[Lazarus] FreePascal TCPIP data tunnel code sample?

[Bo Berglund]

Note: I tried posting this via Gmane in my newsreader, but it did not show
up.
So I post it now directly to the mail list.
Must have been lost at Gmane because another post I made later came through.
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I wonder if someone has built a program that can be used as a "tunnel" of
data from one TCP server to a TCP client on another network?
The program should sit in between in a computer connected to both networks
(Ethernet and WiFi).
If so I would be grateful to share the solutions.

Reason:
I am trying to develop a client program for controlling a data collection
instrument, which has WiFi connectivity only.
Its connection is implemented as a WiFi Access Point to which you connect.
Then you have access to the data source via TCP port 1001. The source is
actually operating via RS232 internally.
There is a protocol involved for commanding actions and for transferring
data in both directions.

Now, I would like to be able to connect to this unit from my place of coding
by having a multi-homed device sitting close to the instrument and
connecting to it via the WiFi AP, but at the same time it is also connected
to the office network by Ethernet.
The device should run a program to connect it to the data port (TCP:1001) of
the WiFi AP and start a TCP server on the Ethernet connection on TCP port
1001.
Then whatever data comes in through the Ethernet port should be sent via the
WiFi connection to the instrument.
All data received from the instrument should be sent out to the connected
client on the Ethernet connection.
So the program I am looking for should not do anything at all with the data
content, except transfer byte-by-byte between the networks.

And this should be running on a Raspberry Pi2B so it can be easily deployed
in the place the instrument is located. Meanwhile I can sit in another
building and test the actual client code.

Is there something like this available already?

-- 
Bo Berglund
Developer in Sweden