Re: netcat missing example (is this even possible?)

[David Fifield <david () bamsoftware com>]

On Wed, Jun 02, 2010 at 03:44:43PM +1000, David Burrows wrote:
> Hi (response below),
>
> On Wed, Jun 2, 2010 at 9:43 AM, David Fifield <david () bamsoftware com> wrote:
>
> > On Wed, Jun 02, 2010 at 03:42:53AM +1000, David Burrows wrote:
> > > Hello again!
> > >
> > > Sorry to reply to my own post so soon, but it appears that I have found a
> > > solution that could save someone the trouble of what I just went though.
> > >
> > > (on server)
> > > socat /dev/urandom TCP4-LISTEN:9999
> > > (on client - substitute localhost for the servers ip if not localhost)
> > > socat TCP4:localhost:9999 PTY,link=/dev/newrandom,raw,echo=0
> > >
> > > The server socat command can be substituted with: ncat -l -k 9999 -c 'cat
> > > /dev/urandom'
> > > I'm not sure if there would be a netcat equivalent of the client
> > connection.
> > > Now you can "dd bs=nnn count=1 /dev/newrandom of=/dev/null" and cat, etc
> > all
> > > works as expected with the newly cloned device.
> >
> > Ncat doesn't have code to create a pty. You could probably do it with a
> > fifo:
> >
> > $ ncat -l -k 9999 --sh-exec "cat /dev/urandom"
> > $ mkfifo /dev/newrandom
> > $ ncat localhost 9999 > /dev/newrandom
>
> Ok this works as expected, except when a test dd process closes the
> /dev/newrandom fifo, the second ncat exits with the error "Broken pipe".

I see that too. I don't have a good solution for you, but as a dumb
workaround you can use a SIGPIPE-ignoring Perl buffer like this.

$ ncat localhost 9999 | perl -e 'use bytes;$SIG{PIPE}="IGNORE";while(sysread(STDIN,$_,1024)){syswrite(STDOUT,$_);}' > 
/dev/newrandom

You might want to double-check that two processes reading from
/dev/newrandom simultaneously will get different random bytes; I'm not
sure that's the case.

David Fifield
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