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Building a Customizable Server-Side Cached Scrolling XML Newsfeed Display

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At EggheadCafe.com, we have resources that are added on a daily basis – both by member visitors and by the staff. These resources are searchable and are broken down by categories such as Hotlinks, Articles, Tips & Tricks, etc. Each evening , we have a script that’s kicked off by the NT Scheduler service at a time when traffic is normally low, that scours our resource database for the most recent items in each category.

It then assembles an 100% HTML include page and caches it on the server’s filesystem. This file is picked up as an ASP include when you view our home page at http://www.eggheadcafe.com. That block you see in the middle of the page with the blue section heading graphics and lists of links comes from this HTML Include file. This is an excellent low-bandwidth way to generate dynamic content that’s fresh daily and keep your server resource usage to a minimum.

Some time ago I had engineered a couple of client – side functions that zoom out to Moreover.com, grab the XML for specific newsfeed categories that are of interest to the developer – type of community that is our primary visitor, and applies an XSLT transform to render this as a scrolling news marquee. I thought, wouldn’t it be cool if we could have some of our own custom newsfeed links to our own featured resources that we could COMBINE with the Moreover feed, and have all of it in a scrolling marquee. For example, Robbe recently released his TurnkeyTools.com service, and wanted to have a way to “feature it” in an unobtrusive way for a period of time.

I went through some development “learning exercises” that revolve around the difficulties involved in loading Moreover’s custom feed XML which has a DTD declaration and an ISO-8859 content-encoding declaration, neither of which the MSXML parser was particularly fond of if you were attempting to do your stuff on the server side, load a second file and do a transform. When I say “not particularly fond of”, what I mean is that simply, if you tried to load this either with XXMLHTTP or with MSXML.DOMDocument “Load” method, the parser just PUKED. (And frankly, Microsoft, the error messages weren’t very helpful either).

Not to be daunted, I eventually came up with an overall solution that’s not only much more elegant and extensible, but conforms better to our philosophy of conserving server resources by caching data that may change, but needs to be served up continuously – and FAST.

In a nutshell, what I did was create two VBScript ASP functions for a new file that is now included in our original scheduled script to create the content page I described above, but the script SAVES the xml file from Moreover AND the 100% HTML result of the XSLT Transform to create the scrolling news marquee, all to the filesystem. So it’s now all part of that same HTML include file — the CPU is not tied up doing XML Loads and XSL Transformations every time the page is requested by a new visitor. And we still get fresh new content every single day. On top of that, I created a SECOND XML file with a schema similar to the feed from Moreover that contains the custom Eggheadcafe.com items that we want to display, and MERGED that with the Moreover XML using DOM methods before applying the transform to create the final HTML. The result? An easy-to-use, server – friendly and extensible method to create custom dynamic newsfeed displays containing both outside and proprietary customized content. Flexibility, code re-use, portability, and speed all wrapped up in one concept.

Let’s take a look at the script and see how this was done:

<%
function GetMoreoverXML(byVal sCategory)
Dim sChoice, sSource, sDest, oHTTP, body8209,sOut,oTS,oFSO,i
if sCategory = "" then sCategory="topinternet"
sSource= "http://p.moreover.com/cgi-local/page?index_" & sCategory

&"+xml"
sDest = Application("FileRoot") & "moreover.xml"
set oHTTP = Server.CreateObject("Microsoft.XMLHTTP")
set oFSO = Server.CreateObject("Scripting.FileSystemObject")
oHTTP.open "GET", sSource, False
oHTTP.send
body8209 = oHTTP.responseBody
set oHTTP = nothing
sOut = ""
For i = 0 to UBound(body8209)
sOut = sOut & chrw(ascw(chr(ascb(midb(body8209,i+1,1)))))
Next
sOut = Replace (sOut,
"encoding=""iso-8859-1""", "")
sOut = Replace(sOut, "<!DOCTYPE moreovernews SYSTEM ""http://p.moreover.com/xml_dtds/
moreovernews.dtd"">", "")
set oTS = oFSO.CreateTextFile(sDest, True)
oTS.Write sOut
oTS.Close
set oTS = Nothing
set oFSO = Nothing
GetMoreoverXML =true
End Function
Function showNews()
on error resume next
Dim xmlDoc
Dim xmlDoc2
Dim xsl
Dim sChoice
Dim tempNodes
Dim docFragment
Set xmlDoc2=Server.createObject
("MSXML2.DOMDocument.3.0")
xmlDoc2.Async=False
xmlDoc2.PreserveWhitespace=false
XmlDoc2.validateOnParse =False
Set xmlDoc = Server.createObject
("MSXML2.DOMDocument.3.0")
xmlDoc.Async=False
xmlDoc2.Load Application("Fileroot") &"moreover.xml"
xmlDoc.Load Application("Fileroot") &"article.xml"
set tempNodes = xmlDoc2.selectNodes("//article")
for i = 0 to tempNodes.length -1
set docFragment = xmlDoc.createDocumentFragment
docFragment.appendChild(
xmlDoc.createElement("article"))
set docFragment = tempNodes(i)
xmlDoc.documentElement.
appendChild(docFragment)
next
set xsl =Server.CreateObject
("MSXML2.DOMDocument.3.0")
xsl.async = false
xsl.load Application("fileroot") &"business2.xsl"
showNews= xmlDoc.transformNode(xsl)
err.clear
sMarqy= "<TABLE CELLSPACING=0
CELLPADDING=0 BORDERCOLOR=#858BFD BORDER=0 ALIGN=CENTER
WIDTH=550 class=contentPurple>"
sMarqy=sMarqy & "<TR>
<TD ALIGN=CENTER><IMG SRC=/images/newheadlines.jpg border=0></TD>
</TR><tr><td><br></td></tr>" & vbcrlf
sMarqy=sMarqy & "<TR><TD align=left>"
sMarqy=sMarqy & " <MARQUEE BGCOLOR=#FFFFFF BORDERCOLOR=#858BFD BEHAVIOR=SCROLL

DATAFORMATAS=HTML DIRECTION=UP
HEIGHT=80 ID=News SCROLLAMOUNT=1
SCROLLDELAY=100
TITLE=Headlines WIDTH=536 HSPACE=0>" &
showNews & "</marquee>"
sMarqy=sMarqy & "</TD></TR></TABLE>"
showNews =sMarqy
end function
%>

The above were causing the parser to choke on load, so rather than going through the newsgroups and docs looking for a possible fix, I reasoned that since they were not required for my purposes, and since we are saving this stuff to the filesystem anyway, let’s just strip them out before we save it, hence the following code:

sOut = Replace (sOut, "encoding=""iso-8859-1""",
"")
sOut = Replace(sOut, "<!DOCTYPE
moreovernews SYSTEM
""http://p.moreover.com/xml_dtds/
moreovernews.dtd"">","")

You’ll also note I have the following code:

For i = 0 to UBound(body8209)
sOut = sOut & chrw(ascw(chr
(ascb(midb(body8209,i+1,1)))))
Next

Why do we do this? Well, the responseBody Property of the XMLHTTP object returns the result as array of unsigned bytes, namely a SAFEARRAY of type VT_ARRAY | VT_UI1. This contains the raw undecoded bytes , and we need to decode it in order to be able to write the results to the filesystem as text. Reading from the inside of the function out, the midb function is used with byte data in a string. Instead of specifying the number of characters, the arguments specify numbers of bytes. So we are getting the Unicode (wide) character value of the Unicode character code of the character represented by the next byte in the string., and adding it to the result string until we are done with our loop through the byte array.

Then we SAVE our Morover XML file to the filesystem In the second function, we do the loads, the merge and the transform.. The merging of the <article> nodes is done as follows:

set tempNodes = xmlDoc2.selectNodes(“//article”)
for i = 0 to tempNodes.length -1
set docFragment = xmlDoc.createDocumentFragment
docFragment.appendChild( xmlDoc.createElement(“article”))
set docFragment = tempNodes(i)
xmlDoc.documentElement.
appendChild(docFragment)
next

We use the createDocumentFragment method of the DOM, appendChild to append the <article> element created with createElement, and we loop through the number of nodes in the "articles.xml" custom document until we’ve added them all. We now have a single XML Document object containing not only the Moreover news items, but our own custom items as well. We apply the transform with the XSL stylesheet, surround it with the desired HTML to create the MARQUEE control, and return the whole shebang from our function as a string, ready to incorporate into the calling script to be merged inline with the larger HTML document and SAVED to the filesytem to be ready to be included in any ASP page using the normal
ASP
<!–#include file= directive.

You can take the first block of code above (surrounded by <% script tags) and pretty much use it as is for the basis of most any such file caching system. The article.xml "Custom" XML file is pretty much a clone of the Moreover XML, except we leave out the unncecessary tags:

<moreovernews>
<article>
<url>http://www.turnkeytools.com/
eggheadbeta.asp</url>
<headline_text>TurnkeyTools: Polls Beta Released</headline_text>
<document_url>http://www.turnkeytools.com/
eggheadbeta.asp</document_url>
<harvest_time>May 12 2001 9:38PM
</harvest_time>
</article>
<article>
<url>http://www.eggheadcafe.com/
articles/20010510.asp</url>
<headline_text>EggheadCafe: Posting Form Data with
XMLHTTP</headline_text>
<document_url>http://www.eggheadcafe.com
/articles/20010510.asp</document_url>
<harvest_time>May 12 2001 9:39PM
</harvest_time>
</article>
</moreovernews>

So there you have it. An extensible, scalable way to construct custom content display on a scheduled basis and cache it on the filesystem.

Dr. Peter Bromberg is a Senior Programmer/Analyst at Fiserv, Inc. in Orlando and a co-developer of the http://EggheadCafe.com developer
website.

Building a Customizable Server-Side Cached Scrolling XML Newsfeed Display
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