[Twisted-Python] LivePage Hello World
dp at twistedmatrix.com
Wed May 21 22:50:51 EDT 2003
On Wednesday, May 21, 2003, at 06:53 PM, Eric Holm wrote:
> I'm trying to get a simple LivePage script going,
> and no luck so far.
Cool! LivePage is not really ready for human consumption yet, but it's
*really* *really* close.
> I started with the example on
> howto/livepage.html, and added enough bits to get
> it to run (the only surprise was that Foo.setUp()
> needs a 3rd, unused argument), and I've attached
> it at the end of this mail.
> When I view the source in the browser, there's
> a bunch of Flash stuff at the bottom (so *that's*
LivePage is really two different things: The InputConduit and the
The InputConduit is responsible for shuttling events from the client
(web browser) to the server (Twisted). The InputConduit is just a
GET request (in the IFrame) with the relevant pieces of information:
1) The name of the client side event ('onclick', 'onchange')
2) The id of the target node ('woven_id_12341234', 'myId')
3) The arguments to pass to the event handler (Usually none.)
When I originally wrote the server-side component that listens for
events from the InputConduit, I wrote it asynchronously; the HTTP
Request would generate an HTTP Response immediately (with no
interesting information in it) and the server-side event handler would
be fired one reactor iteration later. Which brings me to...
The OutputConduit is responsible for shuttling events from the Server
(Twisted) to the Client (web browser). When a Web Browser has visited a
LivePage and created a tree of MVC objects and a DOM tree, LivePage
stores the root of this (the LivePage instance itself) on the
server-side session object. Then, at any time, a server-side event may
cause a Widget to re-render itself and send the updated HTML fragment
the browser to replace the old node (which it locates by id) with the
new, updated HTML string.
The OutputConduit is interesting if you have applications where
server-side events are generated without the user actually interacting
with the web browser. For example, in the NewReality web client, one
user may log on using a web browser while another player may telnet
into the game server. The other player, typing commands into a telnet
window, will generate events which are not directly initiated by the
player using the web browser. In this situation, the OutputConduit is
useful because the server may direct the web browser to update the HTML
the user is seeing without the user actually doing anything, such as
refreshing the page.
To get to the point, I realized that if you are interested in using
LivePage to do normal, DHTML style partial-page refreshes in response
to user events (mouse clicks, dropdown selections, mouseovers) then the
OutputConduit is not required at all. Since the user initiated an HTTP
Request by invoking the client side event handler (onclick for example)
to execute in response to that event. We do this by waiting for the
sent to the OutputConduit while we were waiting into a list, and
rendering them out in a single <script> tag in the HTTP response to the
This is ultimately where LivePage is going; it will allow LivePage
penetration into browsers that will not be able to open a persistent
socket to the server.
But all that has nothing to do with your problem.
> but when fooHappened() runs, I get a
> CACHING [<twisted.web.woven.utils.Script instance at 0x00F3F300>]
> message. The corresponding comment in utils.py
> talks about a conduit not being connected yet,
> but I've no idea how to initiate a connection.
> Anybody have any idea what I'm missing?
The example you pasted was an example of what the OutputConduit is
supposed to let you do. The OutputConduit is implemented using a Flash
movie that opens a raw socket to the Twisted server (on IE Win; on
Mozilla the implementation will probably be different; on other
browsers it will probably use a polling technique to periodically check
for new content)
The Flash movie needs to talk to the server using a special (extra
silly) protocol. The magic incantation to get your Twisted server to
listen on this port and talk this protocol is this:
mktap web --path=/foo/bar --flashconduit=4321
Patches against the documentation in CVS would be gratefully accepted.
If you'd like to talk more about LivePage and where it's going, you can
find me on irc pretty regularly as fzZzy.
If enough people keep bugging me about it, I will write another example
which only uses the InputConduit, which is a technique that has proven
to be far more reliable and cross-browser in the past month. All of
this stuff is going to mature really soon, really fast :-)
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