How to detect unconnected AF_UNIX sockets
mrsam at courier-mta.com
Sun Sep 9 19:43:44 UTC 2012
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.
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