Hello all,

For quite some time now I've been looking for a way to have multiple, random
programs communicate with a single program (which sends/receives data
to/from an RS232 connection, in a way similar to TCP).

For that I need to be able to open a connection to send/receive data, but
also be able to listen for incoming connections from the other side (and
hand them of to whatever program is listening for them).

The problem is that I can't seem to figure out to let multiple, random
programs communicate with the single program which allows the above.

I've been looking at several IPC methods (including using a TCP/IP
connection over 127.0.0.1), but none of them seem to allow for the
'listening' part.

tl;dr:
I'm looking for a userland method which emulates the inter-process
communication(?) ws2_32 / winsock uses. If someone knows about a website
which has information about it or has information otherwise I would be much
obliged.

Regards,
Rudy Wieser

On 2022-06-24, R.Wieser <address@not.available> wrote:

> Hello all,
>
> For quite some time now I've been looking for a way to have multiple,
> random programs communicate with a single program (which sends/receives
> data to/from an RS232 connection, in a way similar to TCP).
>
> For that I need to be able to open a connection to send/receive data,
> but also be able to listen for incoming connections from the other side
> (and hand them of to whatever program is listening for them).

If I understand you correctly, I've written several programs that
perform similar functions, i.e. listen for incoming TCP/IP connections
and pass data back and forth to an RS-232 port.

> The problem is that I can't seem to figure out to let multiple, random
> programs communicate with the single program which allows the above.
>
> I've been looking at several IPC methods (including using a TCP/IP
> connection over 127.0.0.1), but none of them seem to allow for the
> 'listening' part.

You can accept() a TCP/IP connection on a port on which you're
listen()ing, and continue to listen for additional connections.
Be sure to specify a value larger than 1 for the second argument
to listen(), in case multiple connection attempts happen before
you have time to accept them all. Each connection gets a unique
socket handle so you can keep everything separate.

--
/~\ Charlie Gibbs |
\ / <cgibbs@kltpzyxm.invalid> | I used to be indecisive,
X I'm really at ac.dekanfrus | but now I'm not so sure.
/ \ if you read it the right way. |

Charlie,

> If I understand you correctly, I've written several programs
> that perform similar functions, i.e. listen for incoming TCP/IP
> connections and pass data back and forth to an RS-232 port.

Not quite.

The only place TCP/IP has in this is the similarity of the datablocks going
over the eithernet / serial connection, and that I would like to be able to
connect to a serial connection in the same way as WS2_32 / winsock API
allows it for an ethernet one.

IOW, the mentioning of TCP, IP and related is just for comparisions sake.

In a nutshell:

My target is to be able to write (a DLL which would allow) multiple programs
to open multiple connections over a single serial port.

If it where for only a polling read- and write a datablock it would not be
much of a problem. What started to be one is that I would like to be able
to "listen" for incoming serial connections - initiated by programs which
connect to a "gatekeeper" (multiplexer) serial port handler.

Regards,
Rudy Wieser

On Fri, 24 Jun 2022 19:46:04 +0200, R.Wieser wrote:
> Hello all,
>
> For quite some time now I've been looking for a way to have multiple, random
> programs communicate with a single program (which sends/receives data
> to/from an RS232 connection, in a way similar to TCP).
>
> For that I need to be able to open a connection to send/receive data, but
> also be able to listen for incoming connections from the other side (and
> hand them of to whatever program is listening for them).
>
> The problem is that I can't seem to figure out to let multiple, random
> programs communicate with the single program which allows the above.

Is Named Pipe not applicable? It's basically an UDP wrapper/helper, but for
small traffic data.

> I've been looking at several IPC methods (including using a TCP/IP
> connection over 127.0.0.1), but none of them seem to allow for the
> 'listening' part.

TCP only allow specific IP and port to be bound by one listener. UDP doesn't
have this restriction, but unless it's bound to a multicast IP, only one
listener will receive (and hog) data for itself and the rest won't receive
any. Multiple localhost listeners of the same port number, should be bound a
unique local IP address. e.g. 127.0.0.1, 127.0.0.2, ... 127.0.1.1,
127.0.1.2, etc.

> tl;dr:
> I'm looking for a userland method which emulates the inter-process
> communication(?) ws2_32 / winsock uses. If someone knows about a website
> which has information about it or has information otherwise I would be much
> obliged.

Are you trying to avoid using WinSock?

On Sat, 25 Jun 2022 09:16:31 +0200, R.Wieser wrote:
>
> Not quite.
>
> The only place TCP/IP has in this is the similarity of the datablocks going
> over the eithernet / serial connection, and that I would like to be able to
> connect to a serial connection in the same way as WS2_32 / winsock API
> allows it for an ethernet one.
>
> IOW, the mentioning of TCP, IP and related is just for comparisions sake.
>
> In a nutshell:
>
> My target is to be able to write (a DLL which would allow) multiple programs
> to open multiple connections over a single serial port.
>
> If it where for only a polling read- and write a datablock it would not be
> much of a problem. What started to be one is that I would like to be able
> to "listen" for incoming serial connections - initiated by programs which
> connect to a "gatekeeper" (multiplexer) serial port handler.
>
> Regards,
> Rudy Wieser

Isn't that kind of like how PPP work? Something like "TCP/IP over serial
port"? Like how dial-up modem work?

JJ,

> Is Named Pipe not applicable? It's basically an UDP wrapper/helper,
> but for small traffic data.

For straight-forward reading or writing it might be/is. The problem starts
when I need to listen to incoming connection requests (a-la "listen" in
TCP/IP parlance) and have to respond apropriatily.

> TCP only allow specific IP and port to be bound by one listener.

I'm not sure how you came to the conclusion I might be thinking otherwise
....

And two things :

1) My problem is /how/ to create a "listening" method for a serial port
connection and the program which wants to be able to do so.

2) If circumstances dictate it /I just might/ write a multi-casting
listening solution (probably going thru multiple programs listening on the
same port until I find one which will accept the connection). :-)

> Are you trying to avoid using WinSock?

Nope. I'm trying to avoid using ethernet.

Reason ? I've got a number of machines which are behind their own LAN
"modems", effectivily blocking any communication between them (and want to
keep it that way).

Where an ethernet connection is a data highway up for grabs by whatever
"services" (known but especially the unknown ones) might run on either or
both of the Windows machines, a serial connection doesn't suffer from
anything like it.

.... and I could use a simple serial connection on a few DOS machines I still
have (to be able to save/load files and perhaps even sync the time).

Regards,
Rudy Wieser

JJ,

> Isn't that kind of like how PPP work? Something like "TCP/IP over
> serial port"? Like how dial-up modem work?

I think you're looking at the wrong part of the equation there.

AFAIK PPP is just a simple, rather dumb driver which wraps the datablocks it
than puts onto the serial connection and unwraps the received ones - which
it gets or delivers to the TCP/IP stack software. It doesn't do anything in
regard to managing requests toward multiple datastream connections from/to
multiple programs.

My problem isn't the serial connection or how to serialize the datablocks,
but how to allow multiple programs to access it at the same time. I know I
will need a "gate keeper" (multiplexer) program for that.

The whole problem is how to have that "gate keeper" program communicate with
other programs (and vice verse) which want to use the serial connection.

Regards,
Rudy Wieser

On Saturday, June 25, 2022 at 11:00:12 AM UTC+1, R.Wieser wrote:
> JJ,
> > Isn't that kind of like how PPP work? Something like "TCP/IP over
> > serial port"? Like how dial-up modem work?
> I think you're looking at the wrong part of the equation there.
>
> AFAIK PPP is just a simple, rather dumb driver which wraps the datablocks it
> than puts onto the serial connection and unwraps the received ones - which
> it gets or delivers to the TCP/IP stack software. It doesn't do anything in
> regard to managing requests toward multiple datastream connections from/to
> multiple programs.
>
>
> My problem isn't the serial connection or how to serialize the datablocks,
> but how to allow multiple programs to access it at the same time. I know I
> will need a "gate keeper" (multiplexer) program for that.
>
> The whole problem is how to have that "gate keeper" program communicate with
> other programs (and vice verse) which want to use the serial connection.

So is the idea that you have a program X. Other programs can tell X to transmit some data and it does so. Other programs can also ask X to tell them if it receives certain data, and if and when such data turns up you want X to tell the program so?

I think this basic idea is called the "Observer" pattern.

I think you are asking primarily about how the programs actually communicate. I found this https://docs.microsoft.com/en-us/windows/win32/dataxchg/about-dynamic-data-exchange which may be of use (I've never done anything of the sort myself!) Though this page does suggest that you can simply send a message from one program to another, which might do what you want. You just need for the other programs to specify what data they are interested in, and provide a "callback" message for X to send when it turns up.

Hope this is in some way helpful!
Paul.

Paul,

> I think you are asking primarily about how the programs actually
> communicate.

Yep.

> I found this
> https://docs.microsoft.com/en-us/windows/win32/dataxchg/about-dynamic-data-exchange
> which may be of use

I thought the same when I found it, upto the moment I realized that it needs
a messagepump running (read: a window of sorts) to be able to use it.
Although I definitily see that happen for the "server" part, my "client"
parts will, at least for starters, likely be console ones.

> Though this page does suggest that you can simply send a message from
> one program to another, which might do what you want.

Thats another part of the problem : its not a p2p connection, but a "shared
memory" one. Which IIRC could be picked up - and interfered with! - by any
random other program.

> Hope this is in some way helpful!

It is. I had all but forgotten about its existence. :-)

Regards,
Rudy Wieser