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transmission/libtransmission/tr-udp.cc

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// This file Copyright © 2010-2023 Juliusz Chroboczek.
// It may be used under the MIT (SPDX: MIT) license.
// License text can be found in the licenses/ folder.
#include <array>
#include <cerrno>
#include <string>
#ifdef _WIN32
#include <ws2tcpip.h>
#else
#include <netinet/in.h> // IPV6_V6ONLY, IPPROTO_IPV6
#include <sys/socket.h> // setsockopt, SOL_SOCKET, bind
#endif
#include <event2/event.h>
#include <fmt/core.h>
#include "libtransmission/log.h"
#include "libtransmission/net.h"
#include "libtransmission/session.h"
#include "libtransmission/tr-assert.h"
#include "libtransmission/tr-utp.h"
#include "libtransmission/utils.h"
namespace
{
/* Since we use a single UDP socket in order to implement multiple
µTP sockets, try to set up huge buffers. */
void set_socket_buffers(tr_socket_t fd, bool large)
{
static auto constexpr RecvBufferSize = 4 * 1024 * 1024;
static auto constexpr SendBufferSize = 1 * 1024 * 1024;
static auto constexpr SmallBufferSize = 32 * 1024;
int rbuf = 0;
int sbuf = 0;
socklen_t rbuf_len = sizeof(rbuf);
socklen_t sbuf_len = sizeof(sbuf);
int size = large ? RecvBufferSize : SmallBufferSize;
int rc = setsockopt(fd, SOL_SOCKET, SO_RCVBUF, reinterpret_cast<char const*>(&size), sizeof(size));
if (rc < 0)
{
tr_logAddDebug(fmt::format("Couldn't set receive buffer: {}", tr_net_strerror(sockerrno)));
}
size = large ? SendBufferSize : SmallBufferSize;
rc = setsockopt(fd, SOL_SOCKET, SO_SNDBUF, reinterpret_cast<char const*>(&size), sizeof(size));
if (rc < 0)
{
tr_logAddDebug(fmt::format("Couldn't set send buffer: {}", tr_net_strerror(sockerrno)));
}
if (large)
{
rc = getsockopt(fd, SOL_SOCKET, SO_RCVBUF, reinterpret_cast<char*>(&rbuf), &rbuf_len);
if (rc < 0)
{
rbuf = 0;
}
rc = getsockopt(fd, SOL_SOCKET, SO_SNDBUF, reinterpret_cast<char*>(&sbuf), &sbuf_len);
if (rc < 0)
{
sbuf = 0;
}
if (rbuf < RecvBufferSize)
{
tr_logAddDebug(fmt::format("Couldn't set receive buffer: requested {}, got {}", RecvBufferSize, rbuf));
#ifdef __linux__
tr_logAddDebug(fmt::format("Please add the line 'net.core.rmem_max = {}' to /etc/sysctl.conf", RecvBufferSize));
#endif
}
if (sbuf < SendBufferSize)
{
tr_logAddDebug(fmt::format("Couldn't set send buffer: requested {}, got {}", SendBufferSize, sbuf));
#ifdef __linux__
tr_logAddDebug(fmt::format("Please add the line 'net.core.wmem_max = {}' to /etc/sysctl.conf", SendBufferSize));
#endif
}
}
}
void event_callback(evutil_socket_t s, [[maybe_unused]] short type, void* vsession)
{
TR_ASSERT(vsession != nullptr);
TR_ASSERT(type == EV_READ);
auto buf = std::array<unsigned char, 8192>{};
auto from = sockaddr_storage{};
auto fromlen = socklen_t{ sizeof(from) };
auto* const from_sa = reinterpret_cast<sockaddr*>(&from);
auto const rc = recvfrom(s, reinterpret_cast<char*>(std::data(buf)), std::size(buf) - 1, 0, from_sa, &fromlen);
if (rc <= 0)
{
return;
}
/* Since most packets we receive here are µTP, make quick inline
checks for the other protocols. The logic is as follows:
- all DHT packets start with 'd'
- all UDP tracker packets start with a 32-bit (!) "action", which
is between 0 and 3
- the above cannot be µTP packets, since these start with a 4-bit
version number (1). */
auto* const session = static_cast<tr_session*>(vsession);
if (buf[0] == 'd')
{
if (session->dht_)
{
buf[rc] = '\0'; // libdht requires zero-terminated messages
session->dht_->handle_message(std::data(buf), rc, from_sa, fromlen);
}
}
else if (rc >= 8 && buf[0] == 0 && buf[1] == 0 && buf[2] == 0 && buf[3] <= 3)
{
if (!session->announcer_udp_->handle_message(std::data(buf), rc))
{
tr_logAddTrace("Couldn't parse UDP tracker packet.");
}
}
else if (session->allowsUTP() && (session->utp_context != nullptr))
{
if (!tr_utpPacket(std::data(buf), rc, from_sa, fromlen, session))
{
tr_logAddTrace("Unexpected UDP packet");
}
}
}
} // namespace
// BEP-32 explains why we need to bind to one IPv6 address
tr_session::tr_udp_core::tr_udp_core(tr_session& session, tr_port udp_port)
: udp_port_{ udp_port }
, session_{ session }
{
if (std::empty(udp_port_))
{
return;
}
if (auto sock = socket(PF_INET, SOCK_DGRAM, 0); sock != TR_BAD_SOCKET)
{
auto optval = int{ 1 };
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, reinterpret_cast<char const*>(&optval), sizeof(optval));
auto const addr = session_.bind_address(TR_AF_INET);
auto const [ss, sslen] = addr.to_sockaddr(udp_port_);
if (bind(sock, reinterpret_cast<sockaddr const*>(&ss), sslen) != 0)
{
auto const error_code = errno;
tr_logAddWarn(fmt::format(
_("Couldn't bind IPv4 socket {address}: {error} ({error_code})"),
fmt::arg("address", addr.display_name(udp_port_)),
fmt::arg("error", tr_strerror(error_code)),
fmt::arg("error_code", error_code)));
tr_net_close_socket(sock);
}
else
{
tr_logAddInfo(fmt::format("Bound UDP IPv4 address {:s}", addr.display_name(udp_port_)));
session_.setSocketTOS(sock, TR_AF_INET);
set_socket_buffers(sock, session_.allowsUTP());
udp4_socket_ = sock;
udp4_event_.reset(event_new(session_.event_base(), udp4_socket_, EV_READ | EV_PERSIST, event_callback, &session_));
event_add(udp4_event_.get(), nullptr);
}
}
if (!session.has_ip_protocol(TR_AF_INET6))
{
// no IPv6; do nothing
}
else if (auto sock = socket(PF_INET6, SOCK_DGRAM, 0); sock != TR_BAD_SOCKET)
{
auto optval = int{ 1 };
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, reinterpret_cast<char const*>(&optval), sizeof(optval));
auto const addr = session_.bind_address(TR_AF_INET6);
auto const [ss, sslen] = addr.to_sockaddr(udp_port_);
if (bind(sock, reinterpret_cast<sockaddr const*>(&ss), sslen) != 0)
{
auto const error_code = errno;
tr_logAddWarn(fmt::format(
_("Couldn't bind IPv6 socket {address}: {error} ({error_code})"),
fmt::arg("address", addr.display_name(udp_port_)),
fmt::arg("error", tr_strerror(error_code)),
fmt::arg("error_code", error_code)));
tr_net_close_socket(sock);
}
else
{
tr_logAddInfo(fmt::format("Bound UDP IPv6 address {:s}", addr.display_name(udp_port_)));
session_.setSocketTOS(sock, TR_AF_INET6);
set_socket_buffers(sock, session_.allowsUTP());
udp6_socket_ = sock;
udp6_event_.reset(event_new(session_.event_base(), udp6_socket_, EV_READ | EV_PERSIST, event_callback, &session_));
event_add(udp6_event_.get(), nullptr);
#ifdef IPV6_V6ONLY
// Since we always open an IPv4 socket on the same port,
// this shouldn't matter. But I'm superstitious.
int one = 1;
(void)setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, reinterpret_cast<char const*>(&one), sizeof(one));
#endif
}
}
}
tr_session::tr_udp_core::~tr_udp_core()
{
udp6_event_.reset();
if (udp6_socket_ != TR_BAD_SOCKET)
{
tr_net_close_socket(udp6_socket_);
udp6_socket_ = TR_BAD_SOCKET;
}
udp4_event_.reset();
if (udp4_socket_ != TR_BAD_SOCKET)
{
tr_net_close_socket(udp4_socket_);
udp4_socket_ = TR_BAD_SOCKET;
}
}
void tr_session::tr_udp_core::sendto(void const* buf, size_t buflen, struct sockaddr const* to, socklen_t const tolen) const
{
auto const addrport = tr_address::from_sockaddr(to);
if (to->sa_family != AF_INET && to->sa_family != AF_INET6)
{
errno = EAFNOSUPPORT;
}
else if (auto const sock = to->sa_family == AF_INET ? udp4_socket_ : udp6_socket_; sock == TR_BAD_SOCKET)
{
// don't warn on bad sockets; the system may not support IPv6
return;
}
else if (
addrport && addrport->address().is_global_unicast_address() &&
!session_.global_source_address(to->sa_family == AF_INET ? TR_AF_INET : TR_AF_INET6))
{
// don't try to connect to a global address if we don't have connectivity to public internet
return;
}
else if (::sendto(sock, static_cast<char const*>(buf), buflen, 0, to, tolen) != -1)
{
return;
}
auto display_name = std::string{};
if (addrport)
{
auto const& [addr, port] = *addrport;
display_name = addr.display_name(port);
}
tr_logAddWarn(fmt::format(
"Couldn't send to {address}: {errno} ({error})",
fmt::arg("address", display_name),
fmt::arg("errno", errno),
fmt::arg("error", tr_strerror(errno))));
}
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