premiere-libtorrent/include/libtorrent/session_settings.hpp

/*

Copyright (c) 2003-2013, Arvid Norberg
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#ifndef TORRENT_SESSION_SETTINGS_HPP_INCLUDED
#define TORRENT_SESSION_SETTINGS_HPP_INCLUDED

#include "libtorrent/version.hpp"
#include "libtorrent/config.hpp"
#include "libtorrent/version.hpp"

#include <boost/cstdint.hpp>
#include <string>

namespace libtorrent
{

	// The ``proxy_settings`` structs contains the information needed to
	// direct certain traffic to a proxy.
	struct TORRENT_EXPORT proxy_settings
	{
		// defaults constructs proxy settings, initializing it to the default
		// settings.
		proxy_settings() : type(none)
			, port(0), proxy_hostnames(true)
			, proxy_peer_connections(true)
		{}

		// the name or IP of the proxy server. ``port`` is the
		// port number the proxy listens to. If required, ``username`` and ``password``
		// can be set to authenticate with the proxy.
		std::string hostname;

		// when using a proy type that requires authentication, the username
		// and password fields must be set to the credentials for the proxy.
		std::string username;
		std::string password;

		// the type of proxy to use. Assign one of these to the
		// proxy_settings::type field.
		enum proxy_type
		{
			// This is the default, no proxy server is used, all other fields
			// are ignored.
			none,

			// The server is assumed to be a `SOCKS4 server`_ that
			// requires a username.
			//
			// .. _`SOCKS4 server`: http://www.ufasoft.com/doc/socks4_protocol.htm
			socks4,
			// The server is assumed to be a SOCKS5 server (`RFC 1928`_) that
			// does not require any authentication. The username and password are ignored.
			//
			// .. _`RFC 1928`: http://www.faqs.org/rfcs/rfc1928.html
			socks5,

			// The server is assumed to be a SOCKS5 server that supports
			// plain text username and password authentication (`RFC 1929`_). The username
			// and password specified may be sent to the proxy if it requires.
			//
			// .. _`RFC 1929`: http://www.faqs.org/rfcs/rfc1929.html
			socks5_pw,
			// The server is assumed to be an HTTP proxy. If the transport used
			// for the connection is non-HTTP, the server is assumed to support the
			// CONNECT_ method. i.e. for web seeds and HTTP trackers, a plain proxy will
			// suffice. The proxy is assumed to not require authorization. The username
			// and password will not be used.
			//
			// .. _CONNECT: http://tools.ietf.org/html/draft-luotonen-web-proxy-tunneling-01
			http,
			// The server is assumed to be an HTTP proxy that requires
			// user authorization. The username and password will be sent to the proxy.
			http_pw,
			// route through a i2p SAM proxy
			i2p_proxy
		};
		
		// tells libtorrent what kind of proxy server it is. See proxy_type
		// enum for options
		boost::uint8_t type;

		// the port the proxy server is running on
		boost::uint16_t port;

		// defaults to true. It means that hostnames should be
		// attempted to be resolved through the proxy instead of using the local DNS
		// service. This is only supported by SOCKS5 and HTTP.
		bool proxy_hostnames;

		// determines whether or not to excempt peer and
		// web seed connections from using the proxy. This defaults to true, i.e. peer
		// connections are proxied by default.
		bool proxy_peer_connections;
	};

	// This holds most of the session-wide settings in libtorrent. Pass this
	// to session::set_settings() to change the settings, initialize it from
	// session::get_settings() to get the current settings.
	struct TORRENT_EXPORT session_settings
	{
		// initializes the session_settings to the default settings.
		session_settings(std::string const& user_agent = "libtorrent/"
			LIBTORRENT_VERSION);
		~session_settings();

		// automatically set to the libtorrent version you're using
		// in order to be forward binary compatible. This field should not be changed.
		int version;

		// the client identification to the tracker.
		// The recommended format of this string is:
		// "ClientName/ClientVersion libtorrent/libtorrentVersion".
		// This name will not only be used when making HTTP requests, but also when
		// sending extended headers to peers that support that extension.
		std::string user_agent;

		// the number of seconds the tracker
		// connection will wait from when it sent the request until it considers the
		// tracker to have timed-out. Default value is 60 seconds.
		int tracker_completion_timeout;
		
		// the number of seconds to wait to receive
		// any data from the tracker. If no data is received for this number of
		// seconds, the tracker will be considered as having timed out. If a tracker
		// is down, this is the kind of timeout that will occur. The default value
		// is 20 seconds.
		int tracker_receive_timeout;

		// the time to wait when sending a stopped message
		// before considering a tracker to have timed out.
		// this is usually shorter, to make the client quit
		// faster
		//
		// This is given in seconds. Default is
		// 10 seconds.
		int stop_tracker_timeout;

		// the maximum number of bytes in a
		// tracker response. If a response size passes this number it will be rejected
		// and the connection will be closed. On gzipped responses this size is measured
		// on the uncompressed data. So, if you get 20 bytes of gzip response that'll
		// expand to 2 megs, it will be interrupted before the entire response has been
		// uncompressed (given your limit is lower than 2 megs). Default limit is
		// 1 megabyte.
		int tracker_maximum_response_length;

		// controls the number of seconds from a request is sent until
		// it times out if no piece response is returned.
		int piece_timeout;

		// the number of seconds one block (16kB) is expected
		// to be received within. If it's not, the block is
		// requested from a different peer
		int request_timeout;

		// the length of the request queue given in the number
		// of seconds it should take for the other end to send
		// all the pieces. i.e. the actual number of requests
		// depends on the download rate and this number.
		int request_queue_time;
		
		// the number of outstanding block requests a peer is
		// allowed to queue up in the client. If a peer sends
		// more requests than this (before the first one has
		// been sent) the last request will be dropped.
		// the higher this is, the faster upload speeds the
		// client can get to a single peer.
		int max_allowed_in_request_queue;
		
		// the maximum number of outstanding requests to
		// send to a peer. This limit takes precedence over
		// request_queue_time.
		// i.e. no matter the download speed, the number of outstanding requests will never
		// exceed this limit.
		int max_out_request_queue;

		// if a whole piece can be downloaded in this number
		// of seconds, or less, the peer_connection will prefer
		// to request whole pieces at a time from this peer.
		// The benefit of this is to better utilize disk caches by
		// doing localized accesses and also to make it easier
		// to identify bad peers if a piece fails the hash check.
		int whole_pieces_threshold;
		
		// the number of seconds to wait for any activity on
		// the peer wire before closing the connectiong due
		// to time out.
		// This defaults to 120 seconds, since that's what's specified
		// in the protocol specification. After half the time out, a keep alive message
		// is sent.
		int peer_timeout;
		
		// same as peer_timeout, but only applies to url-seeds.
		// this is usually set lower, because web servers are
		// expected to be more reliable.
		// This value defaults to 20 seconds.
		int urlseed_timeout;
		
		// controls the pipelining with the web server. When
		// using persistent connections to HTTP 1.1 servers, the client is allowed to
		// send more requests before the first response is received. This number controls
		// the number of outstanding requests to use with url-seeds. Default is 5.
		int urlseed_pipeline_size;

		// time to wait until a new retry takes place
		int urlseed_wait_retry;
		
		// sets the upper limit on the total number of files this
		// session will keep open. The reason why files are
		// left open at all is that some anti virus software
		// hooks on every file close, and scans the file for
		// viruses. deferring the closing of the files will
		// be the difference between a usable system and
		// a completely hogged down system. Most operating
		// systems also has a limit on the total number of
		// file descriptors a process may have open. It is
		// usually a good idea to find this limit and set the
		// number of connections and the number of files
		// limits so their sum is slightly below it.
		int file_pool_size;
		
		// determines if connections from the
		// same IP address as existing connections should be rejected or not. Multiple
		// connections from the same IP address is not allowed by default, to prevent
		// abusive behavior by peers. It may be useful to allow such connections in
		// cases where simulations are run on the same machie, and all peers in a
		// swarm has the same IP address.
		bool allow_multiple_connections_per_ip;

		// the maximum times we try to connect to a peer before
		// stop connecting again. If a peer succeeds, its failcounter is reset. If
		// a peer is retrieved from a peer source (other than DHT) the failcount is
		// decremented by one, allowing another try.
		int max_failcount;
		
		// the number of seconds to wait to reconnect to a peer.
		// this time is multiplied with the failcount.
		int min_reconnect_time;

		// the number of seconds to wait after a connection
		// attempt is initiated to a peer until it is considered as having timed out.
		// The default is 10 seconds. This setting is especially important in case
		// the number of half-open connections are limited, since stale half-open
		// connection may delay the connection of other peers considerably.
		int peer_connect_timeout;

		// if set to true, upload, download and unchoke limits
		// are ignored for peers on the local network.
		bool ignore_limits_on_local_network;

		// the number of connection attempts that
		// are made per second. If a number < 0 is specified, it will default to
		// 200 connections per second. If 0 is specified, it means don't make
		// outgoing connections at all.
		int connection_speed;

		// if this is set to true, have messages will be sent
		// to peers that already have the piece. This is
		// typically not necessary, but it might be necessary
		// for collecting statistics in some cases. Default is false.
		bool send_redundant_have;

		// prevents outgoing bitfields from being full. If the
		// client is seed, a few bits will be set to 0, and later filled in with
		// have-messages. This is an old attempt to prevent certain ISPs
		// from stopping people from seeding.
		bool lazy_bitfields;

		// if a peer is uninteresting and uninterested for longer
		// than this number of seconds, it will be disconnected.
		// default is 10 minutes
		int inactivity_timeout;

		// the number of seconds between chokes/unchokes.
		// On this interval, peers are re-evaluated for being choked/unchoked. This
		// is defined as 30 seconds in the protocol, and it should be significantly
		// longer than what it takes for TCP to ramp up to it's max rate.
		int unchoke_interval;

		// the number of seconds between
		// each *optimistic* unchoke. On this timer, the currently optimistically
		// unchoked peer will change.
		int optimistic_unchoke_interval;

		// the ip address passed along to trackers as the ``&ip=`` parameter.
		// If left as the default (an empty string), that parameter is omitted.
		// Most trackers ignore this argument. This is here for completeness
		// for edge-cases where it may be useful.
		std::string announce_ip;

		// the number of peers we want from each tracker request. It defines
		// what is sent as the ``&num_want=`` parameter to the tracker.
		// Stopped messages always send num_want=0. This setting control what
		// to say in the case where we actually want peers.
		int num_want;

		// specifies the number of pieces we need before we
		// switch to rarest first picking. This defaults to 4, which means the 4 first
		// pieces in any torrent are picked at random, the following pieces are picked
		// in rarest first order.
		int initial_picker_threshold;

		// the number of allowed pieces to send to choked peers
		// that supports the fast extensions
		int allowed_fast_set_size;

		// options for session_settings::suggest_mode.
		enum suggest_mode_t
		{
			// the default. will not send out suggest messages.
			no_piece_suggestions = 0,

			// send out suggest messages for the most
			// recent pieces that are in the read cache.
			suggest_read_cache = 1
		};

		// this determines which pieces will be suggested to peers
		// suggest read cache will make libtorrent suggest pieces
		// that are fresh in the disk read cache, to potentially
		// lower disk access and increase the cache hit ratio
		//
		// for options, see suggest_mode_t.
		int suggest_mode;

		// the maximum number of bytes a connection may have
		// pending in the disk write queue before its download
		// rate is being throttled. This prevents fast downloads
		// to slow medias to allocate more memory
		// indefinitely. This should be set to at least 16 kB
		// to not completely disrupt normal downloads. If it's
		// set to 0, you will be starving the disk thread and
		// nothing will be written to disk.
		// this is a per session setting.
		//
		// When this limit is reached,
		// the peer connections will stop reading data from their sockets, until the disk
		// thread catches up. Setting this too low will severly limit your download rate.
		int max_queued_disk_bytes;

		// this is the low watermark for the disk buffer queue.
		// whenever the number of queued bytes exceed the
		// max_queued_disk_bytes, libtorrent will wait for
		// it to drop below this value before issuing more
		// reads from the sockets. If set to 0, the
		// low watermark will be half of the max queued disk bytes
		int max_queued_disk_bytes_low_watermark;

		// the number of seconds to wait for a handshake
		// response from a peer. If no response is received
		// within this time, the peer is disconnected.
		int handshake_timeout;

		// determines how the DHT is used. If this is true,
		// the DHT will only be used for torrents where all trackers in its tracker
		// list has failed. Either by an explicit error message or a time out. This
		// is false by default, which means the DHT is used by default regardless of
		// if the trackers fail or not.
		bool use_dht_as_fallback;

		// determines whether or not the torrent's piece hashes
		// are kept in memory after the torrent becomes a seed or not. If it is set to
		// ``true`` the hashes are freed once the torrent is a seed (they're not
		// needed anymore since the torrent won't download anything more). If it's set
		// to false they are not freed. If they are freed, the torrent_info returned
		// by get_torrent_info() will return an object that may be incomplete, that
		// cannot be passed back to async_add_torrent() and add_torrent() for instance.
		bool free_torrent_hashes;

		// indicates whether or not the UPnP implementation
		// should ignore any broadcast response from a device whose address is not the
		// configured router for this machine. i.e. it's a way to not talk to other
		// people's routers by mistake.
		bool upnp_ignore_nonrouters;

		// This is the minimum send buffer target size (send buffer
		// includes bytes pending being read from disk). For good
		// and snappy seeding performance, set this fairly high, to
		// at least fit a few blocks. This is essentially the initial
		// window size which will determine how fast we can ramp up
		// the send rate
		int send_buffer_low_watermark;

		// the upper limit of the send buffer low-watermark.
		//
		// if the send buffer has fewer bytes than this, we'll
		// read another 16kB block onto it. If set too small,
		// upload rate capacity will suffer. If set too high,
		// memory will be wasted.
		// The actual watermark may be lower than this in case
		// the upload rate is low, this is the upper limit.
		int send_buffer_watermark;

		// the current upload rate to a peer is multiplied by
		// this factor to get the send buffer watermark. The
		// factor is specified as a percentage. i.e. 50 indicates
		// a factor of 0.5.
		//
		// This product is clamped to the send_buffer_watermark
		// setting to not exceed the max. For high speed
		// upload, this should be set to a greater value than
		// 100. The default is 50.
		//
		// For high capacity connections, setting this
		// higher can improve upload performance and disk throughput. Setting it too
		// high may waste RAM and create a bias towards read jobs over write jobs.
		int send_buffer_watermark_factor;

#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.16
		// defaults to true. When true, if there is a global upload
		// limit set and the current upload rate is less than 90% of that, another upload
		// slot is opened. If the upload rate has been saturated for an extended period
		// of time, on upload slot is closed. The number of upload slots will never be
		// less than what has been set by ``session::set_max_uploads()``. To query the
		// current number of upload slots, see ``session_status::allowed_upload_slots``.
		bool auto_upload_slots;

		// When set, and ``auto_upload_slots`` is set,
		// the max upload slots setting is used as a minimum number of unchoked slots.
		// This algorithm is designed to prevent the peer from spreading its upload
		// capacity too thin, but still open more slots in order to utilize the full capacity.
		bool auto_upload_slots_rate_based;
#endif

		// the different choking algorithms available. Set
		// session_settings::choking_algorithm to one of these
		enum choking_algorithm_t
		{
			// the traditional choker with a fixed number of unchoke
			// slots, as specified by session::set_max_uploads()..
			fixed_slots_choker,

			// opens at least the number of slots as specified by
			// session::set_max_uploads() but opens up more slots if the upload capacity
			// is not saturated. This unchoker will work just like the ``fixed_slot_choker``
			// if there's no global upload rate limit set.
			auto_expand_choker,

			// opens up unchoke slots based on the upload rate
			// achieved to peers. The more slots that are opened, the marginal upload
			// rate required to open up another slot increases.
			rate_based_choker,
			// attempts to optimize download rate by finding the
			// reciprocation rate of each peer individually and prefers peers that gives
			// the highest *return on investment*. It still allocates all upload capacity,
			// but shuffles it around to the best peers first. For this choker to be
			// efficient, you need to set a global upload rate limit
			// session_settings::upload_rate_limit. For more information about this
			// choker, see the paper_.
			// 
			// .. _paper: http://bittyrant.cs.washington.edu/#papers
			bittyrant_choker
		};

		// specifies which algorithm to use to determine which peers
		// to unchoke. This setting replaces the deprecated settings ``auto_upload_slots``
		// and ``auto_upload_slots_rate_based``. For options, see choking_algorithm_t.
		int choking_algorithm;

		// the different choking algorithms available when seeding. Set
		// session_settings::seed_choking_algorithm to one of these
		enum seed_choking_algorithm_t
		{
			// round-robins the peers that are unchoked when seeding. This
			// distributes the upload bandwidht uniformly and fairly. It minimizes the ability
			// for a peer to download everything without redistributing it.
			round_robin,

			// unchokes the peers we can send to the fastest. This might be
			// a bit more reliable in utilizing all available capacity.
			fastest_upload,

			// prioritizes peers who have just started or are just about to finish
			// the download. The intention is to force peers in the middle of the download to
			// trade with each other.
			anti_leech
		};
 
		// controls the seeding unchoke behavior. For options, see seed_choking_algorithm_t.
		int seed_choking_algorithm;
		
		// specifies if parole mode should be used. Parole mode means
		// that peers that participate in pieces that fail the hash check are put in a mode
		// where they are only allowed to download whole pieces. If the whole piece a peer
		// in parole mode fails the hash check, it is banned. If a peer participates in a
		// piece that passes the hash check, it is taken out of parole mode.
		bool use_parole_mode;

		// the disk write and read  cache. It is specified in units of
		// 16 KiB blocks. Buffers that are part of a peer's send or receive buffer also
		// count against this limit. Send and receive buffers will never be denied to be
		// allocated, but they will cause the actual cached blocks to be flushed or evicted.
		// If this is set to -1, the cache size is automatically set to the amount
		// of physical RAM available in the machine divided by 8. If the amount of physical
		// RAM cannot be determined, it's set to 1024 (= 16 MiB).
		// 
		// Disk buffers are allocated using a pool allocator, the number of blocks that
		// are allocated at a time when the pool needs to grow can be specified in
		// ``cache_buffer_chunk_size``. This defaults to 16 blocks. Lower numbers
		// saves memory at the expense of more heap allocations. It must be at least 1.
		int cache_size;

		// this is the number of disk buffer blocks (16 kiB)
		// that should be allocated at a time. It must be
		// at least 1. Lower number saves memory at the expense
		// of more heap allocations
		int cache_buffer_chunk_size;

		// the number of seconds a write cache entry sits
		// idle in the cache before it's forcefully flushed
		// to disk.
		int cache_expiry;

		// when set to true (default), the disk cache is also used to
		// cache pieces read from disk. Blocks for writing pieces takes presedence.
		bool use_read_cache;

		// defaults to 0. If set to something greater than 0, the
		// disk read cache will not be evicted by cache misses and will explicitly be
		// controlled based on the rarity of pieces. Rare pieces are more likely to be
		// cached. This would typically be used together with ``suggest_mode`` set to
		// ``suggest_read_cache``. The value is the number of pieces to keep in the read
		// cache. If the actual read cache can't fit as many, it will essentially be clamped.
		bool explicit_read_cache;

		// the number of seconds in between each refresh of
		// a part of the explicit read cache. Torrents take turns in refreshing and this
		// is the time in between each torrent refresh. Refreshing a torrent's explicit
		// read cache means scanning all pieces and picking a random set of the rarest ones.
		// There is an affinity to pick pieces that are already in the cache, so that
		// subsequent refreshes only swaps in pieces that are rarer than whatever is in
		// the cache at the time.
		int explicit_cache_interval;

		// the buffer modes to use for reading and writing. Set
		// session_settings::disk_io_read_mode and disk_io_write_mode to one of
		// these.
		enum io_buffer_mode_t
		{
			// This is the default and files are opened normally, with the OS caching
			// reads and writes.
			enable_os_cache = 0,
			// This will open files in unbuffered mode for files where every read and
			// write would be sector aligned. Using aligned disk offsets is a requirement
			// on some operating systems.
			disable_os_cache_for_aligned_files = 1,
			// This opens all files in unbuffered mode (if allowed by the operating system).
			// Linux and Windows, for instance, require disk offsets to be sector aligned,
			// and in those cases, this option is the same as ``disable_os_caches_for_aligned_files``.
			disable_os_cache = 2
		};

		// determines how files are
		// opened when they're in read only mode versus read and write mode. For options,
		// see io_buffer_mode_t.
		//
		// One reason to disable caching is that it may help the operating system from growing
		// its file cache indefinitely. Since some OSes only allow aligned files to be opened
		// in unbuffered mode, It is recommended to make the largest file in a torrent the first
		// file (with offset 0) or use pad files to align all files to piece boundries.
		int disk_io_write_mode;
		int disk_io_read_mode;

		// when set to true, instead of issuing multiple adjacent reads or writes
		// to the disk, allocate a larger buffer, copy all writes into it and
		// issue a single write. For reads, read into a larger buffer and copy
		// the buffer into the smaller individual read buffers afterwards. This
		// may save system calls, but will cost in additional memory allocation
		// and copying.
		bool coalesce_reads;
		bool coalesce_writes;

		// if set to something other than (0, 0) is a range of ports
		// used to bind outgoing sockets to. This may be useful for users whose router
		// allows them to assign QoS classes to traffic based on its local port. It is
		// a range instead of a single port because of the problems with failing to reconnect
		// to peers if a previous socket to that peer and port is in ``TIME_WAIT`` state.
		// 
		//.. warning:: setting outgoing ports will limit the ability to keep multiple
		//	connections to the same client, even for different torrents. It is not
		//	recommended to change this setting. Its main purpose is to use as an
		//	escape hatch for cheap routers with QoS capability but can only classify
		//	flows based on port numbers.
		std::pair<int, int> outgoing_ports;

		// determines the TOS byte set in the IP header of every packet
		// sent to peers (including web seeds). The default value for this is ``0x0``
		// (no marking). One potentially useful TOS mark is ``0x20``, this represents
		// the *QBone scavenger service*. For more details, see QBSS_.
		// 
		// .. _`QBSS`: http://qbone.internet2.edu/qbss/
		char peer_tos;

		// for auto managed torrents, these are the limits
		// they are subject to. If there are too many torrents
		// some of the auto managed ones will be paused until
		// some slots free up.
		// 
		// ``active_dht_limit`` and ``active_tracker_limit`` limits the
		// number of torrents that will be active on the DHT
		// and their tracker. If the active limit is set higher
		// than these numbers, some torrents will be "active" in
		// the sense that they will accept incoming connections,
		// but not announce on the DHT or their trackers.
		//
		// ``active_lsd_limit`` is the max number of torrents to announce to the local network
		// over the local service discovery protocol. By default this is 80, which is no more
		// than one announce every 5 seconds (assuming the default announce interval of 5 minutes).
		// 
		// ``active_limit`` is a hard limit on the number of active torrents. This applies even to
		// slow torrents.
		// 
		// You can have more torrents *active*, even though they are not announced to the DHT,
		// lsd or their tracker. If some peer knows about you for any reason and tries to connect,
		// it will still be accepted, unless the torrent is paused, which means it won't accept
		// any connections.
		//
		// ``active_downloads`` and ``active_seeds`` controls how many active seeding and
		// downloading torrents the queuing mechanism allows. The target number of active
		// torrents is ``min(active_downloads + active_seeds, active_limit)``.
		// ``active_downloads`` and ``active_seeds`` are upper limits on the number of
		// downloading torrents and seeding torrents respectively. Setting the value to
		// -1 means unlimited.
		// 
		// For example if there are 10 seeding torrents and 10 downloading torrents, and
		// ``active_downloads`` is 4 and ``active_seeds`` is 4, there will be 4 seeds
		// active and 4 downloading torrents. If the settings are ``active_downloads`` = 2
		// and ``active_seeds`` = 4, then there will be 2 downloading torrents and 4 seeding
		// torrents active. Torrents that are not auto managed are also counted against these
		// limits. If there are non-auto managed torrents that use up all the slots, no
		// auto managed torrent will be activated.
		int active_downloads;
		int active_seeds;
		int active_dht_limit;
		int active_tracker_limit;
		int active_lsd_limit;
		int active_limit;

		// prefer seeding torrents when determining which torrents to give 
		// active slots to, the default is false which gives preference to
		// downloading torrents
		bool auto_manage_prefer_seeds;
		
		// if true, torrents without any payload transfers are
		// not subject to the ``active_seeds`` and ``active_downloads`` limits. This is intended
		// to make it more likely to utilize all available bandwidth, and avoid having torrents
		// that don't transfer anything block the active slots.
		bool dont_count_slow_torrents;

		// the number of seconds in between recalculating which
		// torrents to activate and which ones to queue
		int auto_manage_interval;
	
		// when a seeding torrent reaches either the share ratio
		// (bytes up / bytes down) or the seed time ratio
		// (seconds as seed / seconds as downloader) or the seed
		// time limit (seconds as seed) it is considered
		// done, and it will leave room for other torrents
		// the default value for share ratio is 2
		// the default seed time ratio is 7, because that's a common
		// asymmetry ratio on connections
		//
		//.. note::
		//	This is an out-dated option that doesn't make much sense.
		//	It will be removed in future versions of libtorrent
		float share_ratio_limit;

		// the seeding time / downloading time ratio limit
		// for considering a seeding torrent to have met the seed limit criteria. See queuing_.
		float seed_time_ratio_limit;

		// the limit on the time a torrent has been an active seed
		// (specified in seconds) before it is considered having met the seed limit criteria.
		// See queuing_.
		int seed_time_limit;

		// controls a feature where libtorrent periodically can disconnect
		// the least useful peers in the hope of connecting to better ones. ``peer_turnover_interval`` controls
		// the interval of this optimistic disconnect. It defaults to every 5 minutes, and
		// is specified in seconds.
		// 
		// ``peer_turnover`` Is the fraction of the peers that are disconnected. This is
		// a float where 1.f represents all peers an 0 represents no peers. It defaults to
		// 4% (i.e. 0.04f)
		//
		// ``peer_turnover_cutoff`` is the cut off trigger for optimistic unchokes. If a torrent
		// has more than this fraction of its connection limit, the optimistic unchoke is
		// triggered. This defaults to 90% (i.e. 0.9f).
		int peer_turnover_interval;
		float peer_turnover;
		float peer_turnover_cutoff;

		// specifies whether libtorrent should close
		// connections where both ends have no utility in keeping the connection open.
		// For instance if both ends have completed their downloads, there's no point
		// in keeping it open. This defaults to ``true``.
		bool close_redundant_connections;

		// the number of seconds between scrapes of
		// queued torrents (auto managed and paused torrents). Auto managed
		// torrents that are paused, are scraped regularly in order to keep
		// track of their downloader/seed ratio. This ratio is used to determine
		// which torrents to seed and which to pause.
		int auto_scrape_interval;

		// the minimum number of seconds between any
		// automatic scrape (regardless of torrent). In case there are a large number
		// of paused auto managed torrents, this puts a limit on how often a scrape
		// request is sent.
		int auto_scrape_min_interval;

		// the maximum number of peers in the list of
		// known peers. These peers are not necessarily connected, so this number
		// should be much greater than the maximum number of connected peers.
		// Peers are evicted from the cache when the list grows passed 90% of
		// this limit, and once the size hits the limit, peers are no longer
		// added to the list. If this limit is set to 0, there is no limit on
		// how many peers we'll keep in the peer list.
		int max_peerlist_size;

		// the max peer list size used for torrents
		// that are paused. This default to the same as ``max_peerlist_size``, but
		// can be used to save memory for paused torrents, since it's not as
		// important for them to keep a large peer list.
		int max_paused_peerlist_size;

		// the minimum allowed announce interval
		// for a tracker. This is specified in seconds, defaults to 5 minutes and
		// is used as a sanity check on what is returned from a tracker. It
		// mitigates hammering misconfigured trackers.
		int min_announce_interval;

		// If true, partial pieces are picked
		// before pieces that are more rare. If false, rare pieces are always
		// prioritized, unless the number of partial pieces is growing out of
		// proportion.
		bool prioritize_partial_pieces;

		// the number of seconds a torrent is considered
		// active after it was started, regardless of
		// upload and download speed. This is so that
		// newly started torrents are not considered
		// inactive until they have a fair chance to
		// start downloading.
		int auto_manage_startup;

		// if set to true, the estimated TCP/IP overhead is
		// drained from the rate limiters, to avoid exceeding
		// the limits with the total traffic
		bool rate_limit_ip_overhead;

		// controls how multi tracker torrents are
		// treated. If this is set to true, all trackers in the same tier are
		// announced to in parallel. If all trackers in tier 0 fails, all trackers
		// in tier 1 are announced as well. If it's set to false, the behavior is as
		// defined by the multi tracker specification. It defaults to false, which
		// is the same behavior previous versions of libtorrent has had as well.
		bool announce_to_all_trackers;

		// controls how multi tracker torrents are
		// treated. When this is set to true, one tracker from each tier is announced
		// to. This is the uTorrent behavior. This is false by default in order
		// to comply with the multi-tracker specification.
		bool announce_to_all_tiers;

		// true by default. It means that trackers may
		// be rearranged in a way that udp trackers are always tried before http
		// trackers for the same hostname. Setting this to fails means that the
		// trackers' tier is respected and there's no preference of one protocol
		// over another.
		bool prefer_udp_trackers;

		// when this is set to true, a piece has to
		// have been forwarded to a third peer before another one is handed out.
		// This is the traditional definition of super seeding.
		bool strict_super_seeding;

		// the number of pieces to send to a peer,
		// when seeding, before rotating in another peer to the unchoke set.
		// It defaults to 3 pieces, which means that when seeding, any peer we've
		// sent more than this number of pieces to will be unchoked in favour of
		// a choked peer.
		int seeding_piece_quota;

		// is a limit of the number of *sparse regions* in
		// a torrent. A sparse region is defined as a hole of pieces we have not
		// yet downloaded, in between pieces that have been downloaded. This is
		// used as a hack for windows vista which has a bug where you cannot
		// write files with more than a certain number of sparse regions. This
		// limit is not hard, it will be exceeded. Once it's exceeded, pieces
		// that will maintain or decrease the number of sparse regions are
		// prioritized. To disable this functionality, set this to 0. It defaults
		// to 0 on all platforms except windows.
		int max_sparse_regions;

		// if lock disk cache is set to true the disk cache
		// that's in use, will be locked in physical memory, preventing it from
		// being swapped out.
		bool lock_disk_cache;

		// the number of piece requests we will reject in a row
		// while a peer is choked before the peer is considered abusive and is
		// disconnected.
		int max_rejects;

		// specifies
		// the buffer sizes set on peer sockets. 0 (which is the default) means
		// the OS default (i.e. don't change the buffer sizes). The socket buffer
		// sizes are changed using setsockopt() with SOL_SOCKET/SO_RCVBUF and
		// SO_SNDBUFFER.
		int recv_socket_buffer_size;
		int send_socket_buffer_size;

		// chooses between two ways of reading back
		// piece data from disk when its complete and needs to be verified against
		// the piece hash. This happens if some blocks were flushed to the disk
		// out of order. Everything that is flushed in order is hashed as it goes
		// along. Optimizing for speed will allocate space to fit all the the
		// remaingin, unhashed, part of the piece, reads the data into it in a single
		// call and hashes it. This is the default. If ``optimizing_hashing_for_speed``
		// is false, a single block will be allocated (16 kB), and the unhashed parts
		// of the piece are read, one at a time, and hashed in this single block. This
		// is appropriate on systems that are memory constrained.
		bool optimize_hashing_for_speed;

		// the number of milliseconds to sleep
		// in between disk read operations when checking torrents. This defaults
		// to 0, but can be set to higher numbers to slow down the rate at which
		// data is read from the disk while checking. This may be useful for
		// background tasks that doesn't matter if they take a bit longer, as long
		// as they leave disk I/O time for other processes.
		int file_checks_delay_per_block;

		// the disk cache algorithms available. Set
		// session_settings::disk_cache_algorithm to one of these.
		enum disk_cache_algo_t
		{
			// This
			// flushes the entire piece, in the write cache, that was least recently
			// written to.
			lru,

			// will flush the largest
			// sequences of contiguous blocks from the write cache, regarless of the
			// piece's last use time.
			largest_contiguous,

			// will prioritize
			// flushing blocks that will avoid having to read them back in to verify
			// the hash of the piece once it's done. This is especially useful for high
			// throughput setups, where reading from the disk is especially expensive.
			avoid_readback
		};

		// tells the disk I/O thread which cache flush
		// algorithm to use. The default algorithm is largest_contiguous. This is
		// specified by the disk_cache_algo_t enum.
		disk_cache_algo_t disk_cache_algorithm;

		// the number of blocks to read into the read
		// cache when a read cache miss occurs. Setting this to 0 is essentially
		// the same thing as disabling read cache. The number of blocks read
		// into the read cache is always capped by the piece boundry.
		// 
		// When a piece in the write cache has ``write_cache_line_size`` contiguous
		// blocks in it, they will be flushed. Setting this to 1 effectively
		// disables the write cache.
		int read_cache_line_size;

		// whenever a contiguous range of this many
		// blocks is found in the write cache, it
		// is flushed immediately
		int write_cache_line_size;

		// the number of seconds from a disk write
		// errors occur on a torrent until libtorrent will take it out of the
		// upload mode, to test if the error condition has been fixed.
		// 
		// libtorrent will only do this automatically for auto managed torrents.
		// 
		// You can explicitly take a torrent out of upload only mode using
		// set_upload_mode().
		int optimistic_disk_retry;

		// controls if downloaded pieces are verified against
		// the piece hashes in the torrent file or not. The default is false, i.e.
		// to verify all downloaded data. It may be useful to turn this off for performance
		// profiling and simulation scenarios. Do not disable the hash check for regular
		// bittorrent clients.
		bool disable_hash_checks;

		// if this is true, disk read operations may
		// be re-ordered based on their physical disk
		// read offset. This greatly improves throughput
		// when uploading to many peers. This assumes
		// a traditional hard drive with a read head
		// and spinning platters. If your storage medium
		// is a solid state drive, this optimization
		// doesn't give you an benefits
		bool allow_reordered_disk_operations;

		// if this is true, i2p torrents are allowed
		// to also get peers from other sources than
		// the tracker, and connect to regular IPs,
		// not providing any anonymization. This may
		// be useful if the user is not interested in
		// the anonymization of i2p, but still wants to
		// be able to connect to i2p peers.
		bool allow_i2p_mixed;

		// the max number of suggested piece indices received
		// from a peer that's remembered. If a peer floods suggest messages, this limit
		// prevents libtorrent from using too much RAM. It defaults to 10.
		int max_suggest_pieces;

		// If set to true (it defaults to false), piece
		// requests that have been skipped enough times when piece messages
		// are received, will be considered lost. Requests are considered skipped
		// when the returned piece messages are re-ordered compared to the order
		// of the requests. This was an attempt to get out of dead-locks caused by
		// BitComet peers silently ignoring some requests. It may cause problems
		// at high rates, and high level of reordering in the uploading peer, that's
		// why it's disabled by default.
		bool drop_skipped_requests;

		// determines if the disk I/O should use a normal
		// or low priority policy. This defaults to true, which means that
		// it's low priority by default. Other processes doing disk I/O will
		// normally take priority in this mode. This is meant to improve the
		// overall responsiveness of the system while downloading in the
		// background. For high-performance server setups, this might not
		// be desirable.
		bool low_prio_disk;

		// the time between local
		// network announces for a torrent. By default, when local service
		// discovery is enabled a torrent announces itself every 5 minutes.
		// This interval is specified in seconds.
		int local_service_announce_interval;

		// the number of seconds between announcing
		// torrents to the distributed hash table (DHT). This is specified to
		// be 15 minutes which is its default.
		int dht_announce_interval;

		// the number of seconds libtorrent
		// will keep UDP tracker connection tokens around for. This is specified
		// to be 60 seconds, and defaults to that. The higher this value is, the
		// fewer packets have to be sent to the UDP tracker. In order for higher
		// values to work, the tracker needs to be configured to match the
		// expiration time for tokens.
		int udp_tracker_token_expiry;

		// if this is set to true, read cache blocks
		// that are hit by peer read requests are removed from the disk cache
		// to free up more space. This is useful if you don't expect the disk
		// cache to create any cache hits from other peers than the one who
		// triggered the cache line to be read into the cache in the first place.
		bool volatile_read_cache;

		// enables the disk cache to adjust the size
		// of a cache line generated by peers to depend on the upload rate
		// you are sending to that peer. The intention is to optimize the RAM
		// usage of the cache, to read ahead further for peers that you're
		// sending faster to.
		bool guided_read_cache;

		// the minimum number of seconds any read
		// cache line is kept in the cache. This defaults to one second but
		// may be greater if ``guided_read_cache`` is enabled. Having a lower
		// bound on the time a cache line stays in the cache is an attempt
		// to avoid swapping the same pieces in and out of the cache in case
		// there is a shortage of spare cache space.
		int default_cache_min_age;

		// the number of optimistic unchoke
		// slots to use. It defaults to 0, which means automatic. Having a higher
		// number of optimistic unchoke slots mean you will find the good peers
		// faster but with the trade-off to use up more bandwidth. When this is
		// set to 0, libtorrent opens up 20% of your allowed upload slots as
		// optimistic unchoke slots.
		int num_optimistic_unchoke_slots;

		// this is a linux-only option and passes in the
		// ``O_NOATIME`` to ``open()`` when opening files. This may lead to
		// some disk performance improvements.
		bool no_atime_storage;

		// the assumed reciprocation rate
		// from peers when using the BitTyrant choker. This defaults to 14 kiB/s.
		// If set too high, you will over-estimate your peers and be more altruistic
		// while finding the true reciprocation rate, if it's set too low, you'll
		// be too stingy and waste finding the true reciprocation rate.
		int default_est_reciprocation_rate;

		// specifies how many percent the
		// extimated reciprocation rate should be increased by each unchoke
		// interval a peer is still choking us back. This defaults to 20%.
		// This only applies to the BitTyrant choker.
		int increase_est_reciprocation_rate;

		// specifies how many percent the
		// estimated reciprocation rate should be decreased by each unchoke
		// interval a peer unchokes us. This default to 3%.
		// This only applies to the BitTyrant choker.
		int decrease_est_reciprocation_rate;

		// defaults to false. If a torrent
		// has been paused by the auto managed feature in libtorrent, i.e.
		// the torrent is paused and auto managed, this feature affects whether
		// or not it is automatically started on an incoming connection. The
		// main reason to queue torrents, is not to make them unavailable, but
		// to save on the overhead of announcing to the trackers, the DHT and to
		// avoid spreading one's unchoke slots too thin. If a peer managed to
		// find us, even though we're no in the torrent anymore, this setting
		// can make us start the torrent and serve it.
		bool incoming_starts_queued_torrents;

		// when set to true, the downloaded counter sent to trackers
		// will include the actual number of payload bytes donwnloaded
		// including redundant bytes. If set to false, it will not include
		// any redundany bytes
		bool report_true_downloaded;

		// defaults to true, and controls when a block
		// may be requested twice. If this is ``true``, a block may only be requested
		// twice when there's ay least one request to every piece that's left to
		// download in the torrent. This may slow down progress on some pieces
		// sometimes, but it may also avoid downloading a lot of redundant bytes.
		// If this is ``false``, libtorrent attempts to use each peer connection
		// to its max, by always requesting something, even if it means requesting
		// something that has been requested from another peer already.
		bool strict_end_game_mode;

		// if set to true, the local peer discovery
		// (or Local Service Discovery) will not only use IP multicast, but also
		// broadcast its messages. This can be useful when running on networks
		// that don't support multicast. Since broadcast messages might be
		// expensive and disruptive on networks, only every 8th announce uses
		// broadcast.
		bool broadcast_lsd;

		// these all determines if libtorrent should attempt to make
		// outgoing connections of the specific type, or allow incoming connection. By
		// default all of them are enabled.
		bool enable_outgoing_utp;
		bool enable_incoming_utp;
		bool enable_outgoing_tcp;
		bool enable_incoming_tcp;

		// the max number of peers we accept from pex messages from a single peer.
		// this limits the number of concurrent peers any of our peers claims to
		// be connected to. If they clain to be connected to more than this, we'll
		// ignore any peer that exceeds this limit
		int max_pex_peers;

		// determines if the storage, when loading
		// resume data files, should verify that the file modification time
		// with the timestamps in the resume data. This defaults to false, which
		// means timestamps are taken into account, and resume data is less likely
		// to accepted (torrents are more likely to be fully checked when loaded).
		// It might be useful to set this to true if your network is faster than your
		// disk, and it would be faster to redownload potentially missed pieces than
		// to go through the whole storage to look for them.
		bool ignore_resume_timestamps;

		// determines if the storage should check
		// the whole files when resume data is incomplete or missing or whether
		// it should simply assume we don't have any of the data. By default, this
		// is determined by the existance of any of the files. By setting this setting
		// to true, the files won't be checked, but will go straight to download
		// mode.
		bool no_recheck_incomplete_resume;

		// defaults to false. When set to true, the client tries
		// to hide its identity to a certain degree. The peer-ID will no longer
		// include the client's fingerprint. The user-agent will be reset to an
		// empty string. It will also try to not leak other identifying information,
		// such as your local listen port, your IP etc.
		// 
		// If you're using I2P, a VPN or a proxy, it might make sense to enable anonymous mode.
		bool anonymous_mode;

		// disables any communication that's not going over a proxy.
		// Enabling this requires a proxy to be configured as well, see ``set_proxy_settings``.
		// The listen sockets are closed, and incoming connections will
		// only be accepted through a SOCKS5 or I2P proxy (if a peer proxy is set up and
		// is run on the same machine as the tracker proxy). This setting also
		// disabled peer country lookups, since those are done via DNS lookups that
		// aren't supported by proxies.
		bool force_proxy;

		// specifies the number of milliseconds between internal
		// ticks. This is the frequency with which bandwidth quota is distributed to
		// peers. It should not be more than one second (i.e. 1000 ms). Setting this
		// to a low value (around 100) means higher resolution bandwidth quota distribution,
		// setting it to a higher value saves CPU cycles.
		int tick_interval;

		// specifies whether downloads from web seeds is reported to the
		// tracker or not. Defaults to on
		bool report_web_seed_downloads;

		// specifies the target share ratio for share mode torrents.
		// This defaults to 3, meaning we'll try to upload 3 times as much as we download.
		// Setting this very high, will make it very conservative and you might end up
		// not downloading anything ever (and not affecting your share ratio). It does
		// not make any sense to set this any lower than 2. For instance, if only 3 peers
		// need to download the rarest piece, it's impossible to download a single piece
		// and upload it more than 3 times. If the share_mode_target is set to more than 3,
		// nothing is downloaded.
		int share_mode_target;

		// sets the session-global limits of upload
		// and download rate limits, in bytes per second. The local rates refer to peers
		// on the local network. By default peers on the local network are not rate limited.
		// 
		// These rate limits are only used for local peers (peers within the same subnet as
		// the client itself) and it is only used when ``session_settings::ignore_limits_on_local_network``
		// is set to true (which it is by default). These rate limits default to unthrottled,
		// but can be useful in case you want to treat local peers preferentially, but not
		// quite unthrottled.
		// 
		// A value of 0 means unlimited.
		int upload_rate_limit;
		int download_rate_limit;
		int local_upload_rate_limit;
		int local_download_rate_limit;

		// sets the rate limit on the DHT. This is specified in
		// bytes per second and defaults to 4000. For busy boxes with lots of torrents
		// that requires more DHT traffic, this should be raised.
		int dht_upload_rate_limit;

		// the max number of unchoked peers in the session. The
		// number of unchoke slots may be ignored depending on what ``choking_algorithm``
		// is set to. A value of -1 means infinite.
		int unchoke_slots_limit;

		// sets the maximum number of half-open connections
		// libtorrent will have when connecting to peers. A half-open connection is one
		// where connect() has been called, but the connection still hasn't been established
		// (nor failed). Windows XP Service Pack 2 sets a default, system wide, limit of
		// the number of half-open connections to 10. So, this limit can be used to work
		// nicer together with other network applications on that system. The default is
		// to have no limit, and passing -1 as the limit, means to have no limit. When
		// limiting the number of simultaneous connection attempts, peers will be put in
		// a queue waiting for their turn to get connected.
		int half_open_limit;

		// sets a global limit on the number of connections
		// opened. The number of connections is set to a hard minimum of at least two per
		// torrent, so if you set a too low connections limit, and open too many torrents,
		// the limit will not be met.
		int connections_limit;

		// the number of extra incoming connections allowed
		// temporarily, in order to support replacing peers
		int connections_slack;

		// the target delay for uTP sockets in milliseconds. A high
		// value will make uTP connections more aggressive and cause longer queues in the upload
		// bottleneck. It cannot be too low, since the noise in the measurements would cause
		// it to send too slow. The default is 50 milliseconds.
		int utp_target_delay;

		// the number of bytes the uTP congestion window can increase
		// at the most in one RTT. This defaults to 300 bytes. If this is set too high,
		// the congestion controller reacts too hard to noise and will not be stable, if it's
		// set too low, it will react slow to congestion and not back off as fast.
		int utp_gain_factor;

		// the shortest allowed uTP socket timeout, specified in milliseconds.
		// This defaults to 500 milliseconds. The timeout depends on the RTT of the connection, but
		// is never smaller than this value. A connection times out when every packet in a window
		// is lost, or when a packet is lost twice in a row (i.e. the resent packet is lost as well).
		// 
		// The shorter the timeout is, the faster the connection will recover from this situation,
		// assuming the RTT is low enough.
		int utp_min_timeout;

		// the number of SYN packets that are sent (and timed out) before
		// giving up and closing the socket.
		int utp_syn_resends;
		
		// the number of resent packets sent on a closed socket before giving up
		int utp_fin_resends;

		// the number of times a packet is sent (and lossed or timed out)
		// before giving up and closing the connection.
		int utp_num_resends;

		// the number of milliseconds of timeout for the initial SYN
		// packet for uTP connections. For each timed out packet (in a row), the timeout is doubled.
		int utp_connect_timeout;

#ifndef TORRENT_NO_DEPRECATE
		// number of milliseconds of delaying ACKing packets the most
		int utp_delayed_ack;
#endif

		// controls if the uTP socket manager is allowed to increase
		// the socket buffer if a network interface with a large MTU is used (such as loopback
		// or ethernet jumbo frames). This defaults to true and might improve uTP throughput.
		// For RAM constrained systems, disabling this typically saves around 30kB in user space
		// and probably around 400kB in kernel socket buffers (it adjusts the send and receive
		// buffer size on the kernel socket, both for IPv4 and IPv6).
		bool utp_dynamic_sock_buf;

		// controls how the congestion window is changed when a packet
		// loss is experienced. It's specified as a percentage multiplier for ``cwnd``. By default
		// it's set to 50 (i.e. cut in half). Do not change this value unless you know what
		// you're doing. Never set it higher than 100.
		int utp_loss_multiplier;

		// the options for session_settings::mixed_mode_algorithm.
		enum bandwidth_mixed_algo_t
		{
			// disables the mixed mode bandwidth balancing
			prefer_tcp = 0,

			// does not throttle uTP, throttles TCP to the same proportion
			// of throughput as there are TCP connections
			peer_proportional = 1

		};

		// determines how to treat TCP connections when there are
		// uTP connections. Since uTP is designed to yield to TCP, there's an inherent problem
		// when using swarms that have both TCP and uTP connections. If nothing is done, uTP
		// connections would often be starved out for bandwidth by the TCP connections. This mode
		// is ``prefer_tcp``. The ``peer_proportional`` mode simply looks at the current throughput
		// and rate limits all TCP connections to their proportional share based on how many of
		// the connections are TCP. This works best if uTP connections are not rate limited by
		// the global rate limiter (which they aren't by default).
		//
		// see bandwidth_mixed_algo_t for options.
		int mixed_mode_algorithm;

		// determines if uTP connections should be throttled by the global rate
		// limiter or not. By default they are.
		bool rate_limit_utp;

		// the value passed in to listen() for the listen socket.
		// It is the number of outstanding incoming connections to queue up while we're not
		// actively waiting for a connection to be accepted. The default is 5 which should
		// be sufficient for any normal client. If this is a high performance server which
		// expects to receive a lot of connections, or used in a simulator or test, it
		// might make sense to raise this number. It will not take affect until listen_on()
		// is called again (or for the first time).
		int listen_queue_size;

		// if true, the ``&ip=`` argument in tracker requests
		// (unless otherwise specified) will be set to the intermediate IP address, if the
		// user is double NATed. If ther user is not double NATed, this option has no affect.
		bool announce_double_nat;

		// the number of peers to try to connect to immediately
		// when the first tracker response is received for a torrent. This is a boost to
		// given to new torrents to accelerate them starting up. The normal connect scheduler
		// is run once every second, this allows peers to be connected immediately instead
		// of waiting for the session tick to trigger connections.
		int torrent_connect_boost;

		// determines if seeding (and finished) torrents
		// should attempt to make outgoing connections or not. By default this is true. It
		// may be set to false in very specific applications where the cost of making
		// outgoing connections is high, and there are no or small benefits of doing so.
		// For instance, if no nodes are behind a firewall or a NAT, seeds don't need to
		// make outgoing connections.
		bool seeding_outgoing_connections;

		// if true (which is the default), libtorrent
		// will not connect to any peers on priviliged ports (<= 1023). This can mitigate
		// using bittorrent swarms for certain DDoS attacks.
		bool no_connect_privileged_ports;

		// the maximum number of alerts queued up internally. If
		// alerts are not popped, the queue will eventually fill up to this level. This
		// defaults to 1000.
		int alert_queue_size;

		// the maximum allowed size (in bytes) to be received
		// by the metadata extension, i.e. magnet links. It defaults to 1 MiB.
		int max_metadata_size;

		// true by default, which means the number of connection
		// attempts per second may be limited to below the ``connection_speed``, in case
		// we're close to bump up against the limit of number of connections. The intention
		// of this setting is to more evenly distribute our connection attempts over time,
		// instead of attempting to connectin in batches, and timing them out in batches.
		bool smooth_connects;

		// defaults to false. When set to true, web connections
		// will include a user-agent with every request, as opposed to just the first
		// request in a connection.
		bool always_send_user_agent;

		// defaults to true. It determines whether the
		// IP filter applies to trackers as well as peers. If this is set to false,
		// trackers are exempt from the IP filter (if there is one). If no IP filter
		// is set, this setting is irrelevant.
		bool apply_ip_filter_to_trackers;

		// used to avoid starvation of read jobs in the disk I/O
		// thread. By default, read jobs are deferred, sorted by physical disk location
		// and serviced once all write jobs have been issued. In scenarios where the
		// download rate is enough to saturate the disk, there's a risk the read jobs will
		// never be serviced. With this setting, every *x* write job, issued in a row, will
		// instead pick one read job off of the sorted queue, where *x* is ``read_job_every``.
		int read_job_every;

		// defaults to true and will attempt to optimize disk reads
		// by giving the operating system heads up of disk read requests as they are queued
		// in the disk job queue. This gives a significant performance boost for seeding.
		bool use_disk_read_ahead;

		// determines whether or not to lock files which libtorrent is downloading
		// to or seeding from. This is implemented using ``fcntl(F_SETLK)`` on unix systems and
		// by not passing in ``SHARE_READ`` and ``SHARE_WRITE`` on windows. This might prevent
		// 3rd party processes from corrupting the files under libtorrent's feet.
		bool lock_files;

		// sets the listen port for SSL connections. If this is set to 0,
		// no SSL listen port is opened. Otherwise a socket is opened on this port. This
		// setting is only taken into account when opening the regular listen port, and
		// won't re-open the listen socket simply by changing this setting.
		// 
		// if this is 0, outgoing SSL connections are disabled
		// 
		// It defaults to port 4433.
		int ssl_listen;

		// ``tracker_backoff`` determines how aggressively to back off from retrying
		// failing trackers. This value determines *x* in the following formula, determining
		// the number of seconds to wait until the next retry:
		// 
		// 	delay = 5 + 5 * x / 100 * fails^2
		// 
		// It defaults to 250.
		// 
		// This setting may be useful to make libtorrent more or less aggressive in hitting
		// trackers.
		// 
		int tracker_backoff;

		// enables banning web seeds. By default, web seeds that send
		// corrupt data are banned.
		bool ban_web_seeds;
		
		// specifies the max number of bytes to receive into
		// RAM buffers when downloading stuff over HTTP. Specifically when specifying a
		// URL to a .torrent file when adding a torrent or when announcing to an HTTP
		// tracker. The default is 2 MiB.
		int max_http_recv_buffer_size;

		// enables or disables the share mode extension. This is
		// enabled by default.
		bool support_share_mode;

		// enables or disables the merkle tree torrent support.
		// This is enabled by default.
		bool support_merkle_torrents;

		// enables or disables reporting redundant bytes to the tracker.
		// This is enabled by default.
		bool report_redundant_bytes;

		// the version string to advertise for this client
		// in the peer protocol handshake. If this is empty
		// the user_agent is used
		std::string handshake_client_version;

		// if this is true, the disk cache uses a pool allocator
		// for disk cache blocks. Enabling this improves
		// performance of the disk cache with the side effect
		// that the disk cache is less likely and slower at
		// returning memory to the kernel when cache pressure
		// is low.
		bool use_disk_cache_pool;
	};

	// structure used to hold configuration options for the DHT
	//
	// The ``dht_settings`` struct used to contain a ``service_port`` member to control
	// which port the DHT would listen on and send messages from. This field is deprecated
	// and ignored. libtorrent always tries to open the UDP socket on the same port
	// as the TCP socket.
	struct dht_settings
	{
		dht_settings()
			: max_peers_reply(100)
			, search_branching(5)
#ifndef TORRENT_NO_DEPRECATE
			, service_port(0)
#endif
			, max_fail_count(20)
			, max_torrents(2000)
			, max_dht_items(700)
			, max_torrent_search_reply(20)
			, restrict_routing_ips(true)
			, restrict_search_ips(true)
			, extended_routing_table(true)
			, aggressive_lookups(true)
			, privacy_lookups(false)
			, enforce_node_id(false)
			, ignore_dark_internet(true)
		{}
		
		// the maximum number of peers to send in a
		// reply to ``get_peers``
		int max_peers_reply;

		// the number of concurrent search request the node will
		// send when announcing and refreshing the routing table. This parameter is
		// called alpha in the kademlia paper
		int search_branching;
		
#ifndef TORRENT_NO_DEPRECATE
		// the listen port for the dht. This is a UDP port.
		// zero means use the same as the tcp interface
		int service_port;
#endif
		
		// the maximum number of failed tries to contact a node
		// before it is removed from the routing table. If there are known working nodes
		// that are ready to replace a failing node, it will be replaced immediately,
		// this limit is only used to clear out nodes that don't have any node that can
		// replace them.
		int max_fail_count;

		// the total number of torrents to track from the DHT. This
		// is simply an upper limit to make sure malicious DHT nodes cannot make us allocate
		// an unbounded amount of memory.
		int max_torrents;

		// max number of items the DHT will store
		int max_dht_items;

		// the max number of torrents to return in a
		// torrent search query to the DHT
		int max_torrent_search_reply;

		// determines if the routing table entries should restrict
		// entries to one per IP. This defaults to true, which helps mitigate some attacks
		// on the DHT. It prevents adding multiple nodes with IPs with a very close CIDR
		// distance.
		//
		// when set, nodes whose IP address that's in
		// the same /24 (or /64 for IPv6) range in the
		// same routing table bucket. This is an attempt
		// to mitigate node ID spoofing attacks
		// also restrict any IP to only have a single
		// entry in the whole routing table
		bool restrict_routing_ips;

		// determines if DHT searches should prevent adding nodes
		// with IPs with very close CIDR distance. This also defaults to true and helps
		// mitigate certain attacks on the DHT.
		bool restrict_search_ips;

		// makes the first buckets in the DHT routing
		// table fit 128, 64, 32 and 16 nodes respectively, as opposed to the
		// standard size of 8. All other buckets have size 8 still.
		bool extended_routing_table;

		// slightly changes the lookup behavior in terms of how
		// many outstanding requests we keep. Instead of having branch factor be a hard
		// limit, we always keep *branch factor* outstanding requests to the closest nodes.
		// i.e. every time we get results back with closer nodes, we query them right away.
		// It lowers the lookup times at the cost of more outstanding queries.
		bool aggressive_lookups;

		// when set, perform lookups in a way that is slightly more expensive, but which
		// minimizes the amount of information leaked about you.
		bool privacy_lookups;

		// when set, node's whose IDs that are not correctly generated based on its external
		// IP are ignored. When a query arrives from such node, an error message is returned
		// with a message saying "invalid node ID".
		bool enforce_node_id;

		// ignore DHT messages from parts of the internet we wouldn't expect
		// to see any traffic from
		bool ignore_dark_internet;
	};


	// The ``pe_settings`` structure is used to control the settings related
	// to peer protocol encryption.
	struct pe_settings
	{
		pe_settings()
			: out_enc_policy(enabled)
			, in_enc_policy(enabled)
			, allowed_enc_level(both)
			, prefer_rc4(false)
		{}

		enum enc_policy
		{
			// Only encrypted connections are allowed. Incoming connections
			// that are not encrypted are closed and if the encrypted outgoing connection
			// fails, a non-encrypted retry will not be made.
			forced,

			// encrypted connections are enabled, but non-encrypted
			// connections are allowed. An incoming non-encrypted connection will
			// be accepted, and if an outgoing encrypted connection fails, a non-
			// encrypted connection will be tried.
			enabled,
			
			// only non-encrypted connections are allowed.
			disabled
		};

		enum enc_level
		{
			plaintext = 1, // use only plaintext encryption
			rc4 = 2, // use only rc4 encryption 
			both = 3 // allow both
		};

		// control the settings for incoming
		// and outgoing connections respectively.
		// see enc_policy enum for the available options.
		boost::uint8_t out_enc_policy;
		boost::uint8_t in_enc_policy;

		// determines the encryption level of the
		// connections.  This setting will adjust which encryption scheme is
		// offered to the other peer, as well as which encryption scheme is
		// selected by the client. See enc_level enum for options.
		boost::uint8_t allowed_enc_level;

		// if the allowed encryption level is both, setting this to
		// true will prefer rc4 if both methods are offered, plaintext
		// otherwise
		bool prefer_rc4;
	};

}

#endif