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From: levy@mtcchi.uucp (2656-Daniel R. Levy(0000000)0000)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Comer/Shein whois server example won't work on Sparcstation
Message-ID: <1990Dec21.184019.22326@mtcchi.uucp>
Date: 21 Dec 90 18:40:19 GMT
References: <1990Dec20.044937.21094@mtcchi.uucp>
Distribution: na
Organization: Memorex Telex Corporation NSBG/STP
Lines: 47

I wrote

>I tried to run the whois server example by Barry Shein in Douglas Comer's
>_Internetworking_With_TCP/IP_ on a Sparcstation running SunOS 4.0.3...  bind()
>fails with EADDRNOTAVAIL even though the program was run with uid=euid=0.
>(Killing inetd, guessing that it might somehow be interfering, did not help.
>It did run fine on two SVR2 machines, an Amdahl and a 3B2.  I do not have any
>other 4BSD machines for testing.) Below is a listing of the program (with some
>debug print statements thrown in) and then the output I get when running it on
>the Sparcstation.  Can anyone please assist... thanks much in advance.

>main(argc,argv)
>char **argv;
>{
	...
>	struct sockaddr_in sa;
>	struct hostent *hp;
>	int s;
	...
>	sa.sin_port = sp->s_port;
>	bcopy((char *)hp->h_addr,(char *)&sa.sin_addr,hp->h_length);
>	sa.sin_family = hp->h_addrtype;
>
>	if ((s = socket(hp->h_addrtype,SOCK_STREAM,0)) < 0) {
>		perror("socket");
>		exit(1);
>	}
>
>	if (bind(s,&sa,sizeof sa) < 0) {
>		perror("bind");
>		exit(1);
>	}
	...
>}

A public thanks to Stuart Levy at the University of Minnesota, who pointed out
the problem:  a struct sockaddr_in has a char sin_zero[8] member which is
supposed to be zeroed; but if a struct sockaddr_in variable is declared auto,
this member is, of course, not guaranteed to be zeroed.  Either declaring sa to
be static or bzero()ing it fixes the problem.  As an experienced C programmer,
I feel kind of sheepish about not catching this sooner, though I could possibly
be excused in that I was not yet familiar with the structures involved....
-- 
* Daniel R. Levy *  uunet!tellab5!mtcchi!levy *                             |
* These views are live; they are not Memorex' *                           --+--
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