Re: Using ncat to read TCP stream --> send HTTP GET request

[David Fifield <david () bamsoftware com>]

On Mon, May 16, 2011 at 12:12:08PM +0000, Elias Home wrote:
> Hello, 
>
> I'm attempting to get two devices to communicate with each other on my network.  The first device (sender) is able to 
> send plain text via TCP to an IPAddress:Port when an event occurs.  The second device (receiver) is triggered by 
> receiving an HTTP GET request; it then closes the socket as it should.  The problem is that the transmitter does not 
> expect the socket to be closed after the string is sent - it is designed to send to a simple "open TCP port" that 
> just monitors for TCP plain text traffic and doesn't respond (and certainly doesn't close the socket). 
>
> I am able to send the following from the transmitter via TCP:  GET /rest/programs/0071/runThe n 
> HTTP/1.1[CRLF]Authorizatio n: Basic xxxxxxxxxx[CRLF][CRLF] 
>
> This works perfectly, however the HTTP server (receiver) replies with a 200 and then closes the socket.  The 
> transmitter doesn't know how to hand this, and nothing works until I reset the socket connection. 
>
>
>
> So, here's what I'm looking to accomplish: 
>
> 1.  Open a port on a Windows PC and listen for TCP plain text data; socket connections should NOT be closed on this 
> port after data is received 
>
> 2.  When a particular plain text string is received over this port, an HTTP GET command must be issued to a different 
> IP address:port.  It should be expected that this socket will be closed by the HTTP server. 
>
> 3.  The utility performing this task must be able to run in the background and be available to repeat this process 
> for an indefinite number of triggers 
>
>
> Is this possible with ncat?  Any help with an appropriate syntax (or other ideas on how to accomplish this) would be 
> greatly appreciated. 

You can try the --sh-exec function and execute a script that reads from
the socket and looks for the magic string. For example, maybe something
like this in server.pl:

#!/usr/bin/perl -w
$|=1;
while (<STDIN>) {
        if (/^GET/) {
                # Do HTTP request.
        } else {
                # Do something else with $_.
        }
}

Then run

        ncat -lk --sh-exec "./server.py" port

David Fifield
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