Friday, June 20, 2008

KnowledgeTree document download via Google Gadget

This is an installment feature for the KT-Gadget, a widget for KnowledgeTree, an open-source document management system.

As mentioned in the previous post, I employed an application proxy to act as a bridge between a Google Gadget and KnowledgeTree's SOAP services. Originally, the application proxy responses were formatted in XML. Moving forward, I decided to adopt the JSON format instead of XML owing to simpler methods in handling JSON feeds from both PHP and (of course) Javascript worlds.

The application proxy's SOAP client is based on PHP and converting an associative array of response items to JSON format is implemented simply by using PHP's json_encode function. At the gadget side, the requests for remote data are invoked using Google's _IG_FetchContent function. Using Javascript's eval() function, the returned JSON text response is converted to an object whose members can be easily accessed using dot or subscript operators.

Here are the details.. To download a document, KT-Gadget sends a request to the helper application by invoking the url:

The JSON response by the application proxy is of the form:

The relevant block of KT-Gadget code is reproduced hereunder:

var url = "" + sessionID__MODULE_ID__ + "&fid=6";
_IG_FetchContent(url, function (jsonFeed) {
var jsonData = eval('(' + jsonFeed + ')');
if (jsonData.response.status_code != 0) {
alert ('Error in retrieving document!');
} else{
dd_link = jsonData.response.message;
_gel("ktg-lnk").innerHTML = '<a href="' + dd_link + '">@';

Once the application proxy has responded, the JSON text response (jsonFeed) is converted to an object (jsonData) using the eval() function. The response contains the download URL the value of which can be referenced as jsonData.response.message.

Where did the Session-ID (sid) and Document-ID (did) used as URL parameters come from? The Session-ID is assigned during login and the Document-ID, together with the rest of the document details, is returned by a call to get_folder_contents.

Here's the login invocation:

The invocation to get_folder_contents:

If you get a "Session is invalid" error, it's because the link is using an ID of an expired session. Change the URL parameter (sid) to a fresh Session-ID returned by the login call to get better results.

You may try out KT-Gadget by adding it to your iGoogle page or view the gadget source code here.


Olivier said...

Hi, this seem to be a gadget specific to pipolteck.
I do have my own KT installed.
How do i specialized this gagdet to use it for my KT installation ?

pipoltek said...


First, you need to make your own proxy application to intercept your requests, say http://my.own.domain/ktg/json/index.php, and point it to your own KT installation. Then, change the gadget code to invoke your proxy url.

I'll post the skeleton code of the proxy app tonight..

pipoltek said...

I have uploaded the package at