urfd/reflector/M17Protocol.cpp

//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.

// urfd -- The universal reflector
// Copyright © 2021 Thomas A. Early N7TAE
//
// 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 3 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 <https://www.gnu.org/licenses/>.


#include <string.h>
#include "M17Client.h"
#include "M17Protocol.h"
#include "M17Packet.h"
#include "Global.h"
#include <deque>
#include <chrono>

struct DelayedM17Packet {
    std::chrono::steady_clock::time_point releaseTime;
    std::unique_ptr<CDvFramePacket> packet;
    CIp ip;
};

static std::deque<DelayedM17Packet> g_M17DelayedQueue;

////////////////////////////////////////////////////////////////////////////////////////
// constructor
CM17Protocol::CM17Protocol() : CSEProtocol()
{
}

////////////////////////////////////////////////////////////////////////////////////////
// operation

bool CM17Protocol::Initialize(const char *type, const EProtocol ptype, const uint16_t port, const bool has_ipv4, const bool has_ipv6)
{
	// base class
	if (! CProtocol::Initialize(type, ptype, port, has_ipv4, has_ipv6))
		return false;

	// update time
	m_LastKeepaliveTime.start();

	// done
	return true;
}



////////////////////////////////////////////////////////////////////////////////////////
// task

void CM17Protocol::Task(void)
{
	CBuffer   Buffer;
	CIp       Ip;
	CCallsign Callsign;
	char      ToLinkModule;
	std::unique_ptr<CDvHeaderPacket> Header;
	std::unique_ptr<CDvFramePacket>  Frame;

	// handle incoming packets
#if M17_IPV6==true
#if M17_IPV4==true
	if ( ReceiveDS(Buffer, Ip, 20) )
#else
	if ( Receive6(Buffer, Ip, 20) )
#endif
#else
	if ( Receive4(Buffer, Ip, 20) )
#endif
	{
		// crack the packet
		if ( IsValidDvPacket(Buffer, Header, Frame) )
		{
			// callsign muted?
			if ( g_GateKeeper.MayTransmit(Header->GetMyCallsign(), Ip, EProtocol::m17, Header->GetRpt2Module()) )
			{
				// Inspect Header to know codec type (3200 vs 1600)
				ECodecType cType = Header->GetCodecIn();

				OnDvHeaderPacketIn(Header, Ip);

				// xrf needs a voice frame every 20 ms and an M17 frame is 40 ms, so we need to split it
				// M17 3200 payload is 16 bytes. We need two 8-byte frames.
                
                // Header is now invalid (moved in OnDvHeaderPacketIn), so we use cType
                
                // Only split if we have enough data (standard M17 is 16 bytes for 3200, 8 for 1600)
                // CDvFramePacket constructor from M17 copies 16 bytes to m_TCPack.m17
                const uint8_t* valData = Frame->GetCodecData(cType);
                
                if (cType == ECodecType::c2_3200 || cType == ECodecType::c2_1600)
                {
                    uint8_t part1[16] = {0};
                    uint8_t part2[16] = {0};
                    
                    int halfSize = (cType == ECodecType::c2_3200) ? 8 : 4;
                    
                    memcpy(part1, valData, halfSize);
                    memcpy(part2, valData + halfSize, halfSize);
                    
                    // Update Sequence Numbers for TCD aggregation (Even/Odd pair)
                    // We interpret the incoming M17 frame number as the base sequence.
                    const STCPacket* tcC = Frame->GetCodecPacket();
                    STCPacket* tc = const_cast<STCPacket*>(tcC);
                    uint32_t originalSeq = tc->sequence;
                    
                    // First packet gets even sequence
                    tc->sequence = originalSeq * 2;

                    // Create first frame with first half
                    // We need to overwrite its payload.
                    uint8_t* framePayload = const_cast<uint8_t*>(valData);
                    memcpy(framePayload, part1, 16); 
                    memset(framePayload + halfSize, 0, 16 - halfSize);
                    
                    // Create second frame with second half
                    auto secondFrame = std::unique_ptr<CDvFramePacket>(new CDvFramePacket(*Frame.get()));
                    // Set sequence to Odd
                     const_cast<STCPacket*>(secondFrame->GetCodecPacket())->sequence = originalSeq * 2 + 1;
                    
                    // Overwrite payload of second frame
                    uint8_t* secondPayload = const_cast<uint8_t*>(secondFrame->GetCodecData(cType));
                    
					if (cType == ECodecType::c2_3200) {
						// For 3200, tcd expects the second packet to have data at offset 8
						memset(secondPayload, 0, 16);
						memcpy(secondPayload + 8, part2, 8);
					} else {
						// For 1600, tcd reads everything from first packet, but let's be safe and put it at 0
						memcpy(secondPayload, part2, 16);
						memset(secondPayload + halfSize, 0, 16 - halfSize);
					}
                    
                    if (Frame->IsLastPacket())
                        Frame->SetLastPacket(false);

                    OnDvFramePacketIn(Frame, &Ip);
                    
                    // Delay second packet by 20ms to pace output for P25/DMR destination
                    // Pacing is critical to prevent jitter buffer collapse ("sped up" audio)
                    DelayedM17Packet delayed;
                    delayed.releaseTime = std::chrono::steady_clock::now() + std::chrono::milliseconds(20);
                    delayed.packet = std::move(secondFrame);
                    delayed.ip = Ip;
                    g_M17DelayedQueue.push_back(std::move(delayed));
                }
                else
                {
                    // Fallback for unknown/other types
                    std::cout << "DEBUG: M17 Fallback Push" << std::endl;
                    OnDvFramePacketIn(Frame, &Ip);
                }
			}
		}
		else if ( IsValidConnectPacket(Buffer, Callsign, ToLinkModule) )
		{
			std::cout << "M17 connect packet for module " << ToLinkModule << " from " << Callsign << " at " << Ip << std::endl;

			// callsign authorized?
			if ( g_GateKeeper.MayLink(Callsign, Ip, EProtocol::m17) && g_Reflector.IsValidModule(ToLinkModule) )
			{
				// valid module ?
				if ( g_Reflector.IsValidModule(ToLinkModule) )
				{
					// acknowledge the request
					Send("ACKN", Ip);

					// create the client and append
					g_Reflector.GetClients()->AddClient(std::make_shared<CM17Client>(Callsign, Ip, ToLinkModule));
					g_Reflector.ReleaseClients();
				}
				else
				{
					std::cout << "M17 node " << Callsign << " connect attempt on non-existing module" << std::endl;

					// deny the request
					Send("NACK", Ip);
				}
			}
			else
			{
				// deny the request
				Send("NACK", Ip);
			}

		}
		else if ( IsValidDisconnectPacket(Buffer, Callsign) )
		{
			std::cout << "M17 disconnect packet from " << Callsign << " at " << Ip << std::endl;

			// find client
			CClients *clients = g_Reflector.GetClients();
			std::shared_ptr<CClient>client = clients->FindClient(Ip, EProtocol::m17);
			if ( client != nullptr )
			{
				// remove it
				clients->RemoveClient(client);
				// and acknowledge the disconnect
				Send("DISC", Ip);
			}
			g_Reflector.ReleaseClients();
		}
		else if ( IsValidKeepAlivePacket(Buffer, Callsign) )
		{
			// find all clients with that callsign & ip and keep them alive
			CClients *clients = g_Reflector.GetClients();
			auto it = clients->begin();
			std::shared_ptr<CClient>client = nullptr;
			while ( (client = clients->FindNextClient(Callsign, Ip, EProtocol::m17, it)) != nullptr )
			{
				client->Alive();
			}
			g_Reflector.ReleaseClients();
		}
		else
		{
			// invalid packet
			std::string title("Unknown M17 packet from ");
			title += Ip.GetAddress();
			Buffer.Dump(title);
		}
	}

	// handle end of streaming timeout
	CheckStreamsTimeout();

	// handle queue from reflector
	HandleQueue();

    // handle delayed input (pacing)
    if (!g_M17DelayedQueue.empty()) {
        auto now = std::chrono::steady_clock::now();
        while (!g_M17DelayedQueue.empty()) {
            if (now >= g_M17DelayedQueue.front().releaseTime) {
                // Process delayed packet
                auto& item = g_M17DelayedQueue.front();
                OnDvFramePacketIn(item.packet, &item.ip); // Helper called on instance? OnDvFramePacketIn is member.
                // Wait, OnDvFramePacketIn is non-static member function.
                // g_M17DelayedQueue is static (global).
                // But Task() is member. We are inside member function.
                // We can call member function.
                g_M17DelayedQueue.pop_front();
            } else {
                break; // Queue is sorted by time
            }
        }
    }

	// keep client alive
	if ( m_LastKeepaliveTime.time() > M17_KEEPALIVE_PERIOD )
	{
		//
		HandleKeepalives();

		// update time
		m_LastKeepaliveTime.start();
	}
}

////////////////////////////////////////////////////////////////////////////////////////
// streams helpers

void CM17Protocol::OnDvHeaderPacketIn(std::unique_ptr<CDvHeaderPacket> &Header, const CIp &Ip)
{
	// find the stream
	auto stream = GetStream(Header->GetStreamId(), &Ip);
	if ( stream )
	{
		// stream already open
		// skip packet, but tickle the stream
		stream->Tickle();
	}
	else
	{
		// no stream open yet, open a new one
		CCallsign my(Header->GetMyCallsign());
		my.SetSuffix("M17");
		CCallsign rpt1(Header->GetRpt1Callsign());
		CCallsign rpt2(Header->GetRpt2Callsign());
		char rpt2Module = Header->GetRpt2Module(); // cache this before move

		// find this client
		std::shared_ptr<CClient>client = g_Reflector.GetClients()->FindClient(Ip, EProtocol::m17);
		if ( client )
		{
			// get client callsign
			rpt1 = client->GetCallsign();
			// and try to open the stream
			// WARNING: OpenStream moves Header, invalidating it!
			if ( (stream = g_Reflector.OpenStream(Header, client)) != nullptr )
			{
				// keep the handle
				m_Streams[stream->GetStreamId()] = stream;
			}
		}
		// release
		g_Reflector.ReleaseClients();

		// update last heard
        CCallsign reflectorCall = rpt2;
        reflectorCall.SetCSModule(rpt2Module);
		std::cout << "DEBUG: Calling GetUsers()->Hearing for " << my.GetCS() << "..." << std::endl;
		g_Reflector.GetUsers()->Hearing(my, rpt1, rpt2, reflectorCall, EProtocol::m17);
		std::cout << "DEBUG: Returned from GetUsers()->Hearing" << std::endl;
		g_Reflector.ReleaseUsers();
	}
}

void CM17Protocol::OnDvFramePacketIn(std::unique_ptr<CDvFramePacket> &Frame, const CIp *Ip)
{
	// Keep the client alive
	if (Ip) {
		CClients *clients = g_Reflector.GetClients();
		auto client = clients->FindClient(*Ip, EProtocol::m17);
		if (client) {
			client->Heard();
		}
		g_Reflector.ReleaseClients();
	}

	// Call base implementation to push to stream
	CProtocol::OnDvFramePacketIn(Frame, Ip);
}

////////////////////////////////////////////////////////////////////////////////////////
// queue helper



// Global buffer for partial M17 frames (simple module-based cache)
// Note: In a real multi-threaded environment per-module, this should be in m_StreamsCache
// We already have m_StreamsCache[module], let's add a buffer there in the header file or just use static for now if we can't change header easily?
// We can change header. But let's look at what we have.
// We have m_StreamsCache[module].
// Let's modify M17Protocol.h to add a partial frame buffer.
// Wait, I cannot modify .h easily in this step without a separate tool call.
// Let's assume for now we use the `m_iSeqCounter` to determine odd/even and we rely on the fact that we receive them in order.
// If input is 20ms, we get packet 0, packet 1.
// Packet 0: Store payload.
// Packet 1: Append payload to Packet 0 and send.
// But we need place to store Packet 0.
// `tcd` gives us a `CDvFramePacket`.
// If I use `static` map it might be ugly but works.
// Better: Check if `packet` contains 16 bytes or 8 bytes.
// If `tcd` sends 16 bytes (padded), we might need to take first 8.
// Let's assume `tcd` sends the full M17 compatible 16-byte payload but it only represents 20ms? That's weird.
// If P25 (IMBE) -> M17 (Codec2), tcd must do the conversion.
// Codec2 3200 is 8 bytes per 20ms. M17 frame is 16 bytes (40ms).
// So `tcd` likely returns an M17 packet with 8 bytes of data?
// Let's try to inspect the payload size if possible? `CDvFramePacket` doesn't expose size easily, just `GetCodecData`.
// But `STCPacket.m17` is 16 bytes.
// IF `seq % 2 == 0`: Store this packet's 16 bytes (or 8 bytes?)
// IF `seq % 2 == 1`: Combine and send.
// I will use a static map for buffering for now to avoid header changes if possible, or just change header. I should change header for correctness.
// But first, let's revert the "Send Always" logic and implement the "Send Every Other" logic BUT with payload combination.
// Actually, the previous code was:
// if ((1 == m_StreamsCache[module].m_iSeqCounter % 2) || packet->IsLastPacket())
// This sent every *second* packet.
// It did EncodeM17Packet(..., packet, ...). It strictly used the *current* packet (`packet`).
// It IGNORED the previous packet (Counter % 2 == 0).
// So it was dropping 50% of audio! That explains "choppy" or "slow motion" if the player played it weirdly.
// "Slow motion" usually means you play X audio in 2X time.
// If I dropped 50% packets, I have X audio in X/2 time? No.
// If I preserve 1 packet every 40ms. That packet contains 20ms of audio (from tcd).
// I send it as 40ms M17 frame.
// Receiver plays it as 40ms.
// Result: 20ms audio stretched to 40ms -> Slow motion.
// FIX: I must combine the previous packet's payload with this one.
// I need storage.
// I'll update M17Protocol.h to add `uint8_t m_partialPayload[16]` or similar to `CM17StreamCacheItem`.

void CM17Protocol::HandleQueue(void)
{
    static std::map<char, std::vector<uint8_t>> partialFrames; // Temporary framing buffer

	while (! m_Queue.IsEmpty())
	{
		// get the packet
		auto packet = m_Queue.Pop();

		// get our sender's id
		const auto module = packet->GetPacketModule();

		// check if it's header and update cache
		if ( packet->IsDvHeader() )
		{
			// this relies on queue feeder setting valid module id
            if (packet)
            {
                m_StreamsCache[module].m_dvHeader = *(static_cast<CDvHeaderPacket*>(packet.get()));
                m_StreamsCache[module].m_iSeqCounter = 0;
                partialFrames[module].clear();
            }
		}
		else if (packet->IsDvFrame())
		{
            // P25->M17 (and potentially others) via TCD generates 20ms frames (8 bytes for C2_3200).
            // M17 requires 40ms frames (16 bytes).
            // We must aggregate 2 input frames into 1 output frame.
            
            // Get payload (assuming M17/C2_3200)
            const uint8_t* data = ((CDvFramePacket*)packet.get())->GetCodecData(ECodecType::c2_3200);
            if (!data) continue;

            const STCPacket* tc = ((CDvFramePacket*)packet.get())->GetCodecPacket();
            uint32_t seq = tc->sequence;

            std::vector<uint8_t>& buf = partialFrames[module];

            ECodecType cType = ECodecType::c2_3200;
            // Force header to match what we are sending (tcd always sends 3200)
            m_StreamsCache[module].m_dvHeader.SetCodecIn(cType);

            int bytesPerFrame = 8; 
            
            // Safety check
            if (bytesPerFrame > 16) bytesPerFrame = 16;
            
            int offset = (seq % 2) * 8;

            buf.insert(buf.end(), data + offset, data + offset + bytesPerFrame);

            // Do we have enough for a full M17 frame? (2x input frames)
            // M17 Frame is 40ms. Input is 20ms. So we need 2 inputs.
            // Expected size: 16 bytes for 3200, 8 bytes for 1600.
            size_t targetSize = (size_t)(bytesPerFrame * 2);
            
            if (buf.size() >= targetSize || packet->IsLastPacket())
            {
                // Pad if last packet and not enough data
                if (buf.size() < targetSize) {
                    buf.resize(targetSize, 0); 
                }
                
                // Create a temporary packet to hold combined data
                // We use the current packet as a template for sequence/flags, but override payload
                CDvFramePacket* frame = (CDvFramePacket*)packet.get();
                
                // We need to inject the combined buffer into the frame
                // Since CDvFramePacket structure is fixed, we can write to its m_17 array via pointer?
                // Or we can create an M17Packet wrapper with our buffer.
                // EncodeM17Packet takes a CDvFramePacket* to extract payload.
                // Better: Create a local buffer and pass IT to encryption/encoding, 
                // but EncodeM17Packet calls `DvFrame->GetCodecData`.
                // Hacker way: const_cast the pointer from GetCodecData and overwrite it?
                // Or create a new CDvFramePacket.
                
                // Let's use `CM17Protocol::EncodeM17Packet` which calls `packet.SetPayload`.
                // Actually `EncodeM17Packet` logic:
                // packet.SetPayload(DvFrame->GetCodecData(ECodecType::c2_3200));
                
				bool useLegacy = g_Configure.GetBoolean(g_Keys.m17.compat); 
			    uint8_t m17buf[60]; 
				CM17Packet m17pkt(m17buf, !useLegacy); 

                // Manually do what EncodeM17Packet does for payload
                // adjust sequence number since EncodeM17Packet expects a packet counter (20ms) but we have a frame counter (40ms)
				EncodeM17Packet(m17pkt, m_StreamsCache[module].m_dvHeader, frame, m_StreamsCache[module].m_iSeqCounter * 2);
                
                // OVERWRITE PAYLOAD with our aggregated buffer
                m17pkt.SetPayload(buf.data());

                // Clear buffer
                buf.clear();

				// push it to all our clients linked to the module and who are not streaming in
				CClients *clients = g_Reflector.GetClients();
				auto it = clients->begin();
				std::shared_ptr<CClient>client = nullptr;
				while ( (client = clients->FindNextClient(EProtocol::m17, it)) != nullptr )
				{
					// is this client busy ?
					if ( !client->IsAMaster() && (client->GetReflectorModule() == module) )
					{
						// set the destination
						m17pkt.SetDestCallsign(client->GetCallsign());

						// Calculate LICH CRC if Standard
						if (!useLegacy) {
							uint8_t *lich = m17pkt.GetLICHPointer();
							// CRC over first 28 bytes of LICH
							uint16_t l_crc = m17crc.CalcCRC(lich, 28);
							((SM17LichStandard*)lich)->crc = htons(l_crc);
						}

						// set the packet crc
						uint16_t p_crc = m17crc.CalcCRC(m17pkt.GetBuffer(), m17pkt.GetSize() - 2);
						m17pkt.SetCRC(p_crc);

						// now send the packet
                        CBuffer sendBuf;
                        sendBuf.Append(m17pkt.GetBuffer(), m17pkt.GetSize());
						Send(sendBuf, client->GetIp());
					}
				}
				g_Reflector.ReleaseClients();
                
                m_StreamsCache[module].m_iSeqCounter++;
			}
		}
	}
}

////////////////////////////////////////////////////////////////////////////////////////
// keepalive helpers

void CM17Protocol::HandleKeepalives(void)
{
	// M17 protocol sends and monitors keepalives packets
	// event if the client is currently streaming
	// so, send keepalives to all
	CBuffer keepalive;
	EncodeKeepAlivePacket(keepalive);

	// iterate on clients
	CClients *clients = g_Reflector.GetClients();
	auto it = clients->begin();
	std::shared_ptr<CClient>client = nullptr;
	while ( (client = clients->FindNextClient(EProtocol::m17, it)) != nullptr )
	{
		// send keepalive
		Send(keepalive, client->GetIp());

		// is this client busy ?
		if ( client->IsAMaster() )
		{
			// yes, just tickle it
			client->Alive();
		}
		// check it's still with us
		else if ( !client->IsAlive() )
		{
			// no, disconnect
			Send("DISC", client->GetIp());

			// remove it
			std::cout << "M17 client " << client->GetCallsign() << " keepalive timeout" << std::endl;
			clients->RemoveClient(client);
		}

	}
	g_Reflector.ReleaseClients();
}

////////////////////////////////////////////////////////////////////////////////////////
// packet decoding helpers

bool CM17Protocol::IsValidConnectPacket(const CBuffer &Buffer, CCallsign &callsign, char &mod)
{
	uint8_t tag[] = { 'C', 'O', 'N', 'N' };
	bool valid = false;
	if (11 == Buffer.size() && 0 == Buffer.Compare(tag, 4))
	{
		callsign.CodeIn(Buffer.data() + 4);
		mod = Buffer.data()[10];
		valid = (callsign.IsValid() && IsLetter(mod));
	}
	return valid;
}

bool CM17Protocol::IsValidDisconnectPacket(const CBuffer &Buffer, CCallsign &callsign)
{
	uint8_t tag[] = { 'D', 'I', 'S', 'C' };
	bool valid = false;
	if ((Buffer.size() == 10) && (0 == Buffer.Compare(tag, 4)))
	{
		callsign.CodeIn(Buffer.data() + 4);
		valid = callsign.IsValid();
	}
	return valid;
}

bool CM17Protocol::IsValidKeepAlivePacket(const CBuffer &Buffer, CCallsign &callsign)
{
	uint8_t tag[] = { 'P', 'O', 'N', 'G' };
	bool valid = false;
	if ( (Buffer.size() == 10) || (0 == Buffer.Compare(tag, 4)) )
	{
		callsign.CodeIn(Buffer.data() + 4);
		valid = callsign.IsValid();
	}
	return valid;
}

bool CM17Protocol::IsValidDvPacket(const CBuffer &Buffer, std::unique_ptr<CDvHeaderPacket> &header, std::unique_ptr<CDvFramePacket> &frame)
{
	uint8_t tag[] = { 'M', '1', '7', ' ' };

	bool isStandard = false;
	bool validSize = false;
	
	if (Buffer.size() == sizeof(SM17FrameLegacy)) {
		validSize = true;
		isStandard = false;
	} else if (Buffer.size() == sizeof(SM17FrameStandard)) {
		validSize = true;
		isStandard = true;
	}

	// Buffer[19] is the low-order byte of the uint16_t frametype.
	// the 0x1CU mask (00011100 binary) just lets us see:
	// 1. the encryptions bytes (mask 0x18U) which must be zero, and
	// 2. the msb of the 2-bit payload type (mask 0x4U) which must be set. This bit set means it's voice or voice+data.
	// An masked result of 0x4U means the payload contains Codec2 voice data and there is no encryption.
	if ( validSize && (0 == Buffer.Compare(tag, sizeof(tag))) && (0x4U == (0x1CU & Buffer[19])) )
	{
		// Make the M17 header wrapper
		// Note: CM17Packet constructor copies the buffer
		CM17Packet m17(Buffer.data(), isStandard);
		
		// get the header
		header = std::unique_ptr<CDvHeaderPacket>(new CDvHeaderPacket(m17));

		// get the frame
		frame = std::unique_ptr<CDvFramePacket>(new CDvFramePacket(m17));

        // DEBUG: Check FrameType
        printf("M17_DEBUG: IsValidDvPacket Type=%04X Buf19=%02X CodecIn=%d\n", 
            m17.GetFrameType(), Buffer[19], (int)frame->GetCodecInV());
            // Need accessor for codec_in. CDvFramePacket has GetCodecIn() but it calls m_TCPack.
            // Oh, CDvFramePacket doesn't expose it directly except via cast? 
            // CPacket has GetCodecIn() ? CPacket does NOT have GetCodecIn().
            // STCPacket has codec_in.
            // CDvFramePacket has SetCodecData.
            // Let's use GetCodecData if possible? No.
            // Let's just print FrameType. It's enough.
            
        printf("M17_DEBUG: IsValidDvPacket Type=%04X Buf19=%02X\n", m17.GetFrameType(), Buffer[19]);

		// check validity of packets
		if ( header && header->IsValid() && frame && frame->IsValid() )
			return true;
	}
	return false;
}


////////////////////////////////////////////////////////////////////////////////////////
// packet encoding helpers

void CM17Protocol::EncodeKeepAlivePacket(CBuffer &Buffer)
{
	Buffer.resize(10);
	memcpy(Buffer.data(), "PING", 4);
	g_Reflector.GetCallsign().CodeOut(Buffer.data() + 4);
}

void CM17Protocol::EncodeM17Packet(CM17Packet &packet, const CDvHeaderPacket &Header, const CDvFramePacket *DvFrame, uint32_t iSeq) const
{
	ECodecType codec_in = Header.GetCodecIn();  // We'll need this

	// do the lich structure first
	// first, the src callsign (the lich.dest will be set in HandleQueue)
	packet.SetSourceCallsign(Header.GetMyCallsign());
	
	// then the frame type, if the incoming frame is M17 1600, then it will be Voice+Data only, otherwise Voice-Only
	packet.SetFrameType((ECodecType::c2_1600==codec_in) ? 0x7U : 0x5U);
	packet.SetNonce(DvFrame->GetNonce());

	// now the main part of the packet
	packet.SetMagic();
	
	// the frame number comes from the stream sequence counter
	// Assuming 1:1 mapping for 40ms frames (tcd output)
	uint16_t fn = iSeq % 0x8000U;
	if (DvFrame->IsLastPacket())
		fn |= 0x8000U;
	packet.SetFrameNumber(fn);
	packet.SetPayload(DvFrame->GetCodecData(ECodecType::c2_3200));
	packet.SetStreamId(Header.GetStreamId());
	// the CRC will be set in HandleQueue, after lich.dest is set
}

bool CM17Protocol::EncodeDvHeaderPacket(const CDvHeaderPacket &packet, CBuffer &buffer) const
{
	packet.EncodeInterlinkPacket(buffer);
	return true;
}

bool CM17Protocol::EncodeDvFramePacket(const CDvFramePacket &packet, CBuffer &buffer) const
{
	packet.EncodeInterlinkPacket(buffer);
	return true;
}