ZLMediaKit/webrtc/Nack.cpp

/*
 * Copyright (c) 2016-present The ZLMediaKit project authors. All Rights Reserved.
 *
 * This file is part of ZLMediaKit(https://github.com/ZLMediaKit/ZLMediaKit).
 *
 * Use of this source code is governed by MIT-like license that can be found in the
 * LICENSE file in the root of the source tree. All contributing project authors
 * may be found in the AUTHORS file in the root of the source tree.
 */

#include "Nack.h"
#include <algorithm>
#include "Common/config.h"

using namespace std;
using namespace toolkit;

namespace mediakit {

// RTC配置项目  [AUTO-TRANSLATED:19940011]
// RTC configuration project
namespace Rtc {
#define RTC_FIELD "rtc."
// ~ nack接收端, rtp发送端  [AUTO-TRANSLATED:e1065811]
// ~ nack receiver, rtp sender
// rtp重发缓存列队最大长度，单位毫秒  [AUTO-TRANSLATED:80bccd26]
// rtp retransmission cache queue maximum length, in milliseconds
const string kMaxRtpCacheMS = RTC_FIELD "maxRtpCacheMS";
// rtp重发缓存列队最大长度，单位个数  [AUTO-TRANSLATED:7d710bf5]
// rtp retransmission cache queue maximum length, in number
const string kMaxRtpCacheSize = RTC_FIELD "maxRtpCacheSize";

// ~ nack发送端，rtp接收端  [AUTO-TRANSLATED:bb169205]
// ~ nack sender, rtp receiver
// 最大保留的rtp丢包状态个数  [AUTO-TRANSLATED:3aeb53f8]
// Maximum number of rtp packet loss states to keep
const string kNackMaxSize = RTC_FIELD "nackMaxSize";
// rtp丢包状态最长保留时间  [AUTO-TRANSLATED:f9306375]
// Maximum retention time for rtp packet loss state
const string kNackMaxMS = RTC_FIELD "nackMaxMS";
// nack最多请求重传次数  [AUTO-TRANSLATED:300be0d0]
// Maximum number of nack retransmission requests
const string kNackMaxCount = RTC_FIELD "nackMaxCount";
// nack重传频率，rtt的倍数  [AUTO-TRANSLATED:924d53d2]
// Nack retransmission frequency, multiple of rtt
const string kNackIntervalRatio = RTC_FIELD "nackIntervalRatio";
// nack包中rtp个数，减小此值可以让nack包响应更灵敏  [AUTO-TRANSLATED:12393868]
// Number of rtp in nack packet, reducing this value can make nack packet response more sensitive
const string kNackRtpSize = RTC_FIELD "nackRtpSize";

static onceToken token([]() {
    mINI::Instance()[kMaxRtpCacheMS] = 5 * 1000;
    mINI::Instance()[kMaxRtpCacheSize] = 2048;
    mINI::Instance()[kNackMaxSize] = 2048;
    mINI::Instance()[kNackMaxMS] = 3 * 1000;
    mINI::Instance()[kNackMaxCount] = 15;
    mINI::Instance()[kNackIntervalRatio] = 1.0f;
    mINI::Instance()[kNackRtpSize] = 8;
});

} // namespace Rtc

void NackList::pushBack(RtpPacket::Ptr rtp) {
    GET_CONFIG(uint32_t, max_rtp_cache_ms, Rtc::kMaxRtpCacheMS);
    GET_CONFIG(uint32_t, max_rtp_cache_size, Rtc::kMaxRtpCacheSize);

    // 记录rtp  [AUTO-TRANSLATED:f08e12e2]
    // Record rtp
    auto seq = rtp->getSeq();
    _nack_cache_seq.emplace_back(seq);
    _nack_cache_pkt.emplace(seq, std::move(rtp));

    // 限制rtp缓存最大个数  [AUTO-TRANSLATED:a6bb50f5]
    // Limit the maximum number of rtp cache
    if (_nack_cache_seq.size() > max_rtp_cache_size) {
        popFront();
    }

    if (++_cache_ms_check < 100) {
        // 每100个rtp包检测下缓存长度，节省cpu资源  [AUTO-TRANSLATED:6399c705]
        // Check the cache length every 100 rtp packets to save cpu resources
        return;
    }
    _cache_ms_check = 0;
    // 限制rtp缓存最大时长  [AUTO-TRANSLATED:83e5be93]
    // Limit the maximum duration of rtp cache
    while (getCacheMS() >= max_rtp_cache_ms) {
        popFront();
    }
}

void NackList::forEach(const FCI_NACK &nack, const function<void(const RtpPacket::Ptr &rtp)> &func) {
    auto seq = nack.getPid();
    for (auto bit : nack.getBitArray()) {
        if (bit) {
            // 丢包  [AUTO-TRANSLATED:ac2c9d55]
            // Packet loss
            RtpPacket::Ptr *ptr = getRtp(seq);
            if (ptr) {
                func(*ptr);
            }
        }
        ++seq;
    }
}

void NackList::popFront() {
    if (_nack_cache_seq.empty()) {
        return;
    }
    _nack_cache_pkt.erase(_nack_cache_seq.front());
    _nack_cache_seq.pop_front();
}

RtpPacket::Ptr *NackList::getRtp(uint16_t seq) {
    auto it = _nack_cache_pkt.find(seq);
    if (it == _nack_cache_pkt.end()) {
        return nullptr;
    }
    return &it->second;
}

uint32_t NackList::getCacheMS() {
    while (_nack_cache_seq.size() > 2) {
        auto back_stamp = getNtpStamp(_nack_cache_seq.back());
        if (back_stamp == -1) {
            _nack_cache_seq.pop_back();
            continue;
        }

        auto front_stamp = getNtpStamp(_nack_cache_seq.front());
        if (front_stamp == -1) {
            _nack_cache_seq.pop_front();
            continue;
        }

        if (back_stamp >= front_stamp) {
            return back_stamp - front_stamp;
        }
        // ntp时间戳回退了，非法数据，丢掉  [AUTO-TRANSLATED:79ddf252]
        // Ntp timestamp has been rolled back, illegal data, discard
        _nack_cache_seq.pop_front();
    }
    return 0;
}

int64_t NackList::getNtpStamp(uint16_t seq) {
    auto it = _nack_cache_pkt.find(seq);
    if (it == _nack_cache_pkt.end()) {
        return -1;
    }
    // 使用ntp时间戳，不会回退  [AUTO-TRANSLATED:2d509f8f]
    // Use ntp timestamp, will not roll back
    return it->second->getStampMS(true);
}

////////////////////////////////////////////////////////////////////////////////////////////////

NackContext::NackContext() {
    setOnNack(nullptr);
}

void NackContext::received(uint16_t seq, bool is_rtx) {
    if (!_started) {
        // 记录第一个seq  [AUTO-TRANSLATED:410c831f]
        // Record the first seq
        _started = true;
        _nack_seq = seq - 1;
    }

    if (seq < _nack_seq && _nack_seq != UINT16_MAX && seq < 1024 && _nack_seq > UINT16_MAX - 1024) {
        // seq回环,清空回环前状态  [AUTO-TRANSLATED:4cb8027e]
        // Seq loop, clear the state before the loop
        makeNack(UINT16_MAX, true);
        _seq.emplace(seq);
        return;
    }

    if (is_rtx || (seq < _nack_seq && _nack_seq != UINT16_MAX)) {
        // seq非回环回退包，猜测其为重传包，清空其nack状态  [AUTO-TRANSLATED:74c7b706]
        // Seq non-loop rollback packet, guess it is a retransmission packet, clear its nack state
        clearNackStatus(seq);
        return;
    }

    auto pr = _seq.emplace(seq);
    if (!pr.second) {
        // seq重复, 忽略  [AUTO-TRANSLATED:95ec10db]
        // Seq duplicate, ignore
        return;
    }

    auto max_seq = *_seq.rbegin();
    auto min_seq = *_seq.begin();
    auto diff = max_seq - min_seq;
    if (diff > (UINT16_MAX >> 1)) {
        // 回环后，收到回环前的大值seq, 忽略掉  [AUTO-TRANSLATED:6a30b91f]
        // After the loop, receive a large seq value before the loop, ignore it
        _seq.erase(max_seq);
        return;
    }
    if (min_seq == (uint16_t)(_nack_seq + 1) && _seq.size() == (size_t)diff + 1) {
        // 都是连续的seq，未丢包  [AUTO-TRANSLATED:62d3ffbd]
        // All are continuous seq, no packet loss
        _seq.clear();
        _nack_seq = max_seq;
    } else {
        // seq不连续，有丢包  [AUTO-TRANSLATED:ba1bfbc2]
        // Seq is not continuous, there is packet loss
        makeNack(max_seq, false);
    }
}

void NackContext::makeNack(uint16_t max_seq, bool flush) {
    // 尝试移除前面部分连续的seq  [AUTO-TRANSLATED:04593c1b]
    // Try to remove the continuous seq in front
    eraseFrontSeq();
    // 最多生成5个nack包，防止seq大幅跳跃导致一直循环  [AUTO-TRANSLATED:9cc5da25]
    // Generate at most 5 nack packets to prevent seq from jumping significantly and causing continuous loops
    auto max_nack = 5u;
    GET_CONFIG(uint32_t, nack_rtpsize, Rtc::kNackRtpSize);
    // kNackRtpSize must between 0 and 16
    nack_rtpsize = std::min<uint32_t>(nack_rtpsize, FCI_NACK::kBitSize);
    while (_nack_seq != max_seq && max_nack--) {
        // 一次不能发送超过16+1个rtp的状态  [AUTO-TRANSLATED:1954831a]
        // Cannot send more than 16+1 rtp states at a time
        uint16_t nack_rtp_count = std::min<uint16_t>(FCI_NACK::kBitSize, max_seq - (uint16_t)(_nack_seq + 1));
        if (!flush && nack_rtp_count < nack_rtpsize) {
            // 非flush状态下，seq个数不足以发送一次nack  [AUTO-TRANSLATED:94f561c1]
            // In non-flush state, the number of seq is not enough to send a nack
            break;
        }
        vector<bool> vec;
        vec.resize(nack_rtp_count, false);
        for (size_t i = 0; i < nack_rtp_count; ++i) {
            vec[i] = _seq.find((uint16_t)(_nack_seq + i + 2)) == _seq.end();
        }
        doNack(FCI_NACK(_nack_seq + 1, vec), true);
        _nack_seq += nack_rtp_count + 1;
        // 返回第一个比_last_max_seq大的元素  [AUTO-TRANSLATED:425c4e63]
        // Return the first element greater than _last_max_seq
        auto it = _seq.upper_bound(_nack_seq);
        // 移除 <=_last_max_seq 的seq  [AUTO-TRANSLATED:a64ff3fd]
        // Remove seq <= _last_max_seq
        _seq.erase(_seq.begin(), it);
    }
}

void NackContext::setOnNack(onNack cb) {
    if (cb) {
        _cb = std::move(cb);
    } else {
        _cb = [](const FCI_NACK &nack) {};
    }
}

void NackContext::doNack(const FCI_NACK &nack, bool record_nack) {
    if (record_nack) {
        recordNack(nack);
    }
    _cb(nack);
}

void NackContext::eraseFrontSeq() {
    // 前面部分seq是连续的，未丢包，移除之  [AUTO-TRANSLATED:ef3eed87]
    // The previous part of the sequence is continuous and has no packet loss, remove it.
    for (auto it = _seq.begin(); it != _seq.end();) {
        if (*it != (uint16_t)(_nack_seq + 1)) {
            // seq不连续，丢包了  [AUTO-TRANSLATED:dcee49fe]
            // The sequence is not continuous, there is packet loss.
            break;
        }
        _nack_seq = *it;
        it = _seq.erase(it);
    }
}

void NackContext::clearNackStatus(uint16_t seq) {
    auto it = _nack_send_status.find(seq);
    if (it == _nack_send_status.end()) {
        return;
    }
    // 收到重传包与第一个nack包间的时间约等于rtt时间  [AUTO-TRANSLATED:f702811e]
    // The time between receiving the retransmitted packet and the first nack packet is approximately equal to the rtt time.
    auto rtt = getCurrentMillisecond() - it->second.first_stamp;
    _nack_send_status.erase(it);

    // 限定rtt在合理有效范围内  [AUTO-TRANSLATED:42fbed04]
    // Limit the rtt within a reasonable and valid range.
    GET_CONFIG(uint32_t, nack_maxms, Rtc::kNackMaxMS);
    GET_CONFIG(uint32_t, nack_maxcount, Rtc::kNackMaxCount);
    _rtt = max<int>(10, min<int>(rtt, nack_maxms / nack_maxcount));
}

void NackContext::recordNack(const FCI_NACK &nack) {
    auto now = getCurrentMillisecond();
    auto i = nack.getPid();
    for (auto flag : nack.getBitArray()) {
        if (flag) {
            auto &ref = _nack_send_status[i];
            ref.first_stamp = now;
            ref.update_stamp = now;
            ref.nack_count = 1;
        }
        ++i;
    }
    // 记录太多了，移除一部分早期的记录  [AUTO-TRANSLATED:6f4ea62d]
    // There are too many records, remove some of the earlier records.
    GET_CONFIG(uint32_t, nack_maxsize, Rtc::kNackMaxSize);
    while (_nack_send_status.size() > nack_maxsize) {
        _nack_send_status.erase(_nack_send_status.begin());
    }
}

uint64_t NackContext::reSendNack() {
    set<uint16_t> nack_rtp;
    auto now = getCurrentMillisecond();
    GET_CONFIG(uint32_t, nack_maxms, Rtc::kNackMaxMS);
    GET_CONFIG(uint32_t, nack_maxcount, Rtc::kNackMaxCount);
    GET_CONFIG(float, nack_intervalratio, Rtc::kNackIntervalRatio);
    for (auto it = _nack_send_status.begin(); it != _nack_send_status.end();) {
        if (now - it->second.first_stamp > nack_maxms) {
            // 该rtp丢失太久了，不再要求重传  [AUTO-TRANSLATED:a0a1e471]
            // This rtp has been lost for too long, no longer require retransmission.
            it = _nack_send_status.erase(it);
            continue;
        }
        if (now - it->second.update_stamp < nack_intervalratio * _rtt) {
            // 距离上次nack不足2倍的rtt，不用再发送nack  [AUTO-TRANSLATED:0e7edf4d]
            // The distance from the last nack is less than 2 times the rtt, no need to send nack again.
            ++it;
            continue;
        }
        // 此rtp需要请求重传  [AUTO-TRANSLATED:c29d8eb5]
        // This rtp needs to request retransmission.
        nack_rtp.emplace(it->first);
        // 更新nack发送时间戳  [AUTO-TRANSLATED:16ef9fac]
        // Update the nack sending timestamp.
        it->second.update_stamp = now;
        if (++(it->second.nack_count) == nack_maxcount) {
            // nack次数太多，移除之  [AUTO-TRANSLATED:1b684a9c]
            // Too many nack times, remove it.
            it = _nack_send_status.erase(it);
            continue;
        }
        ++it;
    }

    int pid = -1;
    vector<bool> vec;
    for (auto it = nack_rtp.begin(); it != nack_rtp.end();) {
        if (pid == -1) {
            pid = *it;
            vec.assign(FCI_NACK::kBitSize, false);
            ++it;
            continue;
        }
        auto inc = *it - pid;
        if (inc > (ssize_t)FCI_NACK::kBitSize) {
            // 新的nack包  [AUTO-TRANSLATED:aec9b818]
            // New nack packet.
            doNack(FCI_NACK(pid, vec), false);
            pid = -1;
            continue;
        }
        // 这个包丢了  [AUTO-TRANSLATED:60f91f2f]
        // This packet is lost.
        vec[inc - 1] = true;
        ++it;
    }
    if (pid != -1) {
        doNack(FCI_NACK(pid, vec), false);
    }

    // 没有任何包需要重传时返回0，否则返回下次重传间隔(不得低于5ms)  [AUTO-TRANSLATED:c326264d]
    // Return 0 when there are no packets to retransmit, otherwise return the next retransmission interval (not less than 5ms).
    return _nack_send_status.empty() ? 0 : _rtt;
}

} // namespace mediakit