Mailinglist Archive: opensuse-programming (38 mails)

[Robert Jenni <jenni@xxxxxxxxx>]

Am Donnerstag, 12. Dezember 2002 13:43 schrieb Kai-Uwe Schmidt:
> > -----Ursprüngliche Nachricht-----
> > Von: dries [mailto:dries@xxxxxxxxxxxxx]
> > Gesendet: Donnerstag, 12. Dezember 2002 17:33
> > An: SuSE Programming English
> > Betreff: Re: [suse-programming-e] How to check in which state is a
>
> socket
>
> > ?
> >
> > Kai-Uwe Schmidt wrote :
> > | Hi folks,
> > |
> > | i have a server process which collects socket connects from clients.
> >
> > Those
> >
> > | connects are stored in a chain. On a special event on the server,
>
> the
>
> > | process has to deliver some data to the clients. So far so good,
>
> but..
>
> > | how do i recognize when i client disconnects, or how can i check the
> >
> > state
> >
> > | of the socket ? my process crash when it tries to send/write data on
>
> the
>
> > | old-socket handle. it all written in C, so there is no way to use
>
> stuff
>
> > | like try() catch() and i dont beleave, i should write an own signal
> >
> > handler
> >
> > | for this write/send statement. there must be a clean way to
> >
> > check/monitor
> >
> > | the state of the socket, but how ?
> >
> > You can determine if a socket is closed if a read from a socket that
>
> says
>
> > there is data (via select) returns a number of 0 bytes on a read.
> >
> > There is also a trick reading zero bytes from the socket (that won't
>
> block
>
> > and
> > can be done at all times) and then checking the the nr of bytes
>
> written.
>
> > I don't know exactly how to do it but try something like this to find
>
> out
>
> >  unsigned char c;
> >  int res;
> >
> >  res = read(socket,&c,0);
> >  printf("%d\n",res);
> >
> >
> > i think res will be negative if socket is not available anymore (you
>
> might
>
> > even be able to check errno to see what happened).
>
> [Kai-Uwe Schmidt] hm, this sounds like an idea, but my tests show that
> status=select(iClientConnect+1,NULL,&fs_write,NULL,&timeout) returns 1
> and status=read(iClientConnect,&c,0) returns 0. Even when I do a
> system("netstat -an | grep <myport>"); before. The system() shows
> nothing after 20 sec where I killed the client-connect. Means IMHO that
> the kernel doesn’t know anything about the socket anymore.
>
> But iWritten=send(iClientConnect,"Test",strlen("Test"),0) crashes the
> process even without writing a core file.
>
> No clue how to proceed, sounds like a bug in my eyes.
>
> Kai-Uwe


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