| /* |
| * 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 my_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, |
| const DcSctpSocketHandoverState* handover_state) |
| : 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_(handover_state ? handover_state->tx.cwnd |
| : options_.cwnd_mtus_initial * options_.mtu), |
| rwnd_(handover_state ? handover_state->tx.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_(handover_state ? handover_state->tx.ssthresh : rwnd_), |
| partial_bytes_acked_( |
| handover_state ? handover_state->tx.partial_bytes_acked : 0), |
| next_tsn_(tsn_unwrapper_.Unwrap( |
| handover_state ? TSN(handover_state->tx.next_tsn) : my_initial_tsn)), |
| last_cumulative_tsn_ack_(tsn_unwrapper_.Unwrap( |
| handover_state ? TSN(handover_state->tx.next_tsn - 1) |
| : TSN(*my_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); |
| } |
| } |
| |
| if (outstanding_data_.empty() && |
| next_tsn_ != last_cumulative_tsn_ack_.next_value()) { |
| return false; |
| } |
| |
| 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." |
| 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)." |
| |
| // Errata: https://datatracker.ietf.org/doc/html/rfc8540#section-3.12 |
| partial_bytes_acked_ -= cwnd_; |
| cwnd_ += options_.mtu; |
| 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; |
| // Errata: https://datatracker.ietf.org/doc/html/rfc8540#section-3.11 |
| partial_bytes_acked_ = 0; |
| |
| // 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(); |
| } |
| |
| HandoverReadinessStatus RetransmissionQueue::GetHandoverReadiness() const { |
| HandoverReadinessStatus status; |
| if (!outstanding_data_.empty()) { |
| status.Add(HandoverUnreadinessReason::kRetransmissionQueueOutstandingData); |
| } |
| if (fast_recovery_exit_tsn_.has_value()) { |
| status.Add(HandoverUnreadinessReason::kRetransmissionQueueFastRecovery); |
| } |
| if (!to_be_retransmitted_.empty()) { |
| status.Add(HandoverUnreadinessReason::kRetransmissionQueueNotEmpty); |
| } |
| return status; |
| } |
| |
| void RetransmissionQueue::AddHandoverState(DcSctpSocketHandoverState& state) { |
| state.tx.next_tsn = next_tsn().value(); |
| state.tx.rwnd = rwnd_; |
| state.tx.cwnd = cwnd_; |
| state.tx.ssthresh = ssthresh_; |
| state.tx.partial_bytes_acked = partial_bytes_acked_; |
| } |
| } // namespace dcsctp |
