XMLHttpRequest and WSRP 2.0 - where we stand?

[Subbu Allamaraju <subbu@bea.com>]

I have been investigating various use cases that developers are trying 
to solve by using XMLHttpRequest in their applications, and how WSRP 
stacks up against those use cases. I do find some limitations in the 
protocol that make it hard to solve some use cases. I would like to find 
out what people think.

Most of the use cases that rely on XMLHttpRequest can be grouped into 
two categories:

a. Downloading data/markup: An example is auto-filling forms based on 
what the user entered previously. This is similar to google-suggest.

b. Submitting data: An example is a user login. Upon login, the browser 
replaces the login form with another markup fragment. Netflix's movie 
rating is another example.

The first use case is idempotent, and URLs to download data/markup can 
be created as resource URLs. Now that WSRP 2.0 provides the portlet's 
context while fetching resources, developers can let portlets return 
xml/markup.

The second use case is typically non-idempotent. Portlets may want to 
change their state while processing data. In some cases, portlets may be 
affecting the state of other portlets either via spec-provided 
coordination mechanisms or some producer-managed sharing.

But it turns out that implementing the second use case is very tricky. 
Let me jot down the key steps that a portlet might try:

a. Create an action URL in the markup.

b. Submit data to the this URL

c. Update browser to use/render returned data/markup

But these steps don't play well with WSRP. In most implementations, the 
generated action URL points to an aggregated page which causes a pbia, 
zero or more handleEvents, and one or more getMarkup calls.

In the current use case, the portlet needs a URL that is guaranteed to 
cause a pbia for the targeted portlet, and return markup for the same 
portlet. That is, the consumer must not return an aggregated page for 
this to work.

The difficulty is that the protocol does not provide a way to create 
such an interaction URL. The nature of the URL is completely up to 
implementations. Implementations cannot solve it either since portlets 
may be creating normal interaction URLs and these special portlet-only 
URLs in the same markup fragment and producers/consumers can't 
distinguish between these two.

Currently, developers can work-around this use case only via resource 
URLs. But resource URLs don't permit state changes, and so limit the 
ability of portlets to handle the use case completely.

I'm seeking comments from this group on how important these use cases 
are for your implementations, and have any thoughts on supporting these 
use cases.

Regards,
Subbu