b2d539be6b
The Data Tracker's purpose is to keep track of all received DATA chunks and to ACK/NACK that data, by generating SACK chunks reflecting its view of what has been received and what has been lost. It also contains logic for _when_ to send the SACKs, as that's different depending on e.g. packet loss. Generally, SACKs are sent every second packet on a connection with no packet loss, and can also be sent on a delayed timer. In case partial reliability is used, and the transmitter has decided that some data shouldn't be retransmitted, it will send a FORWARD-TSN chunk, which this class also handles, by "forgetting" about those chunks. Bug: webrtc:12614 Change-Id: Ifafb0c211f6a47872e81830165ab5fc43ee7f366 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213664 Commit-Queue: Victor Boivie <boivie@webrtc.org> Reviewed-by: Tommi <tommi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33676}
122 lines
4.3 KiB
C++
122 lines
4.3 KiB
C++
/*
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* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef NET_DCSCTP_RX_DATA_TRACKER_H_
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#define NET_DCSCTP_RX_DATA_TRACKER_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <cstdint>
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#include <set>
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#include <string>
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#include <vector>
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#include "absl/strings/string_view.h"
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#include "net/dcsctp/common/sequence_numbers.h"
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#include "net/dcsctp/packet/chunk/data_common.h"
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#include "net/dcsctp/packet/chunk/sack_chunk.h"
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#include "net/dcsctp/packet/data.h"
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#include "net/dcsctp/timer/timer.h"
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namespace dcsctp {
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// Keeps track of received DATA chunks and handles all logic for _when_ to
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// create SACKs and also _how_ to generate them.
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//
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// It only uses TSNs to track delivery and doesn't need to be aware of streams.
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//
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// SACKs are optimally sent every second packet on connections with no packet
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// loss. When packet loss is detected, it's sent for every packet. When SACKs
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// are not sent directly, a timer is used to send a SACK delayed (by RTO/2, or
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// 200ms, whatever is smallest).
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class DataTracker {
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public:
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explicit DataTracker(absl::string_view log_prefix,
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Timer* delayed_ack_timer,
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TSN peer_initial_tsn)
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: log_prefix_(std::string(log_prefix) + "dtrack: "),
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delayed_ack_timer_(*delayed_ack_timer),
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last_cumulative_acked_tsn_(
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tsn_unwrapper_.Unwrap(TSN(*peer_initial_tsn - 1))) {}
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// Call for every incoming data chunk.
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void Observe(TSN tsn,
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AnyDataChunk::ImmediateAckFlag immediate_ack =
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AnyDataChunk::ImmediateAckFlag(false));
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// Called at the end of processing an SCTP packet.
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void ObservePacketEnd();
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// Called for incoming FORWARD-TSN/I-FORWARD-TSN chunks
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void HandleForwardTsn(TSN new_cumulative_ack);
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// Indicates if a SACK should be sent. There may be other reasons to send a
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// SACK, but if this function indicates so, it should be sent as soon as
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// possible. Calling this function will make it clear a flag so that if it's
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// called again, it will probably return false.
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//
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// If the delayed ack timer is running, this method will return false _unless_
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// `also_if_delayed` is set to true. Then it will return true as well.
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bool ShouldSendAck(bool also_if_delayed = false);
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// Returns the last cumulative ack TSN - the last seen data chunk's TSN
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// value before any packet loss was detected.
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TSN last_cumulative_acked_tsn() const {
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return TSN(last_cumulative_acked_tsn_.Wrap());
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}
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// Returns true if the received `tsn` would increase the cumulative ack TSN.
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bool will_increase_cum_ack_tsn(TSN tsn) const;
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// Forces `ShouldSendSack` to return true.
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void ForceImmediateSack();
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// Note that this will clear `duplicates_`, so every SackChunk that is
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// consumed must be sent.
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SackChunk CreateSelectiveAck(size_t a_rwnd);
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void HandleDelayedAckTimerExpiry();
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private:
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enum class AckState {
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// No need to send an ACK.
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kIdle,
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// Has received data chunks (but not yet end of packet).
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kBecomingDelayed,
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// Has received data chunks and the end of a packet. Delayed ack timer is
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// running and a SACK will be sent on expiry, or if DATA is sent, or after
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// next packet with data.
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kDelayed,
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// Send a SACK immediately after handling this packet.
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kImmediate,
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};
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std::vector<SackChunk::GapAckBlock> CreateGapAckBlocks() const;
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void UpdateAckState(AckState new_state, absl::string_view reason);
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static absl::string_view ToString(AckState ack_state);
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const std::string log_prefix_;
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// If a packet has ever been seen.
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bool seen_packet_ = false;
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Timer& delayed_ack_timer_;
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AckState ack_state_ = AckState::kIdle;
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UnwrappedTSN::Unwrapper tsn_unwrapper_;
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// All TSNs up until (and including) this value have been seen.
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UnwrappedTSN last_cumulative_acked_tsn_;
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// Received TSNs that are not directly following `last_cumulative_acked_tsn_`.
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std::set<UnwrappedTSN> additional_tsns;
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std::set<UnwrappedTSN> duplicates_;
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};
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} // namespace dcsctp
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#endif // NET_DCSCTP_RX_DATA_TRACKER_H_
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