libtgvoip/video/VideoFEC.cpp

//
// Created by Grishka on 24/03/2019.
//

#include "VideoFEC.h"
#include "../logging.h"
#include <stdlib.h>

using namespace tgvoip;
using namespace tgvoip::video;

Buffer ParityFEC::Encode(std::vector<Buffer>& packets){
	size_t maxSize=0;

	for(Buffer& pkt:packets){
		maxSize=std::max(maxSize, pkt.Length());
	}
	Buffer result(maxSize+2); // add 2 bytes for length
	uint8_t* _result=*result;
	memset(_result, 0, result.Length());
	for(Buffer& pkt:packets){
		for(size_t i=0;i<pkt.Length();i++){
			_result[i] ^= pkt[i];
		}
		uint16_t len=(uint16_t)pkt.Length();
		_result[maxSize] ^= (uint8_t)len;
		_result[maxSize+1] ^= (uint8_t)(len >> 8);
	}

	return std::move(result);
}

Buffer ParityFEC::Decode(std::vector<Buffer>& dataPackets, Buffer &fecPacket){
	size_t maxSize=0;
	for(Buffer& pkt:dataPackets){
		maxSize=std::max(maxSize, pkt.Length());
	}

	if(fecPacket.Length()<maxSize+2){
		LOGE("ParityFEC: FEC packet too small (%u, expected >=%u)", (unsigned int)fecPacket.Length(), (unsigned int)maxSize+2);
		return Buffer();
	}
	Buffer result=Buffer::CopyOf(fecPacket);
	uint8_t* _result=*result;
	unsigned int emptyCount=0;
	for(Buffer& pkt:dataPackets){
		if(pkt.Length()==0){
			emptyCount++;
			continue;
		}
		for(size_t i=0;i<pkt.Length();i++){
			_result[i] ^= pkt[i];
		}
		uint16_t len=(uint16_t)pkt.Length();
		_result[maxSize] ^= (uint8_t)len;
		_result[maxSize+1] ^= (uint8_t)(len >> 8);
	}
	if(emptyCount!=1){
		LOGE("ParityFEC: %u packets lost", emptyCount);
		return Buffer();
	}

	uint16_t len=(uint16_t)_result[maxSize] | ((uint16_t)_result[maxSize+1] << 8);
	if(len>maxSize){
		LOGE("ParityFEC: incorrect length %u", len);
		return Buffer();
	}
	LOGV("ParityFEC decoded packet size %u", len);

	result.Resize(len);
	return std::move(result);
}