Title: Developing Webserver-Applications with Delphi - PART I
Question: What is a Webserver-App and how can I develop it with Delphi?
Answer:
Release 1 last update: [26.05.2000]
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Developing Webserver-Applications in Delphi
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PART I: CGI and ISAPI-Applications
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- Introduction
I wrote this article to show you the advantages of CGI and
ISAPI, and to show you how easy it is to write such
applications with Delphi.
- About Web-Server-Applications
Webserver-Applications are EXE or DLL-Files which are stored
on a HTTP-Webserver and can be executed by client-requests.
The client can request informations from the Webserver, and
the Webserver-Application can respond on this informations by
giving a MIME-formatted result to the client. This MIME-content
can be defined by any known content-type like "text/plain" for
a standard-text output, "text/html" for a html-content or
"image/gif" for a GIF-image. For example you want execute
the Web-Application output.exe stored on the remote-machine
test.com. This Web-Application give us an GIF-image which
is provided by the server, the output is in the image/gif
format. The file we want to get is given in the first
parameter of the request. To get the image test.gif from the
server, we enter this in our web-browser:
http://test.com/cgi-bin/output.exe/SHOWIMAGE?test.gif
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Description of the different sections in this address:
1. The machine use a Webserver with the HTTP-Protocol
(basis for CGI/ISAPI)
2. Host or IP from the Webserver
3. CGI-Directory which stores the file output.exe
4. Our CGI-Webserver-Application
5. Command for the Webserver-Application
6. First parameter for the application separated through "?"
- About CGI/ISAPI
The technology behind these Webserver-Application are called
CGI or ISAPI. CGI is the classic Webserver-App with the
EXE-extention, and ISAPI is the newer one with the DLL-
extention. Both of have the same functions. There is also
a technology called Win-CGI which works a little differently
than the other technologys, but this is unrelevant when
developing such apps with Delphi.
- Comparing CGI/ISAPI
A CGI Webserver-Application is an standard Windows console
application. Each request message is handled by a seperate
instance of the app. A ISAPI-Application is a DLL-file that
is loaded by the Webserver. The only relevant difference
between the CGI-App is that each request message is handled
on a seperate execution thread by one and the same instance
of the ISAPI-DLL.
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End of this part