boost::asio 干净地断开连接

有时 boost::asio 似乎在我想要之前断开连接，即在服务器正确处理断开连接之前。我不确定这是怎么可能的，因为客户端似乎认为它完全发送了消息，但是当服务器发出错误时，它甚至没有读取消息头......在测试期间，这种情况可能只发生五分之一，服务器收到客户端关闭消息，并干净地断开客户端连接。

错误：“现有连接被远程主机强制关闭”

客户端断开连接：

void disconnect()
{
    boost::system::error_code error;
    //just creates a simple buffer with a shutdown header
    boost::uint8_t *packet = createPacket(PC_SHUTDOWN,0);
    //sends it
    if(!sendBlocking(socket,packet,&error))
    {
        //didnt get here in my tests, so its not that the write failed...
        logWrite(LOG_ERROR,"server",
            std::string("Error sending shutdown message.\n")
            + boost::system::system_error(error).what());
    }

    //actaully disconnect
    socket.close();
    ioService.stop();
}
bool sendBlocking(boost::asio::ip::tcp::socket &socket,
    boost::uint8_t *data, boost::system::error_code* error)
{
    //get the length section from the message
    boost::uint16_t len = *(boost::uint16_t*)(data - 3);
    //send it
    asio::write(socket, asio::buffer(data-3,len+3),
        asio::transfer_all(), *error);
    deletePacket(data);
    return !(*error);
}

服务器：

void Client::clientShutdown()
{
    //not getting here in problem cases
    disconnect();
}
void Client::packetHandler(boost::uint8_t type, boost::uint8_t *data,
    boost::uint16_t len, const boost::system::error_code& error)
{
    if(error)
    {
        //error handled here
        delete[] data;
        std::stringstream ss;
        ss << "Error recieving packet.\n";
        ss << logInfo() << "\n";
        ss << "Error: " << boost::system::system_error(error).what();
        logWrite(LOG_ERROR,"Client",ss.str());

        disconnect();
    }
    else
    {
        //call handlers based on type, most will then call startRead when
        //done to get the next packet. Note however, that clientShutdown
        //does not
        ...
    }
}



void startRead(boost::asio::ip::tcp::socket &socket, PacketHandler handler)
{
    boost::uint8_t *header = new boost::uint8_t[3];
    boost::asio::async_read(socket,boost::asio::buffer(header,3),
        boost::bind(&handleReadHeader,&socket,handler,header, 
        boost::asio::placeholders::bytes_transferred,boost::asio::placeholders::error));
}
void handleReadHeader(boost::asio::ip::tcp::socket *socket, PacketHandler handler,
    boost::uint8_t *header, size_t len, const boost::system::error_code& error)
{
    if(error)
    {
        //error "thrown" here, len always = 0 in problem cases...
        delete[] header;
        handler(0,0,0,error);
    }
    else
    {
        assert(len == 3);
        boost::uint16_t payLoadLen  = *((boost::uint16_t*)(header + 0));
        boost::uint8_t  type        = *((boost::uint8_t*) (header + 2));
        delete[] header;
        boost::uint8_t *payLoad = new boost::uint8_t[payLoadLen];

        boost::asio::async_read(*socket,boost::asio::buffer(payLoad,payLoadLen),
            boost::bind(&handleReadBody,socket,handler,
            type,payLoad,payLoadLen,
            boost::asio::placeholders::bytes_transferred,boost::asio::placeholders::error));
    }
}
void handleReadBody(ip::tcp::socket *socket, PacketHandler handler,
    boost::uint8_t type, boost::uint8_t *payLoad, boost::uint16_t len,
    size_t readLen, const boost::system::error_code& error)
{
    if(error)
    {
        delete[] payLoad;
        handler(0,0,0,error);
    }
    else
    {
        assert(len == readLen);
        handler(type,payLoad,len,error);
        //delete[] payLoad;
    }
}

我想你应该打电话给socket.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ec)在打电话之前在那里socket.close().

The basic_stream_socket::close 的 boost::asio 文档 http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/reference/basic_stream_socket/close/overload2.html states:

对于与正常关闭已连接套接字相关的可移植行为，请在关闭套接字之前调用 shutdown()。

这应该确保在调用 socket.close 之前正确取消套接字上的任何挂起操作并刷新所有缓冲区。