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transmission/libtransmission/tr-dht.cc

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// This file Copyright © 2009-2023 Juliusz Chroboczek.
// It may be used under the MIT (SPDX: MIT) license.
// License text can be found in the licenses/ folder.
#include <algorithm>
#include <array>
#include <chrono>
#include <cstdint> // uint16_t
#include <cstring> // memcpy()
#include <ctime>
#include <deque>
#include <fstream>
#include <map>
#include <memory>
#include <sstream>
#include <string>
#include <string_view>
#include <tuple> // std::tie()
#include <utility>
#ifdef _WIN32
#include <ws2tcpip.h>
#undef gai_strerror
#define gai_strerror gai_strerrorA
#else
#include <sys/socket.h> /* socket(), bind() */
#include <netdb.h>
#include <netinet/in.h> /* sockaddr_in */
#endif
#include <fmt/core.h>
#include "libtransmission/transmission.h"
#include "libtransmission/crypto-utils.h"
#include "libtransmission/file.h"
#include "libtransmission/log.h"
#include "libtransmission/net.h"
#include "libtransmission/peer-mgr.h" // for tr_peerMgrCompactToPex()
#include "libtransmission/quark.h"
#include "libtransmission/timer.h"
#include "libtransmission/tr-assert.h"
#include "libtransmission/tr-dht.h"
#include "libtransmission/tr-strbuf.h"
#include "libtransmission/variant.h"
#include "libtransmission/utils.h" // for tr_time(), _()
using namespace std::literals;
// the dht library needs us to implement these:
extern "C"
{
// This function should return true when a node is blacklisted.
// We don't support using a blacklist with the DHT in Transmission,
// since massive (ab)use of this feature could harm the DHT. However,
// feel free to add support to your private copy as long as you don't
// redistribute it.
int dht_blacklisted(sockaddr const* /*sa*/, int /*salen*/)
{
return 0;
}
void dht_hash(
void* hash_return,
int hash_size,
void const* v1,
int len1,
void const* v2,
int len2,
void const* v3,
int len3)
{
auto* setme = reinterpret_cast<std::byte*>(hash_return);
std::fill_n(static_cast<char*>(hash_return), hash_size, '\0');
auto const sv1 = std::string_view{ static_cast<char const*>(v1), size_t(len1) };
auto const sv2 = std::string_view{ static_cast<char const*>(v2), size_t(len2) };
auto const sv3 = std::string_view{ static_cast<char const*>(v3), size_t(len3) };
auto const digest = tr_sha1::digest(sv1, sv2, sv3);
std::copy_n(std::data(digest), std::min(size_t(hash_size), std::size(digest)), setme);
}
int dht_random_bytes(void* buf, size_t size)
{
tr_rand_buffer(buf, size);
return static_cast<int>(size);
}
int dht_sendto(int sockfd, void const* buf, int len, int flags, struct sockaddr const* to, int tolen)
{
return static_cast<int>(sendto(sockfd, static_cast<char const*>(buf), len, flags, to, tolen));
}
#if defined(_WIN32) && !defined(__MINGW32__)
int dht_gettimeofday(struct timeval* tv, [[maybe_unused]] struct timezone* tz)
{
TR_ASSERT(tz == nullptr);
auto const d = std::chrono::system_clock::now().time_since_epoch();
auto const s = std::chrono::duration_cast<std::chrono::seconds>(d);
tv->tv_sec = s.count();
tv->tv_usec = std::chrono::duration_cast<std::chrono::microseconds>(d - s).count();
return 0;
}
#endif
} // extern "C"
class tr_dht_impl final : public tr_dht
{
private:
using Node = tr_socket_address;
using Nodes = std::deque<Node>;
using Id = std::array<unsigned char, 20>;
enum class SwarmStatus
{
Stopped,
Broken,
Poor,
Firewalled,
Good
};
public:
tr_dht_impl(Mediator& mediator, tr_port peer_port, tr_socket_t udp4_socket, tr_socket_t udp6_socket)
: peer_port_{ peer_port }
, udp4_socket_{ udp4_socket }
, udp6_socket_{ udp6_socket }
, mediator_{ mediator }
, state_filename_{ tr_pathbuf{ mediator_.config_dir(), "/dht.dat" } }
, announce_timer_{ mediator_.timer_maker().create([this]() { on_announce_timer(); }) }
, bootstrap_timer_{ mediator_.timer_maker().create([this]() { on_bootstrap_timer(); }) }
, periodic_timer_{ mediator_.timer_maker().create([this]() { on_periodic_timer(); }) }
{
tr_logAddDebug(fmt::format("Starting DHT on port {port}", fmt::arg("port", peer_port.host())));
// load up the bootstrap nodes
if (tr_sys_path_exists(state_filename_.c_str()))
{
std::tie(id_, bootstrap_queue_) = load_state(state_filename_);
}
get_nodes_from_bootstrap_file(tr_pathbuf{ mediator_.config_dir(), "/dht.bootstrap"sv }, bootstrap_queue_);
get_nodes_from_name("dht.transmissionbt.com", tr_port::from_host(6881), bootstrap_queue_);
bootstrap_timer_->start_single_shot(100ms);
mediator_.api().init(udp4_socket_, udp6_socket_, std::data(id_), nullptr);
on_announce_timer();
announce_timer_->start_repeating(1s);
on_periodic_timer();
}
tr_dht_impl(tr_dht_impl&&) = delete;
tr_dht_impl(tr_dht_impl const&) = delete;
tr_dht_impl& operator=(tr_dht_impl&&) = delete;
tr_dht_impl& operator=(tr_dht_impl const&) = delete;
~tr_dht_impl() override
{
tr_logAddTrace("Uninitializing DHT");
// Since we only save known good nodes,
// only overwrite older data if we know enough nodes.
if (is_ready(AF_INET) || is_ready(AF_INET6))
{
save_state();
}
mediator_.api().uninit();
tr_logAddTrace("Done uninitializing DHT");
}
void add_node(tr_address const& addr, tr_port port) override
{
if (addr.is_ipv4())
{
auto sin = sockaddr_in{};
sin.sin_family = AF_INET;
sin.sin_addr = addr.addr.addr4;
sin.sin_port = port.network();
mediator_.api().ping_node(reinterpret_cast<sockaddr*>(&sin), sizeof(sin));
}
else if (addr.is_ipv6())
{
auto sin6 = sockaddr_in6{};
sin6.sin6_family = AF_INET6;
sin6.sin6_addr = addr.addr.addr6;
sin6.sin6_port = port.network();
mediator_.api().ping_node(reinterpret_cast<sockaddr*>(&sin6), sizeof(sin6));
}
}
void handle_message(unsigned char const* msg, size_t msglen, struct sockaddr* from, socklen_t fromlen) override
{
auto const call_again_in_n_secs = periodic(msg, msglen, from, fromlen);
// Being slightly late is fine,
// and has the added benefit of adding some jitter.
auto const interval = call_again_in_n_secs + std::chrono::milliseconds{ tr_rand_int(1000U) };
periodic_timer_->start_single_shot(interval);
}
private:
[[nodiscard]] constexpr tr_socket_t udpSocket(int af) const noexcept
{
switch (af)
{
case AF_INET:
return udp4_socket_;
case AF_INET6:
return udp6_socket_;
default:
return TR_BAD_SOCKET;
}
}
[[nodiscard]] SwarmStatus swarm_status(int family, int* const setme_node_count = nullptr) const
{
if (udpSocket(family) == TR_BAD_SOCKET)
{
if (setme_node_count != nullptr)
{
*setme_node_count = 0;
}
return SwarmStatus::Stopped;
}
int good = 0;
int dubious = 0;
int incoming = 0;
mediator_.api().nodes(family, &good, &dubious, nullptr, &incoming);
if (setme_node_count != nullptr)
{
*setme_node_count = good + dubious;
}
if (good < 4 || good + dubious <= 8)
{
return SwarmStatus::Broken;
}
if (good < 40)
{
return SwarmStatus::Poor;
}
if (incoming < 8)
{
return SwarmStatus::Firewalled;
}
return SwarmStatus::Good;
}
[[nodiscard]] static constexpr auto is_ready(SwarmStatus const status)
{
return status >= SwarmStatus::Firewalled;
}
[[nodiscard]] bool is_ready(int af) const noexcept
{
return is_ready(swarm_status(af));
}
[[nodiscard]] bool is_ready() const noexcept
{
return is_ready(AF_INET) && is_ready(AF_INET6);
}
///
// how long to wait between adding nodes during bootstrap
[[nodiscard]] static constexpr auto bootstrap_interval(size_t n_added)
{
// Our DHT code is able to take up to 9 nodes in a row without
// dropping any. After that, it takes some time to split buckets.
// So ping the first 8 nodes quickly, then slow down.
if (n_added < 8U)
{
return 2s;
}
if (n_added < 16U)
{
return 15s;
}
return 40s;
}
void on_bootstrap_timer()
{
// Since we don't want to abuse our bootstrap nodes,
// we don't ping them if the DHT is in a good state.
if (is_ready() || std::empty(bootstrap_queue_))
{
return;
}
auto [address, port] = bootstrap_queue_.front();
bootstrap_queue_.pop_front();
add_node(address, port);
++n_bootstrapped_;
bootstrap_timer_->start_single_shot(bootstrap_interval(n_bootstrapped_));
}
///
[[nodiscard]] auto announce_torrent(tr_sha1_digest_t const& info_hash, int af, tr_port port)
{
auto const* dht_hash = reinterpret_cast<unsigned char const*>(std::data(info_hash));
auto const rc = mediator_.api().search(dht_hash, port.host(), af, callback, this);
auto const announce_again_in_n_secs = rc < 0 ? 5s + std::chrono::seconds{ tr_rand_int(5U) } :
25min + std::chrono::seconds{ tr_rand_int(3U * 60U) };
return announce_again_in_n_secs;
}
void on_announce_timer()
{
// don't announce if the swarm isn't ready
if (swarm_status(AF_INET) < SwarmStatus::Poor && swarm_status(AF_INET6) < SwarmStatus::Poor)
{
return;
}
auto const now = tr_time();
for (auto const id : mediator_.torrents_allowing_dht())
{
auto& times = announce_times_[id];
if (auto& announce_after = times.ipv4_announce_after; announce_after < now)
{
auto const announce_again_in_n_secs = announce_torrent(mediator_.torrent_info_hash(id), AF_INET, peer_port_);
announce_after = now + std::chrono::seconds{ announce_again_in_n_secs }.count();
}
if (auto& announce_after = times.ipv6_announce_after; announce_after < now)
{
auto const announce_again_in_n_secs = announce_torrent(mediator_.torrent_info_hash(id), AF_INET6, peer_port_);
announce_after = now + std::chrono::seconds{ announce_again_in_n_secs }.count();
}
}
}
///
void on_periodic_timer()
{
auto const call_again_in_n_secs = periodic(nullptr, 0, nullptr, 0);
// Being slightly late is fine,
// and has the added benefit of adding some jitter.
auto const interval = call_again_in_n_secs + std::chrono::milliseconds{ tr_rand_int(1000U) };
periodic_timer_->start_single_shot(interval);
}
[[nodiscard]] std::chrono::seconds periodic(
unsigned char const* msg,
size_t msglen,
struct sockaddr const* from,
socklen_t fromlen)
{
TR_ASSERT_MSG(msglen == 0 || msg[msglen] == '\0', "libdht requires zero-terminated msg");
auto call_again_in_n_secs = time_t{};
mediator_.api().periodic(msg, msglen, from, static_cast<int>(fromlen), &call_again_in_n_secs, callback, this);
return std::chrono::seconds{ call_again_in_n_secs };
}
static auto remove_bad_pex(std::vector<tr_pex>&& pex)
{
static constexpr auto IsBadPex = [](tr_pex const& candidate)
{
// paper over a bug in some DHT implementation that gives port 1.
// Xref: https://github.com/transmission/transmission/issues/527
return candidate.socket_address.port_ == tr_port::from_host(1);
};
pex.erase(std::remove_if(std::begin(pex), std::end(pex), IsBadPex), std::end(pex));
return pex;
}
static void callback(void* vself, int event, unsigned char const* info_hash, void const* data, size_t data_len)
{
auto* const self = static_cast<tr_dht_impl*>(vself);
auto hash = tr_sha1_digest_t{};
std::copy_n(reinterpret_cast<std::byte const*>(info_hash), std::size(hash), std::data(hash));
if (event == DHT_EVENT_VALUES)
{
auto const pex = remove_bad_pex(tr_pex::from_compact_ipv4(data, data_len, nullptr, 0));
self->mediator_.add_pex(hash, std::data(pex), std::size(pex));
}
else if (event == DHT_EVENT_VALUES6)
{
auto const pex = remove_bad_pex(tr_pex::from_compact_ipv6(data, data_len, nullptr, 0));
self->mediator_.add_pex(hash, std::data(pex), std::size(pex));
}
}
///
void save_state() const
{
auto constexpr MaxNodes = int{ 300 };
auto constexpr PortLen = size_t{ 2 };
auto constexpr CompactAddrLen = size_t{ 4 };
auto constexpr CompactLen = size_t{ CompactAddrLen + PortLen };
auto constexpr Compact6AddrLen = size_t{ 16 };
auto constexpr Compact6Len = size_t{ Compact6AddrLen + PortLen };
auto sins4 = std::array<struct sockaddr_in, MaxNodes>{};
auto sins6 = std::array<struct sockaddr_in6, MaxNodes>{};
auto num4 = int{ MaxNodes };
auto num6 = int{ MaxNodes };
auto const n = mediator_.api().get_nodes(std::data(sins4), &num4, std::data(sins6), &num6);
tr_logAddTrace(fmt::format("Saving {} ({} + {}) nodes", n, num4, num6));
tr_variant benc;
tr_variantInitDict(&benc, 3);
tr_variantDictAddRaw(&benc, TR_KEY_id, std::data(id_), std::size(id_));
if (num4 > 0)
{
auto compact = std::array<char, MaxNodes * CompactLen>{};
char* out = std::data(compact);
for (auto const* in = std::data(sins4), *end = in + num4; in != end; ++in)
{
memcpy(out, &in->sin_addr, CompactAddrLen);
out += CompactAddrLen;
memcpy(out, &in->sin_port, PortLen); // saved in network byte order
out += PortLen;
}
tr_variantDictAddRaw(&benc, TR_KEY_nodes, std::data(compact), out - std::data(compact));
}
if (num6 > 0)
{
auto compact6 = std::array<char, MaxNodes * Compact6Len>{};
char* out6 = std::data(compact6);
for (auto const* in = std::data(sins6), *end = in + num6; in != end; ++in)
{
memcpy(out6, &in->sin6_addr, Compact6AddrLen);
out6 += Compact6AddrLen;
memcpy(out6, &in->sin6_port, PortLen); // saved in network byte order
out6 += PortLen;
}
tr_variantDictAddRaw(&benc, TR_KEY_nodes6, std::data(compact6), out6 - std::data(compact6));
}
tr_variant_serde::benc().to_file(benc, state_filename_);
}
[[nodiscard]] static std::pair<Id, Nodes> load_state(std::string_view filename)
{
// Note that DHT ids need to be distributed uniformly,
// so it should be something truly random
auto id = tr_rand_obj<Id>();
auto nodes = Nodes{};
if (auto otop = tr_variant_serde::benc().parse_file(filename); otop)
{
auto& top = *otop;
if (auto sv = std::string_view{}; tr_variantDictFindStrView(&top, TR_KEY_id, &sv) && std::size(sv) == std::size(id))
{
std::copy(std::begin(sv), std::end(sv), std::begin(id));
}
size_t raw_len = 0U;
std::byte const* raw = nullptr;
if (tr_variantDictFindRaw(&top, TR_KEY_nodes, &raw, &raw_len) && raw_len % 6 == 0)
{
auto* walk = raw;
auto const* const end = raw + raw_len;
while (walk < end)
{
auto addr = tr_address{};
auto port = tr_port{};
std::tie(addr, walk) = tr_address::from_compact_ipv4(walk);
std::tie(port, walk) = tr_port::from_compact(walk);
nodes.emplace_back(addr, port);
}
}
if (tr_variantDictFindRaw(&top, TR_KEY_nodes6, &raw, &raw_len) && raw_len % 18 == 0)
{
auto* walk = raw;
auto const* const end = raw + raw_len;
while (walk < end)
{
auto addr = tr_address{};
auto port = tr_port{};
std::tie(addr, walk) = tr_address::from_compact_ipv6(walk);
std::tie(port, walk) = tr_port::from_compact(walk);
nodes.emplace_back(addr, port);
}
}
}
return std::make_pair(id, nodes);
}
///
static void get_nodes_from_bootstrap_file(std::string_view filename, Nodes& nodes)
{
auto in = std::ifstream{ std::string{ filename } };
if (!in.is_open())
{
return;
}
// format is each line has host, a space char, and port number
auto line = std::string{};
while (std::getline(in, line))
{
auto line_stream = std::istringstream{ line };
auto addrstr = std::string{};
auto hport = uint16_t{};
line_stream >> addrstr >> hport;
if (line_stream.bad() || std::empty(addrstr))
{
tr_logAddWarn(fmt::format(
_("Couldn't parse '{filename}' line: '{line}'"),
fmt::arg("filename", filename),
fmt::arg("line", line)));
}
else
{
get_nodes_from_name(addrstr.c_str(), tr_port::from_host(hport), nodes);
}
}
}
static void get_nodes_from_name(char const* name, tr_port port_in, Nodes& nodes)
{
auto hints = addrinfo{};
hints.ai_socktype = SOCK_DGRAM;
hints.ai_family = AF_UNSPEC;
hints.ai_protocol = 0;
hints.ai_flags = 0;
auto port_str = std::array<char, 16>{};
*fmt::format_to(std::data(port_str), FMT_STRING("{:d}"), port_in.host()) = '\0';
addrinfo* info = nullptr;
if (int const rc = getaddrinfo(name, std::data(port_str), &hints, &info); rc != 0)
{
tr_logAddWarn(fmt::format(
_("Couldn't look up '{address}:{port}': {error} ({error_code})"),
fmt::arg("address", name),
fmt::arg("port", port_in.host()),
fmt::arg("error", gai_strerror(rc)),
fmt::arg("error_code", rc)));
return;
}
for (auto* infop = info; infop != nullptr; infop = infop->ai_next)
{
if (auto addrport = tr_socket_address::from_sockaddr(infop->ai_addr); addrport)
{
nodes.emplace_back(*addrport);
}
}
freeaddrinfo(info);
}
///
tr_port const peer_port_;
tr_socket_t const udp4_socket_;
tr_socket_t const udp6_socket_;
Mediator& mediator_;
std::string const state_filename_;
std::unique_ptr<libtransmission::Timer> const announce_timer_;
std::unique_ptr<libtransmission::Timer> const bootstrap_timer_;
std::unique_ptr<libtransmission::Timer> const periodic_timer_;
Id id_ = {};
Nodes bootstrap_queue_;
size_t n_bootstrapped_ = 0;
struct AnnounceInfo
{
time_t ipv4_announce_after = 0;
time_t ipv6_announce_after = 0;
};
std::map<tr_torrent_id_t, AnnounceInfo> announce_times_;
};
[[nodiscard]] std::unique_ptr<tr_dht> tr_dht::create(
Mediator& mediator,
tr_port peer_port,
tr_socket_t udp4_socket,
tr_socket_t udp6_socket)
{
return std::make_unique<tr_dht_impl>(mediator, peer_port, udp4_socket, udp6_socket);
}
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