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Re: chat on web, Ajax ? [message #177161 is a reply to message #177157]

Fri, 24 February 2012 14:28

Erwin Moller
Messages: 228
Registered: September 2010

Karma:

Senior Member

On 2/24/2012 2:59 PM, sl@exabyte wrote:
> Hi folks.

Hi again,

>
> I thought I have gathered all pieces I need, then suddenly I realise there
> is still one problem.

Some of us guessed by reading your former thread. :-)

>
> I am implementing chat on the web, ie on a browse. On browser, I can only
> use javascript. So the problem is what method to use to listen for incoming
> data.

Yes.
That is the problem: typical http requests data from some server, and
after it arrives, that's it.
A normal http request:
1) Browser sends request to server.
2) server answers
the end.
How to let the browser listen to the server?

Short answer: You cannot. Not without some tricks or additional software
(Java, Flash for example).

Read up here first:
http://en.wikipedia.org/wiki/Push_technology#HTTP_server_push

You can see on that page that a few experiments have been tried, but
none of them if fully reliable.
For example: multipart/x-mixed-replace is not supported by IE, and I
don't know about mobile devices.

You have 2 options:
1) Make a client-pull approach, eg with XHR ("Ajax").
http://en.wikipedia.org/wiki/XMLHttpRequest
Advantage: Easy to implement.
Drawback: All the connected clients will be sending update-requests all
the time. This will lead to extra serverload which can kill the server
if you have many clients trying to chat.

2) Use additional software that CAN listen.
Problem: See former thread: Suppose your server wants to PUSH new data
to some client: How to deliver that behind a firewall/NAT? To which port?

Maybe IP6 and UPNP can help you out? I am not sure to be honest.
http://en.wikipedia.org/wiki/UPNP
UPNP can help you out of the NAT mess, but it isn't supported everywhere
(I disabled it because I don't want programs to open ports on my router.)

I once created a chat application, and resorted to PULL technology
because of all the problems. In my situation that was OK because the
load was low, and the approach worked (This was before the XHR days, and
I used a hidden frame and Javascript to pull the trick.)

Bottomline: Decide if you want to go CLIENT-PULL (easy, but limited) or
SERVER-PUSH (Hard).

But you better go to a networking group instead of this one.
These advanced networking protocols (both IP6 and UPNP) are quite
complex, and this isn't PHP related.

Regards,
Erwin Moller

>
> Ajax ? I am just wondering; Ajax does not seem to bother about port, I mean
> the standard method is "open socket at server, port 8888...".
>
> Of course, when data is sent to a php file on server, it must be port 80.
>
> Is this the only way on a browser ?
>
> Thanks.
>
>

--
"That which can be asserted without evidence, can be dismissed without
evidence."
-- Christopher Hitchens

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[Message index]

		chat on web, Ajax ? By: SL on Fri, 24 February 2012 13:59
		Re: chat on web, Ajax ? By: SL on Fri, 24 February 2012 14:15
		Re: chat on web, Ajax ? By: Captain Paralytic on Fri, 24 February 2012 14:20
		Re: chat on web, Ajax ? By: SL on Fri, 24 February 2012 15:52
		Re: chat on web, Ajax ? By: The Natural Philosoph on Fri, 24 February 2012 15:59
		Re: chat on web, Ajax ? By: SL on Fri, 24 February 2012 16:23
		Re: chat on web, Ajax ? By: Doug Miller on Fri, 24 February 2012 16:52
		Re: chat on web, Ajax ? By: SL on Sat, 25 February 2012 02:01
		Re: chat on web, Ajax ? By: M. Strobel on Fri, 24 February 2012 15:22
		Re: chat on web, Ajax ? By: Erwin Moller on Fri, 24 February 2012 14:28
		Re: chat on web, Ajax ? By: Tim Streater on Fri, 24 February 2012 14:51
		Re: chat on web, Ajax ? By: The Natural Philosoph on Fri, 24 February 2012 15:54
		Re: chat on web, Ajax ? By: Tim Streater on Fri, 24 February 2012 19:02
		Re: chat on web, Ajax ? By: The Natural Philosoph on Fri, 24 February 2012 21:06
		Re: chat on web, Ajax ? By: Tim Streater on Fri, 24 February 2012 21:38
		Re: chat on web, Ajax ? By: The Natural Philosoph on Fri, 24 February 2012 21:51
		Re: chat on web, Ajax ? By: Tim Streater on Fri, 24 February 2012 22:26
		Re: chat on web, Ajax ? By: The Natural Philosoph on Sat, 25 February 2012 13:15
		Re: chat on web, Ajax ? By: Tim Streater on Sat, 25 February 2012 13:20
		Re: chat on web, Ajax ? By: The Natural Philosoph on Sat, 25 February 2012 13:33
		Re: chat on web, Ajax ? By: Tim Streater on Sat, 25 February 2012 13:42
		Re: chat on web, Ajax ? By: SL on Fri, 24 February 2012 16:31
		Re: chat on web, Ajax ? By: The Natural Philosoph on Fri, 24 February 2012 15:48
		Re: chat on web, Ajax ? By: Thomas 'PointedEars' on Fri, 24 February 2012 16:27
		Re: chat on web, Ajax ? By: Jeff North on Sat, 25 February 2012 13:13
		Re: chat on web, Ajax ? By: Arno Welzel on Sun, 26 February 2012 03:54

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