Context independent C++ TCP Server Class

Question

I'm coding a TCP Server class based on the I/O multiplexing (select) way. The basic idea is explained in this chunk of code:

GenericApp.cpp

TServer *server = new Tserver(/*parameters*/);
server->mainLoop();

For now the behavior of the server is independent from the context but in a way that i nedd to improove.

Actual Status

 receive(sockFd , buffer);
 MSGData * msg=     MSGFactory::getInstance()->createMessage(Utils::getHeader(buffer,1024));
 EventHandler * rightHandler =eventBinder->getHandler(msg->type());
 rightHandler->callback(msg);

At this version the main loop reads from the socket, instantiates the right type of message object and calls the appropriate handler(something may not work properly because it compiles but i have not tested it). As you can notice this allows a programmer to define his message types and appropriate handlers but once the main loop is started nothing can be done. I need to make this part of the server more customizable to adapt this class to a bigger quantity of problems.

MainLoop Code

void TServer::mainLoop()
{

    int sockFd;
    int connFd;
    int maxFd;
    int maxi;
    int i;
    int nready; 

    maxFd = listenFd;
    maxi = -1;

     for(i = 0 ; i< FD_SETSIZE ; i++) clients[i] = -1; //Should be in the constructor?

     FD_ZERO(&allset); //Should be in the constructor?
     FD_SET(listenFd,&allset); //Should be in the constructor?


         for(;;)
          {
             rset = allset;
             nready = select (maxFd + 1 , &rset , NULL,NULL,NULL);

             if(FD_ISSET( listenFd , &rset ))
             {
                cliLen = sizeof(cliAddr);
                connFd = accept(listenFd , (struct sockaddr *) &cliAddr, &cliLen);

                 for (i = 0; i < FD_SETSIZE; i++)
                 {  
                     if (clients[i] < 0) 
                    {
                         clients[i] = connFd;   /* save descriptor */
                         break;
                    }
                 }

                 if (i == FD_SETSIZE) //!!HANDLE ERROR

                 FD_SET(connFd, &allset);   /* add new descriptor to set */

                 if (connFd > maxFd) maxFd = connFd;            /* for select */

                 if (i > maxi) maxi = i;                /* max index in client[] array  */

                 if (--nready <= 0)  continue;  
             }

            for (i = 0; i <= maxi; i++)     
             {  
                /* check all clients for data */
                if ( (sockFd = clients[i]) < 0) continue;

                if (FD_ISSET(sockFd, &rset)) 
                {
                    //!!SHOULD CLEAN BUFFER BEFORE READ
                    receive(sockFd , buffer);
                    MSGData * msg =  MSGFactory::getInstance()->createMessage(Utils::getHeader(buffer,1024));
                    EventHandler * rightHandler =eventBinder->getHandler(msg->type());
                    rightHandler->callback(msg);
                }
                   if (--nready <= 0)   break;              /* no more readable descriptors */
                }
           }
 }

Do you have any suggestions on a good way to do this? Thanks.

to me your question is very unclear....

lifeOfPI
– lifeOfPI

2014-07-15 11:07:16 +00:00
Commented Jul 15, 2014 at 11:07 — lifeOfPI
– lifeOfPI, Commented Jul 15, 2014 at 11:07
Take a look at boost::asio

Maxim Egorushkin
– Maxim Egorushkin

2014-07-15 14:09:06 +00:00
Commented Jul 15, 2014 at 14:09 — Maxim Egorushkin
– Maxim Egorushkin, Commented Jul 15, 2014 at 14:09

fjardon · Accepted Answer · 2014-07-15 14:06:05Z

2

Your question requires more than just a stack overflow question. You can find good ideas in these book:

Basically what you're trying to do is a reactor. You can find open source library implementing this pattern. For instance:

If you want yout handler to have the possibility to do more processing you could give them a reference to your TCPServer and a way to register a socket for the following events:

read, the socket is ready for read
write, the socket is ready for write
accept, the listening socket is ready to accept (read with select)
close, the socket is closed
timeout, the time given to wait for the next event expired (select allow to specify a timeout)

So that the handler can implement all kinds of protocols half-duplex or full-duplex:

In your example there is no way for a handler to answer the received message. This is the role of the write event to let a handler knows when it can send on the socket.
The same is true for the read event. It should not be in your main loop but in the socket read handler.
You may also want to add the possibility to register a handler for an event with a timeout so that you can implement timers and drop idle connections.

This leads to some problems:

Your handler will have to implement a state-machine to react to the network events and update the events it wants to receive.
You handler may want to create and connect new sockets (think about a Web proxy server, an IRC client with DCC, an FTP server, and so on...). For this to work it must have the possibility to create a socket and to register it in your main loop. This means the handler may now receive callbacks for one of the two sockets and there should be a parameter telling the callback which socket it is. Or you will have to implement a handler for each socket and they will comunnicate with a queue of messages. The queue is needed because the readiness of one socket is independent of the readiness of the other. And you may read something on one and not being ready to send it on the other.
You will have to manage the timeouts specified by each handlers which may be different. You may end up with a priority queue for timeouts

As you see this is no simple problem. You may want to reduce the genericity of your framework to simplify its design. (for instance handling only half-duplex protocols like simple HTTP)

edited Jul 15, 2014 at 14:06

answered Jul 15, 2014 at 11:26

fjardon

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3 Comments

fitzbutz Over a year ago

I thank you but this does not help me much. I know well that I can find in the literature for help but my goal is to write simple code to understand the basic functioning of the things

fjardon Over a year ago

@GiorgioGambino Did you already write a server using fork or threads ? What's your platform ?

fitzbutz Over a year ago

Yes i did. currently i develop under a 64Bit Linux

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