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Documented preliminary CGI applet.
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Jack Jansen
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<HTML><HEAD><TITLE>Using python to create CGI scripts</TITLE></HEAD>
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<BODY>
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<H1>Using python to create CGI scripts</H1>
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<HR>
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In this document we will (eventually) explain how to create Python CGI scripts
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for use with NetPresenz and probably other Mac-based HTTP servers too.
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Since CGI scripts are AppleEvent servers on the mac we will also learn
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a little about general AppleEvent server programming and about applet
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debugging. <p>
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<blockquote>Note that the current setup is very preliminary, and hence
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itis probably not wise to base your strategic products on the information
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in this document:-) In stead, play with the code here and join the
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<a href="mailto:pythonmac-sig-request@python.org">pythonmac-sig</a>, where
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we I would like to have a discussion on a real design for a Mac CGI framework
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(preferrably something that will make CGI scripts portable to unix and other
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platforms).
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</blockquote>
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<h2>AppleEvent servers</h2>
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Since AppleEvent clients are easier to write and understand than servers
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you should probably read the section on <a href="applescript.html">Open Scripting
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clients in Python</a> first. <p>
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Next, let us have a look at the AE Server framework,
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<a href="../Lib/toolbox/MiniAEFrame.py">MiniAEFrame.py</a>.
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This file contains two classes, <code>MiniApplication</code> and <code>AEServer</code>.
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MiniApplication is a tiny replacement for <code>FrameWork.Application</code>,
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suitable if your application does not need windows and such.
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<blockquote>Actually, Framework.Application has a problem for AE Servers,
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due to the way it expects to be quit through an exception, and raising an exception
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while inside an Apple Event handler is a very bad idea. This will be fixed.
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</blockquote>
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AEServer is a bit of glue that does part of the appleevent decoding for you. You
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call <code>installaehandler</code> passing it the class and id (4-char strings)
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of the event you have a handler for and the handler callback routine. When the
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appleevent occurs your callback is called with the right arguments. For now,
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your argument names are the 4-char values used internally by Open Scripting,
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eventually there will be a translation similar to what the generated OSA client
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suites provide. <p>
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You can test AEServer by double-clicking it. It will react to the standard
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run/open/print/quit OSA commands. If it is running as a normal python script and you
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drag a file onto the interpreter the script will tell you what event is got. <p>
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<h2>A Minimal CGI script</h2>
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To try a CGI script you will first need a http server. I have used the
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shareware
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<a href="http://www.share.com/peterlewis/netpresenz/netpresenz.html">NetPresenz</a>
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by <a href="http://www.share.com/peterlewis/">Peter Lewis</a>
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(don't forget to pay if you give it more than a test run!). Install your
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http server, and make sure that it can serve textual documents. <p>
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Next, let us have a look at our example CGI scripts. CGI scripts have to be
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applications, so we will have to make an applet as explained in
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<a href="example2.html">example 2</a>. Our applet code,
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<a href="cgi/cgitest.cgi.py">cgitest.cgi.py</a> is a rather minimal <code>execfile</code>
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statement. The reason for this is debugging: the real code is in
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<a href="cgi/realcgitest.py">realcgitest.py</a>, and this way you do not have
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to run mkapplet again every time you change the code. Rename realcgitest.py
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to cgitest.cgi.py once you are satisfied that it works. <p>
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The resource file is not very special, with one exception: since we want to do
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our own appleevent handling we don't want the Python initialization code to
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create argc and argv for use, since this might gobble up any appleevents we are
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interested in. For this reason we have included a 'Popt' resource that disables
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the argv initialization. An easy way to create this resource is to drop
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the <code>.rsrc</code> file (or the finished applet, if you like) onto
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<code>EditPythonPrefs</code> and set the "no argv processing" option. <p>
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The code itself is actually not too complicated either. We install handlers
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for "open application" and "quit" (stolen from the test code in MiniAEFrame)
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and the <code>"WWW\275"/"sdoc"</code> event, the event sent on CGI execution.
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The cgi handler pretty-prints the CGI arguments in HTML and returns the whole
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string that is to be passed to the client. The actual parameters passed
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are explained in <a href="http://www.biap.com/datapig/mrwheat/cgi_params.html">
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http://www.biap.com/datapig/mrwheat/cgi_params.html</a>. <p>
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To test the script drop <code>cgitest.cgi.py</code> onto <code>mkapplet</code>,
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move the resulting <code>cgitest.cgi</code> to somewhere where it is reachable
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by NetPresenz, and point your web browser towards it.
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