NetSession.h

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/* Copyright (C) 2022 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef NETSESSION_H
#define NETSESSION_H

#include "lib/external_libraries/enet.h"
#include "network/FSM.h"
#include "network/NetFileTransfer.h"
#include "network/NetHost.h"
#include "ps/CStr.h"

#include <boost/lockfree/queue.hpp>

#include <atomic>

/**
 * Report the peer if we didn't receive a packet after this time (milliseconds).
 */
inline constexpr u32 NETWORK_WARNING_TIMEOUT = 2000;

class CNetClient;
class CNetServerWorker;

class CNetStatsTable;

typedef struct _ENetHost ENetHost;

/**
 * @file
 * Network client/server sessions.
 *
 * Each session has two classes: CNetClientSession runs on the client,
 * and CNetServerSession runs on the server.
 * A client runs one session at once; a server typically runs many.
 */

/**
 * Interface for sessions to which messages can be sent.
 */
class INetSession
{
public:
    virtual ~INetSession() {}
    virtual bool SendMessage(const CNetMessage* message) = 0;
};

/**
 * The client end of a network session.
 * Provides an abstraction of the network interface, allowing communication with the server.
 * The NetClientSession is threaded, so all calls to the public interface must be thread-safe.
 */
class CNetClientSession : public INetSession
{
    NONCOPYABLE(CNetClientSession);

public:
    CNetClientSession(CNetClient& client);
    ~CNetClientSession();

    bool Connect(const CStr& server, const u16 port, ENetHost* enetClient);

    /**
     * The client NetSession is threaded to avoid getting timeouts if the main thread hangs.
     * Call Connect() before starting this loop.
     */
    static void RunNetLoop(CNetClientSession* session);

    /**
     * Shut down the net session.
     */
    void Shutdown();

    /**
     * Processes pending messages.
     */
    void ProcessPolledMessages();

    /**
     * Queue up a message to send to the server on the next Loop() call.
     */
    virtual bool SendMessage(const CNetMessage* message) override;

    /**
     * Number of milliseconds since the most recent packet of the server was received.
     */
    u32 GetLastReceivedTime() const;

    /**
     * Average round trip time to the server.
     */
    u32 GetMeanRTT() const;

    CNetFileTransferer& GetFileTransferer() { return m_FileTransferer; }
private:
    /**
     * Process queued incoming messages.
     */
    void Poll();

    /**
     * Flush queued outgoing network messages.
     */
    void Flush();

    CNetClient& m_Client;

    CNetFileTransferer m_FileTransferer;

    // Net messages received and waiting for fetching.
    boost::lockfree::queue<ENetEvent> m_IncomingMessages;
    // Net messages to send on the next flush() call.
    boost::lockfree::queue<ENetPacket*> m_OutgoingMessages;

    // Last know state. If false, flushing errors are silenced.
    bool m_Connected = false;

    // Wrapper around enet stats - those are atomic as the code is lock-free.
    std::atomic<u32> m_LastReceivedTime;
    std::atomic<u32> m_MeanRTT;

    // If this is true, calling Connect() or deleting the session is an error.
    std::atomic<bool> m_LoopRunning;
    std::atomic<bool> m_ShouldShutdown;

    ENetHost* m_Host;
    ENetPeer* m_Server;
    CNetStatsTable* m_Stats;
};


/**
 * The server's end of a network session.
 * Represents an abstraction of the state of the client, storing all the per-client data
 * needed by the server.
 *
 * Thread-safety:
 * - This is constructed and used by CNetServerWorker in the network server thread.
 */
class CNetServerSession : public CFsm, public INetSession
{
    NONCOPYABLE(CNetServerSession);

public:
    CNetServerSession(CNetServerWorker& server, ENetPeer* peer);

    CNetServerWorker& GetServer() { return m_Server; }

    const CStr& GetGUID() const { return m_GUID; }
    void SetGUID(const CStr& guid) { m_GUID = guid; }

    const CStrW& GetUserName() const { return m_UserName; }
    void SetUserName(const CStrW& name) { m_UserName = name; }

    u32 GetHostID() const { return m_HostID; }
    void SetHostID(u32 id) { m_HostID = id; }

    u32 GetIPAddress() const;

    /**
     * Number of milliseconds since the latest packet of that client was received.
     */
    u32 GetLastReceivedTime() const;

    /**
     * Average round trip time to the client.
     */
    u32 GetMeanRTT() const;

    /**
     * Sends a disconnection notification to the client,
     * and sends a NMT_CONNECTION_LOST message to the session FSM.
     * The server will receive a disconnection notification after a while.
     * The server will not receive any further messages sent via this session.
     */
    void Disconnect(NetDisconnectReason reason);

    /**
     * Sends an unreliable disconnection notification to the client.
     * The server will not receive any disconnection notification.
     * The server will not receive any further messages sent via this session.
     */
    void DisconnectNow(NetDisconnectReason reason);

    /**
     * Send a message to the client.
     */
    virtual bool SendMessage(const CNetMessage* message);

    CNetFileTransferer& GetFileTransferer() { return m_FileTransferer; }

private:
    CNetServerWorker& m_Server;

    CNetFileTransferer m_FileTransferer;

    ENetPeer* m_Peer;

    CStr m_GUID;
    CStrW m_UserName;
    u32 m_HostID;
    CStr m_Password;
};

#endif  // NETSESSION_H