Date: Mon, 10 Sep 2012 12:41:19 +0000 (UTC) From: jb <jb.1234abcd@gmail.com> To: freebsd-questions@freebsd.org Subject: Re: How to detect unconnected AF_UNIX sockets Message-ID: <loom.20120910T142719-111@post.gmane.org> References: <cone.1347219822.563023.17725.1000@monster.email-scan.com>
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Sam Varshavchik <mrsam <at> courier-mta.com> writes:
>
> I'm porting existing code from Linux where a connect() to an AF_UNIX socket
> that exists, but does not have a listener, fails with ECONNREFUSED. This is
> quite agreeable with the comparable scenario in AF_INET, with a connection
> attempt to a port without a listener on it. So the same code handles both
> situations, immediately reporting an error, and without caring much about
> the type of the socket.
>
> But on FreeBSD, according to truss, it seems that a connect() to an AF_UNIX
> socket without a listener still succeeds. A subsequent write() also
> succeeds, and read() blocks.
>
> The fall-out is quite unfortunate, and I was hoping for a way to detect that
> my allegedly connected socket is lying to me, and it's not really connected
> to anything. How would I go about doing that? I tried using the
> LOCAL_CONNWAIT option as documented in unix(4), but that does not appear to
> make any difference, in this situation.
>
>
It seems to work here:
$ uname -a
... FreeBSD 9.1-RC1 #0 ...
$ ls -al /tmp/server
srwxr-xr-x 1 jb wheel 0 Sep 10 14:22 /tmp/server
$ ps auxww |grep -i server-af_unix
$ ./client-af_unix
client af_unix: connect() errno = 61
connect() failed: No such file or directory
$ grep 61 /usr/include/errno.h
#define ECONNREFUSED 61 /* Connection refused */
$
Client code:
...
rc = connect(sd, (struct sockaddr *)&serveraddr, SUN_LEN(&serveraddr));
if (rc < 0)
{
printf("client af_unix: connect() errno = %d\n", errno);
perror("connect() failed");
...
jb
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