Can an AJAX request be left open for multiple responses?

[petermichaux]

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

Thanks,
Peter

[Randy Webb]

pe**********@gm ail.com said the following on 4/13/2006 11:29 PM:

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

Did you try it?

--
Randy
comp.lang.javas cript FAQ - http://jibbering.com/faq & newsgroup weekly
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[petermichaux]

Randy Webb wrote:

pe**********@gm ail.com said the following on 4/13/2006 11:29 PM:

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

Did you try it?

Is this code for yes? I haven't tried. I don't even know where I would
begin yet.

Peter

[Luke Matuszewski]

pe**********@gm ail.com napisal(a):

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.
First of all, the HTTP protocol which is used by UA's or AJAX is
request/response* protocol (* response is not required) - so for one
request only one response can be done - the HTTP 1.1 enhancements (like
persistence and pipelining) happens behind the scenes... and from
within AJAX (XmlHttpObject) there is no way to enable/disable that
(only from browser setting - enabling HTTP 1.1 protocol.
From my point of view there is little point to ask here such generic

question... you will get better answers if problems you ask is more
concrete.

Best regards
Luke M.

[petermichaux]

Luke Matuszewski wrote:

pe**********@gm ail.com napisal(a):

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

First of all, the HTTP protocol which is used by UA's or AJAX is
request/response* protocol (* response is not required) - so for one
request only one response can be done - the HTTP 1.1 enhancements (like
persistence and pipelining) happens behind the scenes... and from
within AJAX (XmlHttpObject) there is no way to enable/disable that
(only from browser setting - enabling HTTP 1.1 protocol.

Hi Luke,

That sounds like a definitive "no". Thanks for the information. That
saves me a lot of time.

Peter

[Tony]

pe**********@gm ail.com wrote:

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

I've faced a similar situation, and AFAIK, you cannot open an
XMLHttpRequest and get back multiple responses. However, it seems that
you can keep the request open for an indefinite time.

Why not make the request, then the response handler can repeat the
request? So basically, you get the sequence:

-> UA sends Request 1
-> UA waits
-> UA gets Response 1
-> UA sends Request 2
etc...

Of course, you need to be aware that most browsers will only allow two
open requests at a time, so by doing this, you limit yourself to only
one usable connection.

[TheBagbournes]

pe**********@gm ail.com wrote:

Luke Matuszewski wrote:

pe**********@gm ail.com napisal(a):

Hi,

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

First of all, the HTTP protocol which is used by UA's or AJAX is
request/response* protocol (* response is not required) - so for one
request only one response can be done - the HTTP 1.1 enhancements (like
persistence and pipelining) happens behind the scenes... and from
within AJAX (XmlHttpObject) there is no way to enable/disable that
(only from browser setting - enabling HTTP 1.1 protocol.

Hi Luke,

That sounds like a definitive "no". Thanks for the information. That
saves me a lot of time.

People are rethinking this: http://alex.dojotoolkit.org/?p=545

But personally, I'd go for DWR's polling approach to "pushing" available
in version 2: http://getahead.ltd.uk/dwr/changelog/dwr20m1

ExG

[petermichaux]

TheBagbournes wrote:

pe**********@gm ail.com wrote:

Is it possible for an AJAX request to be left open for multiple
responses? This could avoid repetitive polling of the server.

People are rethinking this: http://alex.dojotoolkit.org/?p=545

But personally, I'd go for DWR's polling approach to "pushing" available
in version 2: http://getahead.ltd.uk/dwr/changelog/dwr20m1

Thanks for these links. These ideas are very interesting. After reading
a few pages about Comet is sounds like it is still experimental. Maybe
the next generation of web servers will improve things.

I think for my situation it will be ok to just have the client poll the
server every couple of seconds to see if there are any changes. If the
client tries to make a server db change based on stale browser data, I
will produce some sort of error. Probably need this stale checking even
with a Comet-type system.

Thanks again,
Peter

[VK]

TheBagbournes wrote:

People are rethinking this: http://alex.dojotoolkit.org/?p=545

I may be terribly wrong of course, but the above looks like a
promotional scam. I base it on the wording, some details and the total
lack of real explanations and samples.

I believe it is the same pre-historic trick used to animate graphics on
the page before GIF89a format appeared: serve a hugely big content
length header so recipient stays in the receiving mode and keep
uploading packets. That was used for <img>, but maybe somehow it was
twisted for another object.

HTTP is an "ask it - got it - get away" protocol. One must be unsane to
install something on server to allow real long-lasting channels. It is
maybe semi-OK for intranet but on a real web server you will run out of
any resources sooner than you manage to say "oops".

Conventional socket listeners could be helpful and maybe added some day
- but sooner not, for security reasons.

To OP: no, it is not possible.

[TheBagbournes]

VK wrote:

TheBagbournes wrote:

People are rethinking this: http://alex.dojotoolkit.org/?p=545

I may be terribly wrong of course, but the above looks like a
promotional scam. I base it on the wording, some details and the total
lack of real explanations and samples.

I believe it is the same pre-historic trick used to animate graphics on
the page before GIF89a format appeared: serve a hugely big content
length header so recipient stays in the receiving mode and keep
uploading packets. That was used for <img>, but maybe somehow it was
twisted for another object.

HTTP is an "ask it - got it - get away" protocol. One must be unsane to
install something on server to allow real long-lasting channels. It is
maybe semi-OK for intranet but on a real web server you will run out of
any resources sooner than you manage to say "oops".

Conventional socket listeners could be helpful and maybe added some day
- but sooner not, for security reasons.

To OP: no, it is not possible.

Actually, I agree with you. "Comet" sounds flaky, and seems an attempt
to defeat the request/response nature of HTTP.

Take a look at DWR 2 though (and this is not a self-promotional scam -
I'm just a developer who uses it being a bit enthusiastic). The "Reverse
Ajax" capability will be great. The usage is asynchronous calls from
Java in the server. The implementation is a setTimeout() "thread" in the
browser which polls the server with XMLHttpRequests (I don't know if you
can set the frequency - you *should* be able to) and calls your
Javascript methods on receipt.

I've been planning features for our new intranet web app like user
alerts and reminders. Actions due, messages received, system actions
(like shutdown etc). And reverse Ajax is the way I'm planning to go.

I'll have a Javascript object in a page which subscribes to events, and
an event manager servlet started in the server to which you publish
events which broadcasts events to subscribed pages.

ExG