Before diving into writing plugins, I'm going to spend this column giving your a brief overview of how NPDS is constructed. This will help you if you decide to download the source code and modify it or hack around in it.
NPDS is based around nHTTPd 2.02 which is both a server and an enviroment for turning Newton data into HTML. nHTTPd itself does the grunt work of serving off the Newton while its component plugins do the high-level stuff. So how does it all work? Let's walk through installation, registration, activation, and access of a data plugin, specifically, NoteServ.
Noteserv is an application but it allows little user interaction beyond setting its preferences. When it's installed onto a Newton with nHTTPd present, it registers itself with the Plugin Registry and denotes itself as active or inactive. When nHTTPd is opened, it sends an Activate() message to all plugins that are listed as active in the registry. In response, the plugins register their name, application symbol, virttual folder (/html/, /dates/, etc) and a small completion script that accepts a communications endpoint plus the current HTTP request and passes it to the plugin app for processing. At the time nHTTPd is actually Started, it sends another message to each registered plugin "StartupScript()" that tells them that the server is going online. This allows them to do any pre-processing they need to before requests are accepted via HTTP.
Let's move now to what happens when a request is received by nHTTPd: it parses the request and breaks it into a frame with slots for the virtual folder, the requested filename, the raw request, and any form data that's been submitted. This data is passed, along with a reference to the current communications endpoint, to the CompletionScript for the plugin that's registered to handle requests for the given virtual folder. Inside the CompletionScript, the request is submitted to the plugin application and the results are output into the communications endpoint. So, you can see that what we have is two servers for each transaction.. the HTTP server and a data translation server.
However, much of the work of translating can actually be done by nHTTPd. When a file is created, for instance, the current plugin requests that nHTTPd create an HTML template into which the body of the file will be placed. Other functions, such as the Hyperlinker and Percent-Escape translator are also handled by nHTTPd. The CGI system is handled by nHTTPd as are all the server side includes.
You'll learn more about the built-in abilities of nHTTPd as we write the Calls plugin but for now, I suggest that you learn NPDS Scripting as a precursor to more heavy-duty programming that we'll embark upon next time.