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/*
* Copyright (c) 2019 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 "modules/rtp_rtcp/source/rtp_sequence_number_map.h"
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <deque>
#include <iterator>
#include <limits>
#include <optional>
#include "absl/algorithm/container.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/numerics/sequence_number_util.h"
namespace webrtc {
RtpSequenceNumberMap::RtpSequenceNumberMap(size_t max_entries)
: max_entries_(max_entries) {
RTC_DCHECK_GT(max_entries_, 4); // See code paring down to `max_entries_`.
RTC_DCHECK_LE(max_entries_, 1 << 15);
}
RtpSequenceNumberMap::~RtpSequenceNumberMap() = default;
void RtpSequenceNumberMap::InsertPacket(uint16_t sequence_number, Info info) {
RTC_DCHECK(associations_.size() < 2 ||
AheadOf(associations_.back().sequence_number,
associations_.front().sequence_number));
if (associations_.empty()) {
associations_.emplace_back(sequence_number, info);
return;
}
if (AheadOrAt(sequence_number, associations_.front().sequence_number) &&
AheadOrAt(associations_.back().sequence_number, sequence_number)) {
// The sequence number has wrapped around and is within the range
// currently held by `associations_` - we should invalidate all entries.
RTC_LOG(LS_WARNING) << "Sequence number wrapped-around unexpectedly.";
associations_.clear();
associations_.emplace_back(sequence_number, info);
return;
}
std::deque<Association>::iterator erase_to = associations_.begin();
RTC_DCHECK_LE(associations_.size(), max_entries_);
if (associations_.size() == max_entries_) {
// Pare down the container so that inserting some additional elements
// would not exceed the maximum size.
const size_t new_size = 3 * max_entries_ / 4;
erase_to = std::next(erase_to, max_entries_ - new_size);
}
// It is guaranteed that `associations_` can be split into two partitions,
// either partition possibly empty, such that:
// * In the first partition, all elements are AheadOf the new element.
// This is the partition of the obsolete elements.
// * In the second partition, the new element is AheadOf all the elements.
// The elements of this partition may stay.
auto cmp = [](const Association& a, uint16_t sequence_number) {
return AheadOf(a.sequence_number, sequence_number);
};
RTC_DCHECK(erase_to != associations_.end());
erase_to =
std::lower_bound(erase_to, associations_.end(), sequence_number, cmp);
associations_.erase(associations_.begin(), erase_to);
associations_.emplace_back(sequence_number, info);
RTC_DCHECK(associations_.size() == 1 ||
AheadOf(associations_.back().sequence_number,
associations_.front().sequence_number));
}
void RtpSequenceNumberMap::InsertFrame(uint16_t first_sequence_number,
size_t packet_count,
uint32_t timestamp) {
RTC_DCHECK_GT(packet_count, 0);
RTC_DCHECK_LE(packet_count, std::numeric_limits<size_t>::max());
for (size_t i = 0; i < packet_count; ++i) {
const bool is_first = (i == 0);
const bool is_last = (i == packet_count - 1);
InsertPacket(static_cast<uint16_t>(first_sequence_number + i),
Info(timestamp, is_first, is_last));
}
}
std::optional<RtpSequenceNumberMap::Info> RtpSequenceNumberMap::Get(
uint16_t sequence_number) const {
// To make the binary search easier to understand, we use the fact that
// adding a constant offset to all elements, as well as to the searched
// element, does not change the relative ordering. This way, we can find
// an offset that would make all of the elements strictly ascending according
// to normal integer comparison.
// Finding such an offset is easy - the offset that would map the oldest
// element to 0 would serve this purpose.
if (associations_.empty()) {
return std::nullopt;
}
const uint16_t offset =
static_cast<uint16_t>(0) - associations_.front().sequence_number;
auto cmp = [offset](const Association& a, uint16_t sequence_number) {
return static_cast<uint16_t>(a.sequence_number + offset) <
static_cast<uint16_t>(sequence_number + offset);
};
const auto elem = absl::c_lower_bound(associations_, sequence_number, cmp);
return elem != associations_.end() && elem->sequence_number == sequence_number
? std::optional<Info>(elem->info)
: std::nullopt;
}
size_t RtpSequenceNumberMap::AssociationCountForTesting() const {
return associations_.size();
}
} // namespace webrtc
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