authserver在初始化静态变量时，会调用AuthSession::InitHandlers()，初始化全局的业务哈希表Handlers：

std::unordered_map<uint8, AuthHandler> AuthSession::InitHandlers()
{
    std::unordered_map<uint8, AuthHandler> handlers;

    handlers[AUTH_LOGON_CHALLENGE]     = { STATUS_CONNECTED, sizeof(AUTH_LOGON_CHALLENGE_C), &AuthSession::HandleLogonChallenge };
    handlers[AUTH_LOGON_PROOF]         = { STATUS_CONNECTED, sizeof(AUTH_LOGON_PROOF_C),     &AuthSession::HandleLogonProof };
    handlers[AUTH_RECONNECT_CHALLENGE] = { STATUS_CONNECTED, sizeof(AUTH_LOGON_CHALLENGE_C), &AuthSession::HandleReconnectChallenge };
    handlers[AUTH_RECONNECT_PROOF]     = { STATUS_CONNECTED, sizeof(AUTH_RECONNECT_PROOF_C), &AuthSession::HandleReconnectProof };
    handlers[REALM_LIST]               = { STATUS_AUTHED,    REALM_LIST_PACKET_SIZE,         &AuthSession::HandleRealmList };
    handlers[XFER_ACCEPT]              = { STATUS_AUTHED,    XFER_ACCEPT_SIZE,               &AuthSession::HandleXferAccept };
    handlers[XFER_RESUME]              = { STATUS_AUTHED,    XFER_RESUME_SIZE,               &AuthSession::HandleXferResume };
    handlers[XFER_CANCEL]              = { STATUS_AUTHED,    XFER_CANCEL_SIZE,               &AuthSession::HandleXferCancel };

    return handlers;
}

std::unordered_map<uint8, AuthHandler> const Handlers = AuthSession::InitHandlers();

进入main函数之后，程序会创建一个AsyncAcceptor<AuthSession>对象，在它的构造函数中，会调用AsyncAcceptor::AsyncAccept()准备监听指定端口，当然，正式开始监听要等开始事件循环之后，即调用_ioService.run()之后：

//这个函数里用了C++11的lambda表达式，智能指针，move语义，如果不熟悉这些，请先看一下C++11的教程
void AsyncAccept()
{
    _acceptor.async_accept(_socket, [this](boost::system::error_code error)
    {
        if (!error)
        {
            try
			{
                // this-> is required here to fix an segmentation fault in gcc 4.7.2 - reason is lambdas in a templated class
                std::make_shared<T>(std::move(this->_socket))->Start();
            }
            catch (boost::system::system_error const& err)
            {
                TC_LOG_INFO("network", "Failed to retrieve client's remote address %s", err.what());
            }
        }

        // lets slap some more this-> on this so we can fix this bug with gcc 4.7.2 throwing internals in yo face
		this->AsyncAccept();
	});
}<span style="font-family: Arial, Helvetica, sans-serif;"> </span>

        如上图所示，当客户端发起链接请求时，服务器会用智能指针新建一个AuthSession，然后调用其Start函数，它除了清空缓冲区之外，最主要是调用Socket类（AuthSession的基类）的AsyncReadMissingHeaderData函数，注册一个异步的读请求，读取包头：

void AsyncReadMissingHeaderData()
{
    _socket.async_read_some(boost::asio::buffer(_readHeaderBuffer.GetWritePointer(), std::min<std::size_t>(READ_BLOCK_SIZE, _readHeaderBuffer.GetMissingSize())),
        std::bind(&Socket<T, PacketType>::ReadHeaderHandlerInternal, this->shared_from_this(), std::placeholders::_1, std::placeholders::_2));
}

         读取到包头之后，会调用ReadHeaderHandlerInternal函数，它主要是调用了ReadHeaderHandler函数（当然还有一堆的错误判断）

void AuthSession::ReadHeaderHandler()
{
    uint8 cmd = GetHeaderBuffer()[0];
    auto itr = Handlers.find(cmd);
    if (itr != Handlers.end())
    {
        // Handle dynamic size packet
        if (cmd == AUTH_LOGON_CHALLENGE || cmd == AUTH_RECONNECT_CHALLENGE)
        {
            ReadData(sizeof(uint8) + sizeof(uint16)); //error + size
            sAuthLogonChallenge_C* challenge = reinterpret_cast<sAuthLogonChallenge_C*>(GetDataBuffer());

            AsyncReadData(challenge->size);
        }
        else
            AsyncReadData(itr->second.packetSize);
    }
    else
        CloseSocket();
}

         如上图所示，它先读取一个字节的协议号（包头），然后再根据该协议号，决定包体的长度size。最后再注册一个读请求（AsyncReadMissingData函数），请求长度为size的数据。一般而言，包体的长度就是结构体的长度，只有AUTH_LOGON_CHALLENGE和AUTH_RECONNECT_CHALLENGE例外，它们的长度是由sAuthLogonChallenge_C::size字段决定（它们用了一个技巧http://www.cnblogs.com/winkyao/archive/2012/02/14/2351885.html）：

void AsyncReadMissingData()
{
    _socket.async_read_some(boost::asio::buffer(_readDataBuffer.GetWritePointer(), std::min<std::size_t>(READ_BLOCK_SIZE, _readDataBuffer.GetMissingSize())),
        std::bind(&Socket<T, PacketType>::ReadDataHandlerInternal, this->shared_from_this(), std::placeholders::_1, std::placeholders::_2));
}

         读取到包体之后，会调用ReadDataHandler函数，它会根据协议号来调用对应的处理函数，处理完后，再注册一个异步的读事件，读取下一个表头：

void AuthSession::ReadDataHandler()
{
    if (!(*this.*Handlers.at(GetHeaderBuffer()[0]).handler)())
    {
        CloseSocket();
        return;
    }

    AsyncReadHeader();
}

         在处理函数中，首先会将收到的数据强制转换成对应的结构体，如：

sAuthLogonChallenge_C* challenge = reinterpret_cast<sAuthLogonChallenge_C*>(GetDataBuffer());

         然后再进行处理，处理过程中，会将要发给客户端的数据打包成一个ByteBuffer，然后再调用AsyncWrite函数，异步发给客户端：

void AuthSession::AsyncWrite(ByteBuffer& packet)
{
    if (!IsOpen())
        return;

    std::lock_guard<std::mutex> guard(_writeLock);

    bool needsWriteStart = _writeQueue.empty();

    _writeQueue.push(std::move(packet));

    if (needsWriteStart)
        Base::AsyncWrite(_writeQueue.front());
}

         当客户端与服务器断开时（网络错误，帐号密码错误，或登陆成功都会触发此事件），服务器会收到一个error_code不为0的读事件，调用了CloseSocket函数：

virtual void CloseSocket()
{
    if (_closed.exchange(true))
        return;

    boost::system::error_code shutdownError;
    _socket.shutdown(boost::asio::socket_base::shutdown_send, shutdownError);
    if (shutdownError)
        TC_LOG_DEBUG("network", "Socket::CloseSocket: %s errored when shutting down socket: %i (%s)", GetRemoteIpAddress().to_string().c_str(),
            shutdownError.value(), shutdownError.message().c_str());
}

魔兽世界服务器Trinitycore分析三：auth server网络事件的处理