transmission/libtransmission/peer-socket.h

// This file Copyright © 2017-2023 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.

#pragma once

#ifndef __TRANSMISSION__
#error only libtransmission should #include this header.
#endif

#include <atomic>
#include <string>
#include <string_view>
#include <utility> // for std::make_pair()

#include "transmission.h"

#include "error.h"
#include "net.h"
#include "tr-assert.h"
#include "tr-buffer.h"

struct UTPSocket;
struct tr_session;

class tr_peer_socket
{
public:
    using Buffer = libtransmission::Buffer;
    using OutBuf = libtransmission::BufferReader<std::byte>;

    tr_peer_socket() = default;
    tr_peer_socket(tr_session const* session, tr_address const& address, tr_port port, tr_socket_t sock);
    tr_peer_socket(tr_address const& address, tr_port port, struct UTPSocket* const sock);
    tr_peer_socket(tr_peer_socket&& s)
    {
        *this = std::move(s);
    }
    tr_peer_socket(tr_peer_socket const&) = delete;
    tr_peer_socket& operator=(tr_peer_socket&& s)
    {
        close();
        handle = s.handle;
        address_ = s.address_;
        port_ = s.port_;
        type_ = s.type_;
        // invalidate s.type_, s.handle so s.close() won't break anything
        s.type_ = Type::None;
        s.handle = {};
        return *this;
    }
    tr_peer_socket& operator=(tr_peer_socket const&) = delete;
    ~tr_peer_socket()
    {
        close();
    }
    void close();

    size_t try_read(Buffer& buf, size_t max, tr_error** error) const;
    size_t try_write(OutBuf& buf, size_t max, tr_error** error) const;

    [[nodiscard]] constexpr std::pair<tr_address, tr_port> socketAddress() const noexcept
    {
        return std::make_pair(address_, port_);
    }

    [[nodiscard]] constexpr auto const& address() const noexcept
    {
        return address_;
    }

    [[nodiscard]] constexpr auto const& port() const noexcept
    {
        return port_;
    }

    template<typename OutputIt>
    OutputIt display_name(OutputIt out)
    {
        return address_.display_name(out, port_);
    }

    [[nodiscard]] std::string_view display_name(char* out, size_t outlen) const
    {
        return address_.display_name(out, outlen, port_);
    }

    [[nodiscard]] std::string display_name() const
    {
        return address_.display_name(port_);
    }

    [[nodiscard]] constexpr auto is_utp() const noexcept
    {
        return type_ == Type::UTP;
    }

    [[nodiscard]] constexpr auto is_tcp() const noexcept
    {
        return type_ == Type::TCP;
    }

    [[nodiscard]] constexpr auto is_valid() const noexcept
    {
#ifdef WITH_UTP
        return is_tcp() || is_utp();
#else
        return is_tcp();
#endif
    }

    [[nodiscard]] constexpr size_t guess_packet_overhead(size_t n_bytes) const noexcept
    {
        if (is_tcp())
        {
            // https://web.archive.org/web/20140912230020/http://sd.wareonearth.com:80/~phil/net/overhead/
            // TCP over Ethernet:
            // Assuming no header compression (e.g. not PPP)
            // Add 20 IPv4 header or 40 IPv6 header (no options)
            // Add 20 TCP header
            // Add 12 bytes optional TCP timestamps
            // Max TCP Payload data rates over ethernet are thus:
            // (1500-40)/ (38+1500) = 94.9285 %  IPv4, minimal headers
            // (1500-52)/ (38+1500) = 94.1482 %  IPv4, TCP timestamps
            // (1500-52)/ (42+1500) = 93.9040 %  802.1q, IPv4, TCP timestamps
            // (1500-60)/ (38+1500) = 93.6281 %  IPv6, minimal headers
            // (1500-72)/ (38+1500) = 92.8479 %  IPv6, TCP timestamps
            // (1500-72)/ (42+1500) = 92.6070 %  802.1q, IPv6, TCP timestamps

            // So, let's guess around 7% overhead
            return n_bytes / 14U;
        }

        // We only guess for TCP; uTP tracks its overhead via UTP_ON_OVERHEAD_STATISTICS
        return {};
    }

    union
    {
        tr_socket_t tcp;
        struct UTPSocket* utp;
    } handle = {};

    [[nodiscard]] static bool limit_reached(tr_session* const session) noexcept;

private:
    enum class Type
    {
        None,
        TCP,
        UTP
    };

    tr_address address_;
    tr_port port_;

    enum Type type_ = Type::None;

    static inline std::atomic<size_t> n_open_sockets_ = {};
};

tr_peer_socket tr_netOpenPeerSocket(tr_session* session, tr_address const& addr, tr_port port, bool client_is_seed);