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/*
* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "net/dcsctp/tx/retransmission_queue.h"
#include <algorithm>
#include <cstdint>
#include <functional>
#include <iterator>
#include <map>
#include <set>
#include <string>
#include <utility>
#include <vector>
#include "absl/algorithm/container.h"
#include "absl/strings/string_view.h"
#include "absl/types/optional.h"
#include "api/array_view.h"
#include "net/dcsctp/common/math.h"
#include "net/dcsctp/common/sequence_numbers.h"
#include "net/dcsctp/common/str_join.h"
#include "net/dcsctp/packet/chunk/data_chunk.h"
#include "net/dcsctp/packet/chunk/forward_tsn_chunk.h"
#include "net/dcsctp/packet/chunk/forward_tsn_common.h"
#include "net/dcsctp/packet/chunk/idata_chunk.h"
#include "net/dcsctp/packet/chunk/iforward_tsn_chunk.h"
#include "net/dcsctp/packet/chunk/sack_chunk.h"
#include "net/dcsctp/packet/data.h"
#include "net/dcsctp/public/dcsctp_options.h"
#include "net/dcsctp/public/types.h"
#include "net/dcsctp/timer/timer.h"
#include "net/dcsctp/tx/send_queue.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/strings/string_builder.h"
namespace dcsctp {
namespace {
// The number of times a packet must be NACKed before it's retransmitted.
// See https://tools.ietf.org/html/rfc4960#section-7.2.4
constexpr size_t kNumberOfNacksForRetransmission = 3;
// Allow sending only slightly less than an MTU, to account for headers.
constexpr float kMinBytesRequiredToSendFactor = 0.9;
} // namespace
RetransmissionQueue::RetransmissionQueue(
absl::string_view log_prefix,
TSN initial_tsn,
size_t a_rwnd,
SendQueue& send_queue,
std::function<void(DurationMs rtt)> on_new_rtt,
std::function<void()> on_clear_retransmission_counter,
Timer& t3_rtx,
const DcSctpOptions& options,
bool supports_partial_reliability,
bool use_message_interleaving)
: options_(options),
min_bytes_required_to_send_(options.mtu * kMinBytesRequiredToSendFactor),
partial_reliability_(supports_partial_reliability),
log_prefix_(std::string(log_prefix) + "tx: "),
data_chunk_header_size_(use_message_interleaving
? IDataChunk::kHeaderSize
: DataChunk::kHeaderSize),
on_new_rtt_(std::move(on_new_rtt)),
on_clear_retransmission_counter_(
std::move(on_clear_retransmission_counter)),
t3_rtx_(t3_rtx),
cwnd_(options_.cwnd_mtus_initial * options_.mtu),
rwnd_(a_rwnd),
// https://tools.ietf.org/html/rfc4960#section-7.2.1
// "The initial value of ssthresh MAY be arbitrarily high (for
// example, implementations MAY use the size of the receiver advertised
// window).""
ssthresh_(rwnd_),
next_tsn_(tsn_unwrapper_.Unwrap(initial_tsn)),
last_cumulative_tsn_ack_(tsn_unwrapper_.Unwrap(TSN(*initial_tsn - 1))),
send_queue_(send_queue) {}
bool RetransmissionQueue::IsConsistent() const {
size_t actual_outstanding_bytes = 0;
size_t actual_outstanding_items = 0;
std::set<UnwrappedTSN> actual_to_be_retransmitted;
for (const auto& elem : outstanding_data_) {
if (elem.second.is_outstanding()) {
actual_outstanding_bytes += GetSerializedChunkSize(elem.second.data());
++actual_outstanding_items;
}
if (elem.second.should_be_retransmitted()) {
actual_to_be_retransmitted.insert(elem.first);
}
}
return actual_outstanding_bytes == outstanding_bytes_ &&
actual_outstanding_items == outstanding_items_ &&
actual_to_be_retransmitted == to_be_retransmitted_;
}
// Returns how large a chunk will be, serialized, carrying the data
size_t RetransmissionQueue::GetSerializedChunkSize(const Data& data) const {
return RoundUpTo4(data_chunk_header_size_ + data.size());
}
void RetransmissionQueue::RemoveAcked(UnwrappedTSN cumulative_tsn_ack,
AckInfo& ack_info) {
auto first_unacked = outstanding_data_.upper_bound(cumulative_tsn_ack);
for (auto iter = outstanding_data_.begin(); iter != first_unacked; ++iter) {
AckChunk(ack_info, iter);
}
outstanding_data_.erase(outstanding_data_.begin(), first_unacked);
}
void RetransmissionQueue::AckGapBlocks(
UnwrappedTSN cumulative_tsn_ack,
rtc::ArrayView<const SackChunk::GapAckBlock> gap_ack_blocks,
AckInfo& ack_info) {
// Mark all non-gaps as ACKED (but they can't be removed) as (from RFC)
// "SCTP considers the information carried in the Gap Ack Blocks in the
// SACK chunk as advisory.". Note that when NR-SACK is supported, this can be
// handled differently.
for (auto& block : gap_ack_blocks) {
auto start = outstanding_data_.lower_bound(
UnwrappedTSN::AddTo(cumulative_tsn_ack, block.start));
auto end = outstanding_data_.upper_bound(
UnwrappedTSN::AddTo(cumulative_tsn_ack, block.end));
for (auto iter = start; iter != end; ++iter) {
AckChunk(ack_info, iter);
}
}
}
void RetransmissionQueue::AckChunk(
AckInfo& ack_info,
std::map<UnwrappedTSN, TxData>::iterator iter) {
if (!iter->second.is_acked()) {
size_t serialized_size = GetSerializedChunkSize(iter->second.data());
ack_info.bytes_acked += serialized_size;
ack_info.acked_tsns.push_back(iter->first.Wrap());
if (iter->second.is_outstanding()) {
outstanding_bytes_ -= serialized_size;
--outstanding_items_;
}
if (iter->second.should_be_retransmitted()) {
to_be_retransmitted_.erase(iter->first);
}
iter->second.Ack();
ack_info.highest_tsn_acked =
std::max(ack_info.highest_tsn_acked, iter->first);
}
}
void RetransmissionQueue::NackBetweenAckBlocks(
UnwrappedTSN cumulative_tsn_ack,
rtc::ArrayView<const SackChunk::GapAckBlock> gap_ack_blocks,
AckInfo& ack_info) {
// Mark everything between the blocks as NACKED/TO_BE_RETRANSMITTED.
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "Mark the DATA chunk(s) with three miss indications for retransmission."
// "For each incoming SACK, miss indications are incremented only for
// missing TSNs prior to the highest TSN newly acknowledged in the SACK."
//
// What this means is that only when there is a increasing stream of data
// received and there are new packets seen (since last time), packets that are
// in-flight and between gaps should be nacked. This means that SCTP relies on
// the T3-RTX-timer to re-send packets otherwise.
UnwrappedTSN max_tsn_to_nack = ack_info.highest_tsn_acked;
if (is_in_fast_recovery() && cumulative_tsn_ack > last_cumulative_tsn_ack_) {
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "If an endpoint is in Fast Recovery and a SACK arrives that advances
// the Cumulative TSN Ack Point, the miss indications are incremented for
// all TSNs reported missing in the SACK."
max_tsn_to_nack = UnwrappedTSN::AddTo(
cumulative_tsn_ack,
gap_ack_blocks.empty() ? 0 : gap_ack_blocks.rbegin()->end);
}
UnwrappedTSN prev_block_last_acked = cumulative_tsn_ack;
for (auto& block : gap_ack_blocks) {
UnwrappedTSN cur_block_first_acked =
UnwrappedTSN::AddTo(cumulative_tsn_ack, block.start);
for (auto iter = outstanding_data_.upper_bound(prev_block_last_acked);
iter != outstanding_data_.lower_bound(cur_block_first_acked); ++iter) {
if (iter->first <= max_tsn_to_nack) {
ack_info.has_packet_loss =
NackItem(iter->first, iter->second, /*retransmit_now=*/false);
}
}
prev_block_last_acked = UnwrappedTSN::AddTo(cumulative_tsn_ack, block.end);
}
// Note that packets are not NACKED which are above the highest gap-ack-block
// (or above the cumulative ack TSN if no gap-ack-blocks) as only packets
// up until the highest_tsn_acked (see above) should be considered when
// NACKing.
}
void RetransmissionQueue::MaybeExitFastRecovery(
UnwrappedTSN cumulative_tsn_ack) {
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "When a SACK acknowledges all TSNs up to and including this [fast
// recovery] exit point, Fast Recovery is exited."
if (fast_recovery_exit_tsn_.has_value() &&
cumulative_tsn_ack >= *fast_recovery_exit_tsn_) {
RTC_DLOG(LS_VERBOSE) << log_prefix_
<< "exit_point=" << *fast_recovery_exit_tsn_->Wrap()
<< " reached - exiting fast recovery";
fast_recovery_exit_tsn_ = absl::nullopt;
}
}
void RetransmissionQueue::HandleIncreasedCumulativeTsnAck(
size_t outstanding_bytes,
size_t total_bytes_acked) {
// Allow some margin for classifying as fully utilized, due to e.g. that too
// small packets (less than kMinimumFragmentedPayload) are not sent +
// overhead.
bool is_fully_utilized = outstanding_bytes + options_.mtu >= cwnd_;
size_t old_cwnd = cwnd_;
if (phase() == CongestionAlgorithmPhase::kSlowStart) {
if (is_fully_utilized && !is_in_fast_recovery()) {
// https://tools.ietf.org/html/rfc4960#section-7.2.1
// "Only when these three conditions are met can the cwnd be
// increased; otherwise, the cwnd MUST not be increased. If these
// conditions are met, then cwnd MUST be increased by, at most, the
// lesser of 1) the total size of the previously outstanding DATA
// chunk(s) acknowledged, and 2) the destination's path MTU."
if (options_.slow_start_tcp_style) {
cwnd_ += std::min(total_bytes_acked, cwnd_);
} else {
cwnd_ += std::min(total_bytes_acked, options_.mtu);
}
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "SS increase cwnd=" << cwnd_
<< " (" << old_cwnd << ")";
}
} else if (phase() == CongestionAlgorithmPhase::kCongestionAvoidance) {
// https://tools.ietf.org/html/rfc4960#section-7.2.2
// "Whenever cwnd is greater than ssthresh, upon each SACK arrival
// that advances the Cumulative TSN Ack Point, increase
// partial_bytes_acked by the total number of bytes of all new chunks
// acknowledged in that SACK including chunks acknowledged by the new
// Cumulative TSN Ack and by Gap Ack Blocks."
size_t old_pba = partial_bytes_acked_;
partial_bytes_acked_ += total_bytes_acked;
if (partial_bytes_acked_ >= cwnd_ && is_fully_utilized) {
// https://tools.ietf.org/html/rfc4960#section-7.2.2
// "When partial_bytes_acked is equal to or greater than cwnd and
// before the arrival of the SACK the sender had cwnd or more bytes of
// data outstanding (i.e., before arrival of the SACK, flightsize was
// greater than or equal to cwnd), increase cwnd by MTU, and reset
// partial_bytes_acked to (partial_bytes_acked - cwnd)."
cwnd_ += options_.mtu;
partial_bytes_acked_ -= cwnd_;
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "CA increase cwnd=" << cwnd_
<< " (" << old_cwnd << ") ssthresh=" << ssthresh_
<< ", pba=" << partial_bytes_acked_ << " ("
<< old_pba << ")";
} else {
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "CA unchanged cwnd=" << cwnd_
<< " (" << old_cwnd << ") ssthresh=" << ssthresh_
<< ", pba=" << partial_bytes_acked_ << " ("
<< old_pba << ")";
}
}
}
void RetransmissionQueue::HandlePacketLoss(UnwrappedTSN highest_tsn_acked) {
if (!is_in_fast_recovery()) {
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "If not in Fast Recovery, adjust the ssthresh and cwnd of the
// destination address(es) to which the missing DATA chunks were last
// sent, according to the formula described in Section 7.2.3."
size_t old_cwnd = cwnd_;
size_t old_pba = partial_bytes_acked_;
ssthresh_ = std::max(cwnd_ / 2, options_.cwnd_mtus_min * options_.mtu);
cwnd_ = ssthresh_;
partial_bytes_acked_ = 0;
RTC_DLOG(LS_VERBOSE) << log_prefix_
<< "packet loss detected (not fast recovery). cwnd="
<< cwnd_ << " (" << old_cwnd
<< "), ssthresh=" << ssthresh_
<< ", pba=" << partial_bytes_acked_ << " (" << old_pba
<< ")";
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "If not in Fast Recovery, enter Fast Recovery and mark the highest
// outstanding TSN as the Fast Recovery exit point."
fast_recovery_exit_tsn_ = outstanding_data_.empty()
? last_cumulative_tsn_ack_
: outstanding_data_.rbegin()->first;
RTC_DLOG(LS_VERBOSE) << log_prefix_
<< "fast recovery initiated with exit_point="
<< *fast_recovery_exit_tsn_->Wrap();
} else {
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "While in Fast Recovery, the ssthresh and cwnd SHOULD NOT change for
// any destinations due to a subsequent Fast Recovery event (i.e., one
// SHOULD NOT reduce the cwnd further due to a subsequent Fast Retransmit)."
RTC_DLOG(LS_VERBOSE) << log_prefix_
<< "packet loss detected (fast recovery). No changes.";
}
}
void RetransmissionQueue::UpdateReceiverWindow(uint32_t a_rwnd) {
rwnd_ = outstanding_bytes_ >= a_rwnd ? 0 : a_rwnd - outstanding_bytes_;
}
void RetransmissionQueue::StartT3RtxTimerIfOutstandingData() {
// Note: Can't use `outstanding_bytes()` as that one doesn't count chunks to
// be retransmitted.
if (outstanding_data_.empty()) {
// https://tools.ietf.org/html/rfc4960#section-6.3.2
// "Whenever all outstanding data sent to an address have been
// acknowledged, turn off the T3-rtx timer of that address.
// Note: Already stopped in `StopT3RtxTimerOnIncreasedCumulativeTsnAck`."
} else {
// https://tools.ietf.org/html/rfc4960#section-6.3.2
// "Whenever a SACK is received that acknowledges the DATA chunk
// with the earliest outstanding TSN for that address, restart the T3-rtx
// timer for that address with its current RTO (if there is still
// outstanding data on that address)."
// "Whenever a SACK is received missing a TSN that was previously
// acknowledged via a Gap Ack Block, start the T3-rtx for the destination
// address to which the DATA chunk was originally transmitted if it is not
// already running."
if (!t3_rtx_.is_running()) {
t3_rtx_.Start();
}
}
}
bool RetransmissionQueue::IsSackValid(const SackChunk& sack) const {
// https://tools.ietf.org/html/rfc4960#section-6.2.1
// "If Cumulative TSN Ack is less than the Cumulative TSN Ack Point,
// then drop the SACK. Since Cumulative TSN Ack is monotonically increasing,
// a SACK whose Cumulative TSN Ack is less than the Cumulative TSN Ack Point
// indicates an out-of- order SACK."
//
// Note: Important not to drop SACKs with identical TSN to that previously
// received, as the gap ack blocks or dup tsn fields may have changed.
UnwrappedTSN cumulative_tsn_ack =
tsn_unwrapper_.PeekUnwrap(sack.cumulative_tsn_ack());
if (cumulative_tsn_ack < last_cumulative_tsn_ack_) {
// https://tools.ietf.org/html/rfc4960#section-6.2.1
// "If Cumulative TSN Ack is less than the Cumulative TSN Ack Point,
// then drop the SACK. Since Cumulative TSN Ack is monotonically
// increasing, a SACK whose Cumulative TSN Ack is less than the Cumulative
// TSN Ack Point indicates an out-of- order SACK."
return false;
} else if (outstanding_data_.empty() &&
cumulative_tsn_ack > last_cumulative_tsn_ack_) {
// No in-flight data and cum-tsn-ack above what was last ACKed - not valid.
return false;
} else if (!outstanding_data_.empty() &&
cumulative_tsn_ack > outstanding_data_.rbegin()->first) {
// There is in-flight data, but the cum-tsn-ack is beyond that - not valid.
return false;
}
return true;
}
bool RetransmissionQueue::HandleSack(TimeMs now, const SackChunk& sack) {
if (!IsSackValid(sack)) {
return false;
}
size_t old_outstanding_bytes = outstanding_bytes_;
size_t old_rwnd = rwnd_;
UnwrappedTSN cumulative_tsn_ack =
tsn_unwrapper_.Unwrap(sack.cumulative_tsn_ack());
if (sack.gap_ack_blocks().empty()) {
UpdateRTT(now, cumulative_tsn_ack);
}
AckInfo ack_info(cumulative_tsn_ack);
// Erase all items up to cumulative_tsn_ack.
RemoveAcked(cumulative_tsn_ack, ack_info);
// ACK packets reported in the gap ack blocks
AckGapBlocks(cumulative_tsn_ack, sack.gap_ack_blocks(), ack_info);
// NACK and possibly mark for retransmit chunks that weren't acked.
NackBetweenAckBlocks(cumulative_tsn_ack, sack.gap_ack_blocks(), ack_info);
// Update of outstanding_data_ is now done. Congestion control remains.
UpdateReceiverWindow(sack.a_rwnd());
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "Received SACK. Acked TSN: "
<< StrJoin(ack_info.acked_tsns, ",",
[](rtc::StringBuilder& sb, TSN tsn) {
sb << *tsn;
})
<< ", cum_tsn_ack=" << *cumulative_tsn_ack.Wrap() << " ("
<< *last_cumulative_tsn_ack_.Wrap()
<< "), outstanding_bytes=" << outstanding_bytes_ << " ("
<< old_outstanding_bytes << "), rwnd=" << rwnd_ << " ("
<< old_rwnd << ")";
MaybeExitFastRecovery(cumulative_tsn_ack);
if (cumulative_tsn_ack > last_cumulative_tsn_ack_) {
// https://tools.ietf.org/html/rfc4960#section-6.3.2
// "Whenever a SACK is received that acknowledges the DATA chunk
// with the earliest outstanding TSN for that address, restart the T3-rtx
// timer for that address with its current RTO (if there is still
// outstanding data on that address)."
// Note: It may be started again in a bit further down.
t3_rtx_.Stop();
HandleIncreasedCumulativeTsnAck(old_outstanding_bytes,
ack_info.bytes_acked);
}
if (ack_info.has_packet_loss) {
is_in_fast_retransmit_ = true;
HandlePacketLoss(ack_info.highest_tsn_acked);
}
// https://tools.ietf.org/html/rfc4960#section-8.2
// "When an outstanding TSN is acknowledged [...] the endpoint shall clear
// the error counter ..."
if (ack_info.bytes_acked > 0) {
on_clear_retransmission_counter_();
}
last_cumulative_tsn_ack_ = cumulative_tsn_ack;
StartT3RtxTimerIfOutstandingData();
RTC_DCHECK(IsConsistent());
return true;
}
void RetransmissionQueue::UpdateRTT(TimeMs now,
UnwrappedTSN cumulative_tsn_ack) {
// RTT updating is flawed in SCTP, as explained in e.g. Pedersen J, Griwodz C,
// Halvorsen P (2006) Considerations of SCTP retransmission delays for thin
// streams.
// Due to delayed acknowledgement, the SACK may be sent much later which
// increases the calculated RTT.
// TODO(boivie): Consider occasionally sending DATA chunks with I-bit set and
// use only those packets for measurement.
auto it = outstanding_data_.find(cumulative_tsn_ack);
if (it != outstanding_data_.end()) {
if (!it->second.has_been_retransmitted()) {
// https://tools.ietf.org/html/rfc4960#section-6.3.1
// "Karn's algorithm: RTT measurements MUST NOT be made using
// packets that were retransmitted (and thus for which it is ambiguous
// whether the reply was for the first instance of the chunk or for a
// later instance)"
DurationMs rtt = now - it->second.time_sent();
on_new_rtt_(rtt);
}
}
}
void RetransmissionQueue::HandleT3RtxTimerExpiry() {
size_t old_cwnd = cwnd_;
size_t old_outstanding_bytes = outstanding_bytes_;
// https://tools.ietf.org/html/rfc4960#section-6.3.3
// "For the destination address for which the timer expires, adjust
// its ssthresh with rules defined in Section 7.2.3 and set the cwnd <- MTU."
ssthresh_ = std::max(cwnd_ / 2, 4 * options_.mtu);
cwnd_ = 1 * options_.mtu;
// https://tools.ietf.org/html/rfc4960#section-6.3.3
// "For the destination address for which the timer expires, set RTO
// <- RTO * 2 ("back off the timer"). The maximum value discussed in rule C7
// above (RTO.max) may be used to provide an upper bound to this doubling
// operation."
// Already done by the Timer implementation.
// https://tools.ietf.org/html/rfc4960#section-6.3.3
// "Determine how many of the earliest (i.e., lowest TSN) outstanding
// DATA chunks for the address for which the T3-rtx has expired will fit into
// a single packet"
// https://tools.ietf.org/html/rfc4960#section-6.3.3
// "Note: Any DATA chunks that were sent to the address for which the
// T3-rtx timer expired but did not fit in one MTU (rule E3 above) should be
// marked for retransmission and sent as soon as cwnd allows (normally, when a
// SACK arrives)."
for (auto& elem : outstanding_data_) {
UnwrappedTSN tsn = elem.first;
TxData& item = elem.second;
if (!item.is_acked()) {
NackItem(tsn, item, /*retransmit_now=*/true);
}
}
// https://tools.ietf.org/html/rfc4960#section-6.3.3
// "Start the retransmission timer T3-rtx on the destination address
// to which the retransmission is sent, if rule R1 above indicates to do so."
// Already done by the Timer implementation.
RTC_DLOG(LS_INFO) << log_prefix_ << "t3-rtx expired. new cwnd=" << cwnd_
<< " (" << old_cwnd << "), ssthresh=" << ssthresh_
<< ", outstanding_bytes " << outstanding_bytes_ << " ("
<< old_outstanding_bytes << ")";
RTC_DCHECK(IsConsistent());
}
bool RetransmissionQueue::NackItem(UnwrappedTSN tsn,
TxData& item,
bool retransmit_now) {
if (item.is_outstanding()) {
outstanding_bytes_ -= GetSerializedChunkSize(item.data());
--outstanding_items_;
}
switch (item.Nack(retransmit_now)) {
case TxData::NackAction::kNothing:
return false;
case TxData::NackAction::kRetransmit:
to_be_retransmitted_.insert(tsn);
RTC_DLOG(LS_VERBOSE) << log_prefix_ << *tsn.Wrap()
<< " marked for retransmission";
break;
case TxData::NackAction::kAbandon:
AbandonAllFor(item);
break;
}
return true;
}
std::vector<std::pair<TSN, Data>>
RetransmissionQueue::GetChunksToBeRetransmitted(size_t max_size) {
std::vector<std::pair<TSN, Data>> result;
for (auto it = to_be_retransmitted_.begin();
it != to_be_retransmitted_.end();) {
UnwrappedTSN tsn = *it;
auto elem = outstanding_data_.find(tsn);
RTC_DCHECK(elem != outstanding_data_.end());
TxData& item = elem->second;
RTC_DCHECK(item.should_be_retransmitted());
RTC_DCHECK(!item.is_outstanding());
RTC_DCHECK(!item.is_abandoned());
RTC_DCHECK(!item.is_acked());
size_t serialized_size = GetSerializedChunkSize(item.data());
if (serialized_size <= max_size) {
item.Retransmit();
result.emplace_back(tsn.Wrap(), item.data().Clone());
max_size -= serialized_size;
outstanding_bytes_ += serialized_size;
++outstanding_items_;
it = to_be_retransmitted_.erase(it);
} else {
++it;
}
// No point in continuing if the packet is full.
if (max_size <= data_chunk_header_size_) {
break;
}
}
return result;
}
std::vector<std::pair<TSN, Data>> RetransmissionQueue::GetChunksToSend(
TimeMs now,
size_t bytes_remaining_in_packet) {
// Chunks are always padded to even divisible by four.
RTC_DCHECK(IsDivisibleBy4(bytes_remaining_in_packet));
std::vector<std::pair<TSN, Data>> to_be_sent;
size_t old_outstanding_bytes = outstanding_bytes_;
size_t old_rwnd = rwnd_;
if (is_in_fast_retransmit()) {
// https://tools.ietf.org/html/rfc4960#section-7.2.4
// "Determine how many of the earliest (i.e., lowest TSN) DATA chunks
// marked for retransmission will fit into a single packet ... Retransmit
// those K DATA chunks in a single packet. When a Fast Retransmit is being
// performed, the sender SHOULD ignore the value of cwnd and SHOULD NOT
// delay retransmission for this single packet."
is_in_fast_retransmit_ = false;
to_be_sent = GetChunksToBeRetransmitted(bytes_remaining_in_packet);
size_t to_be_sent_bytes = absl::c_accumulate(
to_be_sent, 0, [&](size_t r, const std::pair<TSN, Data>& d) {
return r + GetSerializedChunkSize(d.second);
});
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "fast-retransmit: sending "
<< to_be_sent.size() << " chunks, " << to_be_sent_bytes
<< " bytes";
} else {
// Normal sending. Calculate the bandwidth budget (how many bytes that is
// allowed to be sent), and fill that up first with chunks that are
// scheduled to be retransmitted. If there is still budget, send new chunks
// (which will have their TSN assigned here.)
size_t max_bytes =
RoundDownTo4(std::min(max_bytes_to_send(), bytes_remaining_in_packet));
to_be_sent = GetChunksToBeRetransmitted(max_bytes);
max_bytes -= absl::c_accumulate(
to_be_sent, 0, [&](size_t r, const std::pair<TSN, Data>& d) {
return r + GetSerializedChunkSize(d.second);
});
while (max_bytes > data_chunk_header_size_) {
RTC_DCHECK(IsDivisibleBy4(max_bytes));
absl::optional<SendQueue::DataToSend> chunk_opt =
send_queue_.Produce(now, max_bytes - data_chunk_header_size_);
if (!chunk_opt.has_value()) {
break;
}
UnwrappedTSN tsn = next_tsn_;
next_tsn_.Increment();
// All chunks are always padded to be even divisible by 4.
size_t chunk_size = GetSerializedChunkSize(chunk_opt->data);
max_bytes -= chunk_size;
outstanding_bytes_ += chunk_size;
++outstanding_items_;
rwnd_ -= chunk_size;
auto item_it =
outstanding_data_
.emplace(tsn,
RetransmissionQueue::TxData(
chunk_opt->data.Clone(),
partial_reliability_ ? chunk_opt->max_retransmissions
: absl::nullopt,
now,
partial_reliability_ ? chunk_opt->expires_at
: absl::nullopt))
.first;
if (item_it->second.has_expired(now)) {
// No need to send it - it was expired when it was in the send
// queue.
RTC_DLOG(LS_VERBOSE)
<< log_prefix_ << "Marking freshly produced chunk "
<< *item_it->first.Wrap() << " and message "
<< *item_it->second.data().message_id << " as expired";
AbandonAllFor(item_it->second);
} else {
to_be_sent.emplace_back(tsn.Wrap(), std::move(chunk_opt->data));
}
}
}
if (!to_be_sent.empty()) {
// https://tools.ietf.org/html/rfc4960#section-6.3.2
// "Every time a DATA chunk is sent to any address (including a
// retransmission), if the T3-rtx timer of that address is not running,
// start it running so that it will expire after the RTO of that address."
if (!t3_rtx_.is_running()) {
t3_rtx_.Start();
}
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "Sending TSN "
<< StrJoin(to_be_sent, ",",
[&](rtc::StringBuilder& sb,
const std::pair<TSN, Data>& c) {
sb << *c.first;
})
<< " - "
<< absl::c_accumulate(
to_be_sent, 0,
[&](size_t r, const std::pair<TSN, Data>& d) {
return r + GetSerializedChunkSize(d.second);
})
<< " bytes. outstanding_bytes=" << outstanding_bytes_
<< " (" << old_outstanding_bytes << "), cwnd=" << cwnd_
<< ", rwnd=" << rwnd_ << " (" << old_rwnd << ")";
}
RTC_DCHECK(IsConsistent());
return to_be_sent;
}
std::vector<std::pair<TSN, RetransmissionQueue::State>>
RetransmissionQueue::GetChunkStatesForTesting() const {
std::vector<std::pair<TSN, RetransmissionQueue::State>> states;
states.emplace_back(last_cumulative_tsn_ack_.Wrap(), State::kAcked);
for (const auto& elem : outstanding_data_) {
State state;
if (elem.second.is_abandoned()) {
state = State::kAbandoned;
} else if (elem.second.should_be_retransmitted()) {
state = State::kToBeRetransmitted;
} else if (elem.second.is_acked()) {
state = State::kAcked;
} else if (elem.second.is_outstanding()) {
state = State::kInFlight;
} else {
state = State::kNacked;
}
states.emplace_back(elem.first.Wrap(), state);
}
return states;
}
bool RetransmissionQueue::can_send_data() const {
return cwnd_ < options_.avoid_fragmentation_cwnd_mtus * options_.mtu ||
max_bytes_to_send() >= min_bytes_required_to_send_;
}
bool RetransmissionQueue::ShouldSendForwardTsn(TimeMs now) {
if (!partial_reliability_) {
return false;
}
ExpireOutstandingChunks(now);
if (!outstanding_data_.empty()) {
auto it = outstanding_data_.begin();
return it->first == last_cumulative_tsn_ack_.next_value() &&
it->second.is_abandoned();
}
RTC_DCHECK(IsConsistent());
return false;
}
void RetransmissionQueue::TxData::Ack() {
ack_state_ = AckState::kAcked;
should_be_retransmitted_ = false;
}
RetransmissionQueue::TxData::NackAction RetransmissionQueue::TxData::Nack(
bool retransmit_now) {
ack_state_ = AckState::kNacked;
++nack_count_;
if ((retransmit_now || nack_count_ >= kNumberOfNacksForRetransmission) &&
!is_abandoned_) {
// Nacked enough times - it's considered lost.
if (!max_retransmissions_.has_value() ||
num_retransmissions_ < max_retransmissions_) {
should_be_retransmitted_ = true;
return NackAction::kRetransmit;
}
Abandon();
return NackAction::kAbandon;
}
return NackAction::kNothing;
}
void RetransmissionQueue::TxData::Retransmit() {
ack_state_ = AckState::kUnacked;
should_be_retransmitted_ = false;
nack_count_ = 0;
++num_retransmissions_;
}
void RetransmissionQueue::TxData::Abandon() {
is_abandoned_ = true;
should_be_retransmitted_ = false;
}
bool RetransmissionQueue::TxData::has_expired(TimeMs now) const {
return expires_at_.has_value() && *expires_at_ <= now;
}
void RetransmissionQueue::ExpireOutstandingChunks(TimeMs now) {
for (const auto& elem : outstanding_data_) {
UnwrappedTSN tsn = elem.first;
const TxData& item = elem.second;
// Chunks that are nacked can be expired. Care should be taken not to expire
// unacked (in-flight) chunks as they might have been received, but the SACK
// is either delayed or in-flight and may be received later.
if (item.is_abandoned()) {
// Already abandoned.
} else if (item.is_nacked() && item.has_expired(now)) {
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "Marking nacked chunk "
<< *tsn.Wrap() << " and message "
<< *item.data().message_id << " as expired";
AbandonAllFor(item);
} else {
// A non-expired chunk. No need to iterate any further.
break;
}
}
}
void RetransmissionQueue::AbandonAllFor(
const RetransmissionQueue::TxData& item) {
// Erase all remaining chunks from the producer, if any.
if (send_queue_.Discard(item.data().is_unordered, item.data().stream_id,
item.data().message_id)) {
// There were remaining chunks to be produced for this message. Since the
// receiver may have already received all chunks (up till now) for this
// message, we can't just FORWARD-TSN to the last fragment in this
// (abandoned) message and start sending a new message, as the receiver will
// then see a new message before the end of the previous one was seen (or
// skipped over). So create a new fragment, representing the end, that the
// received will never see as it is abandoned immediately and used as cum
// TSN in the sent FORWARD-TSN.
UnwrappedTSN tsn = next_tsn_;
next_tsn_.Increment();
Data message_end(item.data().stream_id, item.data().ssn,
item.data().message_id, item.data().fsn, item.data().ppid,
std::vector<uint8_t>(), Data::IsBeginning(false),
Data::IsEnd(true), item.data().is_unordered);
TxData& added_item =
outstanding_data_
.emplace(tsn, RetransmissionQueue::TxData(std::move(message_end),
absl::nullopt, TimeMs(0),
absl::nullopt))
.first->second;
// The added chunk shouldn't be included in `outstanding_bytes`, so set it
// as acked.
added_item.Ack();
RTC_DLOG(LS_VERBOSE) << log_prefix_
<< "Adding unsent end placeholder for message at tsn="
<< *tsn.Wrap();
}
for (auto& elem : outstanding_data_) {
UnwrappedTSN tsn = elem.first;
TxData& other = elem.second;
if (!other.is_abandoned() &&
other.data().stream_id == item.data().stream_id &&
other.data().is_unordered == item.data().is_unordered &&
other.data().message_id == item.data().message_id) {
RTC_DLOG(LS_VERBOSE) << log_prefix_ << "Marking chunk " << *tsn.Wrap()
<< " as abandoned";
if (other.should_be_retransmitted()) {
to_be_retransmitted_.erase(tsn);
}
other.Abandon();
}
}
}
size_t RetransmissionQueue::max_bytes_to_send() const {
size_t left = outstanding_bytes_ >= cwnd_ ? 0 : cwnd_ - outstanding_bytes_;
return std::min(rwnd(), left);
}
ForwardTsnChunk RetransmissionQueue::CreateForwardTsn() const {
std::map<StreamID, SSN> skipped_per_ordered_stream;
UnwrappedTSN new_cumulative_ack = last_cumulative_tsn_ack_;
for (const auto& elem : outstanding_data_) {
UnwrappedTSN tsn = elem.first;
const TxData& item = elem.second;
if ((tsn != new_cumulative_ack.next_value()) || !item.is_abandoned()) {
break;
}
new_cumulative_ack = tsn;
if (!item.data().is_unordered &&
item.data().ssn > skipped_per_ordered_stream[item.data().stream_id]) {
skipped_per_ordered_stream[item.data().stream_id] = item.data().ssn;
}
}
std::vector<ForwardTsnChunk::SkippedStream> skipped_streams;
skipped_streams.reserve(skipped_per_ordered_stream.size());
for (const auto& elem : skipped_per_ordered_stream) {
skipped_streams.emplace_back(elem.first, elem.second);
}
return ForwardTsnChunk(new_cumulative_ack.Wrap(), std::move(skipped_streams));
}
IForwardTsnChunk RetransmissionQueue::CreateIForwardTsn() const {
std::map<std::pair<IsUnordered, StreamID>, MID> skipped_per_stream;
UnwrappedTSN new_cumulative_ack = last_cumulative_tsn_ack_;
for (const auto& elem : outstanding_data_) {
UnwrappedTSN tsn = elem.first;
const TxData& item = elem.second;
if ((tsn != new_cumulative_ack.next_value()) || !item.is_abandoned()) {
break;
}
new_cumulative_ack = tsn;
std::pair<IsUnordered, StreamID> stream_id =
std::make_pair(item.data().is_unordered, item.data().stream_id);
if (item.data().message_id > skipped_per_stream[stream_id]) {
skipped_per_stream[stream_id] = item.data().message_id;
}
}
std::vector<IForwardTsnChunk::SkippedStream> skipped_streams;
skipped_streams.reserve(skipped_per_stream.size());
for (const auto& elem : skipped_per_stream) {
const std::pair<IsUnordered, StreamID>& stream = elem.first;
MID message_id = elem.second;
skipped_streams.emplace_back(stream.first, stream.second, message_id);
}
return IForwardTsnChunk(new_cumulative_ack.Wrap(),
std::move(skipped_streams));
}
void RetransmissionQueue::PrepareResetStreams(
rtc::ArrayView<const StreamID> streams) {
// TODO(boivie): These calls are now only affecting the send queue. The
// packet buffer can also change behavior - for example draining the chunk
// producer and eagerly assign TSNs so that an "Outgoing SSN Reset Request"
// can be sent quickly, with a known `sender_last_assigned_tsn`.
send_queue_.PrepareResetStreams(streams);
}
bool RetransmissionQueue::CanResetStreams() const {
return send_queue_.CanResetStreams();
}
void RetransmissionQueue::CommitResetStreams() {
send_queue_.CommitResetStreams();
}
void RetransmissionQueue::RollbackResetStreams() {
send_queue_.RollbackResetStreams();
}
} // namespace dcsctp