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Re: ncat - UNIX-domain sockets support
From: David Fifield <david () bamsoftware com>
Date: Tue, 20 Nov 2012 22:15:26 -0800

On Tue, Nov 13, 2012 at 04:13:48AM -0500, Tomas Hozza wrote:
I'm not sure that automatic generation of a source socket filename is
ready, so I removed it. Is this an essential feature that other
netcats have?

It is an essential feature for DATAGRAM UNIX domain sockets. When client
connects to the server and doesn't create its own socket (source socket)
it won't be able to receive any messages from the server. So if user
connecting to a DATAGRAM UNIX domain socket didn't specified a source
socket, then it has to be generated in order for client to receive
messages from the server.

Also older netcats had this feature. 

Okay, I see this now in netcat-openbsd:
        /* Get name of temporary socket for unix datagram client */
        if ((family == AF_UNIX) && uflag && !lflag) {
                if (sflag) {
                        unix_dg_tmp_socket = sflag;
                } else {
                        strlcpy(unix_dg_tmp_socket_buf, "/tmp/nc.XXXXXXXXXX",
                                UNIX_DG_TMP_SOCKET_SIZE);
                        if (mkstemp(unix_dg_tmp_socket_buf) == -1)
                                err(1, "mkstemp");
                        unix_dg_tmp_socket = unix_dg_tmp_socket_buf;
                }
        }

I agree now that Ncat should do something compatible. Would you produce
a new patch (you can base it on your old patch) adding support for this
automatic creation? The only thing is that we shouldn't use a hardcoded
"/tmp". This page has a code example that reads the TMPDIR and TMP
environment variables in addition to using mkstemp:

http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/avoid-race.html#TEMPORARY-FILES

There is code in ncat_connect to delete the source socket, but
1) it deletes the file even if not automatically generated; i.e., if the
user used --source, and 

Actually it doesn't matter if it was generated or specified by user. It had
to be created by Ncat when it was connecting and should be removed, because
it is just temporary and only for the client to be able receive messages.

This seems weird to me. If I make my own socket in the filesystem and
tell Ncat to use it, I don't expect it to be deleted. But that's what
netcat-openbsd does, and I think we should be compatible in this case.

David Fifield
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