ncat: terminate when remote EOF

[Matthias Wächter <matthias () waechter wiz at>]

Hi guys,

Thanks for this great tool. However, I just don’t understand how to tell 
ncat to terminate when the remote end has closed the session.

Take for example, a simple HTTP session. When I have told the server 
what page I want to receive, i.e., sending GET, Host: and empty line, 
and the server has returned the data, the server closes its end of the 
connection. Using "telnet server 80", or "nc server 80", or even "socat 
- TCP:server:80" for that, all lead to the same result: When the server 
is done, the program exits. In this discipline, telnet and nc are the 
fastest, terminating without any delay, and socat offers the option "-t" 
to specify the delay between EOF and termination. Specifying "-t0" 
brings socat to the same zero-delay like telnet and nc.

Not so with ncat. After the server has sent the data and is obviously 
done, the session stays open until either (a) the client terminates it, 
or (b) sends additional data, which then breaks the pipe, or (c) -i 
<timeout> was specified, and that inactivity timeout ran out.

As my script connects the input to ncat with another program, I cannot 
control to send additional data into the pipe. Also the output is out of 
reach, so even if I planned to analyze the output to identify the 
semantic end of the stream, I cannot, and it’s stupid anyway since the 
stream already tells by EOF when it’s time to go. So the only thing that 
comes close to what I need is "-i <timeout>".

IMO, timeouts should be used to cope with higher-layer errors (e.g., 
remote application takes too long to process my query), or with 
lower-layer errors (network stall), but not for the normal case when 
there is no error present. Say, I want to have a timeout of 10 seconds, 
for the case where the remote script rarely takes long to gather the 
data; if I need to take that timeout for any connection that returns my 
data even within 10 milliseconds, my script will crawl like a snail for 
every connection.

Isn’t there something in ncat that behaves like "socat -t0"? Do I miss 
the obvious?

Note: My script isn’t about HTTP, so wget/curl won’t catch it at all. I 
definitely need nc/ncat/socat for the job, and I want to offer 
compatibility with each of them.

Thanks in advance,
– Matthias
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