standalones interacting over the web

[Alex Tweedly]

Hi Nick. I've gone back to your original question. The "right" way to do 
this undoubtedly involves sockets, which in turn requires a private web 
server (or very permissive web hosting company), so isn't readily 
available to most of us.

But there is a way to do it using only simple ordinary Web server and 
client features. I've done it as a proof of concept using on-rev, but 
the server part of it is *so* simple I could probably do it in php if I 
had to.

Theory (simple web-based chat application)

Client

The client (which can be found at 
http://www.tweedly.org/async_web_chat_released.rev ) uses "load url" to 
request the latest update from the chat server. If it times out, it 
simply tries again :-0  If it receives data, it appends that data to the 
scrolling text window, and repeats forever (or until stopped).

The client can also "say" something to the server.

Server (is even more simple - see the text of the scripts below)

saysomething.irev
takes a single parameter (i.e.  tweedly.org/saysomething.irev?say=the 
text ) and appends this to a file (called, imaginatively, my.txt)

listen.irev
takes a single parameter (i.e. tweedly.org/listen.irev?lastline=23 )  
which is the last line of the file which that client has already 
received. It then checks if the file has grown longer - in which case it 
sends the additional lines to the client. Otherwise, it waits for 100 
msec, and then tries again.

Eventually, if there is no new data, the client will time out - then it 
does an "unload url" to cancel the request, and tries again.

The nice thing is you can test and debug this with a browser - try
  www.tweedly.org/listen.irev?lastline=1
  http://www.tweedly.org/saysomething.irev?say=ALEX:says%20this
  www.tweedly.org/listen.irev?lastline=1

saysomething.irev
> <?rev
>
> set the errormode to inline
>
> put $_GET["say"] into tSay
>
> open file "my.txt" for text append
> put  "open result = " & the result
> write tSay & CR to file "my.txt"
>
> put URL("file:my.txt") into t
> put the number of lines in t
> ?>
listen.irev
> <?rev
>
> put $_GET["lastline"] into tLast
>
>
> repeat with i = 1 to 100
>   put URL ("file:my.txt") into tData
>   if the number of lines in tData > tLast then
>     delete line 1 to tLast in tData
>     put tData
>     exit repeat
>   end if
>   wait for 100 millisec
>   put empty into tData
> end repeat
> if tData is empty then
>     put "no new data"
> end if
> ?>
NOTE - I do not recommedn this if you intend to scle in any way, but for 
small number of users, with small data rates this should be just fine.

-- Alex.


Nicolas Cueto wrote:
> Where in the Rev documentation (or sample stacks?) should I be looking to
> learn how to do the following?
>
> Given 6 identical standalones running of 6 computers all internet connected,
> I want an event X triggered on any one of those computers to be immediately
> relayed to the other 5 computers.
>
> An example of what I'm planning is a multiple-choice quiz. As soon as the
> contestant on computer A buzzes in, her choice should display immediately on
> the other contestants' computers B thru F.
>
> My guess is that to enable stacks to "wait", sockets will be involved.
>
> I'm also guessing that these are the three Rev elements (one local, two
> server-side) I'll nee for this multi-player multiple-choice quiz standalone:
>
> 1) the stack itself
>
> 2) a Rev cgi-script to co-ordinate the interaction between standalones
>
> 3) an SQL table to store or temporarily hold game-related variables
>
> Thank you.
>
> --
> Nicolas Cueto
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