Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!ucsd!ucbvax!fiamass.ie!fiamass
From: fiamass@fiamass.ie (fiamass)
Newsgroups: comp.protocols.tcp-ip
Subject: select() call weirdness
Message-ID: <9101171257.AA13517@fiamass.ie>
Date: 17 Jan 91 12:57:45 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 74


We are having a problem with the select() system call on a Sun Sparc 4/65
running SunOS 4.1.  We have a non blocking socket which we use to issue 
a connect().  This call returns EINPROGRESS as per the documentation.  The 
documentation states that under these circumstatances a select() call for 
write on that socket can be done to determine when the socket is fully
connected. Now here is our problem, we make a select() call which 
always seems to return telling me 
that the socket is now connected. So on I go and issue a write() which
causes the program to bomb out!  It is as if the write call does not return.
Here us the code. Has anyone any ideas?

#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

main()
{
char			hostname[128];
struct 		sockaddr_in     sockaddr_in_struct;  
int	      sockid;
struct 		sockaddr_in server;
int retval,length,a,b,c;
char x;
struct fd_set readfds,writefds,exceptfds;
struct timeval timeout;
struct hostent *hp,*gethostbyname();

/* Get  a socket */
	sockid	= 		socket(AF_INET,SOCK_STREAM,0);

/* make in NONBLOCKING */
	x=1;
	if(ioctl(sockid,FIONBIO,&x)==-1)
			printf("Cannot unblock sock socket");
	server.sin_family = AF_INET;

/* fill in server details */	
	hp = gethostbyname ("server");
	if(hp==0)
		perror("gethostbyname");
	
	(void)bcopy((char *)hp->h_addr,(char *)&server.sin_addr,hp->h_length);
/* set up the servers port number */
	server.sin_port = (unsigned short)htons(1395);

/* connect up the socket */
/* this call returns with EINPROGRESS */	
	if(connect(sockid,(struct sockaddr *)&server,sizeof(server))==-1)
		perror("Connect returns ");

/* set up the select call */
	timeout.tv_sec=0;
	timeout.tv_usec=0;
	FD_ZERO(&writefds);
	FD_SET(sockid,&writefds);
	select(FD_SETSIZE,(fd_set *)NULL,&writefds,(fd_set *)NULL,&timeout);

	/* now see if we can legally write in this socket */
	if(FD_ISSET(sockid,&writefds)){
		printf("Select says OK to write\n");
		/* we get as far as here and then we are bombed back to SUNOS*/
		if(write(sockid,"abcdefghij",10) == -1){
			perror("Write failed !!");
			printf("Explain that one !!\n");
      }
    }
printf ("This line never gets printed because the write() call never returns");
}