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transmission/libtransmission/announcer-udp.cc

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// This file Copyright © 2010-2023 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#include <algorithm> // for std::find_if()
#include <array>
#include <chrono> // operator""ms, literals
#include <climits> // CHAR_BIT
#include <cstddef> // std::byte
#include <cstdint> // uint32_t, uint64_t
#include <cstring> // memcpy()
#include <ctime>
#include <future>
#include <list>
#include <memory>
#include <optional>
#include <string>
#include <string_view>
#include <utility>
#include <vector>
#ifdef _WIN32
#include <ws2tcpip.h>
#undef gai_strerror
#define gai_strerror gai_strerrorA
#else
#include <netdb.h> // gai_strerror()
#include <netinet/in.h> // IPPROTO_UDP, in_addr
#include <sys/socket.h> // sockaddr_storage, AF_INET
#endif
#include <fmt/core.h>
#define LIBTRANSMISSION_ANNOUNCER_MODULE
#include "libtransmission/announcer.h"
#include "libtransmission/announcer-common.h"
#include "libtransmission/crypto-utils.h" // for tr_rand_obj()
#include "libtransmission/interned-string.h"
#include "libtransmission/log.h"
#include "libtransmission/net.h"
#include "libtransmission/peer-mgr.h" // for tr_pex::fromCompact4()
#include "libtransmission/tr-assert.h"
#include "libtransmission/tr-buffer.h"
#include "libtransmission/utils.h"
#include "libtransmission/web-utils.h"
#define logwarn(interned, msg) tr_logAddWarn(msg, (interned).sv())
#define logdbg(interned, msg) tr_logAddDebug(msg, (interned).sv())
#define logtrace(interned, msg) tr_logAddTrace(msg, (interned).sv())
namespace
{
using namespace std::literals;
// size defined by bep15
using tau_connection_t = uint64_t;
using tau_transaction_t = uint32_t;
using InBuf = libtransmission::BufferReader<std::byte>;
using PayloadBuffer = libtransmission::StackBuffer<4096, std::byte>;
constexpr auto TauConnectionTtlSecs = time_t{ 45 };
auto tau_transaction_new()
{
return tr_rand_obj<tau_transaction_t>();
}
// used in the "action" field of a request. Values defined in bep 15.
enum tau_action_t
{
TAU_ACTION_CONNECT = 0,
TAU_ACTION_ANNOUNCE = 1,
TAU_ACTION_SCRAPE = 2,
TAU_ACTION_ERROR = 3
};
// --- SCRAPE
struct tau_scrape_request
{
tau_scrape_request(tr_scrape_request const& in, tr_scrape_response_func on_response)
: on_response_{ std::move(on_response) }
{
this->response.scrape_url = in.scrape_url;
this->response.row_count = in.info_hash_count;
for (int i = 0; i < this->response.row_count; ++i)
{
this->response.rows[i].seeders = -1;
this->response.rows[i].leechers = -1;
this->response.rows[i].downloads = -1;
this->response.rows[i].info_hash = in.info_hash[i];
}
// build the payload
auto buf = PayloadBuffer{};
buf.add_uint32(TAU_ACTION_SCRAPE);
buf.add_uint32(transaction_id);
for (int i = 0; i < in.info_hash_count; ++i)
{
buf.add(in.info_hash[i]);
}
this->payload.insert(std::end(this->payload), std::begin(buf), std::end(buf));
}
[[nodiscard]] auto has_callback() const noexcept
{
return !!on_response_;
}
void requestFinished() const
{
if (on_response_)
{
on_response_(response);
}
}
void fail(bool did_connect, bool did_timeout, std::string_view errmsg)
{
response.did_connect = did_connect;
response.did_timeout = did_timeout;
response.errmsg = errmsg;
requestFinished();
}
void onResponse(tau_action_t action, InBuf& buf)
{
response.did_connect = true;
response.did_timeout = false;
if (action == TAU_ACTION_SCRAPE)
{
for (int i = 0; i < response.row_count; ++i)
{
if (std::size(buf) < sizeof(uint32_t) * 3)
{
break;
}
auto& row = response.rows[i];
row.seeders = buf.to_uint32();
row.downloads = buf.to_uint32();
row.leechers = buf.to_uint32();
}
requestFinished();
}
else
{
std::string const errmsg = action == TAU_ACTION_ERROR && !std::empty(buf) ? buf.to_string() : _("Unknown error");
fail(true, false, errmsg);
}
}
[[nodiscard]] constexpr auto expiresAt() const noexcept
{
return created_at_ + TR_SCRAPE_TIMEOUT_SEC.count();
}
std::vector<std::byte> payload;
time_t sent_at = 0;
tau_transaction_t const transaction_id = tau_transaction_new();
tr_scrape_response response = {};
private:
time_t const created_at_ = tr_time();
tr_scrape_response_func on_response_;
};
// --- ANNOUNCE
struct tau_announce_request
{
tau_announce_request(uint32_t announce_ip, tr_announce_request const& in, tr_announce_response_func on_response)
: on_response_{ std::move(on_response) }
{
// https://www.bittorrent.org/beps/bep_0015.html sets key size at 32 bits
static_assert(sizeof(tr_announce_request::key) * CHAR_BIT == 32);
response.seeders = -1;
response.leechers = -1;
response.downloads = -1;
response.info_hash = in.info_hash;
// build the payload
auto buf = PayloadBuffer{};
buf.add_uint32(TAU_ACTION_ANNOUNCE);
buf.add_uint32(transaction_id);
buf.add(in.info_hash);
buf.add(in.peer_id);
buf.add_uint64(in.down);
buf.add_uint64(in.leftUntilComplete);
buf.add_uint64(in.up);
buf.add_uint32(get_tau_announce_event(in.event));
buf.add_uint32(announce_ip);
buf.add_uint32(in.key);
buf.add_uint32(in.numwant);
buf.add_port(in.port);
payload.insert(std::end(payload), std::begin(buf), std::end(buf));
}
[[nodiscard]] auto has_callback() const noexcept
{
return !!on_response_;
}
void requestFinished() const
{
if (on_response_)
{
on_response_(this->response);
}
}
void fail(bool did_connect, bool did_timeout, std::string_view errmsg)
{
this->response.did_connect = did_connect;
this->response.did_timeout = did_timeout;
this->response.errmsg = errmsg;
this->requestFinished();
}
void onResponse(tau_action_t action, InBuf& buf)
{
auto const buflen = std::size(buf);
this->response.did_connect = true;
this->response.did_timeout = false;
if (action == TAU_ACTION_ANNOUNCE && buflen >= 3 * sizeof(uint32_t))
{
response.interval = buf.to_uint32();
response.leechers = buf.to_uint32();
response.seeders = buf.to_uint32();
response.pex = tr_pex::from_compact_ipv4(std::data(buf), std::size(buf), nullptr, 0);
requestFinished();
}
else
{
std::string const errmsg = action == TAU_ACTION_ERROR && !std::empty(buf) ? buf.to_string() : _("Unknown error");
fail(true, false, errmsg);
}
}
[[nodiscard]] constexpr auto expiresAt() const noexcept
{
return created_at_ + TR_ANNOUNCE_TIMEOUT_SEC.count();
}
enum tau_announce_event
{
// Used in the "event" field of an announce request.
// These values come from BEP 15
TAU_ANNOUNCE_EVENT_NONE = 0,
TAU_ANNOUNCE_EVENT_COMPLETED = 1,
TAU_ANNOUNCE_EVENT_STARTED = 2,
TAU_ANNOUNCE_EVENT_STOPPED = 3
};
std::vector<std::byte> payload;
time_t sent_at = 0;
tau_transaction_t const transaction_id = tau_transaction_new();
tr_announce_response response = {};
private:
[[nodiscard]] static constexpr tau_announce_event get_tau_announce_event(tr_announce_event e)
{
switch (e)
{
case TR_ANNOUNCE_EVENT_COMPLETED:
return TAU_ANNOUNCE_EVENT_COMPLETED;
case TR_ANNOUNCE_EVENT_STARTED:
return TAU_ANNOUNCE_EVENT_STARTED;
case TR_ANNOUNCE_EVENT_STOPPED:
return TAU_ANNOUNCE_EVENT_STOPPED;
default:
return TAU_ANNOUNCE_EVENT_NONE;
}
}
time_t const created_at_ = tr_time();
tr_announce_response_func on_response_;
};
// --- TRACKER
struct tau_tracker
{
using Mediator = tr_announcer_udp::Mediator;
tau_tracker(Mediator& mediator, tr_interned_string key_in, tr_interned_string host_in, tr_port port_in)
: key{ key_in }
, host{ host_in }
, port{ port_in }
, mediator_{ mediator }
{
}
void sendto(std::byte const* buf, size_t buflen)
{
TR_ASSERT(addr_);
if (!addr_)
{
return;
}
auto const& [ss, sslen] = *addr_;
mediator_.sendto(buf, buflen, reinterpret_cast<sockaddr const*>(&ss), sslen);
}
void on_connection_response(tau_action_t action, InBuf& buf)
{
this->connecting_at = 0;
this->connection_transaction_id = 0;
if (action == TAU_ACTION_CONNECT)
{
this->connection_id = buf.to_uint64();
this->connection_expiration_time = tr_time() + TauConnectionTtlSecs;
logdbg(this->key, fmt::format("Got a new connection ID from tracker: {}", this->connection_id));
}
else if (action == TAU_ACTION_ERROR)
{
std::string errmsg = !std::empty(buf) ? buf.to_string() : _("Connection failed");
this->failAll(true, false, errmsg);
logdbg(this->key, std::move(errmsg));
}
this->upkeep();
}
void upkeep(bool timeout_reqs = true)
{
time_t const now = tr_time();
// do we have a DNS request that's ready?
if (addr_pending_dns_ && addr_pending_dns_->wait_for(0ms) == std::future_status::ready)
{
addr_ = addr_pending_dns_->get();
addr_pending_dns_.reset();
addr_expires_at_ = now + DnsRetryIntervalSecs;
}
// are there any requests pending?
if (this->isIdle())
{
return;
}
// update the addr if our lookup is past its shelf date
if (!addr_pending_dns_ && addr_expires_at_ <= now)
{
addr_.reset();
addr_pending_dns_ = std::async(std::launch::async, lookup, this->host, this->port, this->key);
return;
}
logtrace(
this->key,
fmt::format(
"connected {} ({} {}) -- connecting_at {}",
is_connected(now),
this->connection_expiration_time,
now,
this->connecting_at));
/* also need a valid connection ID... */
if (addr_ && !is_connected(now) && this->connecting_at == 0)
{
this->connecting_at = now;
this->connection_transaction_id = tau_transaction_new();
logtrace(this->key, fmt::format("Trying to connect. Transaction ID is {}", this->connection_transaction_id));
auto buf = PayloadBuffer{};
buf.add_uint64(0x41727101980LL);
buf.add_uint32(TAU_ACTION_CONNECT);
buf.add_uint32(this->connection_transaction_id);
this->sendto(std::data(buf), std::size(buf));
}
if (timeout_reqs)
{
timeout_requests(now);
}
if (addr_ && is_connected(now))
{
send_requests();
}
}
private:
using Sockaddr = std::pair<sockaddr_storage, socklen_t>;
using MaybeSockaddr = std::optional<Sockaddr>;
[[nodiscard]] constexpr bool is_connected(time_t now) const noexcept
{
return connection_id != tau_connection_t{} && now < connection_expiration_time;
}
[[nodiscard]] static MaybeSockaddr lookup(tr_interned_string host, tr_port port, tr_interned_string logname)
{
auto szport = std::array<char, 16>{};
*fmt::format_to(std::data(szport), FMT_STRING("{:d}"), port.host()) = '\0';
auto hints = addrinfo{};
hints.ai_family = AF_INET; // https://github.com/transmission/transmission/issues/4719
hints.ai_protocol = IPPROTO_UDP;
hints.ai_socktype = SOCK_DGRAM;
addrinfo* info = nullptr;
if (int const rc = getaddrinfo(host.c_str(), std::data(szport), &hints, &info); rc != 0)
{
logwarn(
logname,
fmt::format(
_("Couldn't look up '{address}:{port}': {error} ({error_code})"),
fmt::arg("address", host.sv()),
fmt::arg("port", port.host()),
fmt::arg("error", gai_strerror(rc)),
fmt::arg("error_code", static_cast<int>(rc))));
return {};
}
auto ss = sockaddr_storage{};
auto const len = info->ai_addrlen;
memcpy(&ss, info->ai_addr, len);
freeaddrinfo(info);
logdbg(logname, "DNS lookup succeeded");
return std::make_pair(ss, len);
}
[[nodiscard]] bool isIdle() const noexcept
{
return std::empty(announces) && std::empty(scrapes) && !addr_pending_dns_;
}
void failAll(bool did_connect, bool did_timeout, std::string_view errmsg)
{
for (auto& req : this->scrapes)
{
req.fail(did_connect, did_timeout, errmsg);
}
for (auto& req : this->announces)
{
req.fail(did_connect, did_timeout, errmsg);
}
this->scrapes.clear();
this->announces.clear();
}
///
void timeout_requests(time_t now)
{
if (this->connecting_at != 0 && this->connecting_at + ConnectionRequestTtl < now)
{
auto empty_buf = PayloadBuffer{};
on_connection_response(TAU_ACTION_ERROR, empty_buf);
}
timeout_requests(this->announces, now, "announce");
timeout_requests(this->scrapes, now, "scrape");
}
template<typename T>
void timeout_requests(std::list<T>& requests, time_t now, std::string_view name)
{
for (auto it = std::begin(requests); it != std::end(requests);)
{
if (auto& req = *it; req.expiresAt() <= now)
{
logtrace(this->key, fmt::format("timeout {} req {}", name, fmt::ptr(&req)));
req.fail(false, true, "");
it = requests.erase(it);
}
else
{
++it;
}
}
}
///
void send_requests()
{
TR_ASSERT(!addr_pending_dns_);
TR_ASSERT(addr_);
TR_ASSERT(this->connecting_at == 0);
TR_ASSERT(this->connection_expiration_time > tr_time());
send_requests(this->announces);
send_requests(this->scrapes);
}
template<typename T>
void send_requests(std::list<T>& reqs)
{
auto const now = tr_time();
for (auto it = std::begin(reqs); it != std::end(reqs);)
{
auto& req = *it;
if (req.sent_at != 0) // it's already been sent; we're awaiting a response
{
++it;
continue;
}
logdbg(this->key, fmt::format("sending req {}", fmt::ptr(&req)));
req.sent_at = now;
send_request(std::data(req.payload), std::size(req.payload));
if (req.has_callback())
{
++it;
continue;
}
// no response needed, so we can remove it now
it = reqs.erase(it);
}
}
void send_request(std::byte const* payload, size_t payload_len)
{
logdbg(this->key, fmt::format("sending request w/connection id {}", this->connection_id));
auto buf = PayloadBuffer{};
buf.add_uint64(this->connection_id);
buf.add(payload, payload_len);
this->sendto(std::data(buf), std::size(buf));
}
public:
tr_interned_string const key;
tr_interned_string const host;
tr_port const port;
time_t connecting_at = 0;
time_t connection_expiration_time = 0;
tau_connection_t connection_id = {};
tau_transaction_t connection_transaction_id = {};
std::list<tau_announce_request> announces;
std::list<tau_scrape_request> scrapes;
private:
Mediator& mediator_;
std::optional<std::future<MaybeSockaddr>> addr_pending_dns_ = {};
MaybeSockaddr addr_ = {};
time_t addr_expires_at_ = 0;
static inline constexpr auto DnsRetryIntervalSecs = time_t{ 3600 };
static inline constexpr auto ConnectionRequestTtl = int{ 30 };
};
// --- SESSION
class tr_announcer_udp_impl final : public tr_announcer_udp
{
public:
explicit tr_announcer_udp_impl(Mediator& mediator)
: mediator_{ mediator }
{
}
void announce(tr_announce_request const& request, tr_announce_response_func on_response) override
{
auto* const tracker = getTrackerFromUrl(request.announce_url);
if (tracker == nullptr)
{
return;
}
// Since size of IP field is only 4 bytes long, we can only announce IPv4 addresses
auto const addr = mediator_.announce_ip();
uint32_t const announce_ip = addr && addr->is_ipv4() ? addr->addr.addr4.s_addr : 0;
tracker->announces.emplace_back(announce_ip, request, std::move(on_response));
tracker->upkeep(false);
}
void scrape(tr_scrape_request const& request, tr_scrape_response_func on_response) override
{
auto* const tracker = getTrackerFromUrl(request.scrape_url);
if (tracker == nullptr)
{
return;
}
tracker->scrapes.emplace_back(request, std::move(on_response));
tracker->upkeep(false);
}
void upkeep() override
{
for (auto& tracker : trackers_)
{
tracker.upkeep();
}
}
// @brief process an incoming udp message if it's a tracker response.
// @return true if msg was a tracker response; false otherwise
bool handle_message(uint8_t const* msg, size_t msglen) override
{
if (msglen < sizeof(uint32_t) * 2)
{
return false;
}
// extract the action_id and see if it makes sense
auto buf = PayloadBuffer{};
buf.add(msg, msglen);
auto const action_id = static_cast<tau_action_t>(buf.to_uint32());
if (!isResponseMessage(action_id, msglen))
{
return false;
}
/* extract the transaction_id and look for a match */
tau_transaction_t const transaction_id = buf.to_uint32();
for (auto& tracker : trackers_)
{
// is it a connection response?
if (tracker.connecting_at != 0 && transaction_id == tracker.connection_transaction_id)
{
logtrace(tracker.key, fmt::format("{} is my connection request!", transaction_id));
tracker.on_connection_response(action_id, buf);
return true;
}
// is it a response to one of this tracker's announces?
if (auto& reqs = tracker.announces; !std::empty(reqs))
{
auto it = std::find_if(
std::begin(reqs),
std::end(reqs),
[&transaction_id](auto const& req) { return req.transaction_id == transaction_id; });
if (it != std::end(reqs))
{
logtrace(tracker.key, fmt::format("{} is an announce request!", transaction_id));
auto req = *it;
it = reqs.erase(it);
req.onResponse(action_id, buf);
return true;
}
}
// is it a response to one of this tracker's scrapes?
if (auto& reqs = tracker.scrapes; !std::empty(reqs))
{
auto it = std::find_if(
std::begin(reqs),
std::end(reqs),
[&transaction_id](auto const& req) { return req.transaction_id == transaction_id; });
if (it != std::end(reqs))
{
logtrace(tracker.key, fmt::format("{} is a scrape request!", transaction_id));
auto req = *it;
it = reqs.erase(it);
req.onResponse(action_id, buf);
return true;
}
}
}
/* no match... */
return false;
}
private:
// Finds the tau_tracker struct that corresponds to this url.
// If it doesn't exist yet, create one.
tau_tracker* getTrackerFromUrl(tr_interned_string announce_url)
{
// build a lookup key for this tracker
auto const parsed = tr_urlParseTracker(announce_url);
TR_ASSERT(parsed);
if (!parsed)
{
return nullptr;
}
// see if we already have it
auto const key = tr_announcerGetKey(*parsed);
for (auto& tracker : trackers_)
{
if (tracker.key == key)
{
return &tracker;
}
}
// we don't have it -- build a new one
trackers_.emplace_back(mediator_, key, tr_interned_string(parsed->host), tr_port::from_host(parsed->port));
auto* const tracker = &trackers_.back();
logtrace(tracker->key, "New tau_tracker created");
return tracker;
}
[[nodiscard]] static constexpr bool isResponseMessage(tau_action_t action, size_t msglen) noexcept
{
if (action == TAU_ACTION_CONNECT)
{
return msglen == 16;
}
if (action == TAU_ACTION_ANNOUNCE)
{
return msglen >= 20;
}
if (action == TAU_ACTION_SCRAPE)
{
return msglen >= 20;
}
if (action == TAU_ACTION_ERROR)
{
return msglen >= 8;
}
return false;
}
std::list<tau_tracker> trackers_;
Mediator& mediator_;
};
} // namespace
std::unique_ptr<tr_announcer_udp> tr_announcer_udp::create(Mediator& mediator)
{
return std::make_unique<tr_announcer_udp_impl>(mediator);
}
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