[TUHS] sockets (was Re: First appearance of named pipes)

[Steffen Nurpmeso]

Peter Pentchev wrote in
<20200328111428.GA1431416 at straylight.m.ringlet.net>:
 |On Sat, Mar 28, 2020 at 01:12:35PM +0200, Peter Pentchev wrote:
 |> On Thu, Mar 26, 2020 at 01:38:17PM +1100, Dave Horsfall wrote:
 |>> On Wed, 25 Mar 2020, Grant Taylor via TUHS wrote:
 |>> 
 |>>> · netcat's STDOUT to grep's STDIN
 |>>> · grep's STDOUT to netcat's STDIN
 |>> 
 |>> Are you trying to set up a loop of processes or something?  I'm \
 |>> not sure if
 |>> that is even possible, although you can't rule out creative uses \
 |>> of dup2()
 |>> etc...
 |> 
 |> This can't really be done with netcat, but it's quite easy to do with
 |> socat; here's an example with a trivial program that reads lines from
 |> its standard input and writes a single line to its standard output:
 |> 
 |>     [roam at straylight ~]$ socat -v tcp4:nimbus.fccf.net:25 exec:./heysmtp.\
 |>     py
  ...

perl(1) has IPC::Open2 for that:

  use IPC::Open2;
  # We use `csop' for hashing
  my $MAILX = 'LC_ALL=C s-nail -#:/';

  sub hash_em{
     die "hash_em: open: $^E"
        unless my $pid = open2 *RFD, *WFD, $MAILX;
     foreach my $e (@ENTS){
        print WFD "csop hash32 $e->{name}\n";
        my $h = <RFD>;
        chomp $h;
        $e->{hash} = $h
     }
     print WFD "x\n";
     waitpid $pid, 0;
  }

  hash_em()

 |...but, of course, this is still not what Derek was talking about
 |earlier - there is no separation of the file descriptors connected to
 |the socket: closing the stdout one would not result in a FIN being sent
 |along the line.

Just wanted to add earlier in the thread that on some systems
shutdown(2) equals close(2).  At least it was like that on Mac OS
X (by then) Snow Leopard.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)