LinuxQuestions.org - connect() with timeout

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connect() with timeout

Im trying to put a timeout on a connect call, and it works fine if I try to contact www.google.com on say port 81, but for some reason if I try to connect to an unopen port on 127.0.0.1 or my router's IP, it succesds all the time.

The method I used is : first I set the socket to non-blocking, tried connecting with connect(), not bothering to check the return value because its always -1, then using select() to check if the socket could be written to.

heres my code:

Code:

bool TcpClient::Connect(        const char* host,

                                const unsigned short port,

                                const unsigned short timeOut)

{

        // get the IP address

        struct hostent* h=gethostbyname(host);

        if (!h) return false;



        // create socket and set it to non-blocking

        sockfd=socket(PF_INET,SOCK_STREAM,0);

        fcntl(sockfd,F_SETFL,O_NONBLOCK);



        // set up address structure

        remoteAddr.sin_port=htons(port);

        memcpy(&(remoteAddr.sin_addr.s_addr),h->h_addr,sizeof(remoteAddr.sin_addr.s_addr));



        // attempt to connect

        connect(sockfd,(struct sockaddr*)&remoteAddr,sizeof(struct sockaddr));



        // set up file descriptor set

        FD_ZERO(&fds);

        FD_SET(sockfd,&fds);



        // set up timeval struct

        tv.tv_sec=timeOut;

        tv.tv_usec=0;



        // monitor the socket

        if (select(sockfd+1,NULL,&fds,NULL,&tv)<=0) 

        {

                close(sockfd);

                return false;

        }



        return true;

}

Thanks for any help.

hmm.. i think Ive found a solution. if I just call send(sockfd,0,0,0) and I get a return value of 0, then its connected.

A method I have used before is to create a signal handler function for SIGALRM, and before calling connect call alarm(timeout); and after the connect call alarm(0);

When the alarm goes off and your signal handler returns, connect will exit, and you just turn off the alarm with the alarm(0).

Hi -

There are several ways for a sockets client to "connect() with timeout":

Quote:

1. Timeout with "select()"
I really wouldn't recommend this one for your situation. At best, if I was using UDP "sendto()" and "recvfrom ()", I might use "select()" to verify that the socket became writeable or readable within a specific time before I used it.

Quote:

2. Sigalarm
_john_i_'s suggestion is a good one. For example:

Code:

  /* Adapted from W. Richard Stevens, "Unix Network Programming" */

  oldsigfunc = signam (SIGALRM, mynewfunc);

  if (alarm (nsec) != 0) {

    printf ("WARNING: Alarm already set!\n");

  }



  /* Try to connect */

  iretval = connect (sockfd, &sa, slen);

  if (iretval  < 0) {

    close (sockfd);

    if (errno == EINTR)

      printf ("WARNING: timeout occurred...\n");

  }



  /* Clear Alarm/reset original SIGALRM handler */

  alarm (0);

  signal (SIGALRM, oldsigfunc);



  /* ... continue or not, based on "iretval" ... */

Quote:

3. "setsockopt (SO_RCVTIMEO)"
This is the best option of all ... if your stack supports it.

My version of Stevens (the 2nd Edition, 1998) states that you CANNOT use "setsockopt(SO_RCVTIMEO)" to set a connect timeout. This is no longer true on most OS's, and it has been available on Linux since kernel 2.3.41.
<= If at all possible, I'd encourage you to consider SO_RECVTIMEO

'Hope that helps .. PSM

PS:
Here are some links:
http://publib.boulder.ibm.com/infoce...2/gtpc2m2u.htm
http://linuxreviews.org/man/socket/