premiere-libtorrent/include/libtorrent/kademlia/routing_table.hpp

/*

Copyright (c) 2006-2018, Arvid Norberg
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    * Redistributions in binary form must reproduce the above copyright
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      from this software without specific prior written permission.

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*/

#ifndef ROUTING_TABLE_HPP
#define ROUTING_TABLE_HPP

#include <vector>
#include <set>
#include <unordered_set>
#include <cstdint>
#include <tuple>
#include <array>

#include <libtorrent/fwd.hpp>
#include <libtorrent/kademlia/node_id.hpp>
#include <libtorrent/kademlia/node_entry.hpp>
#include <libtorrent/assert.hpp>
#include <libtorrent/time.hpp>
#include <libtorrent/aux_/vector.hpp>

namespace libtorrent { namespace dht {

struct settings;
struct dht_logger;

using bucket_t = aux::vector<node_entry>;

struct routing_table_node
{
	bucket_t replacements;
	bucket_t live_nodes;
};

struct ipv4_hash
{
	using argument_type = address_v4::bytes_type;
	using result_type = std::size_t;
	result_type operator()(argument_type const& ip) const
	{
		return std::hash<std::uint32_t>()(*reinterpret_cast<std::uint32_t const*>(&ip[0]));
	}
};

struct ipv6_hash
{
	using argument_type = address_v6::bytes_type;
	using result_type = std::size_t;
	result_type operator()(argument_type const& ip) const
	{
		return std::hash<std::uint64_t>()(*reinterpret_cast<std::uint64_t const*>(&ip[0]));
	}
};

struct TORRENT_EXTRA_EXPORT ip_set
{
	void insert(address const& addr);
	bool exists(address const& addr) const;
	void erase(address const& addr);

	void clear()
	{
		m_ip4s.clear();
		m_ip6s.clear();
	}

	bool operator==(ip_set const& rh)
	{
		return m_ip4s == rh.m_ip4s && m_ip6s == rh.m_ip6s;
	}

	std::size_t size() const { return m_ip4s.size() + m_ip6s.size(); }

	// these must be multisets because there can be multiple routing table
	// entries for a single IP when restrict_routing_ips is set to false
	std::unordered_multiset<address_v4::bytes_type, ipv4_hash> m_ip4s;
	std::unordered_multiset<address_v6::bytes_type, ipv6_hash> m_ip6s;
};

// Each routing table bucket represents node IDs with a certain number of bits
// of prefix in common with our own node ID. Each bucket fits 8 nodes (and
// sometimes more, closer to the top). In order to minimize the number of hops
// necessary to traverse the DHT, we want the nodes in our buckets to be spread
// out across all possible "sub-branches". This is what the "classify" refers
// to. The 3 (or more) bits following the shared bit prefix.
TORRENT_EXTRA_EXPORT std::uint8_t classify_prefix(int bucket_idx, bool last_bucket
	, int bucket_size, node_id nid);

TORRENT_EXTRA_EXPORT bool all_in_same_bucket(span<node_entry const> b
	, node_id const& id, int bucket_index);

// differences in the implementation from the description in
// the paper:
//
// * Nodes are not marked as being stale, they keep a counter
// 	that tells how many times in a row they have failed. When
// 	a new node is to be inserted, the node that has failed
// 	the most times is replaced. If none of the nodes in the
// 	bucket has failed, then it is put in the replacement
// 	cache (just like in the paper).
// * The routing table bucket sizes are larger towards the "top" of the routing
// 	table. This is to get closer to the target in fewer round-trips.
// * Nodes with lower RTT are preferred and may replace nodes with higher RTT
// * Nodes that are "verified" (i.e. use a node-ID derived from their IP) are
// 	preferred and may replace nodes that are not verified.

TORRENT_EXTRA_EXPORT bool mostly_verified_nodes(bucket_t const&);
TORRENT_EXTRA_EXPORT bool compare_ip_cidr(address const& lhs, address const& rhs);

class TORRENT_EXTRA_EXPORT routing_table
{
public:
	// TODO: 3 to improve memory locality and scanning performance, turn the
	// routing table into a single vector with boundaries for the nodes instead.
	// Perhaps replacement nodes should be in a separate vector.
	using table_t = aux::vector<routing_table_node>;

	routing_table(node_id const& id, udp proto
		, int bucket_size
		, dht::settings const& settings
		, dht_logger* log);

	routing_table(routing_table const&) = delete;
	routing_table& operator=(routing_table const&) = delete;

#if TORRENT_ABI_VERSION == 1
	void status(session_status& s) const;
#endif

	void status(std::vector<dht_routing_bucket>& s) const;

	void node_failed(node_id const& id, udp::endpoint const& ep);

	// adds an endpoint that will never be added to
	// the routing table
	void add_router_node(udp::endpoint const& router);

	// iterates over the router nodes added
	using router_iterator = std::set<udp::endpoint>::const_iterator;
	router_iterator begin() const { return m_router_nodes.begin(); }
	router_iterator end() const { return m_router_nodes.end(); }

	enum add_node_status_t {
		failed_to_add = 0,
		node_added,
		need_bucket_split
	};
	add_node_status_t add_node_impl(node_entry e);

	bool add_node(node_entry const& e);

	// this function is called every time the node sees
	// a sign of a node being alive. This node will either
	// be inserted in the k-buckets or be moved to the top
	// of its bucket.
	bool node_seen(node_id const& id, udp::endpoint const& ep, int rtt);

	// this may add a node to the routing table and mark it as
	// not pinged. If the bucket the node falls into is full,
	// the node will be ignored.
	void heard_about(node_id const& id, udp::endpoint const& ep);

	// change our node ID. This can be expensive since nodes must be moved around
	// and potentially dropped
	void update_node_id(node_id const& id);

	node_entry const* next_refresh();

	enum
	{
		// nodes that have not been pinged are considered failed by this flag
		include_failed = 1
	};

	// fills the vector with the count nodes from our buckets that
	// are nearest to the given id.
	void find_node(node_id const& id, std::vector<node_entry>& l
		, int options, int count = 0);
	void remove_node(node_entry* n, bucket_t* b);

	int bucket_size(int bucket) const
	{
		int num_buckets = int(m_buckets.size());
		if (num_buckets == 0) return 0;
		if (bucket >= num_buckets) bucket = num_buckets - 1;
		table_t::const_iterator i = m_buckets.begin();
		std::advance(i, bucket);
		return int(i->live_nodes.size());
	}

	void for_each_node(std::function<void(node_entry const&)> live_cb
		, std::function<void(node_entry const&)> replacements_cb) const;

	void for_each_node(std::function<void(node_entry const&)> f) const
	{ for_each_node(f, f); }

	int bucket_size() const { return m_bucket_size; }

	// returns the number of nodes in the main buckets, number of nodes in the
	// replacement buckets and the number of nodes in the main buckets that have
	// been pinged and confirmed up
	std::tuple<int, int, int> size() const;

	std::int64_t num_global_nodes() const;

	// the number of bits down we have full buckets
	// i.e. essentially the number of full buckets
	// we have
	int depth() const;

	int num_active_buckets() const { return int(m_buckets.size()); }

	int bucket_limit(int bucket) const;

#if TORRENT_USE_INVARIANT_CHECKS
	void check_invariant() const;
#endif

	bool is_full(int bucket) const;

	bool native_address(address const& addr) const
	{
		return (addr.is_v4() && m_protocol == udp::v4())
			|| (addr.is_v6() && m_protocol == udp::v6());
	}

	bool native_endpoint(udp::endpoint const& ep) const
	{ return ep.protocol() == m_protocol; }

	node_id const& id() const
	{ return m_id; }

	table_t const& buckets() const
	{ return m_buckets; }

private:

#ifndef TORRENT_DISABLE_LOGGING
	dht_logger* m_log;
	void log_node_failed(node_id const& nid, node_entry const& ne) const;
#endif

	table_t::iterator find_bucket(node_id const& id);
	void remove_node_internal(node_entry* n, bucket_t& b);

	void split_bucket();

	// return a pointer the node_entry with the given endpoint
	// or 0 if we don't have such a node. Both the address and the
	// port has to match
	std::tuple<node_entry*, routing_table::table_t::iterator, bucket_t*>
	find_node(udp::endpoint const& ep);

	// if the bucket is not full, try to fill it with nodes from the
	// replacement list
	void fill_from_replacements(table_t::iterator bucket);

	void prune_empty_bucket();

	dht::settings const& m_settings;

	// (k-bucket, replacement cache) pairs
	// the first entry is the bucket the furthest
	// away from our own ID. Each time the bucket
	// closest to us (m_buckets.back()) has more than
	// bucket size nodes in it, another bucket is
	// added to the end and it's split up between them
	table_t m_buckets;

	node_id m_id; // our own node id
	udp m_protocol; // protocol this table is for

	// the last seen depth (i.e. levels in the routing table)
	// it's mutable because it's updated by depth(), which is const
	mutable int m_depth;

	// the last time we refreshed our own bucket
	// refreshed every 15 minutes
	mutable time_point m_last_self_refresh;

	// this is a set of all the endpoints that have
	// been identified as router nodes. They will
	// be used in searches, but they will never
	// be added to the routing table.
	std::set<udp::endpoint> m_router_nodes;

	// these are all the IPs that are in the routing
	// table. It's used to only allow a single entry
	// per IP in the whole table.
	ip_set m_ips;

	// constant called k in paper
	int const m_bucket_size;
};

TORRENT_EXTRA_EXPORT routing_table::add_node_status_t
replace_node_impl(node_entry const& e, bucket_t& b, ip_set& ips
	, int bucket_index, int bucket_size_limit, bool last_bucket
#ifndef TORRENT_DISABLE_LOGGING
	, dht_logger* log
#endif
	);

} } // namespace libtorrent::dht

#endif // ROUTING_TABLE_HPP