.HasClientSentConnectionOption(k1ACK, perspective)) {
71 one_immediate_ack_ = true;
72 }
73 }
74
RecordPacketReceived(const QuicPacketHeader & header,QuicTime receipt_time,const QuicEcnCodepoint ecn)75 void QuicReceivedPacketManager::RecordPacketReceived(
76 const QuicPacketHeader& header, QuicTime receipt_time,
77 const QuicEcnCodepoint ecn) {
78 const QuicPacketNumber packet_number = header.packet_number;
79 QUICHE_DCHECK(IsAwaitingPacket(packet_number))
80 << " packet_number:" << packet_number;
81 was_last_packet_missing_ = IsMissing(packet_number);
82 if (!ack_frame_updated_) {
83 ack_frame_.received_packet_times.clear();
84 }
85 ack_frame_updated_ = true;
86
87 // Whether |packet_number| is received out of order.
88 bool packet_reordered = false;
89 if (LargestAcked(ack_frame_).IsInitialized() &&
90 LargestAcked(ack_frame_) > packet_number) {
91 // Record how out of order stats.
92 packet_reordered = true;
93 ++stats_->packets_reordered;
94 stats_->max_sequence_reordering =
95 std::max(stats_->max_sequence_reordering,
96 LargestAcked(ack_frame_) - packet_number);
97 int64_t reordering_time_us =
98 (receipt_time - time_largest_observed_).ToMicroseconds();
99 stats_->max_time_reordering_us =
100 std::max(stats_->max_time_reordering_us, reordering_time_us);
101 }
102 if (!LargestAcked(ack_frame_).IsInitialized() ||
103 packet_number > LargestAcked(ack_frame_)) {
104 ack_frame_.largest_acked = packet_number;
105 time_largest_observed_ = receipt_time;
106 }
107 ack_frame_.packets.Add(packet_number);
108 MaybeTrimAckRanges();
109
110 if (save_timestamps_) {
111 // The timestamp format only handles packets in time order.
112 if (save_timestamps_for_in_order_packets_ && packet_reordered) {
113 QUIC_DLOG(WARNING) << "Not saving receive timestamp for packet "
114 << packet_number;
115 } else if (!ack_frame_.received_packet_times.empty() &&
116 ack_frame_.received_packet_times.back().second > receipt_time) {
117 QUIC_LOG(WARNING)
118 << "Receive time went backwards from: "
119 << ack_frame_.received_packet_times.back().second.ToDebuggingValue()
120 << " to " << receipt_time.ToDebuggingValue();
121 } else {
122 ack_frame_.received_packet_times.push_back(
123 std::make_pair(packet_number, receipt_time));
124 }
125 }
126
127 if (ecn != ECN_NOT_ECT) {
128 if (!ack_frame_.ecn_counters.has_value()) {
129 ack_frame_.ecn_counters = QuicEcnCounts();
130 }
131 switch (ecn) {
132 case ECN_NOT_ECT:
133 QUICHE_NOTREACHED();
134 break; // It's impossible to get here, but the compiler complains.
135 case ECN_ECT0:
136 ack_frame_.ecn_counters->ect0++;
137 break;
138 case ECN_ECT1:
139 ack_frame_.ecn_counters->ect1++;
140 break;
141 case ECN_CE:
142 ack_frame_.ecn_counters->ce++;
143 break;
144 }
145 }
146
147 if (least_received_packet_number_.IsInitialized()) {
148 least_received_packet_number_ =
149 std::min(least_received_packet_number_, packet_number);
150 } else {
151 least_received_packet_number_ = packet_number;
152 }
153 }
154
MaybeTrimAckRanges()155 void QuicReceivedPacketManager::MaybeTrimAckRanges() {
156 while (max_ack_ranges_ > 0 &&
157 ack_frame_.packets.NumIntervals() > max_ack_ranges_) {
158 ack_frame_.packets.RemoveSmallestInterval();
159 }
160 }
161
IsMissing(QuicPacketNumber packet_number)162 bool QuicReceivedPacketManager::IsMissing(QuicPacketNumber packet_number) {
163 return LargestAcked(ack_frame_).IsInitialized() &&
164 packet_number < LargestAcked(ack_frame_) &&
165 !ack_frame_.packets.Contains(packet_number);
166 }
167
IsAwaitingPacket(QuicPacketNumber packet_number) const168 bool QuicReceivedPacketManager::IsAwaitingPacket(
169 QuicPacketNumber packet_number) const {
170 return quic::IsAwaitingPacket(ack_frame_, packet_number,
171 peer_least_packet_awaiting_ack_);
172 }
173
GetUpdatedAckFrame(QuicTime approximate_now)174 const QuicFrame QuicReceivedPacketManager::GetUpdatedAckFrame(
175 QuicTime approximate_now) {
176 if (time_largest_observed_ == QuicTime::Zero()) {
177 // We have received no packets.
178 ack_frame_.ack_delay_time = QuicTime::Delta::Infinite();
179 } else {
180 // Ensure the delta is zero if approximate now is "in the past".
181 ack_frame_.ack_delay_time = approximate_now < time_largest_observed_
182 ? QuicTime::Delta::Zero()
183 : approximate_now - time_largest_observed_;
184 }
185
186 const size_t initial_ack_ranges = ack_frame_.packets.NumIntervals();
187 uint64_t num_iterations = 0;
188 while (max_ack_ranges_ > 0 &&
189 ack_frame_.packets.NumIntervals() > max_ack_ranges_) {
190 num_iterations++;
191 QUIC_BUG_IF(quic_rpm_too_many_ack_ranges, (num_iterations % 100000) == 0)
192 << "Too many ack ranges to remove, possibly a dead loop. "
193 "initial_ack_ranges:"
194 << initial_ack_ranges << " max_ack_ranges:" << max_ack_ranges_
195 << ", current_ack_ranges:" << ack_frame_.packets.NumIntervals()
196 << " num_iterations:" << num_iterations;
197 ack_frame_.packets.RemoveSmallestInterval();
198 }
199 // Clear all packet times if any are too far from largest observed.
200 // It's expected this is extremely rare.
201 for (auto it = ack_frame_.received_packet_times.begin();
202 it != ack_frame_.received_packet_times.end();) {
203 if (LargestAcked(ack_frame_) - it->first >=
204 std::numeric_limits<uint8_t>::max()) {
205 it = ack_frame_.received_packet_times.erase(it);
206 } else {
207 ++it;
208 }
209 }
210
211 #if QUIC_FRAME_DEBUG
212 QuicFrame frame = QuicFrame(&ack_frame_);
213 frame.delete_forbidden = true;
214 return frame;
215 #else // QUIC_FRAME_DEBUG
216 return QuicFrame(&ack_frame_);
217 #endif // QUIC_FRAME_DEBUG
218 }
219
DontWaitForPacketsBefore(QuicPacketNumber least_unacked)220 void QuicReceivedPacketManager::DontWaitForPacketsBefore(
221 QuicPacketNumber least_unacked) {
222 if (!least_unacked.IsInitialized()) {
223 return;
224 }
225 // ValidateAck() should fail if peer_least_packet_awaiting_ack shrinks.
226 QUICHE_DCHECK(!peer_least_packet_awaiting_ack_.IsInitialized() ||
227 peer_least_packet_awaiting_ack_ <= least_unacked);
228 if (!peer_least_packet_awaiting_ack_.IsInitialized() ||
229 least_unacked > peer_least_packet_awaiting_ack_) {
230 peer_least_packet_awaiting_ack_ = least_unacked;
231 bool packets_updated = ack_frame_.packets.RemoveUpTo(least_unacked);
232 if (packets_updated) {
233 // Ack frame gets updated because packets set is updated because of stop
234 // waiting frame.
235 ack_frame_updated_ = true;
236 }
237 }
238 QUICHE_DCHECK(ack_frame_.packets.Empty() ||
239 !peer_least_packet_awaiting_ack_.IsInitialized() ||
240 ack_frame_.packets.Min() >= peer_least_packet_awaiting_ack_);
241 }
242
GetMaxAckDelay(QuicPacketNumber last_received_packet_number,const RttStats & rtt_stats) const243 QuicTime::Delta QuicReceivedPacketManager::GetMaxAckDelay(
244 QuicPacketNumber last_received_packet_number,
245 const RttStats& rtt_stats) const {
246 if (AckFrequencyFrameReceived() ||
247 last_received_packet_number < PeerFirstSendingPacketNumber() +
248 min_received_before_ack_decimation_) {
249 return local_max_ack_delay_;
250 }
251
252 // Wait for the minimum of the ack decimation delay or the delayed ack time
253 // before sending an ack.
254 QuicTime::Delta ack_delay = std::min(
255 local_max_ack_delay_, rtt_stats.min_rtt() * ack_decimation_delay_);
256 return std::max(ack_delay, kAlarmGranularity);
257 }
258
MaybeUpdateAckFrequency(QuicPacketNumber last_received_packet_number)259 void QuicReceivedPacketManager::MaybeUpdateAckFrequency(
260 QuicPacketNumber last_received_packet_number) {
261 if (AckFrequencyFrameReceived()) {
262 // Skip Ack Decimation below after receiving an AckFrequencyFrame from the
263 // other end point.
264 return;
265 }
266 if (last_received_packet_number <
267 PeerFirstSendingPacketNumber() + min_received_before_ack_decimation_) {
268 return;
269 }
270 ack_frequency_ = unlimited_ack_decimation_
271 ? std::numeric_limits<size_t>::max()
272 : kMaxRetransmittablePacketsBeforeAck;
273 }
274
MaybeUpdateAckTimeout(bool should_last_packet_instigate_acks,QuicPacketNumber last_received_packet_number,QuicTime last_packet_receipt_time,QuicTime now,const RttStats * rtt_stats)275 void QuicReceivedPacketManager::MaybeUpdateAckTimeout(
276 bool should_last_packet_instigate_acks,
277 QuicPacketNumber last_received_packet_number,
278 QuicTime last_packet_receipt_time, QuicTime now,
279 const RttStats* rtt_stats) {
280 if (!ack_frame_updated_) {
281 // ACK frame has not been updated, nothing to do.
282 return;
283 }
284
285 if (!ignore_order_ && was_last_packet_missing_ &&
286 last_sent_largest_acked_.IsInitialized() &&
287 last_received_packet_number < last_sent_largest_acked_) {
288 // Only ack immediately if an ACK frame was sent with a larger largest acked
289 // than the newly received packet number.
290 ack_timeout_ = now;
291 return;
292 }
293
294 if (!should_last_packet_instigate_acks) {
295 return;
296 }
297
298 ++num_retransmittable_packets_received_since_last_ack_sent_;
299
300 MaybeUpdateAckFrequency(last_received_packet_number);
301 if (num_retransmittable_packets_received_since_last_ack_sent_ >=
302 ack_frequency_) {
303 ack_timeout_ = now;
304 return;
305 }
306
307 if (!ignore_order_ && HasNewMissingPackets()) {
308 ack_timeout_ = now;
309 return;
310 }
311
312 const QuicTime updated_ack_time = std::max(
313 now, std::min(last_packet_receipt_time, now) +
314 GetMaxAckDelay(last_received_packet_number, *rtt_stats));
315 if (!ack_timeout_.IsInitialized() || ack_timeout_ > updated_ack_time) {
316 ack_timeout_ = updated_ack_time;
317 }
318 }
319
ResetAckStates()320 void QuicReceivedPacketManager::ResetAckStates() {
321 ack_frame_updated_ = false;
322 ack_timeout_ = QuicTime::Zero();
323 num_retransmittable_packets_received_since_last_ack_sent_ = 0;
324 last_sent_largest_acked_ = LargestAcked(ack_frame_);
325 }
326
HasMissingPackets() const327 bool QuicReceivedPacketManager::HasMissingPackets() const {
328 if (ack_frame_.packets.Empty()) {
329 return false;
330 }
331 if (ack_frame_.packets.NumIntervals() > 1) {
332 return true;
333 }
334 return peer_least_packet_awaiting_ack_.IsInitialized() &&
335 ack_frame_.packets.Min() > peer_least_packet_awaiting_ack_;
336 }
337
HasNewMissingPackets() const338 bool QuicReceivedPacketManager::HasNewMissingPackets() const {
339 if (one_immediate_ack_) {
340 return HasMissingPackets() && ack_frame_.packets.LastIntervalLength() == 1;
341 }
342 return HasMissingPackets() &&
343 ack_frame_.packets.LastIntervalLength() <= kMaxPacketsAfterNewMissing;
344 }
345
ack_frame_updated() const346 bool QuicReceivedPacketManager::ack_frame_updated() const {
347 return ack_frame_updated_;
348 }
349
GetLargestObserved() const350 QuicPacketNumber QuicReceivedPacketManager::GetLargestObserved() const {
351 return LargestAcked(ack_frame_);
352 }
353
PeerFirstSendingPacketNumber() const354 QuicPacketNumber QuicReceivedPacketManager::PeerFirstSendingPacketNumber()
355 const {
356 if (!least_received_packet_number_.IsInitialized()) {
357 QUIC_BUG(quic_bug_10849_1) << "No packets have been received yet";
358 return QuicPacketNumber(1);
359 }
360 return least_received_packet_number_;
361 }
362
IsAckFrameEmpty() const363 bool QuicReceivedPacketManager::IsAckFrameEmpty() const {
364 return ack_frame_.packets.Empty();
365 }
366
OnAckFrequencyFrame(const QuicAckFrequencyFrame & frame)367 void QuicReceivedPacketManager::OnAckFrequencyFrame(
368 const QuicAckFrequencyFrame& frame) {
369 int64_t new_sequence_number = frame.sequence_number;
370 if (new_sequence_number <= last_ack_frequency_frame_sequence_number_) {
371 // Ignore old ACK_FREQUENCY frames.
372 return;
373 }
374 last_ack_frequency_frame_sequence_number_ = new_sequence_number;
375 ack_frequency_ = frame.packet_tolerance;
376 local_max_ack_delay_ = frame.max_ack_delay;
377 ignore_order_ = frame.ignore_order;
378 }
379
380 } // namespace quic
381