libdatachannel/src/rtcpnackresponder.cpp

/**
 * libdatachannel streamer example
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; If not, see <http://www.gnu.org/licenses/>.
 */

#if RTC_ENABLE_MEDIA

#include "rtcpnackresponder.hpp"

namespace rtc {

RtcpNackResponder::Storage::Element::Element(binary_ptr packet, uint16_t sequenceNumber, std::shared_ptr<Element> next)
: packet(packet), sequenceNumber(sequenceNumber), next(next) { }

unsigned RtcpNackResponder::Storage::size() { return storage.size(); }

RtcpNackResponder::Storage::Storage(unsigned _maximumSize): maximumSize(_maximumSize) {
	assert(maximumSize > 0);
	storage.reserve(maximumSize);
}

std::optional<binary_ptr> RtcpNackResponder::Storage::get(uint16_t sequenceNumber) {
	auto position = storage.find(sequenceNumber);
	return position != storage.end() ? std::make_optional(storage.at(sequenceNumber)->packet) : nullopt;
}

void RtcpNackResponder::Storage::store(binary_ptr packet) {
	if (!packet || packet->size() < 12) {
		return;
	}
	auto rtp = reinterpret_cast<RTP *>(packet->data());
	auto sequenceNumber = rtp->seqNumber();

	assert((storage.empty() && !oldest && !newest) || (!storage.empty() && oldest && newest));

	if (size() == 0) {
		newest = std::make_shared<Element>(packet, sequenceNumber);
		oldest = newest;
	} else {
		auto current = std::make_shared<Element>(packet, sequenceNumber);
		newest->next = current;
		newest = current;
	}

	storage.emplace(sequenceNumber, newest);

	if (size() > maximumSize) {
		assert(oldest);
		if (oldest) {
			storage.erase(oldest->sequenceNumber);
			oldest = oldest->next;
		}
	}
}

RtcpNackResponder::RtcpNackResponder(unsigned maxStoredPacketCount)
: MediaHandlerElement(), storage(std::make_shared<Storage>(maxStoredPacketCount)) { }

ChainedIncomingControlProduct RtcpNackResponder::processIncomingControlMessage(message_ptr message) {
	std::optional<ChainedOutgoingProduct> optPackets = ChainedOutgoingProduct(nullptr);
	auto packets = make_chained_messages_product();

	unsigned int i = 0;
	while (i < message->size()) {
		auto nack = reinterpret_cast<RTCP_NACK *>(message->data() + i);
		i += nack->header.header.lengthInBytes();
		// check if rtcp is nack
		if (nack->header.header.payloadType() != 205 || nack->header.header.reportCount() != 1) {
			continue;
		}
		
		auto fieldsCount = nack->getSeqNoCount();

		std::vector<uint16_t> missingSequenceNumbers{};
		for(unsigned int i = 0; i < fieldsCount; i++) {
			auto field = nack->parts[i];
			auto newMissingSeqenceNumbers = field.getSequenceNumbers();
			missingSequenceNumbers.insert(missingSequenceNumbers.end(), newMissingSeqenceNumbers.begin(), newMissingSeqenceNumbers.end());
		}
		packets->reserve(packets->size() + missingSequenceNumbers.size());
		for (auto sequenceNumber: missingSequenceNumbers) {
			auto optPacket = storage->get(sequenceNumber);
			if (optPacket.has_value()) {
				auto packet = optPacket.value();
				packets->push_back(packet);
			}
		}
	}

	if (!packets->empty()) {
		return {message, ChainedOutgoingProduct(packets)};
	} else {
		return {message, nullopt};
	}
}

ChainedOutgoingProduct RtcpNackResponder::processOutgoingBinaryMessage(ChainedMessagesProduct messages, message_ptr control) {
	for (auto message: *messages) {
		storage->store(message);
	}
	return {messages, control};
}

} // namespace rtc

#endif /* RTC_ENABLE_MEDIA */