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Diffstat (limited to 'net/dcsctp/tx/retransmission_queue.cc')
| -rw-r--r-- | net/dcsctp/tx/retransmission_queue.cc | 889 |
1 files changed, 889 insertions, 0 deletions
diff --git a/net/dcsctp/tx/retransmission_queue.cc b/net/dcsctp/tx/retransmission_queue.cc new file mode 100644 index 0000000000..ef2f0e3172 --- /dev/null +++ b/net/dcsctp/tx/retransmission_queue.cc @@ -0,0 +1,889 @@ +/* + * 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 <unordered_map> +#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/pair_hash.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; +} // 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), + 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; + + 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()); + } + + if (elem.second.should_be_retransmitted()) { + actual_to_be_retransmitted.insert(elem.first); + } + } + + return actual_outstanding_bytes == outstanding_bytes_ && + 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 it = outstanding_data_.begin(); it != first_unacked; ++it) { + ack_info.bytes_acked_by_cumulative_tsn_ack += it->second.data().size(); + ack_info.acked_tsns.push_back(it->first.Wrap()); + if (it->second.is_outstanding()) { + outstanding_bytes_ -= GetSerializedChunkSize(it->second.data()); + } else if (it->second.should_be_retransmitted()) { + to_be_retransmitted_.erase(it->first); + } + } + + 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) { + if (!iter->second.is_acked()) { + ack_info.bytes_acked_by_new_gap_ack_blocks += + iter->second.data().size(); + if (iter->second.is_outstanding()) { + outstanding_bytes_ -= GetSerializedChunkSize(iter->second.data()); + } + 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); + ack_info.acked_tsns.push_back(iter->first.Wrap()); + } + } + } +} + +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) { + if (iter->second.is_outstanding()) { + outstanding_bytes_ -= GetSerializedChunkSize(iter->second.data()); + } + + if (iter->second.Nack()) { + ack_info.has_packet_loss = true; + to_be_retransmitted_.insert(iter->first); + RTC_DLOG(LS_VERBOSE) << log_prefix_ << *iter->first.Wrap() + << " marked for retransmission"; + } + } + } + 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_by_cumulative_tsn_ack + + ack_info.bytes_acked_by_new_gap_ack_blocks); + } + + 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_by_cumulative_tsn_ack > 0 || + ack_info.bytes_acked_by_new_gap_ack_blocks > 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)." + int count = 0; + for (auto& elem : outstanding_data_) { + UnwrappedTSN tsn = elem.first; + TxData& item = elem.second; + if (!item.is_acked()) { + if (item.is_outstanding()) { + outstanding_bytes_ -= GetSerializedChunkSize(item.data()); + } + if (item.Nack(/*retransmit_now=*/true)) { + to_be_retransmitted_.insert(tsn); + RTC_DLOG(LS_VERBOSE) << log_prefix_ << "Chunk " << *tsn.Wrap() + << " will be retransmitted due to T3-RTX"; + ++count; + } + } + } + + // 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_ + << ", rtx-packets=" << count << ", outstanding_bytes " + << outstanding_bytes_ << " (" << old_outstanding_bytes + << ")"; + RTC_DCHECK(IsConsistent()); +} + +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; + 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 remaining_cwnd_bytes = + outstanding_bytes_ >= cwnd_ ? 0 : cwnd_ - outstanding_bytes_; + size_t max_bytes = RoundDownTo4(std::min( + std::min(bytes_remaining_in_packet, rwnd()), remaining_cwnd_bytes)); + + 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(); + to_be_sent.emplace_back(tsn.Wrap(), chunk_opt->data.Clone()); + + // 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; + rwnd_ -= chunk_size; + outstanding_data_.emplace( + tsn, RetransmissionQueue::TxData(std::move(chunk_opt->data), + chunk_opt->max_retransmissions, now, + chunk_opt->expires_at)); + } + } + + 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::ShouldSendForwardTsn(TimeMs now) { + if (!partial_reliability_) { + return false; + } + ExpireChunks(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; +} + +bool RetransmissionQueue::TxData::Nack(bool retransmit_now) { + ack_state_ = AckState::kNacked; + ++nack_count_; + if ((retransmit_now || nack_count_ >= kNumberOfNacksForRetransmission) && + !is_abandoned_) { + should_be_retransmitted_ = true; + return true; + } + return false; +} + +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 { + if (ack_state_ != AckState::kAcked && !is_abandoned_) { + if (max_retransmissions_.has_value() && + num_retransmissions_ >= *max_retransmissions_) { + return true; + } else if (expires_at_.has_value() && *expires_at_ <= now) { + return true; + } + } + return false; +} + +void RetransmissionQueue::ExpireChunks(TimeMs now) { + for (const auto& elem : outstanding_data_) { + UnwrappedTSN tsn = elem.first; + const TxData& item = elem.second; + + // Chunks that are in-flight (possibly lost?), nacked or to be retransmitted + // can be expired easily. There is always a risk that a message is expired + // that was already received by the peer, but for which there haven't been + // a SACK received. But that's acceptable, and handled. + if (item.is_abandoned()) { + // Already abandoned. + } else if (item.has_expired(now)) { + RTC_DLOG(LS_VERBOSE) << log_prefix_ << "Marking chunk " << *tsn.Wrap() + << " and message " << *item.data().message_id + << " as expired"; + ExpireAllFor(item); + } else { + // A non-expired chunk. No need to iterate any further. + break; + } + } +} + +void RetransmissionQueue::ExpireAllFor( + 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(); + } + } +} + +ForwardTsnChunk RetransmissionQueue::CreateForwardTsn() const { + std::unordered_map<StreamID, SSN, StreamID::Hasher> + 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::unordered_map<std::pair<IsUnordered, StreamID>, MID, UnorderedStreamHash> + 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 |