xahaud/src/SNTPClient.cpp

#include "SNTPClient.h"

#include <boost/bind.hpp>
#include <boost/make_shared.hpp>

#include <openssl/rand.h>

#include "utils.h"
#include "Config.h"
#include "Log.h"

// #define SNTP_DEBUG

static uint8_t SNTPQueryData[48] =
{ 0x1B,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 };

// NTP query frequency - 4 minutes
#define NTP_QUERY_FREQUENCY		(4 * 60)

// NTP minimum interval to query same servers - 3 minutes
#define NTP_MIN_QUERY			(3 * 60)

// NTP sample window (should be odd)
#define NTP_SAMPLE_WINDOW		9

// NTP timestamp constant
#define NTP_UNIX_OFFSET			0x83AA7E80

// NTP timestamp validity
#define NTP_TIMESTAMP_VALID		((NTP_QUERY_FREQUENCY + NTP_MIN_QUERY) * 2)

// SNTP packet offsets
#define NTP_OFF_INFO			0
#define NTP_OFF_ROOTDELAY		1
#define NTP_OFF_ROOTDISP		2
#define NTP_OFF_REFERENCEID		3
#define NTP_OFF_REFTS_INT		4
#define NTP_OFF_REFTS_FRAC		5
#define NTP_OFF_ORGTS_INT		6
#define NTP_OFF_ORGTS_FRAC		7
#define NTP_OFF_RECVTS_INT		8
#define NTP_OFF_RECVTS_FRAC		9
#define NTP_OFF_XMITTS_INT		10
#define NTP_OFF_XMITTS_FRAC		11


SNTPClient::SNTPClient(boost::asio::io_service& service) : mSocket(service), mTimer(service), mResolver(service),
		mOffset(0), mLastOffsetUpdate((time_t) -1), mReceiveBuffer(256)
{
	if (!theConfig.RUN_STANDALONE)
	{
		mSocket.open(boost::asio::ip::udp::v4());
		mSocket.async_receive_from(boost::asio::buffer(mReceiveBuffer, 256), mReceiveEndpoint,
			boost::bind(&SNTPClient::receivePacket, this, boost::asio::placeholders::error,
				boost::asio::placeholders::bytes_transferred));

		mTimer.expires_from_now(boost::posix_time::seconds(NTP_QUERY_FREQUENCY));
		mTimer.async_wait(boost::bind(&SNTPClient::timerEntry, this, boost::asio::placeholders::error));
	}
}

void SNTPClient::resolveComplete(const boost::system::error_code& error, boost::asio::ip::udp::resolver::iterator it)
{
	if (!error)
	{
		boost::asio::ip::udp::resolver::iterator sel = it;
		int i = 1;
		while (++it != boost::asio::ip::udp::resolver::iterator())
			if ((rand() % ++i) == 0)
				sel = it;
		if (sel != boost::asio::ip::udp::resolver::iterator())
		{
			boost::mutex::scoped_lock sl(mLock);
			SNTPQuery& query = mQueries[*sel];
			time_t now = time(NULL);
			if ((query.mLocalTimeSent == now) || ((query.mLocalTimeSent + 1) == now))
			{ // This can happen if the same IP address is reached through multiple names
				Log(lsTRACE) << "SNTP: Redundant query suppressed";
				return;
			}
			query.mReceivedReply = false;
			query.mLocalTimeSent = now;
			RAND_bytes(reinterpret_cast<unsigned char *>(&query.mQueryNonce), sizeof(query.mQueryNonce));
			reinterpret_cast<uint32*>(SNTPQueryData)[NTP_OFF_XMITTS_INT] = time(NULL) + NTP_UNIX_OFFSET;
			reinterpret_cast<uint32*>(SNTPQueryData)[NTP_OFF_XMITTS_FRAC] = query.mQueryNonce;
			mSocket.async_send_to(boost::asio::buffer(SNTPQueryData, 48), *sel,
				boost::bind(&SNTPClient::sendComplete, this,
					boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
		}
	}
}

void SNTPClient::receivePacket(const boost::system::error_code& error, std::size_t bytes_xferd)
{
	if (!error)
	{
		boost::mutex::scoped_lock sl(mLock);
#ifdef SNTP_DEBUG
		Log(lsTRACE) << "SNTP: Packet from " << mReceiveEndpoint;
#endif
		std::map<boost::asio::ip::udp::endpoint, SNTPQuery>::iterator query = mQueries.find(mReceiveEndpoint);
		if (query == mQueries.end())
			Log(lsDEBUG) << "SNTP: Reply from " << mReceiveEndpoint << " found without matching query";
		else if (query->second.mReceivedReply)
			Log(lsDEBUG) << "SNTP: Duplicate response from " << mReceiveEndpoint;
		else
		{
			query->second.mReceivedReply = true;
			if (time(NULL) > (query->second.mLocalTimeSent + 1))
				Log(lsWARNING) << "SNTP: Late response from " << mReceiveEndpoint;
			else if (bytes_xferd < 48)
				Log(lsWARNING) << "SNTP: Short reply from " << mReceiveEndpoint
					<< " (" << bytes_xferd << ") " << mReceiveBuffer.size();
			else if (reinterpret_cast<uint32*>(&mReceiveBuffer[0])[NTP_OFF_ORGTS_FRAC] != query->second.mQueryNonce)
				Log(lsWARNING) << "SNTP: Reply from " << mReceiveEndpoint << "had wrong nonce";
			else
				processReply();
		}
	}

	mSocket.async_receive_from(boost::asio::buffer(mReceiveBuffer, 256), mReceiveEndpoint,
		boost::bind(&SNTPClient::receivePacket, this, boost::asio::placeholders::error,
			boost::asio::placeholders::bytes_transferred));
}

void SNTPClient::sendComplete(const boost::system::error_code& error, std::size_t)
{
	if (error)
		Log(lsWARNING) << "SNTP: Send error";
}

void SNTPClient::processReply()
{
	assert(mReceiveBuffer.size() >= 48);
	uint32 *recvBuffer = reinterpret_cast<uint32*>(&mReceiveBuffer.front());

	unsigned info = ntohl(recvBuffer[NTP_OFF_INFO]);
	int64_t timev = ntohl(recvBuffer[NTP_OFF_RECVTS_INT]);
	unsigned stratum = (info >> 16) & 0xff;

	if ((info >> 30) == 3)
	{
		Log(lsINFO) << "SNTP: Alarm condition " << mReceiveEndpoint;
		return;
	}
	if ((stratum == 0) || (stratum > 14))
	{
		Log(lsINFO) << "SNTP: Unreasonable stratum (" << stratum << ") from " << mReceiveEndpoint;
		return;
	}

	time_t now = time(NULL);
	timev -= now;
	timev -= NTP_UNIX_OFFSET;

	// add offset to list, replacing oldest one if appropriate
	mOffsetList.push_back(timev);
	if (mOffsetList.size() >= NTP_SAMPLE_WINDOW)
		mOffsetList.pop_front();
	mLastOffsetUpdate = now;

	// select median time
	std::list<int> offsetList = mOffsetList;
	offsetList.sort();
	int j = offsetList.size();
	std::list<int>::iterator it = offsetList.begin();
	for (int i = 0; i < (j / 2); ++i)
		++it;
	mOffset = *it;
	if ((j % 2) == 0)
		mOffset = (mOffset + (*--it)) / 2;

	if ((mOffset == -1) || (mOffset == 1)) // small corrections likely do more harm than good
		mOffset = 0;

#ifndef SNTP_DEBUG
	if (timev || mOffset)
#endif
		Log(lsTRACE) << "SNTP: Offset is " << timev << ", new system offset is " << mOffset;
}

void SNTPClient::timerEntry(const boost::system::error_code& error)
{
	if (!error)
	{
		doQuery();
		mTimer.expires_from_now(boost::posix_time::seconds(NTP_QUERY_FREQUENCY));
		mTimer.async_wait(boost::bind(&SNTPClient::timerEntry, this, boost::asio::placeholders::error));
	}
}

void SNTPClient::addServer(const std::string& server)
{
	boost::mutex::scoped_lock sl(mLock);
	mServers.push_back(std::make_pair(server, (time_t) -1));
}

void SNTPClient::init(const std::vector<std::string>& servers)
{
	std::vector<std::string>::const_iterator it = servers.begin();
	if (it == servers.end())
	{
		Log(lsINFO) << "SNTP: no server specified";
		return;
	}
	do
		addServer(*it++);
	while (it != servers.end());
	queryAll();
}

void SNTPClient::queryAll()
{
	while (doQuery())
		nothing();
}

bool SNTPClient::getOffset(int& offset)
{
	boost::mutex::scoped_lock sl(mLock);
	if ((mLastOffsetUpdate == (time_t) -1) || ((mLastOffsetUpdate + NTP_TIMESTAMP_VALID) < time(NULL)))
		return false;
	offset = mOffset;
	return true;
}

bool SNTPClient::doQuery()
{
	boost::mutex::scoped_lock sl(mLock);
	std::vector< std::pair<std::string, time_t> >::iterator best = mServers.end();
	for (std::vector< std::pair<std::string, time_t> >::iterator it = mServers.begin(), end = best;
			it != end; ++it)
		if ((best == end) || (it->second == (time_t) -1) || (it->second < best->second))
			best = it;
	if (best == mServers.end())
	{
		Log(lsINFO) << "SNTP: No server to query";
		return false;
	}
	time_t now = time(NULL);
	if ((best->second != (time_t) -1) && ((best->second + NTP_MIN_QUERY) >= now))
	{
		Log(lsTRACE) << "SNTP: All servers recently queried";
		return false;
	}
	best->second = now;

	boost::asio::ip::udp::resolver::query query(boost::asio::ip::udp::v4(), best->first, "ntp");
	mResolver.async_resolve(query,
		boost::bind(&SNTPClient::resolveComplete, this,
		boost::asio::placeholders::error, boost::asio::placeholders::iterator));
#ifdef SNTP_DEBUG
	Log(lsTRACE) << "SNTP: Resolve pending for " << best->first;
#endif
	return true;
}
// vim:ts=4