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Bob
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 Posted: Sun Feb 29, 2004 5:00 am Post subject: Help with Function Conversion, Win32 -> CGI |
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I'm a longtime Delphi (desktop) developer and now need to create my first
web server app. I've got to convert a very intense calculation function that
is in a unit of a desktop app, about 9,000 lines of code, into web server
app. The function doesn't access a database and I'm going for max
compatibility so I think my target app is CGI.
The app itself is real simple (even though its big). It has about 200
arguments which it pulls from INI files, if I can't work with INI's in CGI I
could take from an HTML file, load it into a TStringList and parse out my
args. Then I do a bunch of calcs... hopefully I can use Delphi's Math unit
in a CGI app? Then the app produces an HTML file. Currently the app builds
the HTML file in a TStringList then just uses StringList1.SaveToFile() with
an HTML extension. Thats it.
Here are a couple questions I have:
- How do I pass the name and location of the file containing the args,
like this:
www.myserver.com/calc.exe/?args=www.clientserver.com/calcargs.html
- if so how do I retrieve the the file name within the app... is there a
function that returns the URL used to call the app?
- How do I return the name and location of the file containing the results
back to the client?
Thanks in advance...
-Bob
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Ben Hochstrasser
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| Posted: Sun Feb 29, 2004 10:32 am Post subject: Re: Help with Function Conversion, Win32 -> CGI |
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Bob wrote:
The environment variable "SCRIPT_NAME" contains the name of the .exe.
The environment variable "QUERY_STRING" contains "args=www.client......"
| Quote: | - if so how do I retrieve the the file name within the app... is
there a
function that returns the URL used to call the app?
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HTTP_HOST contains "www.myserver.com"; So the complete URI would be
%HTTP_HOST%%SCRIPT_NAME%?%QUERY_STRING%
| Quote: | - How do I return the name and location of the file containing the
results
back to the client?
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You simply write them to stdout:
writeln("Content-type: text/html");
writeln; // important - empty lines after the header
writeln(myStringList.Text);
cgi applications are console applications; below is a very very simple
example:
program cgitest;
{$APPTYPE CONSOLE}
uses Windows;
{$R *.RES}
function GetEnv(EnvString: String): String;
var
EnvVar: Array[0..255] of Char;
n: integer;
begin
n := GetEnvironmentVariable(PChar(EnvString), @EnvVar, SizeOf(EnvVar));
if n > 0 then
Result := Copy(EnvVar, 0, n)
else
Result := '(not set)';
end;
procedure PrintVar(Varname: string);
begin
writeln('<tr><td>',VarName,'</td><td>',GetEnv(VarName),'</td></tr>');
end;
begin
writeln('Content-type: text/html');
writeln;
writeln('<http><head><title>CGI Test</title></head>');
writeln('<body><h1>CGI Test</h1>');
writeln('<table border=1>');
writeln('<tr><th>Variable</th><th>Contents</th></tr>');
PrintVar('PATH_INFO');
PrintVar('PATH_TRANSLATED');
PrintVar('REMOTE_HOST');
PrintVar('REMOTE_ADDR');
PrintVar('GATEWAY_INTERFACE');
PrintVar('SCRIPT_NAME');
PrintVar('SCRIPT_FILENAME');
PrintVar('REQUEST_METHOD');
PrintVar('HTTP_ACCEPT');
PrintVar('HTTP_ACCEPT_CHARSET');
PrintVar('HTTP_ACCEPT_ENCODING');
PrintVar('HTTP_ACCEPT_LANGUAGE');
PrintVar('HTTP_FROM');
PrintVar('HTTP_HOST');
PrintVar('HTTP_REFERER');
PrintVar('HTTP_USER_AGENT');
PrintVar('QUERY_STRING');
PrintVar('SERVER_SOFTWARE');
PrintVar('SERVER_NAME');
PrintVar('SERVER_PROTOCOL');
PrintVar('SERVER_PORT');
PrintVar('CONTENT_TYPE');
PrintVar('CONTENT_LENGTH');
PrintVar('USER_NAME');
PrintVar('USER_PASSWORD');
PrintVar('AUTH_TYPE');
writeln('</table></body></html>');
end.
--
Ben
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Bob
Guest
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| Posted: Sun Feb 29, 2004 5:19 pm Post subject: Re: Help with Function Conversion, Win32 -> CGI |
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| Quote: | You simply write them to stdout:
writeln("Content-type: text/html");
writeln; // important - empty lines after the header
writeln(myStringList.Text);
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So, if I have the headers (with empty lines after) in the string list I only
need to do
writeln(myStringList.Text); ?
How does the client know the CGI app is done? In your example you writing
writeln's until you end with
writeln('</table></body></html>');
Does this tell the client your done or does it not matter?
Thanks, -Bob
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Ben Hochstrasser
Guest
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| Posted: Sun Feb 29, 2004 7:29 pm Post subject: Re: Help with Function Conversion, Win32 -> CGI |
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Bob wrote:
| Quote: | So, if I have the headers (with empty lines after) in the string list
I only need to do
writeln(myStringList.Text); ?
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Yes.
| Quote: | How does the client know the CGI app is done? In your example you
writing writeln's until you end with
writeln('</table></body></html>');
Does this tell the client your done or does it not matter?
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The client doesn't know - the server who is running your cgi via
CreateProcess() (or the unix equivalent) knows when the cgi ended. Then
it will [usually] close the connection. At which point the client has no
alternative (this is the case when you have eg "Content-type:
text/plain")
It is considered good practice, however, to put a
"Content-Length: 12345" in the cgi header, so the client has a vague idea
how much data will be coming. For the sake of simplicity I skipped that
one. So, to be complete, you'd have to say:
writeln('Content-type: text/html');
writeln('Content-length: ', Length(myStringList.Text));
writeln;
writeln(myStringList.Text);
Note that for static pages the http server supplies a suitable header. A
cgi must do that itself - the server will just execute the cgi and
redirect its output to the client.
I recommend you to bookmark http://www.htmlhelp.com/faq/cgifaq.html
unless you want to skim through a whole lot of RFCs.
There's only two or three things that are important:
- cgi applets are console applications as they employ stdin and stdout
- cgi applets gather information from the hosting server's environment
variables
- cgi applets better don't crash. Be sure to use try...except clauses so
that at least the header plus some error messages are generated.
- cgi applets better be small. If you expect a lot of concurrent users,
move stuff into a common dll. (Ideally the cgi.exe is only a stub which
parses the arguments and then calls the dll)
Oops, that's four things already ;-)
--
Ben
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Bob
Guest
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| Posted: Mon Mar 01, 2004 4:05 pm Post subject: Re: Help with Function Conversion, Win32 -> CGI |
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| Quote: | There's only two or three things that are important:
- cgi applets are console applications as they employ stdin and stdout
- cgi applets gather information from the hosting server's environment
variables
- cgi applets better don't crash. Be sure to use try...except clauses so
that at least the header plus some error messages are generated.
- cgi applets better be small. If you expect a lot of concurrent users,
move stuff into a common dll. (Ideally the cgi.exe is only a stub which
parses the arguments and then calls the dll)
Oops, that's four things already ;-)
--
Ben
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(you got me on the 4th one)
What is too big? This is a really big calculation, maybe a 1MB compiled.
What kind of DLL do I create? Just a regular DLL or a ISAPI DLL?
Seems creating two processes would take longer, use more resources?
Thanks, -Bob
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Ben Hochstrasser
Guest
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| Posted: Mon Mar 01, 2004 4:37 pm Post subject: Re: Help with Function Conversion, Win32 -> CGI |
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Bob wrote:
| Quote: | (you got me on the 4th one)
What is too big? This is a really big calculation, maybe a 1MB
compiled.
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well, if you have 20 concurrent uses you'd need 20..80 MB RAM (depends
how these applications behave memory-wise).
| Quote: | What kind of DLL do I create? Just a regular DLL or a ISAPI DLL?
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It would be just a standard DLL, because the cgi is a plain old console
application. ISAPI DLLs have the same use - load once, use multiple; but
they're loaded by the web server, not a cgi process (thus modifying an
ISAPI DLL [usually] means to stop the server, update the ISAPI DLL,
restart the server...)
| Quote: | Seems creating two processes would take longer, use more resources?
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Well, ideally the .cgi alone could be loaded off the disk cache. The dll
would have to be loaded only the first time and would remain in memory
until the last instance of your cgi unloaded it. (You may start a dummy
process just to ensure the dll remains loaed...)
So - go ahead and try w/o creating a dll. If your system load exceeds
some healthy maximum over extended periods of time consider splitting
off a dll.
--
Ben
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