Responding to Client-Side Data

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One of the greatest things about scripting, in general, is the new level interactivity it engenders. If you've ever visited a web site where you filled out a form, navigated using a pop-up menu, or were served content based on your browser, you've benefited from scripting. The NPDS scripting system doesn't allow much in the way of actual interaction (YET) but it does have access to several parameters that tell you a bit about who the person is on the other end of the connection.

In implementing SSA, I have made an effort to maintain syntax and variable names that are consistent with other platforms' scripting implementations. This will help users who come to us from other languages (ie Perl) as well as make applicable to NPDS scripting some of the literature on the web that pertains to CGIs.

Environment and Request Variables

Being a evolving subset of the Common Gateway Interface, NPDS SSA provides the scripter with the following run-time CGI variables. (Bold Values are literals, others are dynamic values).

Variable

String Returned

SERVER_SOFTWARE

nHTTPd/2.02 (Newton)

SERVER_NAME

IP Address of Server

SERVER_PROTOCOL

HTTP/1.0

GATEWAY_INTERFACE

CGI/1.0 (NPDS_SSA)

SERVER_PORT

Current Server Port

REMOTE_ADDR

Client IP Address

REMOTE_HOST

Client DNS (If Resolved)

HTTP_USER_AGENT

Client Browser

SCRIPT_NAME

Title of Current Script

Some of these are pretty useless for now but will not be in the future ;-) Note, however, what you DO have access to from your SSI scripts that you can exploit readily.. Client IP Address (DNS as well if it's already been determined) and Client Browser. Can you think of a situation where these might be of use?

Let's go all out here and write an SSI that will show the notes posted via the web but only if the user is coming from within a specific LAN. Furthermore, let's return this listing in two different formats, table and list, depending on the browser/platform. Of course, visitors from outside the LAN are given a polite error message.. How's that for a "Simple" Script ? Getting pretty powerful here, eh?

Background

IP Testing with CheckIP()

How do we check to see that an IP is within range? Luckily for you, NPDS has a built-in IP checker method called CheckIP(). To see if the IP "128.174.5.58" is within the range "128.174.4.255" to "128.174.5.255" you would use CheckIP() like so:

|NPDS|:CheckIP("128.174.5.58", ["128.174.4.255", "128.174.5.255"])

Using CGI Variables

The variables returned by the tokens such as SERVER_NAME, etc. are all simple string values. You treat them exactly like they were strings.

Example:

If the Remote Address of the Client was "127.0.0.1" then theAddr:= "REMOTE_ADDR" would evaluate to theAddr:= "127.0.0.1".

Using NoteServ's ReturnNoteList() Method

The NoteServ Server Side Includes for displaying HTML-formatted lists of Notes are implemented using a common (and still under development) Method, ReturnNoteList.

In order to return a list of posted notes, you write:

|NoteServ|:ReturnNoteList({order: 'ascending, criteria: 'timestamp}, '|pHTML:MAVON|, 'list)

While a table of the same notes is created by:

|NoteServ|:ReturnNoteList({order: 'ascending, criteria: 'timestamp}, '|pHTML:MAVON|, 'table)

Restricted Access Script

Name: Restricted List

SSI: COOL_LIST

func(nullvar)

begin

//define the beginning and end of your LAN here

local lanstart:= "130.126.49.1";

local lanend:= "130.126.49.255";

//check the IP against a range

if |NPDS|:CheckIP("REMOTE_ADDR", [lanstart, lanend]) then

begin

//Mozilla and compatibles get a Table view and others get a list.

if StrPos("HTTP_USER_AGENT", "Mozilla", 0) > 0 then

//return a table view

return |NoteServ|:ReturnNoteList({order: 'ascending, criteria: 'timestamp}, '|pHTML:MAVON|, 'table);

else

//return a list view

return |NoteServ|:ReturnNoteList({order: 'ascending, criteria: 'timestamp}, '|pHTML:MAVON|, 'list);

end;

else

return "<STRONG>Sorry! Access to this discussion board is limited to my local network.</STRONG>";

end

It's pretty much that easy. Note the syntax of the nested if..then..else statements1 as well as the use of the StrPos()2 method to search for a substring within the user agent field. Finally, make sure to notice the use of the |NoteServ| compiler variable to save us from having to type the full reference to NotePad server GetRoot().|pHTML:MAVON|

References

1. NPL: 3-1 to 3-3
2. NPR: 23-26

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