server push to desktop client

[Kee Nethery]

Normal data flow is Mac app contacts a central server and sees if there is updated data to acquire. If yes, it acquires it.

This is the normal flow because of firewalls and ports.

For the server to really push data to a Mac client, the Mac client has to be a server, with a routable IP address / port. Most client machines are behind firewalls that allow them to initiate contact, but do not allow random external machines to contact them.

So the normal setup is, server has a dns entry on an IP address that anyone can reach from anywhere on the Internet. Server is listening on a single port for incoming connections.

Assuming the same data (updates) goes to each client, server has a text page containing a single integer. That integer is the number of the latest update. Client hits that web page periodically to see if its internal integer is different from the server. It’s a very quick exchange.

Client sees their internal integer isn’t the same. Let’s say client has 92 and server has 103.

Client then hits pages 93 to 103 to get all the updates. For example:

http://my.server.com/updates/93.txt
All the way to:
http://my.server.com/updates/103.txt

On the server side, you create update pages and increment the integer at something like:

http://my.server.com/updates/last.txt

The server is fast because it serves up static pages and the fastest page is last.txt because it’s only (in this example) three characters “103”.

I’m assuming all clients get the same data.

When each client gets unique data, you’ll probably have a database on the server and clients will do hits against the server to see if they have new data to gather, and if yes, they’ll do their query with their userid to gather their data.

 The trade off between server text pages and server database responses is one of those things you’ll need to figure out which is most efficient for you. Could be you ship a client that can do both and the very first hit to the server is a static page that tells the client “text” or “database” and then the client does the right thing. Could periodically check that page and perhaps you have a flag on it like “database always” that tells the client to stop checking, all updates forever will be the database update process.

But ... client pulls from the server because most servers cannot push through firewalls and routers an NAT servers to initiate first contact with a client.

Kee Nethery

> On Nov 4, 2019, at 11:26 PM, Phil Davis via use-livecode <use-livecode at lists.runrev.com> wrote:
> 
> I need to make a desktop app (Mac only for now) that receives pushed data from a LC server. I've never done this - all the desktop <-> server interactions I've programmed have used the traditional client-server model. So I'm looking for approaches/tips/ideas from anyone who has experience with other approaches.
> 
> I'm not sure what protocol to use.
> 
> And maybe I'm making it too hard. Can FTP watch a server folder, and detect and respond to the creation of a file in the folder? Maybe I could use a method like that, if that's a capability of FTP.
> 
> Thanks for any input you may offer.
> 
> -- 
> Phil Davis
> 503-307-4363
> 
> 
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