addrman.h
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	// Copyright (c) 2012 Pieter Wuille
	// Copyright (c) 2012-2016 The Bitcoin Core developers
	// Distributed under the MIT software license, see the accompanying
	// file COPYING or http://www.opensource.org/licenses/mit-license.php.

	#ifndef BITCOIN_ADDRMAN_H
	#define BITCOIN_ADDRMAN_H

	#include <netaddress.h>
	#include <protocol.h>
	#include <random.h>
	#include <sync.h>
	#include <timedata.h>
	#include <util/system.h>

	#include <cstdint>
	#include <map>
	#include <set>
	#include <vector>

	/**
	* Extended statistics about a CAddress
	*/
	class CAddrInfo : public CAddress {
	public:
	//! last try whatsoever by us (memory only)
	int64_t nLastTry{0};

	//! last counted attempt (memory only)
	int64_t nLastCountAttempt{0};

	private:
	//! where knowledge about this address first came from
	CNetAddr source;

	//! last successful connection by us
	int64_t nLastSuccess{0};

	//! connection attempts since last successful attempt
	int nAttempts{0};

	//! reference count in new sets (memory only)
	int nRefCount{0};

	//! in tried set? (memory only)
	bool fInTried{false};

	//! position in vRandom
	int nRandomPos{-1};

	friend class CAddrMan;

	public:
	ADD_SERIALIZE_METHODS;

	template <typename Stream, typename Operation>
	inline void SerializationOp(Stream &s, Operation ser_action) {
	READWRITEAS(CAddress, *this);
	READWRITE(source);
	READWRITE(nLastSuccess);
	READWRITE(nAttempts);
	}

	CAddrInfo(const CAddress &addrIn, const CNetAddr &addrSource)
	: CAddress(addrIn), source(addrSource) {}

	CAddrInfo() : CAddress(), source() {}

	//! Calculate in which "tried" bucket this entry belongs
	int GetTriedBucket(const uint256 &nKey) const;

	//! Calculate in which "new" bucket this entry belongs, given a certain
	//! source
	int GetNewBucket(const uint256 &nKey, const CNetAddr &src) const;

	//! Calculate in which "new" bucket this entry belongs, using its default
	//! source
	int GetNewBucket(const uint256 &nKey) const {
	return GetNewBucket(nKey, source);
	}

	//! Calculate in which position of a bucket to store this entry.
	int GetBucketPosition(const uint256 &nKey, bool fNew, int nBucket) const;

	//! Determine whether the statistics about this entry are bad enough so that
	//! it can just be deleted
	bool IsTerrible(int64_t nNow = GetAdjustedTime()) const;

	//! Calculate the relative chance this entry should be given when selecting
	//! nodes to connect to
	double GetChance(int64_t nNow = GetAdjustedTime()) const;
	};

	/** Stochastic address manager
	*
	* Design goals:
	* * Keep the address tables in-memory, and asynchronously dump the entire
	* table to peers.dat.
	* * Make sure no (localized) attacker can fill the entire table with his
	* nodes/addresses.
	*
	* To that end:
	* * Addresses are organized into buckets.
	* * Addresses that have not yet been tried go into 1024 "new" buckets.
	* * Based on the address range (/16 for IPv4) of the source of
	* information, 64 buckets are selected at random.
	* * The actual bucket is chosen from one of these, based on the range in
	* which the address itself is located.
	* * One single address can occur in up to 8 different buckets to increase
	* selection chances for addresses that
	* are seen frequently. The chance for increasing this multiplicity
	* decreases exponentially.
	* * When adding a new address to a full bucket, a randomly chosen entry
	* (with a bias favoring less recently seen
	* ones) is removed from it first.
	* * Addresses of nodes that are known to be accessible go into 256 "tried"
	* buckets.
	* * Each address range selects at random 8 of these buckets.
	* * The actual bucket is chosen from one of these, based on the full
	* address.
	* * When adding a new good address to a full bucket, a randomly chosen
	* entry (with a bias favoring less recently
	* tried ones) is evicted from it, back to the "new" buckets.
	* * Bucket selection is based on cryptographic hashing, using a
	* randomly-generated 256-bit key, which should not
	* be observable by adversaries.
	* * Several indexes are kept for high performance. Defining DEBUG_ADDRMAN
	* will introduce frequent (and expensive)
	* consistency checks for the entire data structure.
	*/

	//! total number of buckets for tried addresses
	#define ADDRMAN_TRIED_BUCKET_COUNT_LOG2 8

	//! total number of buckets for new addresses
	#define ADDRMAN_NEW_BUCKET_COUNT_LOG2 10

	//! maximum allowed number of entries in buckets for new and tried addresses
	#define ADDRMAN_BUCKET_SIZE_LOG2 6

	//! over how many buckets entries with tried addresses from a single group (/16
	//! for IPv4) are spread
	#define ADDRMAN_TRIED_BUCKETS_PER_GROUP 8

	//! over how many buckets entries with new addresses originating from a single
	//! group are spread
	#define ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP 64

	//! in how many buckets for entries with new addresses a single address may
	//! occur
	#define ADDRMAN_NEW_BUCKETS_PER_ADDRESS 8

	//! how old addresses can maximally be
	#define ADDRMAN_HORIZON_DAYS 30

	//! after how many failed attempts we give up on a new node
	#define ADDRMAN_RETRIES 3

	//! how many successive failures are allowed ...
	#define ADDRMAN_MAX_FAILURES 10

	//! ... in at least this many days
	#define ADDRMAN_MIN_FAIL_DAYS 7

	//! how recent a successful connection should be before we allow an address to
	//! be evicted from tried
	#define ADDRMAN_REPLACEMENT_SECONDS (4 * 60 * 60)

	//! the maximum percentage of nodes to return in a getaddr call
	#define ADDRMAN_GETADDR_MAX_PCT 23

	//! the maximum number of nodes to return in a getaddr call
	#define ADDRMAN_GETADDR_MAX 2500

	//! Convenience
	#define ADDRMAN_TRIED_BUCKET_COUNT (1 << ADDRMAN_TRIED_BUCKET_COUNT_LOG2)
	#define ADDRMAN_NEW_BUCKET_COUNT (1 << ADDRMAN_NEW_BUCKET_COUNT_LOG2)
	#define ADDRMAN_BUCKET_SIZE (1 << ADDRMAN_BUCKET_SIZE_LOG2)

	//! the maximum number of tried addr collisions to store
	#define ADDRMAN_SET_TRIED_COLLISION_SIZE 10

	/**
	* Stochastical (IP) address manager
	*/
	class CAddrMan {
	protected:
	//! critical section to protect the inner data structures
	mutable CCriticalSection cs;

	private:
	//! last used nId
	int nIdCount GUARDED_BY(cs);

	//! table with information about all nIds
	std::map<int, CAddrInfo> mapInfo GUARDED_BY(cs);

	//! find an nId based on its network address
	std::map<CNetAddr, int> mapAddr GUARDED_BY(cs);

	//! randomly-ordered vector of all nIds
	std::vector<int> vRandom GUARDED_BY(cs);

	// number of "tried" entries
	int nTried GUARDED_BY(cs);

	//! list of "tried" buckets
	int vvTried[ADDRMAN_TRIED_BUCKET_COUNT][ADDRMAN_BUCKET_SIZE] GUARDED_BY(cs);

	//! number of (unique) "new" entries
	int nNew GUARDED_BY(cs);

	//! list of "new" buckets
	int vvNew[ADDRMAN_NEW_BUCKET_COUNT][ADDRMAN_BUCKET_SIZE] GUARDED_BY(cs);

	//! last time Good was called (memory only)
	int64_t nLastGood GUARDED_BY(cs);

	//! Holds addrs inserted into tried table that collide with existing
	//! entries. Test-before-evict discipline used to resolve these collisions.
	std::set<int> m_tried_collisions;

	protected:
	//! secret key to randomize bucket select with
	uint256 nKey;

	//! Source of random numbers for randomization in inner loops
	FastRandomContext insecure_rand;

	//! Find an entry.
	CAddrInfo Find(const CNetAddr &addr, int pnId = nullptr)
	EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! find an entry, creating it if necessary.
	//! nTime and nServices of the found node are updated, if necessary.
	CAddrInfo *Create(const CAddress &addr, const CNetAddr &addrSource,
	int *pnId = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Swap two elements in vRandom.
	void SwapRandom(unsigned int nRandomPos1, unsigned int nRandomPos2)
	EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Move an entry from the "new" table(s) to the "tried" table
	void MakeTried(CAddrInfo &info, int nId) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Delete an entry. It must not be in tried, and have refcount 0.
	void Delete(int nId) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Clear a position in a "new" table. This is the only place where entries
	//! are actually deleted.
	void ClearNew(int nUBucket, int nUBucketPos) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Mark an entry "good", possibly moving it from "new" to "tried".
	void Good_(const CService &addr, bool test_before_evict, int64_t time)
	EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Add an entry to the "new" table.
	bool Add_(const CAddress &addr, const CNetAddr &source,
	int64_t nTimePenalty) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Mark an entry as attempted to connect.
	void Attempt_(const CService &addr, bool fCountFailure, int64_t nTime)
	EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Select an address to connect to, if newOnly is set to true, only the new
	//! table is selected from.
	CAddrInfo Select_(bool newOnly) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! See if any to-be-evicted tried table entries have been tested and if so
	//! resolve the collisions.
	void ResolveCollisions_() EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Return a random to-be-evicted tried table address.
	CAddrInfo SelectTriedCollision_() EXCLUSIVE_LOCKS_REQUIRED(cs);

	#ifdef DEBUG_ADDRMAN
	//! Perform consistency check. Returns an error code or zero.
	int Check_() EXCLUSIVE_LOCKS_REQUIRED(cs);
	#endif

	//! Select several addresses at once.
	void GetAddr_(std::vector<CAddress> &vAddr) EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Mark an entry as currently-connected-to.
	void Connected_(const CService &addr, int64_t nTime)
	EXCLUSIVE_LOCKS_REQUIRED(cs);

	//! Update an entry's service bits.
	void SetServices_(const CService &addr, ServiceFlags nServices)
	EXCLUSIVE_LOCKS_REQUIRED(cs);

	public:
	/**
	* serialized format:
	* * version byte (currently 1)
	* * 0x20 + nKey (serialized as if it were a vector, for backward
	* compatibility)
	* * nNew
	* * nTried
	* * number of "new" buckets XOR 2**30
	* * all nNew addrinfos in vvNew
	* * all nTried addrinfos in vvTried
	* * for each bucket:
	* * number of elements
	* * for each element: index
	*
	* 2**30 is xorred with the number of buckets to make addrman deserializer
	* v0 detect it as incompatible. This is necessary because it did not check
	* the version number on deserialization.
	*
	* Notice that vvTried, mapAddr and vVector are never encoded explicitly;
	* they are instead reconstructed from the other information.
	*
	* vvNew is serialized, but only used if ADDRMAN_UNKNOWN_BUCKET_COUNT didn't
	* change, otherwise it is reconstructed as well.
	*
	* This format is more complex, but significantly smaller (at most 1.5 MiB),
	* and supports changes to the ADDRMAN_ parameters without breaking the
	* on-disk structure.
	*
	* We don't use ADD_SERIALIZE_METHODS since the serialization and
	* deserialization code has very little in common.
	*/
	template <typename Stream> void Serialize(Stream &s) const {
	LOCK(cs);

	uint8_t nVersion = 1;
	s << nVersion;
	s << uint8_t(32);
	s << nKey;
	s << nNew;
	s << nTried;

	int nUBuckets = ADDRMAN_NEW_BUCKET_COUNT ^ (1 << 30);
	s << nUBuckets;
	std::map<int, int> mapUnkIds;
	int nIds = 0;
	for (const auto &entry : mapInfo) {
	mapUnkIds[entry.first] = nIds;
	const CAddrInfo &info = entry.second;
	if (info.nRefCount) {
	// this means nNew was wrong, oh ow
	assert(nIds != nNew);
	s << info;
	nIds++;
	}
	}
	nIds = 0;
	for (const auto &entry : mapInfo) {
	const CAddrInfo &info = entry.second;
	if (info.fInTried) {
	// this means nTried was wrong, oh ow
	assert(nIds != nTried);
	s << info;
	nIds++;
	}
	}
	for (int bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {
	int nSize = 0;
	for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
	if (vvNew[bucket][i] != -1) nSize++;
	}
	s << nSize;
	for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
	if (vvNew[bucket][i] != -1) {
	int nIndex = mapUnkIds[vvNew[bucket][i]];
	s << nIndex;
	}
	}
	}
	}

	template <typename Stream> void Unserialize(Stream &s) {
	LOCK(cs);

	Clear();

	uint8_t nVersion;
	s >> nVersion;
	uint8_t nKeySize;
	s >> nKeySize;
	if (nKeySize != 32) {
	throw std::ios_base::failure(
	"Incorrect keysize in addrman deserialization");
	}

	s >> nKey;
	s >> nNew;
	s >> nTried;
	int nUBuckets = 0;
	s >> nUBuckets;
	if (nVersion != 0) {
	nUBuckets ^= (1 << 30);
	}

	if (nNew > ADDRMAN_NEW_BUCKET_COUNT * ADDRMAN_BUCKET_SIZE) {
	throw std::ios_base::failure(
	"Corrupt CAddrMan serialization, nNew exceeds limit.");
	}

	if (nTried > ADDRMAN_TRIED_BUCKET_COUNT * ADDRMAN_BUCKET_SIZE) {
	throw std::ios_base::failure(
	"Corrupt CAddrMan serialization, nTried exceeds limit.");
	}

	// Deserialize entries from the new table.
	for (int n = 0; n < nNew; n++) {
	CAddrInfo &info = mapInfo[n];
	s >> info;
	mapAddr[info] = n;
	info.nRandomPos = vRandom.size();
	vRandom.push_back(n);
	if (nVersion != 1 \|\| nUBuckets != ADDRMAN_NEW_BUCKET_COUNT) {
	// In case the new table data cannot be used (nVersion unknown,
	// or bucket count wrong), immediately try to give them a
	// reference based on their primary source address.
	int nUBucket = info.GetNewBucket(nKey);
	int nUBucketPos = info.GetBucketPosition(nKey, true, nUBucket);
	if (vvNew[nUBucket][nUBucketPos] == -1) {
	vvNew[nUBucket][nUBucketPos] = n;
	info.nRefCount++;
	}
	}
	}
	nIdCount = nNew;

	// Deserialize entries from the tried table.
	int nLost = 0;
	for (int n = 0; n < nTried; n++) {
	CAddrInfo info;
	s >> info;
	int nKBucket = info.GetTriedBucket(nKey);
	int nKBucketPos = info.GetBucketPosition(nKey, false, nKBucket);
	if (vvTried[nKBucket][nKBucketPos] == -1) {
	info.nRandomPos = vRandom.size();
	info.fInTried = true;
	vRandom.push_back(nIdCount);
	mapInfo[nIdCount] = info;
	mapAddr[info] = nIdCount;
	vvTried[nKBucket][nKBucketPos] = nIdCount;
	nIdCount++;
	} else {
	nLost++;
	}
	}
	nTried -= nLost;

	// Deserialize positions in the new table (if possible).
	for (int bucket = 0; bucket < nUBuckets; bucket++) {
	int nSize = 0;
	s >> nSize;
	for (int n = 0; n < nSize; n++) {
	int nIndex = 0;
	s >> nIndex;
	if (nIndex >= 0 && nIndex < nNew) {
	CAddrInfo &info = mapInfo[nIndex];
	int nUBucketPos =
	info.GetBucketPosition(nKey, true, bucket);
	if (nVersion == 1 &&
	nUBuckets == ADDRMAN_NEW_BUCKET_COUNT &&
	vvNew[bucket][nUBucketPos] == -1 &&
	info.nRefCount < ADDRMAN_NEW_BUCKETS_PER_ADDRESS) {
	info.nRefCount++;
	vvNew[bucket][nUBucketPos] = nIndex;
	}
	}
	}
	}

	// Prune new entries with refcount 0 (as a result of collisions).
	int nLostUnk = 0;
	for (std::map<int, CAddrInfo>::const_iterator it = mapInfo.begin();
	it != mapInfo.end();) {
	if (it->second.fInTried == false && it->second.nRefCount == 0) {
	std::map<int, CAddrInfo>::const_iterator itCopy = it++;
	Delete(itCopy->first);
	nLostUnk++;
	} else {
	it++;
	}
	}
	if (nLost + nLostUnk > 0) {
	LogPrint(BCLog::ADDRMAN,
	"addrman lost %i new and %i tried addresses due to "
	"collisions\n",
	nLostUnk, nLost);
	}

	Check();
	}

	void Clear() {
	LOCK(cs);
	std::vector<int>().swap(vRandom);
	nKey = insecure_rand.rand256();
	for (size_t bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {
	for (size_t entry = 0; entry < ADDRMAN_BUCKET_SIZE; entry++) {
	vvNew[bucket][entry] = -1;
	}
	}
	for (size_t bucket = 0; bucket < ADDRMAN_TRIED_BUCKET_COUNT; bucket++) {
	for (size_t entry = 0; entry < ADDRMAN_BUCKET_SIZE; entry++) {
	vvTried[bucket][entry] = -1;
	}
	}

	nIdCount = 0;
	nTried = 0;
	nNew = 0;
	// Initially at 1 so that "never" is strictly worse.
	nLastGood = 1;
	mapInfo.clear();
	mapAddr.clear();
	}

	CAddrMan() { Clear(); }

	~CAddrMan() { nKey.SetNull(); }

	//! Return the number of (unique) addresses in all tables.
	size_t size() const {
	// TODO: Cache this in an atomic to avoid this overhead
	LOCK(cs);
	return vRandom.size();
	}

	//! Consistency check
	void Check() {
	#ifdef DEBUG_ADDRMAN
	{
	LOCK(cs);
	int err;
	if ((err = Check_())) {
	LogPrintf("ADDRMAN CONSISTENCY CHECK FAILED!!! err=%i\n", err);
	}
	}
	#endif
	}

	//! Add a single address.
	bool Add(const CAddress &addr, const CNetAddr &source,
	int64_t nTimePenalty = 0) {
	LOCK(cs);
	bool fRet = false;
	Check();
	fRet \|= Add_(addr, source, nTimePenalty);
	Check();
	if (fRet) {
	LogPrint(BCLog::ADDRMAN, "Added %s from %s: %i tried, %i new\n",
	addr.ToStringIPPort(), source.ToString(), nTried, nNew);
	}
	return fRet;
	}

	//! Add multiple addresses.
	bool Add(const std::vector<CAddress> &vAddr, const CNetAddr &source,
	int64_t nTimePenalty = 0) {
	LOCK(cs);
	int nAdd = 0;
	Check();
	for (const CAddress &a : vAddr) {
	nAdd += Add_(a, source, nTimePenalty) ? 1 : 0;
	}
	Check();
	if (nAdd) {
	LogPrint(BCLog::ADDRMAN,
	"Added %i addresses from %s: %i tried, %i new\n", nAdd,
	source.ToString(), nTried, nNew);
	}
	return nAdd > 0;
	}

	//! Mark an entry as accessible.
	void Good(const CService &addr, bool test_before_evict = true,
	int64_t nTime = GetAdjustedTime()) {
	LOCK(cs);
	Check();
	Good_(addr, test_before_evict, nTime);
	Check();
	}

	//! Mark an entry as connection attempted to.
	void Attempt(const CService &addr, bool fCountFailure,
	int64_t nTime = GetAdjustedTime()) {
	LOCK(cs);
	Check();
	Attempt_(addr, fCountFailure, nTime);
	Check();
	}

	//! See if any to-be-evicted tried table entries have been tested and if so
	//! resolve the collisions.
	void ResolveCollisions() {
	LOCK(cs);
	Check();
	ResolveCollisions_();
	Check();
	}

	//! Randomly select an address in tried that another address is attempting
	//! to evict.
	CAddrInfo SelectTriedCollision() {
	CAddrInfo ret;
	{
	LOCK(cs);
	Check();
	ret = SelectTriedCollision_();
	Check();
	}
	return ret;
	}

	/**
	* Choose an address to connect to.
	*/
	CAddrInfo Select(bool newOnly = false) {
	CAddrInfo addrRet;
	{
	LOCK(cs);
	Check();
	addrRet = Select_(newOnly);
	Check();
	}
	return addrRet;
	}

	//! Return a bunch of addresses, selected at random.
	std::vector<CAddress> GetAddr() {
	Check();
	std::vector<CAddress> vAddr;
	{
	LOCK(cs);
	GetAddr_(vAddr);
	}
	Check();
	return vAddr;
	}

	//! Mark an entry as currently-connected-to.
	void Connected(const CService &addr, int64_t nTime = GetAdjustedTime()) {
	LOCK(cs);
	Check();
	Connected_(addr, nTime);
	Check();
	}

	void SetServices(const CService &addr, ServiceFlags nServices) {
	LOCK(cs);
	Check();
	SetServices_(addr, nServices);
	Check();
	}
	};

	#endif // BITCOIN_ADDRMAN_H

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