Important Procedures for an Internet Access Control Application - Suggested Improvements
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If you are going to use this application in an Internet café with a large number of workstations, say, 500 or more, I would suggest looking into optimizing the code with critical sections and other functions that deal with bottleneck situations. Also, if you are going to use the application in any other setting (other than an Internet cafe), I would suggest that you create a function to check that all connecting clients have a unique name before registering them. This will avoid confusion on the server's part when communicating with clients.
A further improvement that you can make is to create a function to check whether or not a client is still connected, I’ve avoided this because I wanted to keep the communication between the client and the server to a minimum. Also, the server and client are set up in such a way that, if the client disconnects, the server will immediately detect and confirm it on the server interface. The kind of function I’m referring to is known as a "heartbeat" function or "keep-alives" by communication software developers. It includes placing a timer on the client application that sends a periodic message back to the server to indicate that it is still connected and alive. This is only necessary if you anticipate long hours of inactivity between the server and client. Also, for future changes in the communication format I’ve written a parse function that breaks communication down into four parts. It is based on the current parse() function:
function parse4(s : string; var Token1,Token2,Token3,Token4: string) :
boolean;
var
P1,P2,P3 : integer;
begin
P1 := Pos(':',s);
P2 := Pos('@',s);
P3 := Pos(';',s);
//Test if both delimiters are present, in the right order and
//at least 1 char apart
if ((P1 > 0) and (P2 > 0) and (P3 > 0) and (P2 > P1) and (P3 > P2) and (Abs(P3-P2) > 1) and (Abs(P2-P1) > 1))
then begin
Token1 := Copy(s,1,P1-1);
Token2 := Copy(s,P1+1,P2-P1-1);
Token3 := Copy(s,P2+1,P3-P2-1);
Token4 := Copy(s,P3+1,Length(s)-P3);
Result := True; //valid string
end
else Result := False; //invalid string
end;
It is extremely easy to modify this function if you ever need to. What’s more, you do not have to worry about using common delimiters, because all communication takes place internally between the client and server; no user input is required at all in this case. You would have to worry about delimiters if you want to use the server application as a chat server; then of course you cannot use common delimiters, because users will use common delimiters like “@” if they are sending an email address to someone else on a chat. My current communication protocol would crash if that were to happen.
Conclusion
The next article in the series will deal with the last remaining section of the server application, which is user management. This module will enable the server administrator to add, remove or to view user information.
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